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Über dieses Buch

"Advances in FRP Composites in Civil Engineering" contains the papers presented at the 5th International Conference on Fiber Reinforced Polymer (FRP) Composites in Civil Engineering in 2010, which is an official conference of the International Institute for FRP in Construction (IIFC). The book includes 7 keynote papers which are presented by top professors and engineers in the world and 203 papers covering a wide spectrum of topics. These important papers not only demonstrate the recent advances in the application of FRP composites in civil engineering, but also point to future research endeavors in this exciting area. Researchers and professionals in the field of civil engineering will find this book is exceedingly valuable. Prof. Lieping Ye and Dr. Peng Feng both work at the Department of Civil Engineering, Tsinghua University, China. Qingrui Yue is a Professor at China Metallurgical Group Corporation.

Inhaltsverzeichnis

Frontmatter

Keynote Papers

Frontmatter

Innovative Textile-Based Composites for Strengthening and Seismic Retrofitting of Concrete and Masonry Structures

The author reviews experimental studies which have provided fundamental knowledge on the use of a new generation of composite materials, namely textile-reinforced mortars (TRM), as strengthening and seismic retrofitting materials of concrete and masonry structures. TRMs are investigated as a means: to provide confinement in plain and reinforced concrete (RC), to increase the deformation capacity of old-type RC columns subjected to simulated seismic loading, to increase the shear and flexural resistance of RC members and to increase the out-of-plane or in-plane strength of unreinforced masonry walls. In all cases, the ef-fectiveness of TRM systems is quantified through comparison with equivalent fiber-reinforced polymer (FRP) ones. Based on the results it is concluded that TRM jacketing is an extremely promising new technique, which will enjoy the attention of the research community and will be employed in numerous applications in the next decades.

Thanasis Triantafillou

Strengthening of Concrete, Metallic and Timber Construction Materials with FRP Composites

This paper provides a review of research being conducted at The University of Hong Kong (HKU) on the strengthening of concrete, metallic and timber construction materials with externally bonded fibre-reinforced polymer (FRP) composites. The motivation of such research is to enhance our understanding of the interfacial behaviour between the FRP and the three different substrate materials via FRP-to-concrete, -metal, and-timber joint tests. Of the three substrate materials, concrete has clearly experienced the most research activity to date by the wider research community, followed by that of metal and then that of timber. In order to progress the extensive knowledge base of FRP-to- concrete behaviour, research at HKU is aimed at enhancing the bond strength of the FRP via the addition of anchorage. The anchor of choice is the so called FRP anchor and its effectiveness in anchoring FRP flexural strengthening applied to reinforced concrete (RC) slabs is also presented. For the metal and timber substrate materials, HKU research is more focused at this stage on understanding the influence of key fundamental variables affecting interfacial behaviour such as FRP geometry, surface preparation and substrate material characteristics.

S. T. Smith

Multifunctional and Robust Composite Material Structures for Sustainable Construction

The multifunctional use of FRP composites offers the potential to contribute to the emergence of a new generation of lightweight engineering structures for an innovative infrastructure that meets the challenges with which today’s construction industry is faced. Six axes of development are discussed, which address the potential innovations and the main problems to be overcome to allow the widespread application of multifunctional lightweight FRP composites in civil infrastructure. Three axes are related to the structural robustness of FRP structures. Structural robustness is primarily dependent on a material-tailored structural concept and system ductility and can be obtained particularly thanks to ductile adhesive joints. Further three axes explore the opportunities for innovation through a multifunctional use of FRP materials. Structural functions are combined with building physics functions, energy supply, and architectural functions.

Thomas Keller

Hybrid FRP-Concrete-Steel Double-Skin Tubular Structural Members

Hybrid FRP-concrete-steel double-skin tubular members (DSTMs) are a new form of hybrid structural members composed of an inner steel tube, an outer FRP tube and a concrete infill between them. The two tubes may be concentrically placed to produce a section form more suitable for columns, or eccentrically placed to produce a section form more suitable for beams. These hybrid structural members possess many important advantages over conventional structural members, including their excellent corrosion resistance as well as excellent ductility and seismic resistance. This paper explains the rationale and advantages of this new form of structural members and discusses their potential applications before presenting a summary of the recent and current studies on their structural behaviour and design. These studies form part of a major on-going research programme at The Hong Kong Polytechnic University (PolyU).

J. G. Teng, T. Yu, Y. L. Wong

Durability of GFRP Reinforcement Bars

Results of a 3-year-long investigation of durability of one type of glass fiber reinforced vinylester composite reinforcement bar are summarized. Bars were cast in concrete beams and subjected to simultaneous sustained load and exposure to one of four different environments: ambient indoor laboratory, natural outdoor weathering in central Pennsylvania, high-alkaline aqueous solution at 60°C, and alternating −17°C dry freeze and room-temperature water immersion. The conditioned beams were tested to determine crack width in the concrete, local bond-slip behavior of the bars, and tensile stress-strain behavior of bars extracted from the beams. Over time, crack widths increased by up to 75% while local ultimate bond strength in the anchorage zone remained essentially constant or increased. Tensile strength decreased by as much as 25% in the high moisture environments and was essentially constant in the indoor and outdoor environments. These results suggest promising durability characteristics of GFRP bars under realistic service conditions.

Charles E. Bakis

FRP Design Using Structural Mechanics Models

The application and expansion of FRP reinforced concrete has been hindered and obstructed through the misconception and misunderstanding that empirically derived rules developed for steel reinforced concrete in cracked regions can be used either directly or as a guidance for FRP reinforced concrete. This assumption is incorrect because the empirical rules developed for steel reinforced concrete in cracked regions, as with all empirical rules, should only be used within the bounds of the testing regimes from which they were developed, which for steel reinforced concrete is normal strength concrete with high ductile steel that has very good bond. As these bounds do not apply to FRP reinforced concrete, the steel RC empirical rules for cracked concrete are of little or no help for FRP RC. In fact, they are often misleading and as such prevent the widespread use of FRP reinforcement. It will be shown and illustrated in this presentation that generic mechanics based rules can be developed at all load conditions for RC beams that applies to both steel and FRP reinforcement. And, furthermore, that these generic mechanics based design rules allay many of the misconceptions inferred by the empirically based RC design rules such as that moment redistribution cannot occur with brittle FRP reinforced concrete which is simply not the case.

D. J. Oehlers, M. Haskett, Ali Mohamed, W. Lucas, R. Muhamad

Finite Element Modelling of FRP-to-Concrete Bond Behaviour Using the Concrete Damage Plasticity Theory Combined with a Plastic Degradation Model

The technique of externally bonding fibre reinforced polymer (FRP) composites has been becoming popular worldwide for retrofitting existing reinforced concrete (RC) structures. A major failure mode in such strengthened structures is the debonding of FRP from the concrete substrate. The bond behaviour between FRP and concrete thus plays a crucial role in these structures. The FRP-to-concrete bond behaviour has been extensively investigated experimentally, commonly using the pull-off test of FRP-to-concrete bonded joint. Comparatively, much less research has been concerned with the numerical simulation of this bond behaviour, chiefly due to difficulties in accurately modelling the complex behaviour of concrete. This paper proposes a robust finite element (FE) model for simulating the bond behaviour in the entire loading process in the pull-off test. A concrete damage plasticity model based on the plastic degradation theory is proposed to overcome the weakness of the elastic degradation theory which has been commonly adopted in previous studies. The model produces results in very close agreement with test data.

J. F. Chen, Y. Tao

FRP Materials and Sustainability

Frontmatter

Fiber Reinforced Cementitious Composites (FRCC) Plate for the Anchoring of FRP Sheet on Concrete Member

To increase the bond capacity of FRP sheets employed in the strengthening of concrete members, various anchoring methods have been proposed and used. In this paper, a new anchoring approach with the gluing of precast fiber reinforced cementitious composites (FRCC) plate on top of the FRP sheet will be discussed. The direct shear bond test is employed to measure the failure load and study the failure mechanisms. Several sets of tests have been performed with different FRCC composition and different length of the FRCC plate. Comparison with the control sample shows that the installation of FRCC plate can significantly increase the bond capacity (by up to 100%).

Qingxu Jin, Christopher K. Y. Leung

Study of Tensile Behavior for Interval Impregnated Hybrid Carbon/Basalt Fiber Sheet (C/BFS)

This paper presents a inter-ply hybrid fiber sheet C/BFS (carbon/basalt fiber sheet) in order to solve the problems encountered in the application of FRP in the present strengthening engineering, such as inconvenient transportation, not ideal adhesive interface and low tension control stress. Interval impregnated inter-ply hybrid method was adopted to enhance the performance of C/BFS, not only increases the adaptability to the structure shape but also raises the utilization ratio of fiber strength. Mechanical tensile tests were conducted on interval impregnated C/BFS with different lengths (2m/5m/10m). Test results show that the prestress degree of C/BFS can be over 50% of its design stress after interval impregnation.

Gang Wu, W. J. Jing, Z. S. Wu

Statistical Studies on Material Behavior of CFRP Sheets under Uniaxial Loads and Its Application in Reliability Analysis

The uniaxial load tests were conducted to investigate the material behavior of CFRP sheets. The results show that the probability distribution of CFRP tensile strength can be described by the three-parameter Weibull distribution. The design formulae for determining flexural capacity of reinforced concrete strengthened with CFRP sheet are proposed. The Monte Carlo procedure is applied to simulate the flexural capacity of reinforced concrete strengthened with CFRP sheet, and the results show that the flexural capacity can be considered to obey the normal distribution. By using the JC method, the reliability index is calculated based on the statistics of flexural capacity and load effect. After the analysis of the effect of the partial factor of CFRP sheet on the reliability index, the results reveal that the reliability index of all design points are the most close to target reliability index overall when the partial factor of CFRP sheet is 1.25, and in this condition the reliability index of three failure modes is larger than the target reliability index. Therefore, the partial factor is suggested to be 1.25, which can meet the requirement of reliability design.

Wenwei Wang, Wei Yang

Comprehensive Characterization of BFRP Applied in Civil Engineering

In the present study, BFRP rebars for internal concrete reinforcement and wet lay-ups for external rehabilitation have been systematically characterized on the basic physicochemical properties and durability performance of the BFRP materials subjected to hygrothermal ageing, freeze-thaw cycles and elevated temperatures. The basic mechanical performances of BFRP are tested according to ACI 440.3R, which indicates the better modulus and stiffness than GFRP, but inferior to CFRP. Hygrotheral ageing in distilled water and alkaline solution immersion leads to deterioration of both mechanical and thermal properties. The water uptake and thermal properties due to the long term immersion ageing were performed to understand the degradation mechanisms. After extreme freeze-thaw cycles ranging from −30°C to 30°C, no adverse effects were found for the properties of BFRP and the bonding between BFRP and concrete blocks. The elevated temperature leads the mechanical properties BFRP rebars to be reduced remarkably. The residual properties exceed the half room temperature values at the temperature much higher than the glass transition temperature of the system. Compared to the CFRP and GFRP, the promising properties of the BFRP rebar and wet lay-up clearly illustrates the high potential for the application in civil engineering.

Hui Li, Guijun Xian, Bo Xiao, Jingyu Wu

Influence of Elevated Temperature on the Mechanical and Thermal Performance of BFRP Rebar

Compared to glass fiber reinforced polymer (GFRP) rebars, basalt fiber reinforced polymer (BFRP) rebars possess many advantages as internal reinforcement of concrete structures, in terms of the enhanced corrosion resistance. In the present study, mechanical and thermal properties of BFRP rebar at elevated temperatures and after elevated temperature treatment were conducted. The study is believe to offer the basic mechanical and thermal property data of BFRP rebars during and post- fire, which is helpful for the the safe design of BFRP in rehabilitation when considering the fire hazarder. The tensile properties of BFRP rebars were performed in the temperature ranging from room temperature to 350°C. Three stages of deterioration of the tensile strength and modulus are observed based on the degradation rate. It was found that the strength and stiffness of BFRPs still remain high values (e.g., more than half of the room temperature values) even at the temperature much higher than Tg (glass transition temperature) of the system. The deterioration is attributed to the decreased force transferring capacity of the resin. In addition, BFRP rebars were treated at elevated temperatures for various periods in an oven. The oxidation of the resin and the deterioration of the interface between fiber and resin bring in remarkable degradation of the mechanical and thermal properties.

Jingyu Wu, Hui Li, Guijun Xian

Composite Decks and Sustainable Development: a Case Study

Composite materials, based on glass fibers are promising candidates for civil engineering and building applications. Sustainable development issues are of prime importance worldwide. Therefore, new structures made out of new materials as well more conventional materials should be analyzed to provide more precise data about greenhouse gas release. In this work, a short-span bridge deck is used as a case study. Three different cases are considered: a reinforced concrete deck, a steel deck and a composite deck. The three cases are discussed regarding carbon dioxide release.

Monssef Drissi-Habti, Xavier Chapeleau, Sébastien Cournée

Matrix and Fabric Impregnation Influence on Textile Reinforcement Concrete Behaviour

This study aims to analyze the textile reinforced concrete tensile (TRC) behaviour. Firstly A tensile test suitable for this type of cracking material is designed and validated. The second phase aims to highlights the influence of several parameters considered as critical (the material, the thickness of the composite, the impregnation of the fibres, the fibre volume ratio) in the textile reinforced concrete (TRC) behaviour in terms of mechanical performance (strength and stiffness) or the amount of damage correlated with the crack opening measured using image correlation analysis.

Raphaël Contamine, Amir Si Larbi, Patrice Hamelin

Discrete Fiber Reinforced Polyurea for Hazard Mitigation

This research investigated the development and characterization of different discrete fiber-reinforced polyurea systems for infrastructure applications. The behavior of various systems consisting of several polyureas with different fiber configurations was evaluated. Polyurea coating systems were previously evaluated for blast mitigation and impact resistance, and showed to be adequate in containing debris scatter from blast and impact (Carey and Myers, 2009a, 2009b). The purpose of further testing was an effort to develop a polyurea system for multi-hazard and/or repair-retrofit applications. The addition of fiber to a polymer coating provides improved stiffness and strength to the composite system while the polyurea base material provides ductility. Coupon tensile testing was conducted to determine the material mechanical properties in this study. The two parameters that were varied throughout testing were fiber volume fraction and fiber length. E-Glass fiber was used during specimen fabrication. Several optimal composite configurations of polyurea and fiber resulted from this coupon testing.

N. L. Carey, J. J. Myers

Experimental Research on the Fundamental Mechanical Properties of Presoaked Basalt Fiber Concrete

Presoaked basalt fiber concrete (PBFC) is a new kind of concrete reinforced with random short presoaked basalt fibers. In the paper, the applicability of the presoaked basalt fiber (PBF) as a strengthening material was investigated through various experimental works for mechanical characteristics and strengthening effects by changing its dosage and length, and compared with ordinary concrete. Experimental researches showed that: adding the presoaked basalt fiber on the condition of constant in matrix concrete, the influence on compressive strength was not noteworthy, but tensile strength was improved significantly. Form the results of the tests, it is concluded that presoaked basalt fiber can significantly reduce the brittleness of concrete, improving the toughness and deformation resistance. The presoaked basalt fiber can be regarded as a strengthening material for concrete structures.

Jianxun Ma, Xuemei Qiu, Litao Cheng, Yunlong Wang

All FRP Structures

Frontmatter

Shear Buckling of GFRP Beam Webs

Slender webs of glass fiber-reinforced polymer (GFRP) beams are sensitive to shear buckling. Shear buckling can bee seen as an in-plane biaxial compression-tension buckling problem. The transverse tensile load thereby delays the onset of buckling and increases the ultimate load. Thin-walled GFRP plates of two different fiber stacking sequences, [0/90]S and [90/0]S, were subjected to in-plane biaxial compression-tension loading. The buckling loads were almost duplicated by increasing the tensile load while the ultimate loads were increased by up to 20%. The fiber stacking sequence thereby had significant effects on buckling mode shape and buckling and ultimate loads.

Behzad D. Manshadi, Anastasios P. Vassilopoulos, Thomas Keller

Shear Wrinkling of GFRP Webs in Cell-Core Sandwiches

Glass fiber-reinforced (GFRP) cell-core sandwich structures are increasingly used in bridge deck and roof construction. GFRP cell-core sandwiches are composed of the outer GFRP face sheets, a foam core and a grid of GFRP webs integrated into the core in order to reinforce the shear load capacity. One of the critical failure modes is shear wrinkling, a local buckling failure in the sandwich webs due to shear loading. Shear wrinkling is a biaxial compression-tension wrinkling problem and, for this reason, the numerous results of pure compressive wrinkling research are not necessarily applicable. The details and results of in-plane biaxial compression-tension wrinkling experiments on GFRP sandwich laminates, stabilized by a polyurethane foam core, are presented. It is shown that an increasing transverse tension load significantly decreases the wrinkling load. These results are confirmed by finite element calculations.

Behzad D. Manshadi, Anastasios P. Vassilopoulos, Julia de Castro, Thomas Keller

Pin-Bearing Strengths for Design of Bolted Connections in Pultruded Structures

Presented in this paper are pin-bearing strengths of pultruded FRP materials that are required to check for bearing resistance when designing bolted connections. Bearing failure is the distinct failure mode with a strength formula that requires its ‘own’ material strength property, which we call the bearing strength. Using a test method developed at the University of Warwick a series of pin-bearing strength tests have been conducted to characterise the web material from a 203 mm × 203 mm × 9.53 mm wide flange standard shape. Testing is performed with the loading oriented at either 0, 45 or 90° to the direction of pultrusion. Reported are the salient test results and characteristic values determined using the guidance in Annex D to Eurocode 0.

B. Zafari, J. T. Mottram

Development of an Effective Joining Method for a Pultruded Hybrid CFRP/GFRP Laminate

This paper presents results from an experimental investigation on the tensile behavior of double lap joints in pultruded hybrid CFRP/GFRP laminates. A number of hybrid FRP coupon specimens with bolted-only and bonded-and-bolted joints were tested. The results show that a combined use of steel bolts, adhesive bonding and V-notch splice plates in double lap joints was found to be an effective method for joining hybrid FRP laminates. The rough surface of V-notch splice plates and adhesive bonding contributes to improve the stiffness of joints.

Nguyen Duc Hai, Hiroshi Mutsuyoshi, Kensuke Shiroki, Tatsuya Ishihama

A Consistent Design Concept for Bolted Connections in Standardized GFRP-Profiles

This paper presents a consistent design concept for bolted connections of standardized GFRP-profiles. All test specimens have been taken either from pultruded flat-profiles or the webs of standard pultrusion I or U-profiles from Fiberline Composites A/S. At first the orthotropic material properties of the laminates were determined by experimental tests, including short term and long term properties as well as influence of temperature and media. Experimental results have been confirmed by numerical simulations; taking the complex limit state conditions into account introducing the fracture criteria of Puck. Afterwards relevant functions to determine resistances have been developed for different limit state conditions. To obtain characteristic values, these functions have been calibrated according to the reliability requirements of EN 1990. Using simplified engineering models for the practical design of bolted connections therefore a complete and consistent design concept is provided.

Matthias Oppe, Jan Knippers

Composite Behavior of a Pultruded Hybrid CFRP-GFRP Beam with UFC Deck

Hybrid Fiber Reinforced Polymer (HFRP), which is composed of Carbon FRP (CFRP) and Glass FRP (GFRP), has many advantages over conventional materials such as light weight, high specific strength, and corrosion resistance. HFRP is expected to find its application in severe corrosive environments or where light-weight rapid construction is required. This paper presents the development of a composite beam using an HFRP I-beam and precast Ultra-high strength Fiber reinforced Concrete (UFC) slab. UFC has high strength and high ductility, so it allows for reduction of the cross-section area and self weight. Full-scale flexural beam tests were conducted with different geometry of UFC slab and shear connection methods between the UFC slab and HFRP beam. For the composite beams with bolted-only connection, slip occurred between the HFRP beam and the UFC slab. On the other hand, slip was not observed in the composite beams with bonded-and-bolted connections. The flexural stiffness of beam specimens with bonded-and-bolted connection increased significantly compared with that of bolted-only connection specimens. Delamination failure was not observed in the compressive flange of the composite beams and the high tensile strength of the CFRP in the bottom flange could be utilized effectively by addition of the UFC slab on the top flange.

Hiroshi Mutsuyoshi, Kensuke Shiroki, Nguyen Duc Hai, Tatsuya Ishihama

Sensitivity Studies on Local Flange Buckling Equations for Pultruded Beams and Columns

The objective of this research was to investigate the sensitivity of a proposed design equation for local flange buckling in pultruded I sections to the mechanical properties of the elements of the section and to determine the accuracy of the equation that includes the effect of the rotational restraint at the web-flange junction. The web-flange junction stiffness is shown to contribute significantly to the flange buckling resistance of the cross-section and it is more significant in beams than in columns. The predicted buckling loads were compared with the results of tests and professional factors for LRFD calibrations have been developed. The sensitivity study was performed with respect to the orthotropic in-plane stiffness properties of the pultruded material in an effort to determine to what degree they contribute to the calculated buckling resistance of the section. Finally, the practicality of using the equation for the design of macroscopically non-homogeneous members is discussed.

M. J. McCarthy, L. C. Bank

Analytical Study on Buckling Modes of Simply Supported Delaminated Composite Beams

Based on the two-dimensional elasticity theory, the buckling modes of delaminated composite beams are studied in this paper. Firstly, critical buckling loads are obtained. Then, the displacement modes of the beam are given by substituting the critical loads back to the eigenvalue equations. The possible contact between the delaminated interfaces is considered, and “Free” and “contact” modes are separately computed. According to the situations of the vertical displacements and normal stresses on the delaminated interfaces, the real buckling modes can be judged.

Zhu Bo, Zhou Ding, Liu Weiqing

Interlaminar Behavior of Paulownia Wood Sandwich Composites with Grooves

Some grooves were arranged on the surface of the paulownia wood core, with the resins fulfilled. After solidifying, the resins left in the grooves strongly bonded the faces and core together. Therefore, the adhesive capacity between the faces and the core was enhanced. VARIM process was used to manufacture the specimens with different groove widths, depths and distances, and the DCB method was used to test the interfacial strength of the sandwich beams. Based on the energy release ratios from the test data, some factors are analyzed. It was found that the grooves can improve both the processing and interfacial properties. The present analysis provides the basis for the wide applications of paulownia wood sandwiches in future.

Wan Li, Liu Weiqing, Fang Hai, Zhou Ding

GFRP Structures Subjected to Dynamic Action

The good ratio between strength and dead load defines the composite material as an efficacious solution for structural rehabilitation of historical buildings. The composite material with polymeric matrix, known with FRP acronym (Fiber Reinforced Polymers), is widely used in civil engineering as sheets, bars and strips. Recently a new technology was adopted to improve the structural response — with limited increment of dead load — with reversible and independent solution. The GFRP pultruded profiles allow the building of all-composite structure both for over elevation frame, structures and beams for increment of flexural stiffness of deck. The present work proposes and analyses the solution for seismic behaviour GFRP (Glass Fiber Reinforced Polymers) applications to evaluate the performances respect to dynamic actions considering the global effect on historical structure.

Giosuè Boscato, Salvatore Russo

GFRP Members in Free Vibrations Field, Dynamic Parameters of Profiles and 3D Structure

The study examines the topic of dynamic identification of the pultruded elements and GFRP (Glass Fiber Reinforced Polymers) structural systems starting from the definition and quantification of the fundamental parameters of dynamic engineering, natural frequencies, modes of vibration and damping. The research illu-strates the results of an extended campaign of experimental tests on mono-dimensional elements, panels and framework systems, subject to free vibration. The boundary conditions for the structural elements are simply supported, for the 3D structure are supported configuration. The tests concern profiles with open cross-sections with one or two axis of symmetry, tubular sections and panel. As regards the all-GFRP structures have been investigated the three-dimensional frame (5m × 5m for the plan and 2.5m for the high), it is an auxiliary floor built in historical building of Vicenza, Italy.

Giosué Boscato, Salvatore Russo

Experimental Design on Multi Layers of LVL Fiber Reinforced Wood Composite Using Bagasse as Core Structure

The multi layers of laminated veneer lumber(LVL) fiber reinforced wood composite were constructed. It was comprised of peeled rubber and eucalyptus woods sheet obtained from commercial forest. Epoxy and vinyl ester cured bagasse were used as core and the fiber glass woven as reinforcement. Those constituents were alternately laid and bonded with epoxy and vinyl ester resins and compression molded. The 2k experimental design method was applied to study the effect of those parameters on the mechanical properties by mean of flexural properties It was found that, within the statistical result, there is no significant effect of those parameters on the flexural properties of the LVL. It would be contributed from the less brittle bagasse core. Then, the over all strength would not be enhanced and no contribution from the other strong constituents.

U. Meekum

Shear Behavior of Glue-Laminated Composite Sandwich Beams

The shear behaviour of a new generation composite sandwich structure made up of glass fibre reinforced polymer skins and modified phenolic core material was investigated in view of using this composite material as a shear loading component in structural glue-laminated beams. Characterisation of the shear strength and stiffness of the fibre composite skins and the modified phenolic core material was conducted following the ASTM-D5379/D5379M-93 test standard. The shear behaviour of the individual and the glue-laminated composite sandwiches was investigated under asymmetrical beam shear test. The results of the experimental investigation showed that the asymmetrical beam shear test gives a good estimation of the shear strength and stiffness of the glue-laminated composite sandwiches. A theoretical prediction of the shear strength of the composite sandwich beams with high strength core material was proposed and comparison with experimental results showed a good correlation. The results of the study suggest the high possibility of using composite sandwich construction in the development of structural laminated beams to carry shear.

Allan Manalo, Thiru Aravinthan, Warna Karunasena

Flexural Behavior of FRP Reinforced Glubam Beams

A new type of rectangular glued laminated bamboo (glubam) beam had adopted in the world first truck-safe modern bamboo bridge in Leiyang, Hunan, by the authors. The glubam beams can further be enhanced by FRP. This paper analyzes the effect of some parameters, such as FRP thickness, span-depth ratio, strengthen measures, types of node on bending properties. The basic mechanical model is established to predict the failure. Through the experimental work, the flexural stiffness and ultimate load of FRP reinforced beams are compared with those of unreinforced beams. The result show that the analytical model can forecast the flexural behavior of FRP reinforced glubam beams well.

Quan Zhou, Yan Xiao

Trial Design of Cable-Stayed Bridges Using Hybrid Composite Girders and Applicability to Free Passage Over Railway

A pultruted hybrid composite girder is being developed consisting of carbon and glass fibers. The innovative feature is the optimum use of CFRP and GFRP in the flanges to maximize structural performance while reducing the overall cost by using glass fibers in the web section. In this paper, the cable-stayed bridges were trially designed using the developed hybrid composite girders. In order to utilize the lightweight of FRP, the construction site was selected to the free passage over the busy railway as a case study. The cable-stayed bridges were two continuous-span bridges with the span lengths of 5.5 m and 24.0 m. As a result, the feasibility of the proposed structures and the reduction of total cost were confirmed.

Hitoshi Nakamura, Ken-ichi Maeda, Hiroshi Mutsuyoshi, Kenji Yaginuma, Takahiro Matsui

Performance Based Design of Laminated FRP Box Girders for Short Span Bridges

All-advanced composite bridge superstructure represents a significant advance in the use of advanced composites in civil-structures. However, one of the critical obstacles to extensive use of advanced composites in construction is the lack of simplified and practical design guidelines. In this paper, an iterative performance based multi-scale analysis and design approach for all-advanced composite bridge superstructure is proposed. The bridge superstructure is formed from laminated FRP box girder and chopped FRP top surface plate. Several laminate designs are examined and the performance of the most efficient material and structural design of the proposed bridge is compared to a slab on prestressed concrete bridge. The results show that the proposed procedure leads to an efficient use of the materials with highest structural performance.

Husham Almansour, Moe Cheung

A Design Concept for an All Composite Road Bridge

The present paper describes a design concept for an all composite road bridge. Most of the components, including the deck to girder connection, are made entirely using the pultrusion process. The stiffness of the girders is tailored to meet the deflection requirements. The analysis results have shown that the structure can carry the specified loads with safety.

Benedict Leo, Anup Chakrabortty, Amar Khennane

Mechanical Model and Analysis of FRP Woven Web Structures

The fiber-reinforced polymer (FRP) woven web structure (WWS) is an innovative large-span spatial structure composed of FRP strips. The FRP strips are crossed each other and woven to form a flexible web plane, and the web is stressed integrally in out-of-plane. The WWS is a tensegrity spatial structure system made of flexible members, which has four mechanical statues. The basic assumptions and the 3D fundamental mechanical model of the simple FRP WWS which has ring beams and central symmetry FRP strips are studied. The mechanical equations are drawn. Based on the equations, three load cases of FRP WWS including integrally pre-stressed in out-of-plane, full span load and half span load are analyzed in theoretical method. The fundamental mechanical model of FRP WWS is established that provides the theoretical approach for analyzing FRP WWS.

Yujun Qi, Peng Feng, Lieping Ye

GFRP-Polyurethane Sandwich Panels under Reversed Bending Fatigue

Sandwich panels composed of lightweight polyurethane core and GFRP skins have a great potential for a variety of applications. Some of the promising applications include cladding of buildings, in which the lightweight panels are used to provide the building envelope in terms of insulation and protection from the elements, and in lightweight decking applications of pedestrian bridges or platforms. In cladding applications, although the panels are not of the load-bearing type, they are subjected to a strong wind pressure or suction. In this case the panels are repeatedly loaded in cyclic bending, which may cause fatigue problems. This study investigates sandwich panels in four point reversed cyclic bending. The panels were exposed to various stress levels and for each level; the number of cycles to failure was established. Stiffness degradation characteristics were also measured at various stages of loading. It was shown that at a cyclic load of ±30% of the ultimate monotonic flexural strength, the panels were able to sustain over 2 million cycles.

Hale Mathieson, Amir Fam

Development and Experimental Verification of a Pedestrian Slab Bridge Using GFRP Pultrusion Profiles

This paper deals with the development and the experimental verification of a newly proposed pedestrian slab bridge using GFRP pultrusion profiles bonded together by adhesive layers. The innovative feature is the appropriate adoption of semi-fixed support conditions with anchor bolts at both ends, in order to sharply reduce the bending deflection. By the drastic reduction of the bending deflection which often becomes dominant in the design of GFRP pedestrian bridges, the economic efficiency is also drastically due to be improved.

Seigo Fujita, Ken-ichi Maeda, Hitoshi Nakamura, Nobuhiko Kitayama, Tetsuya Watanabe

Study on Dynamic Characteristics of Light-Weight FRP Footbridge

Comparing to footbridges made of traditional materials, FRP (fiber reinforced polymer) footbridges have many advantages, such as rapid installation, corrosion resistance, waterproof property, pleased appearance, lasting color, overloading resistance, good fatigue performance, good seismic performance, and potential capacity to build greater span. A tentative FRP cable-stayed bridge is investigated, in which the design method and the design indices for FRP footbridges are studied. It is found that the vibration comfort of FRP footbridge are the main controlling factors for structural design. The indices for the pedestrian vibration comfort requirements are also summarized, and the frequency limit, acceleration limit and excitation load are analyzed. Considering the finite element analysis and the field measurement results, it is concluded that the acceleration should be the controlling indicator, and a simplified excitation load model and the calculation method for acceleration are proposed. For the cable-stayed FRP footbridge, the results of finite element analysis and field measurement show that it can’t meet the designing requirements. Hence, the improvement of overlaying a concrete layer is proposed. After it, the behaviors of the FRP footbridge meet the requirements. All these works make out the design approach and the design indices for FRP footbridges, which are proved practical and reasonable through the actual FRP footbridge.

Feifei Jin, Peng Feng, Lieping Ye

Honeycomb Fiber-Reinforced Polymer Sandwich Panels for Fish Culture Tanks

The U.S. aquaculture gross revenues have grown from $350 million in 1985 to nearly $900 million in 1996, and while large overseas markets are available for native products, the national aquaculture production was only about 3 percent of world production value. It is argued that the utilization of impaired mine waters abundant in West Virginia (WV) and the other mid-Appalachian states for fish culture can substantially increase aquaculture economic development. Approximately 878.12 million L of water per day are discharged in WV from both active and abandoned mines, and if only 30% of these water resources were used for aquaculture, the expansion of this industry in WV would be significant. The primary limitation to the effective utilization of discharged waters is the lack of suitable fish culture tanks that can be easily installed in rugged terrains surrounding mine water treatment plants. Such topographical constraints do not easily permit the construction of cast-in-place concrete tanks, and therefore, FRP sandwich materials offer an economical alternative for production of modular, transportable, light, and durable fish culture raceway systems. This study is concerned with the development and evaluation of prototype fish culture tanks using a honeycomb FRP (HFRP) sandwich panel with sinusoidal core geometry, which is produced by KSCI by the contact-molding process. Based on defined functional requirements, a raceway system consisting of four staggered tanks is designed, and each tank is 1.83×9.14-0.91m, with a middle partition along the 9.14m length to carry out parallel aquaculture studies. Representative panel samples of the side and bottom walls as well as the side-to-bottom panel connections are tested within the linear range and eventually to failure. The linear response of the samples is analyzed by the finite element method.

Julio F. Davalos, Avinash Vantaram, An Chen, Indrajit Ray, Jerry D. Plunkett

FRP Hybrid Structures and Concrete-Filled FRP Tubes

Frontmatter

Hybrid FRP-Concrete Structural Member: Research and Development in North America

In recent years, fibre reinforced polymers (FRPs) have become the focus of numerous research projects in the field of civil engineering. FRPs are a structural material known to possess high strength, high resistance to corrosion and high strength-to-weight ratio. It is also easy to install in both new as well as existing structures. Hybrid FRP-concrete structural members, in particular, have shown significant promise in a wide range of applications. This paper will investigate and discuss in detail the research performed on hybrid FRP-concrete structural members in North America. Emphasis will be placed on the design philosophies and results from both experimental and analytical testing.

Donna Chen, Raafat El-Hacha

Hybrid FRP-Concrete Structural Member: Research and Development in Europe and Asia

Approximately 40% of Canadian bridges currently in service were constructed forty to fifty years ago. Many existing structures suffer from structural integrity problems, such as corrosion, and require significant repairs. In some cases, complete replacement of the structure is necessary. Fibre reinforced polymers (FRPs) have shown great potential as a structural material due to its high strength, resistance to corrosion, light weight and ease of construction. Hybrid FRP-concrete structural members have become of particular interest. This paper will investigate the different applications of hybrid FRP-concrete structural members and the experimental research studies performed on these members in Europe and Asia. Summaries of results from experimental tests and analytical investigations are provided with a focus on the effect of factors such as the type of shear bond used at the FRP-concrete interface and FRP fabrication methods on the ultimate load resistance and failure mode.

Donna Chen, Raafat El-Hacha

Experimental Study on Flexural Behaviour of Hybrid GFRP/Concrete Bridge Deck

A novel cost-effective hybrid GFRP/ Concrete deck system consists of the corrugated pultruded GFRP plate with T-upstands for the tension part and concrete with distributing reinforcing bars for the compression part was proposed. Static tests on six full-scale models with different influence factors such as penetrating bars and surface treatment under sagging moments were conducted and observed to evaluate the load-carrying capacity and failure modes of proposed hybrid deck system. Results from experimental work indicate that both surface treatment and penetrating bars improve the connection between GFRP plate and concrete, also promote the ultimate strength and whole rigidity of hybrid deck; moreover the effect of surface treatment is better than that of penetrating bars. The overall investigation showed that the presented hybrid GFRP/concrete concept is a vi-able option for beam-and-slab bridges.

Yuqing Liu, Jun He, Haifeng Fan, Airong Chen, Liang Dai

Experimental Study of GFRP-Concrete Hybrid Beams

A new design concept that led to a hybrid beam is proposed. It comprises a U-shaped GFRP pultruded profile in which concrete was casted. Results are presented from 6 beams tested to ultimate failure, four of which having a fiber-reinforced plastic(FRP)-reinforced concrete construction of combined tensile reinforcement and permanent shuttering, while the others are conventional reinforced concrete beams as a comparison. It is shown that in comparison with an equivalent reinforced concrete beam, hybrid beam gives a great increase in bearing capacity but decrease in ductility.

Fei Zhao, Chaohe Chen, Wenjuan Lou, Peng Feng

In-Situ Load Tests and FE Modeling of Concrete Bridge with FRP Stay-in-Place Forms

Two in-situ load tests were performed on a highway bridge with FRP Stay-in-Place (SIP) formwork that also serves as positive flexural reinforcement for the bridge deck as part of a long-term monitoring program. The load tests conducted consisted of positioning a wheel of a tri-axle dump truck with calibrated loading at a series of target locations in a line parallel to the girders at mid-span of the deck. Portable strain sensors were used to determine the distribution of the wheel loads within the FRP-SIP bridge deck and draw-wire transducers were used to measure deck deflections. Wheel load distribution widths are calculated using the measured strain values and the results are compared with wheel load distribution widths found in the AASHTO-LRFD and AASHTO Standard specifications. A 3-D finite element model was created to analyze the performance of the bridge subjected to traffic load and concrete shrinkage.

B. Wan, C. M. Foley

Structural Performance Evaluation of Precast FRP-Concrete Composite Deck with Concrete Wedge for Cable-Stayed Bridge

Despite of the large contribution of the deck in the whole weight of the superstructure, the deck occupies a small portion of the construction costs in cable-stayed bridges. The application of high performance materials for the deck can represent a fair alternative to reduce the weight of the deck and improve the economic efficiency of the bridge even if high performance materials are costly. Accordingly, KICT developed a precast FRP-concrete composite deck to provide such solution. The self-weight of this new-type deck is reduced to 60% compared to the conventional precast concrete deck. In this study, experiments on several beams were performed in order to investigate the behavioral characteristics of the deck and verify its structural performance.

S. Y. Park, K. Cho, S. T. Kim, J. R. Cho, B. S. Kim

Static and Fatigue Behaviors of Precast FRP-Concrete Composite Deck for Cable-Stayed Bridge

The precast FRP-concrete composite deck enables a reduction of the weight by 50% compared to reinforced concrete decks owing to the composition of a FRP panel with concrete. Therefore, the application of such deck in cable-stayed bridge will reduce effectively the weight of the superstructure leading also to substantial savings of the materials required for the superstructure and substructure and, subsequently, to achieve significant improvement of the economic efficiency. In view of these advantages, a precast FRP-concrete composite deck is selected and newly designed as a deck economically applicable to cable-stayed bridge. The applicability of the deck system is verified through static and fatigue tests.

Keunhee Cho, Sung Yong Park, Sung Tae Kim, Byung-Suk Kim

Experimental Studies on FRP-Concrete Composite Deck with FRP Perfobond Shear Connectors

Push-out tests were conducted to investigate the shear performance of FRP perfobond shear connectors. Shear failure was observed on the ribs of connectors at ultimate. Based on test results, the FRP perfobond connectors showed relatively high shear capacity and could be applied to the FRP-concrete composite deck. Then the simply supported FRP-concrete composite deck with FRP perfobond shear connectors was tested under monotonic load. The load versus mid-span deflection response of composite deck behaved linearly up to the ultimate load. Shear failure occurred on the webs of FRP deck near the upper flange, while the FRP perfobond shear connectors remained intact without any damage. The measured maximum mid-span deflection was 25.4 mm, corresponding to 1/63 of the simply supported span, which demonstrated the large deformability of FRP-concrete composite deck.

Weichen Xue, Chang Ge, Yuan Tan, Yongsheng Wang

Numerical and Experimental Investigation of Concrete-Filled FRP Tube

This study is to investigate nonlinear failure behavior of the concrete-filled FRP (CFFRP) hybrid tube structure. This study consists of two phases. First, a CFFRP tube is fabricated and tested to investigate the flexural failure behavior of CFFRP tube. Second phase involves practical nonlinear finite element analysis of the CFFRP tube up to failure. FRP tube is modeled by layered shell elements and filled concrete is idealized by fiber beam element. Failure theory for the prediction of the strength of unidirectional composite materials is considered. Uniaxial constitutive models for the concrete and steel material are selected in this study. The adopted material model is integrated into the ABAQUS elements through a user-defined material subroutine (UMAT). Within a developed nonlinear finite element framework, the FE results have been compared to experimental results. It has been found that the proposed finite element model is capable of predicting the ini-tial cracking load level, the yield load, and the ultimate load with acceptable accuracy.

Wonseok Chung, Hoon Jang, Zu-Og An

An Experimental Investigation into the Behaviour of Filament Wound Hybrid FRP-Concrete Beam

This study presents the results of an experimental investigation into the performance of hybrid beams wrapped with filament winding. A cost-effective pultruded profile was used to reduce the high initial cost of the beam. High strength concrete was cast on top of the pultruded profile to take the compressive forces and CFRP laminate at the bottom to take the tensile forces. The whole system was then wrapped with GFRP using filament winding to eliminate the debonding of the concrete from the pultruded profile. Two different lay-up types of wrapping ±45° and 90°/±45° were used. The experimental results show that the wrapping did not only eliminate the debonding of concrete from the pultruded profile but also increased the overall stiffness and the load carrying ability of the beam. As a result, the beams carried a significant amount of load before failure.

A. Chakrabortty, A. Khennane, E. V. Morozov

Experimental Study on Bending Performances of FRP-Concrete Composite T-Beams with Prefabricated BFRP Shell

FRP-Concrete composite beams with prefabricated BFRP shell are further studied in this paper. Based on previous research experience, several specimens of FRP-Concrete composite T-beams were designed with steel bar as the main reinforcement and lower FRP participation proportion than before to improve the performance, in which the FRP-concrete interface was wet-bonding combined with a new type of FRP shear Key (FSK-WB), and the prefabricated BFRP section was made by the vacuum infusion molding technique and then filled with freshly-cast concrete. Bending experiments of six composite beams and two RC beams, under either static or cyclic load, were conducted. The experiment results indicate that this kind of FRP-concrete composite beam has the advantages of higher bearing capacity, proper post-yield stiffness, better recoverability, and at the same time without reducing the ductility. On the other hand, these beams will use less FRP materials to obtain durability, thus reduce the materials cost. The FSK-WB interface is proved to be safe and reliable.

Hong Zhu, Pu Zhang, Gang Wu, Zhishen Wu

A Comparative Study of Various FRP Shear Connectors for Sandwich Concrete Walls

There is a great demand to improve both the structural and thermal characteristics of insulated precast concrete sandwich panels. This paper addresses the potential of using a number of Glass Fibre Reinforced Polymer (GFRP) connectors developed in this research program as an alternative to metallic connectors. The objective is to reduce thermal bridging in the sandwich panels, while transferring shear forces to develop composite action within the panel. The panel incorporates a new system of concrete wythes and studs connected by the GFRP connectors, where the studs are not in direct contact with the wythes. The load-slip response of the system has been established through shear tests. It was also shown that adhesion between the insulating foam and concrete provides significant shear resistance prior to engaging the GFRP connectors.

G. D. Woltman, D. G. Tomlinson, A. Fam

Smart FRP Structures

Frontmatter

Effectiveness of Smart Dampers for Hybrid FRP Cable in Long-Span Cable-Stayed Bridge

This paper presents a theoretical evaluation of modal damping of hybrid FRP cable with smart dampers for long-span cable-stayed bridge. Based on previous studies of FRP and hybrid FRP cables, hybrid FRP cable exhibited advantages in static and dynamic behavior compared with conventional steel cables and newly developed CFRP cables. One of the advantages is its designable sectional structure that can improve internal damping and benefit vibrational control of stay cable under various excitations. To validate the effectiveness of hybrid FRP cable with smart damper design, the principle and design consideration of smart dampers were first described. Based on the energy principle, the theoretical expression on modal damping was derived for in-plane vibration. Finally, in terms of a detail designed hybrid FRP cable with smart damper, the damping ratio was evaluated which demonstrated the effectiveness of smart damper design.

Xin Wang, Zhishen Wu

A Smart FRP-Concrete Composite Beam Using FBG Sensors

A new kind of smart FRP-concrete composite beam, which consists of a FRP box beam combined with a thin layer of concrete in the compression zone, was developed by using two embedded FBG sensors. The fabrication process of the smart FRP-concrete composite beam was introduced. The proposed smart composite beam was tested in 4-point bending to verify the operation of the embedded FBG sensors. The experimental results indicate the output of embedded FBG sensors in the smart beam agrees well with that of surface-bonded strain gauges over the entire load range. The proposed smart FRP-concrete composite beam can reveal the true internal strain from 0 to the failure of the beam and will have wide applications for long-term monitoring in civil engineering.

Yanlei Wang, Qingduo Hao, Jinping Ou

Smart CFRP Systems— Fiber Bragg Gratings for Fiber Reinforced Polymers

Since 1970 the development of optical fiber measurement systems has begun. Especially the measuring of strain and temperature with Fiber Bragg Gratings (FBG) is interesting, because there are a large number of advantages in opposite to electrical measuring methods. Examples are small dimensions, low weight, high static and dynamic resolution of measured values, corrosion resistance, variable forms, multiplex behavior, long distance monitoring and high durability. In the past there were several attempts to use optical systems for monitoring of concrete structures. One example is the strain measurement in bar reinforcement. Another possibility is the embedding of optical fibers with FBG in Carbon Fiber Reinforced Polymers. Fiber Re-inforced Polymers (FRP) have got more and more important during the last decade. In civil engineering the main usage of FRP is the repair of concrete structures. CFRP systems for retrofitting of concrete structures with optical sensors have already been discussed in several publications. It could be shown, that the reinforcing function of the CFRP can be ideally connected with the measurement and monitoring functions of the optical sensors like FBGS. The main problem is the fixing of the glass fiber and the small FBG at the designated position. In this paper the possibility of setting the glass fiber with embroidery at the reinforcing fiber material will be presented. Experiments will show the functionality of the method.

Stefan Käseberg, Klaus Holschemacher

Sensor CFRP-Sheets for the Controlled Strengthening and Retrofitting of Reinforced Concrete Members

The reinforcement of bearing structures with secondary glued reinforcement has been practiced successfully for a long time. Thereby steel plates have been used for circa 50 years and FRP plates have been used for circa 25 years. Compared to steel the carbon fiber has some important advantages, for example the higher elastic modulus (up to 50%) and the higher tension strength. The load bearing behavior of Carbon Fiber Reinforced Polymer (CFRP) is significantly influenced by the properties of the matrix, the fiber and the interface between both. Thereby some important disadvantages of the brittle materials must be considered, for example the low ductility of the bond between CFRP and concrete and brittle failure of FRP. With embedded sensor systems it is possible to measure crack propagation and strains. In this paper a sensor based CFRP system will be presented, that can be used for strengthening and measuring. On the basis of four point bending tests on beams (dimensions of 700×150×150 mm) the potential of the system is introduced. Primarily a comparison of two different measurement methods (Strain Gauge and Fiber Bragg) is shown.

Klaus Holschemacher, Stefan Käseberg

Electrically Conductive Nanocomposite Coating for Strain and Health Monitoring

FRP bridge decks are designed to withstand high load levels and a lifetime of several ten years, facing an extremely high number of load cycles. The fatigue life and degradation of the mechanical properties are needed to be essentially considered during the service of the FRP deck. In the present study, a novel electrically conductive coating was developed with a function of strain monitoring for the FRP bridge deck. An epoxy resin was modified with multi-walled nanotube (MWCNT) in order to achieve electrical conductivity. Processing, structure and properties of the MWCNT-epoxy nanocomposite were optimized, and the correlation between the strain level and electrical conductivity of the coating was set up. The conductivity of the coating on the FRP bridge deck is tracked with a simple electrical measurement, and the strain of the FRP bridge deck is obtained through the determined conductivity ∼ strain relationship. It is worth noting that the damage modes of the coatings (also the coated FRP surface) can be determined from the conductivity curves. Together with the easy application and data collection, such coating has a high potential for the application in stress/strain and health monitoring.

Jianlin Luo, Hui Li, Guijun Xian

Smart Composites for Durable Infrastructures — Importance of Structural Health Monitoring (SHM)

The goal of this contribution is to share some ideas that can bring heavier discussion among the population of bridge researchers and engineers about SHM. For existing infrastructures, an emphasis will be made on how critical the detection of the onset of corrosion as well as its rate of proliferation within steels. In the case of new bridges, design and conception should include smart materials and structures. Smart composites, that are integrating embedded sensors, can bring significant advances in civil engineering applications. So is the case of nano-sensors, that will surely offer additional valuable solutions in the mid-term future. The issues related to standards in using composites in civil engineering are also addressed.

Monssef Drissi-Habti

Concrete Structures Reinforced or Prestressed with FRP

Frontmatter

Experimental Study on the Tension Stiffening Effect of GFRP RC Elements

Direct tension test experiments are accepted to be adequate to study the tension stiffening effect of fibre reinforced polymer reinforced concrete (FRP RC) members. In this paper, an experimental program on direct tension tests on GFRP RC is presented. Four different reinforcing ratios were considered; the ties were instrumented to analyze the member behaviour (load-strain relationship and crack width). Measured member deformation and crack widths are compared with those calculated using the procedures of available codes for steel reinforced concrete, like EC-2 and ACI 224, as well as with ACI 440 for FRP reinforced concrete structures.

M. Baena, A. Turon, Ll. Torres, C. Miàs, C. Barris, G. Barbeta

Behavior of High-Strength Concrete Beams Reinforced with Different Types of Flexural Reinforcement and Fiber

Six high-strength concrete beam specimens reinforced with different types of flexural reinforcement were constructed and tested. All beam specimens consisted of two layers of flexural reinforcements. Three types of conventional steel bars, CFRP bars, and GFRP bars were used as a flexural reinforcement. While three beam specimens were reinforced with single type of flexural reinforcement, the other three beams were reinforced with combination of two types of flexural reinforcement. In addition, four more high-strength concrete beam specimens were constructed and tested to investigate the influence of fibers on the behavior of FRP bar-reinforced concrete beams. Two types of hooked steel fiber and crimped synthetic fiber were used.

J. M. Yang, K. H. Min, H. O. Shin, Y. S. Yoon

Deflection Behaviour of Concrete Beams Reinforced with Different Types of GFRP Bars

GFRP bars are non noncorrosive reinforcing materials having relatively lower tensile modulus compared to steel. The design of flexural concrete members reinforced with GFRP bars are usually governed by serviceability limits, deflection, and crack width. This paper describes an experimental study conducted to investigate the deflection behavior of concrete beams reinforced with GFRP bars. The bars came from three different manufacturers. A total of 8 beams measuring 4250 mm long ×200 mm wide×400 mm deep were built and tested up to failure under four-point bending. The study’s main parameters were reinforcement type (GFRP and steel) and amount (three reinforcement ratios). The midspan deflection of all the beams tested were recorded and compared. The test results were used to assess the equations in different FRP codes and guidelines.

S. El-Gamal, B. AbdulRahman, B. Benmokrane

Behavior of Continuous Concrete Beams Reinforced with FRP Bars

Continuous concrete beams are commonly used elements in structures such as parking garages and overpasses which might be exposed to extreme weather conditions and the application of de-icing salts. Therefore, the use of the non-corrodible fiber reinforced polymer (FRP) bars in these types of structures is beneficial. However, due to the linear-elastic behavior of FRP materials up to failure, the ability of such materials to redistribute loads and moments in continuous beams is questionable. To date, unlike simply supported structures, very few experimental studies investigated the behavior of continuous concrete beams reinforced with FRP bars. Due to the lack of research, recently published design guidelines for FRP-reinforced structures provided limited provisions regarding continuous beams. The objectives of this research are to investigate the behavior of continuous concrete beams reinforced with carbon and glass FRP bars and provide design guidelines to predict the failure load and failure location. This paper presents the experimental results of two reinforced concrete beams with rectangular cross section of 200×300 mm continuous over two spans of 2800 mm each. One beam was reinforced with CFRP longitudinal bars while the other reinforced with GFRP bars. Both beams were reinforced with steel stirrups and provided with different reinforcement configurations at critical sections. Beams were tested under concentrated monotonic loads applied at the mid-point of each span. It is concluded that the FRP-reinforced concrete beams were able to redistribute the connecting moment over the intermediate support. Also, the Canadian code CSA-S806-02 could reasonably predict the failure load of the tested beams; however, it fails to predict the failure location.

Mostafa El-Mogy, Amr El-Ragaby, Ehab El-Salakawy

Testing of Large-Scale Two-Way Concrete Slabs Reinforced with GFRP Bars

Few studies were conducted to investigate the structural behavior of GFRP-reinforced concrete two-way slabs. This paper presents preliminary results of an extended research project aims to developing the FRP technology reinforcing bar for parking garage structures and to introducing design guidelines for such structures. The results of five full-scale isolated interior parking flat slabs which are part of a 20-specimen experimental program are presented and discussed. Four slabs were reinforced with GFRP bars and one reference slab was reinforced with steel. The test parameters are: (i) reinforcement type and ratio; (ii) slab thickness; (iii) column size; and (iv) compressive reinforcement. The test results showed that there was no significant difference between the specimens in term of general behavior and mode of failure.

C. Dulude, E. Ahmed, S. El-Gamal, B. Benmokrane

Development Length of Glass Fiber Reinforced Plastic (GFRP)/Steel Wire Composite Rebar

The bond between glass fiber reinforced plastic (GFRP)/steel wire composite rebars and concrete is the key problem to the performance of concrete structures reinforced with GFRP/steel wire composite rebars. In this study, pull-out test was tested to experimentally investigate the bond strength of GFRP/steel wire composite rebars to concrete. The test variables were the nominal diameter, the embedded length, the concrete compressive strength, the concrete cover thickness and the concrete cast depth. Based on the two modification factors of 1.2 and 1.6 to account for the top rebar effect and concrete cover effect, respectively, a new formula is proposed for the calculation of development length for GFRP/steel wire composite rebars.

Qingduo Hao, Yanlei Wang, Jinping Ou

Deformation Behavior of Concrete Two-Way Slabs Reinforced with BFRP Bars Subjected to Eccentric Loading

Based on the punching shear test results of 9 simply supported concrete two-way slabs reinforced with basalt fiber reinforced polymer (BFRP) bars subjected to eccentric concentrated loading, the deflection distribution and the load-deflection characteristics of test slabs are investigated. The test results show that the deforma-tions of test slabs before punching shear failure are caused by bending moments. The concrete strength, the ratio of FRP bars reinforcement, the location of concentrated load and the ratio of punching span are the main factors that affect the load-deflection curves and the energy dissipations capacity of concrete two-way slabs reinforced with FRP bars under eccentric concentrated load.

Haitang Zhu, Yakun Zhang, Danying Gao, Zhilong Xiao

Experimental Study on the Flexural Behavior of Concrete Beam Hybrid Reinforced with FRP Bars and Steel Bars

The hybrid reinforced concrete structure combine the advantages of reinforced concrete structure and FRP structure together, it could resolve the problem of the durability of RC structure and brittle failure of FRP structure. In order to investigate the flexural behavior of concrete beam hybrid reinforced with FRP bars and steel bars, three different area ratio of FRP bar to steel bar hybrid reinforced concrete beams, one FRP reinforced concrete beam and one reinforced concrete beam static flexural test were made. Mechanics characteristic, flexural capacity of normal section and deflection of hybrid reinforced beams were analyzed. The results show that the average concrete strains of different height keep plane, the flexural capacities calculate by proposed formula was close to the tested value. The load-deflection curve decreased gradually after steel bars yielded.

Wenjie Ge, Jiwen Zhang, Hang Dai, Yongming Tu

Study on the Flexural Capacity of Concrete Beam Hybrid Reinforced with FRP Bars and Steel Bars

Two Nominal reinforcement ratios and three failure modes were put forward according to the characteristic of FRP bar and the criterion of appropriate hybrid reinforcement beam was given. Flexural capacity of appropriate hybrid reinforcement beam was analyzed according to the theory of reinforcement concrete and flexural capacities simplified calculate formula of appropriate hybrid reinforcement beam was proposed. three different area ratio of FRP bar to steel bar hybrid reinforced concrete beams, one FRP reinforced concrete beam and one reinforced concrete beam static flexural test were made and the tested results show that the flexural capacities calculate by proposed simplified formula was close to the tested value.

Jiwen Zhang, Wenjie Ge, Hang Dai, Yongming Tu

Experiments According to ETAG to Determine Friction Effects on Deviated CFRP-Strips

In recent years the Institute of Building Structures and Structural Design, University of Stuttgart (ITKE), has undertaken a large amount of experimental work to determine the load bearing capacity, strain responses up to failure and the failure mode of CFRP-Strips at different deviation saddle geometries. Several tests with different deviation angles and deviation saddle radii were carried out. The results have shown that the tensile strength of the CFRP-Strip is reduced significantly by deviation, even if the deviation radius in proportion to the thickness of the CFRP-Strips is comparatively large. Further tests were carried out to determine the influence of other important parameters on the load bearing capacity of the strip such as surface properties of the saddle including the friction of the saddle surface. The results of these tests show that, with the help of a polyethylene layer (HD-PE) between the CFRP-Strip and the deviation saddle friction could be reduced, which lead to an increase in tensile strength. The effect of these parameters on the load bearing capacity of the CFRP-Strip is published in this paper.

Mohamed Hwash, Jan Knippers

Study of Static Load Tests of Bond-Type Anchors for CFRP Tendons

As a novel type of bond-type anchors, straight pipe plus inner cone bond-type anchors for CFRP tendons have a better development prospect, because which have advantages of both straight pipe bond-type anchors and inner cone bond-type anchors. However, the study at home and abroad is very little. In this paper, through carrying out static load tests for four groups of anchor assemblies, the failure modes, load-slip behavior and the strain development of CFRP tendons in the loading process are researched. The results showed that straight pipe plus inner cone bond-type anchors for CFRP tendons had a good anchorage performance. The research work done for bond-type anchors of CFRP tendons used in pilot project of suspended construction had provided reliable basis.

Wen-hua Cai, Ji-wen Zhang, Shu-ting Liang, Yong-ming Tu

Bond Type Anchorage Systems for Permanent High Strength CFRP Ground Anchors

CFRP ground anchors have an integral place in the ground anchor industry, providing designer and contractors with a corrosion resilient anchor which minimises the labour intensive corrosion protection required when using steel strands. Successful anchoring of long strand lengths in a confined ground anchor environment has been the greatest constraint in the development of CFRP ground anchors. Recent research undertaken at Monash University and Geotechnical Engineering has developed a reliable and compact bond type anchorage head system, practical for permanent ground anchor applications. Laboratory and full scale testing has been successfully carried out. This paper provides tests results on a four and ten strand CFRP modified bond type anchor head system with a reduced bond length. Results showed failure of specimens were within the CFRP fibres due to tensile rupture. Negligible movement at the bond anchor head were recorded.

Matthew Sentry, Riadh Al-Mahaidi, Abdelmalek Bouazza, Len Carrigan

Flexure-Shear Analysis of Concrete Beam Reinforced with GFRP Bars

This paper gives the details of flexure-shear analysis of concrete beams reinforced with GFRP rebars. The influence of vertical reinforcement ratio, longitudinal reinforcement ratio and compressive strength of concrete on shear strength of GFRP reinforced concrete beam is studied. The critical value of shear span to depth ratio (a/d) at which the mode of failure changes from flexure to shear is studied. The failure load of the beam is predicted for various values of a/d ratio. The prediction show that the longitudinally FRP reinforced concrete beams having no stirrups fail in shear for a/d ratio less than 9.0. It is expected that the predicted data is useful for structural engineers to design the FRP reinforced concrete members.

S. Ramadass, Job Thomas

Effect of Bond Parameters on Recoverability of RC Bridge Columns Reinforced with Ordinary Rebars and Steel Fiber Composite Bars

In this study, effects of bond parameters on post-earthquake recoverability of RC bridge columns reinforced with ordinary deformed bars and innovative composite bars: steel fiber composite bars (SFCBs), are studied. A computer program is employed to investigate the effect of bond parameters on column post-yield stiffness and residual deformations. Then, the required recoverability is examined for experimentally tested columns with different unbonded length of longitudinal ordinary rebars, available from literature, and two tested scale-model RC bridge columns reinforced with different products of SFCBs, i.e. steel basalt-fiber composite bars (SBFCBs) and steel carbon-fiber composite bars (SCFCBs). The study showed that weaken bond between deformed bars and the surrounding concrete has no clear effect on column residual deformations, however, mitigation of residual deformations could be when columns are reinforced with SFCBs. Furthermore, bond effect could play an important role in the recoverability of structures reinforced with SFCBs, where both the achieved post-yield stiffness and residual deformations could be controlled.

Mohamed F. M. Fahmy, Z. S. Wu, G. Wu

Effect of Reinforcement Detailing on the Behavior of GFRP-RC Beam-Column Joints

The behavior of FRP bars under tension-compression load reversals in RC beam-column joints and frame structures has not yet been fully explored. This research project is attempting to partially fulfill this gab by investigating the structural performance and ultimate capacity of concrete beam-column connections totally reinforced with FRP bars. A total of three full-scale exterior beam-column joint (T-shaped) prototypes were constructed and tested under simulated seismic load conditions. The main test parameter was the detailing of the beam longitudinal bars within the joint by using either straight bars or bent bars. Test results are presented in terms of load vs. drift ratio, and strains in longitudinal reinforcement. The experimental results showed a superior performance for the GFRP reinforcement when bar slippage within is prevented through proper detailing of the beam bars within the joint.

Mohamed Mady, Mohamed Hasaballa, Amr El-Ragaby, Ehab El-Salakawy

Long-Term Performance

Frontmatter

Interfacial Crack Growth Behavior on RC Beams Strengthened with Prestressed CFL under Cyclic Bending Loads

The interfacial fatigue crack growth behavior on the interface between prestressed FRP and concrete of the strengthened beams under cyclic bending loads were studied by fracture mechanics theoretical method and fatigue crack growth testing method. The results showed that the interfacial crack growth process on the RC beams strengthened with prestressed carbon fiber laminate (CFL) under cyclic bending loads could be divided into three stages: 1) rapid growth stage; 2) steady growth stage; 3) unstable growth stage. In the rapid growth stage and steady growth stage, the interfacial fatigue crack growth rate could be described effectively with Paris-Erdogan expression. Where, the stress intensity factor of the interfacial crack, KII, could be obtained by calculating the energy release rate of the interfacial crack, GII, with the fracture mechanics theoretical method.

Hao Zhou, Peiyan Huang, Zhengwei Li, Xiaohong Zheng, Jianhe Xie

Effects on the Fatigue Lives of RC Beams Strengthened with CFL at Elevated Temperature under Cyclic Bending Loads

The fatigue behavior of RC beams strengthened with carbon fiber laminate (CFL) was experimental studied and theoretical analyzed under cyclic bending loads in several different temperatures (5°C, 20°C, 50°C and 80°C), which the temperatures approached the weather in subtropical zone such as southern China. The effect of the temperature on fatigue lives of the RC beams strengthened with CFL was discussed. Furthermore, a calculation equation of the fatigue lives of the strengthened beams was proposed under the coupling action from the temperature and the load conditions. Using the equation, the fatigue lives and fatigue limits of the RC beams strengthened with CFL were estimated accurately from the coupling action from the temperatures and the bending loads. The preliminary validity check was completed with the verify tests.

Peiyan Huang, Haiyang Wang, Hao Zhou, Xinyan Guo, Zhilin Zhou

Fatigue-Loading Effect on RC Beams Strengthened with Externally Bonded FRP

External bonding of fiber reinforced polymers (FRP) on concrete beams is particularly attractive for the strengthening of civil engineering structures in order to increase their mechanical resistance. The composite material is generally bonded on the tensile part of the beam. In order to design these bonded reinforcements, an iterative computational method based on section equilibrium and material properties (concrete, steel, adhesive and composite) has been developed: this method can be extended to describe the fatigue behavior of RC beams. This paper focuses on the damage behavior of concrete structures subjected to fatigue loading. A specific modeling coupled with an experimental investigation on large-scale beams made it possible to compare the theoretical and experimental fatigue behaviors of RC beams with and without composite reinforcements Results showed that the beam deflection and the strain in each material could be calculated with a sufficient accuracy, so that the fatigue behavior of the FRP strengthened beams was correctly estimated by the model.

E. Ferrier, A. Limam, P. Hamelin, M. Quiertant

Box Girders under Extreme Long-Time Static and Fatigue Loading

This paper discusses aspects of the extreme long-time behavior of filament wound E-glass fiber reinforced epoxy box girders. Theoretical and experimental data are compared and show good agreement. The performance of these GFRP box girders during 25 years of static loading and 100 million fatigue cycles is excellent.

Urs Meier, Robert Müller, Michel Barbezat, Giovanni Pietro Terrasi

Experimental Study of Time-dependent Behaviour of Concrete Members Reinforced with GFRP Bars

This study presents the results and discussion of an experimental tests program in which 8 concrete beams reinforced with glass fibre reinforced polymer (GFRP) were maintained under a constant load for a period of 150 days. Two different ratios of reinforcement and two different levels of sustained load were used. The beams were instrumented and monitored to analyze the time-dependent behaviour due to concrete creep and shrinkage.

The measured deflections are compared with those calculated using methodologies available for steel reinforced concrete structures as CEB procedure, as well as with ACI 440.1R-06 and CSA-S806-02 for FRP reinforced concrete structures. The comparisons of the theoretical and experimental long-term deflections indicate that CEB procedure gives reasonable predictions in all 8 beams. However, some differences can be found when ACI 440.1R-06 or CSA-S806-02 procedures are applied.

C. Miàs, Ll. Torres, A. Turon, M. Baena, I. Vilanova, M. Llorens

Hygrothermal Ageing of Basalt Fiber Reinforced Epoxy Composites

Due to its low price and high chemical resistance, basalt fiber is emerging as a novel reinforcement for fiber reinforced polymer (FRP) composites used in civil engineering in recent years. Compared to widely applied glass fiber based FRP (GFRP) and carbon fiber based FRP (CFRP), however, much less research works on the durability performances of basalt fiber reinforced polymer (BFRP), have been done by now, which seriously hinders its wide and safe application. In the present study, unidirectional basalt fiber fabric reinforced epoxy composites were prepared with a wet lay-up process. Such BFRP materials are expected to be used for external rehabilitation, strengthening or renewal of structures. Durability studies were performed on cured BFRP strips through water, alkali solution immersion at various temperatures. The evolution of the water uptake and mechanical properties with the ageing time was investigated. The aim of the study is to demonstrate the feasibility of using BFRP in severe civil environments, and to disclose the possible degradation mechanisms. As shown, tensile strength of the BFRP samples shows remarkable degradation due to water and alkaline solution immersion, while the tensile modulus is affected slightly. In addition, the mechanical property degradation of the BFRP samples in water is much less than that in alkaline solutions. The results indicate the current basalt fiber need to be modified in its chemical compositions, surface treat-ment for enhanced durability performance.

Bo Xiao, Hui Li, Guijun Xian

Moisture Diffusion in FRP Adhesively-Bonded Joints under Hot/Wet Environments

Fibre Reinforced Polymer (FRP) bridge deck systems are finding increasing usage in the constructions of new bridges and renovations of old bridges. Especially hybrid structures are competitive, i.e. steel girders combined with a pultruded FRP bridge deck. Adhesive bonding which provides smoother load transition is often the most attractive joining technique for the connection between steel girders and FRP decks. However, the long-term performance of this connection is not clearly defined. So the durability modelling and life-time prediction of the adhesively bonded joint are still issues which designers and engineers have to face. As a first step of the PhD research, moisture diffusion in FRP adhesively bonded joints is discussed and analyzed numerically. The moisture concentration distribution of FRP adhesively bonded joints after 70 years was obtained, which can subsequently be used as input for the next step stress-strain analysis allowing for the incorporation of moisture-dependent mechanical properties in the FE model.

Xu Jiang, Henk Kolstein, Frans S. K. Bijlaard

Durability of CFRP Bonding System under Freeze-Thaw Cycling

This paper presents the results of an experimental study on the behavior of externally-bonded fiber reinforced polymer (EB-FRP) joints under freeze-thaw cycling. Four series of single shear tests were conducted on 26 specimens. The parameters considered were the exposure condition, concrete grade, and the number of freeze-thaw cycle. The behavior of the CFRP-concrete interface in the shear direction was investigated. The test results demonstrate that the bond strength, bond stiffness, interfacial fracture energy, and maximum slip of the joints decrease with the increase in the number of freeze-thaw cycle, and also are affected by the testing environment. It is also found that the depth of the cracking and the effective bond length increase with an increase in the cycle number, and thus affecting the bond stiffness and strength. The deterioration of the bond strength is considered due to the damage of the concrete under the freeze-thaw cycling.

Yanchun Yun, Yufei Wu

Bond Strength of Glass FRP Bars in Concrete Subjected to Freeze-Thaw Cycles and Sustained Loads

In reinforced concrete structures, temperature-induced stresses can be a major concern in regions of drastic temperature changes. FRP reinforced concrete elements are specially susceptible to more damage due to temperature changes because of the mismatching thermal properties between FRP bars and concrete. Furthermore, sustained loads may also damage the bond between FRP bars and concrete and can lead to an unexpected increase of the required anchoring length. Therefore, this research program is designed to investigate experimentally the durability of FRP bond to concrete elements subjected to the effects of freeze-thaw cycles and sustained loads. A FRP-reinforced concrete specimen was developed to apply axial-tension sustained loads to GFRP bars eccentrically located within the concrete environment. Test specimens were subjected simultaneously to the dual effects of 250 freeze-thaw cycles along with sustained load. A total of six test specimens were constructed and tested. The test parameters included bar diameter and concrete cover. After conditioning, each test specimen was sectioned to two replicates (halves) for pull-out test. Another series of twelve unconditioned standard pull-out specimens were constructed and tested as control. Test results are presents in terms of bond-slip relationships and ultimate pull-out strength. Test results showed that freeze-thaw cycles along with sustained load resulted in increase in the bond strength of GFRP bars to con-crete.

Juliana Alves, Amr El-Ragaby, Ehab El-Salakawy

Long-Term Durability of FRP Cables under Maritime Conditions

Six types of FRP cables were subjected to an exposure test lasting more than fifteen years under maritime conditions, and the retrieved cables were evaluated mainly by SEM and FT-IR microscopy. Loss of surface resin was observed for all the tested FRP cables; however, deterioration between the fiber and matrix resin was not found by SEM. Observation by FT-IR microscopy detected surface deterioration of AFRP cables, and the feasibility of this method for evaluating the deterioration of some FRP cables was indicated.

Itaru Nishizaki, Iwao Sasaki

Temperature Effects on Full Scale FRP Bridge Using Innovative Composite Components

Numerous large-scale demonstrator projects around the world have shown the viability of composite materials for bridge applications. Most of the projects have been directed towards the better understanding of bridge behaviour in strength and serviceability. However, the behaviour under different environmental conditions and longer term effects on durability are yet to be fully understood. This paper presents the results of an investigation on effects of temperature change into the structural behaviour of a FRP demonstrator trial bridge. It was installed at the University of Southern Queensland, Toowoomba Campus using innovative sandwich composites. It has been found that temperatures in different locations of the bridge vary for different locations within the bridge. The variation is found to reverse during day and night time. Based on the meas-ured temperature variation, some important recommendations are provided on the effects of temperature for innovative fibre composite bridge.

C. S. Sirimanna, M. M. Islam, T. Aravinthan

Modeling the Effect of Repeated Loading on the Behaviour of CFRP Confined Bond of Corroded Reinforcement

In steel-reinforced concrete, the transfer of forces between concrete and reinforcing steel bars dictates the general behaviour of the structure. This transfer is affected by several factors such as the corrosion of steel reinforcement, the presence of FRP confinement and the loading regime. This study used design of experiment methodology to examine the experimental data available on the behaviour of corroded steel-FRP confined concrete bond under repeated loading. The fatigue bond life of a CFRP wrapped bond critical zone was studied as a function of the corrosion level and the repeated applied load range. The analysis of the unbalanced experimental data concluded that the loading range, accounting for 52.4% of the total variability, is the significant factor that affects the performance of the CFRP confined tested specimens. Based on the statistical analysis, a model was developed that relates the fatigue bond life of a CFRP confined bond critical zone to the corrosion level and the applied loading range. The proposed model satisfactory predicts the experimental behaviour.

Safeer Abbas, Ahmad Rteil

Effects of Accelerated Ageing on the Adhesive Bond Between Concrete Specimens and External CFRP Reinforcements

CFRP strengthened concrete specimens were submitted to accelerated ageing conditions (40°C and 95% R.H.) and the time evolution of the adhesive bond strength was monitored using either pull-off or shear loading tests. In a parallel investigation, effects of hydrothermal ageing on the microstructure of the bulk epoxy adhesives were assessed by means of thermal analyses and tensile tests. From those experiments, it was found that the property evolution of the concrete/FRP bonded interface is primarily dependent on the sensitivity of the polymer to ageing conditions, but also on the type of test used for the mechanical characterizations. These trends were supported by numerical modeling based on finite element analysis.

K. Benzarti, M. Quiertant, C. Marty, S. Chataigner, C. Aubagnac

Parametric Analysis for Creep of High-Strength Concrete Columns Confined by AFRP

This paper investigates the effect of various material and geometric parameters on the creep of axially loaded fiber-wrapped high-strength concrete column (FWHSCC). For this purpose, a total of twenty-eight FWHSCCs, classified into nine groups, with different intrinsic factors such as the type and amount of fiber reinforced polymer (FRP), the creep of FRP, the water-cement ratio, the aggregate-cement ratio, the silica fume content and the compressive strength of high-strength concrete (HSC) core, and extrinsic factors including the level of loads applied to columns and the radius of column section, were analyzed by the model for predicting the creep of FWHSCC. The results of this parametric study indicate that the creep of FWHSCC is mainly affected by the composition and compressive strength of the concrete core, while the others only have slight influence on the compliance function of creep of FWHSCC.

Yishuo Ma, Yuanfeng Wang

Fire, Impact and Blast Loading

Frontmatter

Glassy-Rubbery Transition Behavior of Epoxy Resins Used in FRP Structural Strengthening Systems

The glass transition behavior of five different epoxies, commercially available as primers and saturants for FRP strengthening systems, have been investigated using dynamic mechanical analysis. Glass transition temperatures,

T

g

, were assigned using three methods: storage modulus onset, loss modulus peak, and tan δ peak. Based on the

T

g

values, a comparison of the five epoxies as well as the three different methods of

T

g

assignment were made. It was observed that post-curing during the DMA test procedure can have a dramatic effect on the glass transition behavior, with

T

g

values increasing up to 22°C on two short exposures to the maximum test temperature. For a given product, the difference in

T

g

values as a function of test method ranged from 12°C to 42°C on the first thermal cycle. Two

T

g

values were observed for one of the products, indicating the presence of secondary polymer as a blend or copolymer. Epoxy polymers used as saturants showed a higher transition temperature than those used as primers and adhesives.

Anurag Jaipuriar, Jeffrey P. Flood, Charles E. Bakis, Maria M. Lopez, Xiongjun He

Fire Tests on RC Beams Strengthened with NSM

The use of Near Surface Mounted (NSM) FRP for strengthening and rehabilitation of reinforced concrete structures has been the subject of various research projects in recent years. FRP strengthening systems are known to perform weak at elevated temperatures. This can be attributed to the relatively poor performance of both adhesive and FRP matrix polymers at temperatures in the range of their glass transition temperatures. Hence, there is a need for thermal protection of such elements. An investigation on the fire endurance of NSM FRP concrete beams under standard fire conditions was undertaken. Six reinforced concrete beam were strengthened in flexure with NSM bars and insulated with different insulation system. Temperatures and deflections were measured during fire testing. Test results indicated that insulated NSM FRP strengthened beams can achieve a fire endurance of at least two hours.

A. Palmieri, S. Matthys, L. Taerwe

Fire Performance of Water-Cooled Cellular GFRP Columns

Structural fire endurance experiments were conducted on full-scale cellular glass fiber reinforced (GFRP) columns under axial compression and subjected to ISO 834 fire exposure from one side. Unprotected columns could resist fire for more than 30 min, which is sufficient for occupants to be evacuated from smaller buildings. The closed cellular cross section prevented the rapid heating of the webs, which could therefore continue stabilizing the face sheet on the cold side against buckling. Water cooling was proved to offer an effective active fire protection system. The structural function of the column could be maintained for two hours. Previously developed models were capable of predicting the time-dependent temperature responses, modulus degradation and time-to-failure.

Yu Bai, Thomas Keller, Erich Hugi, Carsten Ludwig

Flexural and Punching Performances of FRP and Fiber Reinforced Concrete on Impact Loading

In this study, in order to observe the behaviors of fiber reinforced polymer (FRP) strengthened and steel fiber reinforced concrete specimens for impact and static loads, flexural and punching tests were performed. For the one-way flexural and two-way punching tests, concrete specimens with the dimensions of 50×100×350 mm and 50×350×350 mm were fabricated. The steel fiber reinforced concrete specimens showed much enhanced resistance on two-way punching of static and impact loads. Also, the FRP strengthening system provided the outstanding performance under punching resistance. Because of large tensile strength and toughness of ultra high performance concrete (UHPC) in itself, the UHPC specimens retrofitted with FRP showed marginally enhanced strength and energy dissipating capacity.

K.-H. Min, J.-M. Yang, D.-Y. Yoo, Y.-S. Yoon

Protection of Aged Cement Clinker Silo against High Impact and High Temperature Discharge

Located in the outskirts of Lhasa (the capital of Tibet) at an altitude of more than 4000 meters above sea level, this cement clinker silo is a cylindrical, reinforced concrete structure measuring 45m high. An annual maintenance service discovered extensive cracks and severe concrete spalling within the clinker’s inner walls. Some of the beams have been badly damaged and even fractured. In several areas, the concrete cover had already spalled to such depth that the rebars were exposed. The damage to the concrete cover was caused by the highly abrasive effect of the clinker during discharge operations while the constant impact force on the inner concrete walls and beams was the cause of the extensive structural cracks and fracture in some beams. Moreover, the operating temperature in the silo is about 150 deg C, a high temperature dry heat environment which accelerated the concrete spalling process. A strengthening scheme using TYFO®SEH 51 and TYFO®T, a high temperature resistant epoxy was adopted to strengthen the damaged beams. The TYFO® T was proposed in view of the constant high operating temperature of 150 deg C. Since the structural members were constantly exposed to recurring high impact and abrasive actions, a mixture of high temperature resistant TYFO® T and silicon carbide powder was used as an external protective layer. Despite the harsh and unforgiving environment, the project took only one month to complete and the silo resumed production in January 2009 and has been incident-free to date.

Lim Boon Kok, Yang Ming Hui

Nonlinear Response of Steel-Fiber Reinforced Concrete Beams under Blast Loading: Material Modeling and Simulation

Steel fiber reinforced concrete (SFRC) is widely used in the constructional field especially in defense related structures which often subjected to various types of static and dynamic forces. This paper describes the experimental investigation results of SFRC specimens under the effect of compressive and tensile loading. Variables considered are type, aspect ratio and percentage volume of fractions of steel fibers. New mathematical general material constitutive stress-strain relationship for fibrous and conventional concrete were predicted statistically by using SPSS-program, this by basing on the present experimental data. Nonlinear transient dynamic analysis of reinforced concrete beams subjected to blast loading using the finite element method is presented. Eight-node serendipity degenerated plate elements have been used to represent the concrete beam structures. Implicit Newmark with corrector-predictor algorithm is employed for time integration of the equation of the motion. A computer program coded in FORTRAN language is written to implement the present study to give a complete listing of stress and deformation in every concrete or steel layer at any time. The numerical results show good agreement with other published studies’ results which include deflections.

James H. Haido, B. H. Abu Bakar, J. Jayaprakash, Ayad A. Abdul-Razzak

Fire Behaviour of CFRP Prestressed High Strength Concrete Slabs

More sustainable precast concrete elements are emerging utilizing high-performance, self-consolidating, fibre-reinforced concrete (HPSCC) reinforced with high-strength, lightweight, and non-corroding prestressed carbon fibre reinforced polymer reinforcement. One example of this is a new type of precast carbon FRP pretensioned HPSCC member intended as load-bearing elements for building envelopes. Their performance in fire must be understood before they can be widely used with confidence. It is known that the bond strength between both steel and FRP reinforcing bars and concrete deteriorates at elevated temperature and that high strength concrete tends to an explosive spalling failure when subjected to a fire. The bond strength reductions in fire, their impacts on the load-bearing capacity of prestressed concrete elements, and the spalling behaviour of HPSCC remain largely unknown. This paper gives insight in the fire behaviour of CFRP prestressed HPSCC slabs and presents selected results of an experimental fire test study on thin-walled slabs.

Giovanni P. Terrasi, Alex Stutz, Michel Barbezat, Luke A. Bisby

Finite Element Modeling of Insulated FRP-Strengthened RC Beams Exposed to Fire

This paper presents a finite element (FE) model for the thermo-mechanical analysis of insulated FRP-strengthened reinforced concrete (RC) beams exposed to fire. In the model, the effects of loading, thermal expansion of materials, and degradations in both the mechanical properties of materials and the bond behavior at FRP-to-concrete and steel-to-concrete interfaces due to elevated temperatures are all considered. The validity of the FE model is demonstrated through comparisons of FE predictions with results from existing standard fire tests on insulated FRP-strengthened RC beams.

J. G. Dai, W. Y. Gao, J. G. Teng

Effect of Fire and High Temperature on the Properties of Self Compacted Concrete

The use of self-compacted concrete increased significantly during the last few decades. Self-compacted concrete exhibits significantly higher compressive strength than normal concrete, which allows structural members to carry higher loads. The influence of elevated temperature on the properties of concrete is important for fire resistance studies. Fire remains one of the most serious potentials hazardous to any building. In this study, the effect of high temperature on the properties of self-compacted concrete (SCC) compared with the ordinary concrete (NC) was investigated. The effect of cooling technique on the properties of SCC and NC was discussed. The properties of SCC and NC were measured after exposed to 200°C, 400°C and 600°C for two hours. Results from these tests show that the mechanical properties decreased with increasing temperatures. The mechanical properties of SCC cooled gradually are better than that cooled suddenly by water.

M. A. Helal, Kh. M. Heiza

Educations, Applications and Design Guidelines

Frontmatter

IIFC Educational Modules on Polymer Composites in Construction

The next generation of engineers, faced with rapidly deteriorating infrastructure, is destined to face many difficult decisions in maintaining and preserving our civil infrastructure systems. The International Institute for FRP in Construction (IIFC) recognizes the need for the development, advancement, and application of fibre reinforced polymers (FRPs) in construction applications. Many FRP technologies are recognized as important tools for construction and repair of buildings, bridges, and infrastructure. However, these technologies will not become commonplace until the broader civil engineering community is aware of their benefits and potential applications. A key group that will play a role in shaping the future of the construction industry is the next generation of civil engineers. As such, the IIFC Working Group on Education is, in conjunction with the ISIS Canada Research Network, in the process of developing a series of educational modules on FRP technologies for use in engineering curricula. The overarching goal of these modules is to enable and encourage the teaching of FRP technologies in curricula where such topics are not currently covered. This non-research paper presents a brief overview of the educational modules that are being developed by the IIFC Working Group on Education and which will be made freely available for use by all interested parties.

Luke A. Bisby

Challenges in the Design and Delivery of an Online Postgraduate Course in Fibre Composites

Practicing engineers seek to enhance their careers through upgrading skills. Coursework based postgraduate programs are being offered by various institutions targeting these engineers. While face-to-face lectures are feasible in certain circumstances, these courses are ideally suited for web-based delivery, due its flexibility in learning and teaching. Due to industry driven demand, a postgraduate certificate program was introduced recently at the University of Southern Queensland (USQ), Toowoomba, Australia. One of the courses that was introduced as part this program is the Mechanics and Technology of Fibre Composites (ENG8803). With the expertise developed over the years at USQ through the Centre of Excellence in Engineered Fibre Composites (CEEFC) and the experience of providing online and distance courses at USQ, this was an ideal course within the postgraduate program. One of the major challenges faced in the design and delivery of this course is the need to cater for a diverse student cohort with varying industry experience. This course was successfully delivered for the first time in 2008 and employed a variety of online assessment tools. The experiences of the author in developing the course on fibre composites within the graduate program and an evaluation on the effectiveness of the diverse assessment strategies from a student learning perspective are presented in this paper. Enhancement to the course materials through multi-media resources is also discussed.

Thiru Aravinthan

Virtual Practice with Computer Aided Software toward Better Understanding of RC Beams Strengthened by External Bonded FRP

This paper focuses on a computer solution that proposes the non-linear behaviour analysis of reinforced concrete beams strengthened by means of external bonded FRP. This analysis considers actual material behaviour laws. It takes into account the sliding effect at the composite-to-concrete interface and the durability of the strengthened structure via the study of the materials fatigue and the interface visco-elastic properties. After research development, this software is currently used in Lyon 1 University by student at a Master level. In the case of FRP strengthening course deliver in the university, students are asked to practice FRP virtually thanks to modelling to better understanding the effect of those materials of RC beams strengthening. Parametrical studies are carried out in order to understand the influence of FRP properties on the beams me-chanical behaviour.

Ferrier Emmanuel, Hamelin Patrice, Bigaud David

Structural Remediation of Unreinforced Brick Masonry Walls of Heritage Palace Building with Carbon Fibre Reinforced Polymers

A sprawling palace complex built in the year circa. 1893 and belonging to the Nizam family, rulers of the erstwhile princely state of Hyderabad in India, is currently being developed as a luxury heritage palace hotel by a leading hotel group from India. Various functional buildings are integrated to form the palace complex of around 940,000 square meters area. The original construction of the palace features mainly of a load bearing masonry structure comprising of burnt brick masonry with lime mortar. Years of disuse and exposure to environmental vagaries had resulted in various distresses to the structures. The present developers thought it prudent to conduct a structural audit of the palace complex to assess the present condition of the various structures. Subsequent to a structural audit, it was noted that, amongst other anomalies, various sections of the load bearing masonry walls of various buildings were non-compliant to the allowable values of slenderness ratios. This necessitated certain remediation measures to the deficient masonry wall panels. A remediation scheme using carbon fibre reinforced polymer (CFRP) bands as localised intermediate stiffeners onto the walls was found appropriate and thus adopted considering various advantages it offered. This paper describes the site case study on the installation of a particular proprietary CFRP system in achieving the desired objective of carrying out structural remediation of masonry walls.

S. K. Savardekar, R. Jamaji, K. R. Raikar

Inspection, Analysis and Loading Test of a Slab Bridge Strengthened with FRP Laminates

The advantages of FRP as a strengthening material have been widely recognized in recent years. Typical applications of FRP have extended from repairing of cracked columns, beams, bridge decks to enhancing the load capacity of critical structural components. As a demonstration of application of FRP laminates in concrete bridge decks with no transverse reinforcement, the Rolla Bridge in Missouri is selected for this study, which is a two-span simply supported reinforced concrete slab with no transverse steel reinforcement. The original construction combined with the presence of very rigid parapets caused the formation of a wide longitudinal crack which resulted in the slab to behave as two separate elements. The strengthening scheme was designed to avoid further cracking and such that the transverse flexural capacity be higher than the cracking moment. An initial load test, to evaluate the structural behavior, was performed prior the strengthening. The retrofitting of the structure was employed after the major cracks were injected to allow continuity in the cross section. Once the repair work was completed, another load test, identical in procedure to the previous one, was performed to evaluate the efficiency of the strengthening. No additional cracking was observed in the concrete decks as a result of the strengthening program.

Dongming Yan, Chenglin Wu, Jianbo Li, Genda Chen

Structural Performance of Concrete Bridge Deck with Internal FRP Reinforcement

In-situ load tests were performed for a highway bridge with deck containing a novel FRP grillage system. Strains under the deck and top and bottom flanges of girders at various locations were recorded when dump trucks were placed on the bridge. Loading protocols were designed to evaluate: (a) the bridge deck deflection relative to the girders; (b) girder lane load distribution factors; (c) transverse wheel loading distribution widths; and (d) strain distribution over the height of the girder-deck composite section. It was found that lane load distribution factors for wide-flange bulb-tee composite bridge girder systems can be computed accurately with standard design/analysis procedures found in modern bridge specifications. The strain gradients over the height of girders clearly exhibit composite behavior. There was no significant degradation of this bridge from 2005 to 2007.

B. Wan, C. M. Foley

Guidelines for Design of Honeycomb FRP Sandwich Panels

Honeycomb Fiber-Reinforced Polymer (HFRP) sandwich panels with sinusoidal core geometry have shown to be successful both for new construction and rehabilitation of existing bridge decks. The development of standards and guidelines is needed in order to promote wider acceptance of composite sandwich products in construction. Much effort has been devoted to the modeling, optimization, and strength evaluation of the HFRP panel at West Virginia University, in terms of both experimental investigations and analytical solutions. This paper first summarizes all the findings, including out-of-plane compression failure and buckling, shear buckling, shear failure, and delamination at interface due to shear-tension coupling of out-of-plane shear; and progressive failure of laminated facesheet. And then, using the analytical models obtained, parametric studies are carried out and equations are provided to describe the influence of such parameters as interface bonding layer numbers, core wall thicknesses, and facesheet configurations. Next, through correlations with existing experimental results, design guidelines are proposed considering various failure modes. Finally, the proposed guidelines are used to evaluate the strength of HFRP sandwich panels and verify their applicability in practice. All methods presented in this paper can be extended to study other types of sandwich panels.

An Chen, Julio F. Davalos

Load-Bearing Properties of an FRP Bridge after Nine Years of Exposure

FRP is used for corrosion protection and/or as structural members utilizing its anti-corrosion properties. Moreover, since the weight of a superstructure can be significantly reduced due to its specific strength, FRP is expected to offer structural functionalities such as rapid construction, substructure downsizing, and improved seismic performance. We constructed an FRP bridge made entirely of pultruded and hand-lay-up GFRP materials, and have been monitoring its functionality and durability. This paper reports the changes in structural load-bearing behavior during nine years of field exposure. Loading response of the FRP bridge after long-term exposure was almost the same as that just after its completion and deterioration in structural performance has not been observed in nine years. The results prove that FRP materials have good durability and functionality for long-term field exposure as structural materials for bridges.

Iwao Sasaki, Itaru Nishizaki

Cost Optimum Design of Structural Fibre Composite Sandwich Panel for Flooring Applications

A new type of FRP composite panel suitable for civil engineering constructions has been invented by the Australian manufacturers. This new type of FRP structural sandwich Panel is made of fibre glass skins and modified phenolic core material with a density relatively higher than the normal sandwich panel. This panel is used for civil engineering applications of flooring system and glue laminate FRP beams. The extensive experimental work has been carried out by the Centre of Excellence in Engineered Fibre Composites (CEEFC) at the University of Southern Queensland to find the strength parameters of this new sandwich panel. This research aims to develop an optimum design of the new FRP sandwich floor panel by using Finite Element (FE) and Genetic Algorithm (GA) method. The numerical FE shows a relatively accurate simulation for the behaviour of the FRP panel. The materials cost was regarded as an objective function with the EUROCOMP design constraints. The optimization shows that the skins orientations 0/90o would produce the best design for one-way spaning floor panel.

Ziad K. Awad, Thiru Aravinthan, Yan Zhuge

Bond and Interfacial Stresses Between FRP and Concreter

Frontmatter

Effect of Load Distribution on IC Debonding in FRP-Plated RC Beams

Intermediate crack debonding (IC debonding) is a common failure mode for RC beams flexurally-strengthened with externally bonded FRP reinforcement. Although numerous studies have been carried out on IC debonding, the vast majority of them have been concerned with beams subjected to three- or four- point bending despite the fact that a uniformly distributed load (UDL) is a more common loading condition in practice. This paper presents the first ever finite element study into the effect of load distribution on IC debonding failure. A recently developed FE model was employed to simulate the IC debonding failure of three beams tested by other researchers under different load distributions and then to simulate the IC debonding failure of a beam under UDL. The numerical predictions are found to be in close agreement with the test re-sults and confirm the experimental observation that the IC debonding strain in the FRP plate (and hence the IC debonding moment of the strengthened section) increases as the load distribution becomes more uniform.

J. G. Teng, G. M. Chen, J. F. Chen

Effect of Bar-Cutoff and Bent-Point Locations on Debonding Loads in RC Beams Strengthened with CFRP Plates

In recent years, the use of Fibre Reinforced Polymer (FRP) composites for external strengthening of concrete structures has emerged as one of the most promising technologies in material and structural engineering. Although bonding of FRP to the soffit and side faces of reinforced concrete beams increases their flexural and shear capacities, debonding of FRP layers from the concrete substrate frequently happens and decreases the expected failure capacity. Over the last two decades, many parameters such as surface preparation of concrete specimens, compressive strength of concrete and geometrical dimensions of the FRP plate including bonded length, thickness and width, number of plies, and taper end effects have been shown to affect the debonding failure of RC beams strengthened with FRP laminates. An experimental study was performed to determine the effects of bar-cutoff or bend-point location on design debonding loads of RC beams strengthened with CFRP sheets. A total of seven 3-m long beams were produced, strengthened and tested under a 3-point loading. Two specimens served as control, while two had two different types of bar-cutoff locations and two had two different types of bend-point locations. Finally, the last one with four U-shaped strips to prevent debonding of the FRP sheet was used as a bar-cutoff specimen. The analysis of the experimental results was focused mainly on crack distribution and crack widths. The results of the experimental program showed distinct effects of bar-cutoff and bend-point on the total beam behaviour and debonding load, which will be discussed in the fall paper.

M. R. Eftekhar, D. Mostofinejad

Meso-Scale Modelling of FRP-to-Concrete Bond Behaviour Using LSDYNA

This paper presents a preliminary investigation into the modelling of FRP-to-concrete bond behaviour using the K&C concrete damage model in LSDYNA explicit. The proposed FE model adopts the first order eight node hexahedron 3D solid element with one integration point and a sub-millimetre mesh. Results show that the model can simulate the static FRP-to-concrete bond behaviour with good accuracy and mesh objectivity. Further research is being undertaken to investigate its suitability for modelling the dynamic FRP-to-concrete bond behaviour.

X. Q. Li, J. F. Chen, Y. Lu

Investigation on Fracture Behavior of FRP-Concrete Interface under Direct Shear

In this study, the existing researches on debonding performance of FRP-Concrete Interface under direct shear are reviewed and compared at first, and then the hypothesis is put forward that ultimate bearing capacity of FRP-Concrete Interface under pure shear is combined of fracture-resisting force at the undamaged area and friction stress transferred along the already debonded surface. Following that, the formulae on fracture energy and friction stress for FRP-Concrete Interface under pure shear are deduced, through which the values for fracture energy and friction stress at the FRP-Concrete Interface are obtained based on the experimental results of eight specimens with FRP-Concrete Interface. On the basis of theoretical analysis mentioned above, such conclusions can be reached that the friction-resisting stress transferred along the already deteriorated bi-material interface is independent of length of FRP bonded onto concrete substrates and concrete strength, but relies on the tension rigidity; on the contrary, cohesive fracture energy is dependent on length and tension stiffness of FRP bonded to concrete substrate. Besides, the percentage of the fracture-resisting force in the ultimate debonding load for the interface decreases with the bonding length of FRP increasing, but increases with the increase of the layers of the FRP.

Feng-Chen An, Shuang-Yin Cao, Jin-Long Pan, Qian Ge

Towards a Standard Test Method for Assessing FRP-to-Concrete Bond Characteristics

It is well established that debonding of adhesive-applied FRP retrofit materials from their concrete substrate often is a critical limit state. This paper adopts the use of a simple concrete beam specimen similar to that used to determine the modulus of rupture of concrete. To achieve controlled debonding behaviour, the beam is notched to represent cracked concrete. This paper addresses specific issues associated with standardising such a test specimen including a) the width of the FRP relative to the concrete substrate width; b) the geometry of the induced notch; and c) the effect of providing an initially unbonded region in the vicinity of the notch. Conclusions provide recommended specimen geometry which satisfies the objectives of such a standardised test.

Troy Eveslage, John Aidoo, William Bro, Kent A. Harries

Examination of Interfacial Stresses due to Crack Propagation in FRP Retrofitted RC Beams

The present study investigates the stresses on the concrete substrate at the vicinity of the FRP fabrics. In this experimental research, 4 RC beams are prepared from which 2 beams are unstrengthened and 2 beams are strengthened with CFRP fabrics. Dimensions of the beams are 150mm×150mm×1000mm, and all of them are precracked at the middle section of the beam. The aim of the research is to identify the effect of the cracks on the stresses at the bond region between the FRP layer and the concrete substrate. An innovative experimental process is proposed in order to observe these stresses, which are critical parameters in debonding mode of failure in FRP retrofitted RC beams.

Mohammad Zaman Kabir, Ata Hojatkashani

A Rigorous Solution for Interfacial Stresses in Plated Beams

A significant increase in the strength and performance of RC, timber and metallic beams can be achieved by bonding an FRP composite, steel or metallic plate on the tension face of a beam. One of the major failure modes in these plated beams is the premature debonding of the plate from the original beam in a brittle manner. This failure is often attributed to the interfacial shear and normal stresses developed between the adherends, which has led to the development of many analytical solutions over the last two decades. Most of the previous solutions have failed to include the effect of the adherend shear deformation due to difficulties in arriving at the exact solution, although a very few solutions have considered this effect in different approximate methods. The few solutions which included the effect of shear deformation of adherends are limited to one or two specific loading conditions. This paper presents a rigorous analytical solution for predicting the interfacial stresses in plated beams under an arbitrary loading with the axial, bending and shear deformations of the adherends considered simultaneously in closed form using Timoshenko’s beam theory. The solution is applicable for any prismatic cross section with any linear elastic material for the adherends and thin or thick plates bonded either symmetrically or asymmetrically to the beam. The present solution is compared with previous analytical solutions.

V. Narayanamurthy, J. F. Chen, J. Cairns

Evaluation of the Bond Behavior at the Intermediate Crack Element with a Special Test Procedure

The bond behavior of externally bonded reinforcement is one main parameter for the load bearing capacity of strengthened reinforced concrete structures. Because of the low bond force transfer at the outmost bending crack, the bond forces have also been transferred to elements between the cracks in order to effectively utilize the permissible stress of the CFRP strip. Two different experimental series on the bond behavior on the intermediate crack element were carried out. Small tests on an idealized intermediate crack element were made to evaluate the bond stress increase. In the second series parts of a structural element, which had the length of an intermediate crack element were tested to find out about other effects which only occur in the structural element. Based on these experimental data and the differential equation of the sway bond a new concept for the bond behavior of externally bonded reinforcement has been found out.

Wolfgang Finckh, Konrad Zilch

Numerical Modeling of the FRP/Concrete Interfacial Behavior of FRP Shear-Strengthened Beams

In this paper, we compare the validity of two approaches to simulate the FRP/concrete interfacial behavior of FRP shear-strengthened beams. In the first approach, the FRP/concrete interfacial behavior is modeled with two-dimensional interface elements. These elements are provided in directions parallel and perpendicular to fibers orientation. In this case, the bond—slip behavior between concrete and FRP is established on the basis of experimental results obtained from shear-lap specimens. In the second approach, the slip between concrete and FRP is simulated by one-directional truss elements aligned in a discrete manner. In this case, the bond—slip model of the FRP/concrete interface is a bilinear relationship. The accuracy of each approach to simulate the FRP/concrete interfacial behavior is investigated by comparing them with experimental results. The significance of both approaches is discussed.

Ahmed Godat, Pierre Labossière, Kenneth W. Neale

Analysis of Interfacial Bond Stress of Bonding Anchors for FRP Tendon

An analytic interfacial bonding stress solution of bonding anchors for FRP tendon, loaded by axial force, is studied in this article. Based on the assumptions and differential equations of force equilibrium, the distribution of shear stress through the thickness of the anchors is derived, the calculating formula of interfacial bonding Stress is obtained. The presented calculating formula agrees well with the result of finite element analysis (FEA). Furthermore, based on the analytic solution, the factors affecting the distribution of interfacial bonding stress are discussed, including elastic modulus of material and geometry parameters.

Qilin Zhao, Fei Li, Haosen Chen

Debonding Behavior of Skew FRP-Bonded Concrete Joints

In fibre reinforced polymer (FRP) shear-strengthened RC beams, the fiber orientation in FRP may not coincide with the crack opening direction of concrete (the pullout direction of FRP). FRP under such a stress condition is hereafter termed “skew FRP”. The issue of how to predict the bond strength between a concrete substrate and a skew FRP remains unsolved. This paper presents both experimental and predicted results on the pullout strength of FRP in a series of skew FRP-bonded concrete joints, in which the angle between the fibre orientation and the pullout direction of FRP varied from 0° to 45°. Both FRP plates and FRP sheets were used in the tests. It was found that the above-mentioned angle influences significantly the pullout strength of FRP, in other words, the debonding stress of fibers, due to the skew effects existing in the bond interface. Such effects should be appropriately considered particularly when evaluating the shear contribution of FRP in FRP shear-strengthened RC beams.

J. G. Dai, Y. B. Cao

Effectiveness of U-Shaped CFRP Wraps as End Anchorages in Predominant Flexure and Shear Region

U-shaped external anchorage have been used to enhance the shear resistance and performance of RC beams strengthened by externally bonded CFRP plates but the reported results are not adequate yet to draw rational conclusions. One factor that could affect the ultimate strength and mode of failure is the depth of the end anchorage used. Varying end anchorage depths were considered in this study to investigate the effectiveness of U-shaped end anchorages along with determining ultimate load carrying capacity and failure modes of strengthened beams in predominant flexure and shear loading regions. Full depth U-shaped anchorages at plate cut-off points were found to be effective in strengthened RC beams in the predominant shear loading region while depth of the end anchorage was not found to be factor that affects the load carrying capacity of the strengthened RC beams.

A. A. R. Khan, Tehmina Ayub

Behavior of an Innovative End-Anchored Externally Bonded CFRP Strengthening System under Low Cycle Fatigue

Building and bridge columns are particularly vulnerable when earthquakes occur. Retrofit of deficient reinforced concrete columns with CFRP jackets and bonded CFRP plates is an efficient method to increase their strength and ductility and then to enhance their seismic resistance. However, issues related to anchorage of the plates can be a concern when strengthening flexural concrete members. This study presents specific end-anchors reinforcement systems which were designed and tested under monotonic and low cycle fatigue loading and compared with a reference system commercially available. A total of 16 specimens were tested up to failure, to check the performances of these anchors. It appears that anchors increase the ultimate capacity and ductility of bonded plates.

R. Sadone, M. Quiertant, S. Chataigner, J. Mercier, E. Ferrier

Experimental Investigation of CF Anchorage System Used for Seismic Retrofitting of RC Columns

This paper investigates the suitability and effectiveness of CF anchorage system in strengthening the bond in between the CFRP retrofit sheet and structure junction. i.e. column beam or column slab junction. For this purpose, a detailed experimental program was conducted, which is presented here briefly. Five different anchorage systems are discussed here. Results of the experimental observations are discussed in the form of load-slip curves, ultimate capacity and failure modes. The test result, in general indicates that the use of CF anchor provides an enhancement in the overall seismic capacity of strengthened specimen.

Q. Sami, E. Ferrier, L. Michel, A. Si-Larbi, P. Hamelin

Experimental Study on Grooving Detail for Elimination of Debonding of FRP Sheets from Concrete Surface

Debonding of FRP sheets from concrete surface has been a challenging phenomenon attracting many researches in recent years. Surface preparation of concrete before attaching FRP sheets is considered a suitable method to postpone debonding, but with limited effects. Grooving is an innovative technique to overcome debonding of FRP laminates from concrete surface, which has been recently used in Isfahan University of Technology (IUT). In this paper, the effect of different factors influencing the grooving capability is addressed aiming at reducing the debonding potential of FRP sheets from the concrete surface. These factors include the width and the depth of the grooves. The laboratory specimens included about thirty 100×100×500 mm plain concrete beams. Having been grooved on the surface, the specimens were reinforced with CFRP sheets and underwent the four-point flexural test so as to measure the ultimate loading capacity. The outcomes demonstrate that, debonding can be completely averted or at least to a large extent limited by considering specified width and depth for the grooves.

D. Mostofinejad, M. J. Hajrasouliha

Interfacial Behavior between Mechanically Fastened FRP Laminates and Concrete Substrate

This study addresses the interfacial behavior between Mechanically Fastened FRP (MF-FRP) laminates and concrete substrate. For this purpose, a simplified numerical model is formulated with the aim of developing a suitable bearing stress-slip relationship to model the mechanical behavior of the FRP/concrete interface. The proposed relationship is significantly different from another proposal found in the literature as it was calibrated using experimental results from tests on MF-FRP connections realized with multiple fasteners.

E. Martinelli, A. Napoli, R. Realfonzo

FRP-to-Concrete Joint Assemblies Anchored with Multiple FRP Anchors: Experimental Investigation

Higher strains can be developed in fibre-reinforced polymer (FRP) composites which are bonded to the surfaces of concrete members if the FRP is anchored. Anchors made from FRP (also known as FRP spike anchors but herein referred to as FRP anchors) are a promising type of anchorage as they can be applied to a variety of different shaped structural elements and they have been shown to be effective in enhancing the strain capacity of externally bonded FRP. Limited research, however, has been conducted on understanding and quantifying the strength and behaviour of such anchors in isolation and research to date has been on mainly single anchors. A series of tests is therefore reported in this paper on FRP-to-concrete joints anchored with two FRP anchors with the main test variable being the relative position of the anchors. Displacement controlled tests have enabled the complete load-slip responses of the joints to be captured which in turn provides valuable insights to be gained in understanding the behaviour of the anchored joint over the complete loading range. The tests reported in this paper advance our understanding of FRP anchor groups in anchoring externally bonded FRP strengthening systems.

H. W. Zhang, S. T. Smith

Temperature and Water-Immersion Effect on Mode II Fracture Behavior of CFRP-Concrete Interface

Rehabilitation and retrofit of concrete structural members using externally bonded Fiber Reinforced Polymer (FRP) strips has been gaining steadily use in recent years because of its many advantages, such as ease and speed of construction, low cost, low maintenance, and high strength to weight ratio. An important design issue with significant performance and safety implications is the debonding of externally bonded FRP strips in flexural members, where the delamination is primarily due to Mode II facture. A lot of research has been done in this area, but there are concerns about interface durability. This study is based on a fracture mechanics approach using Mode II single shear test to evaluate the durability of Carbon FRP (CFRP)-concrete interface subject to two combined environmental conditioning variables: (1) immersion in deionized water varying from 0 to 15 weeks; and simultaneously (2) controlled temperatures varying from 25°C to 60°C of the same samples immersed in water. Anew method to obtain the fracture energy release rate and the cohesive law is proposed based on J-integral, by measuring load and slip at the debonding end only, which was verified by the traditional strain-based method. The durability of the interface is characterized by the fracture energy release rate. By comparing the results with those from unconditioned companion specimens, it is found that considerable degradation of the interface integrity resulted with increased moisture duration and temperature. The test results will be further used to develop a model to predict the long-term behaviour of the interface based on Arrhenius or other relations.

Fatemeh Sedigh Imani, An Chen, Julio F. Davalos, Indrajit Ray

Ultrasonic Evaluation of CFRP-Concrete Interface for Specimens under Temperature and Water-Immersion Aging Effects

Ultrasonic non-destructive evaluation (NDE) techniques are widely used for structural health monitoring of concrete/FRP structures. In this study, experimental and processing schemes of surface acoustic waves (SAW) are described for assessing concrete/CFRP specimens subjected to accelerated aging conditions. Ultrasonic waves are generated and received at one side using narrow-band transducers of 110 kHz center frequency. The received signals are filtered and amplified then digitized and processed to extract various parameters in both time and frequency domains. These parameters include ultrasound propagation speed, maximum amplitude, total power, and the slope at maximum power spectrum. Changes in these parameters due to water immersion aging at different temperatures were monitored over 10 weeks. Results indicated a notable decrease in measured ultrasonic parameters over time, particularly after the first 2 weeks. This may indicate a debonding or deterioration in the concrete/FRP samples. This behavior showed good agreement with the findings of a parallel destructive study on Mode-II fracture loading of CFRP-concrete samples, tested to obtain fracture energy and define traction-separation response under temperature and water-immersion aging effects.

A. M. Mahmoud, H. H. Ammar, O. M. Mukdadi, I. Ray, F. Imani, A. Chen, J. F. Davalos

Modified Beam Bond Test on Externally Bonded and Near Surface Mounted FRP Strengthened RC Beams

The paper concerns bond behavior between composite carbon fibre reinforced polymer (CFRP) materials and concrete in externally bonded (EB) and near surface mounted (NSM) FRP strengthened reinforced concrete (RC) beams. Bond mechanism was investigated on the modified bond test in aspect of six parameters: beam’s span and depth, longitudinal steel reinforcement ratio, type of the CFRP strips/sheets, CFRP bond length, and concrete compressive strength. In order to confirm the influence of the existing steel reinforcement ratio on the FRP-to-concrete bond conditions, the longitudinal steel bars in some beams were cut through at the mid-span. The test confirmed an important rule of the internal steel bars on the FRP-to-concrete interfaces and the final failure modes.

Renata Kotynia

Experimental Investigation on Bond of NSM Strengthened RC Structures

Near Surface Mounted (NSM) FRP reinforcement is being increasingly recognized as a valid alternative to externally bonded reinforcement (EBR) for enhancing the flexural strength and shear resistance of deficient reinforced concrete members. As this technology emerges, the structural behaviour of NSM FRP strengthened elements needs to be characterized, and bond between NSM FRP bars and concrete is the first issue to be addressed. This paper presents, as part of a study in the framework of a Round Robin Testing (RRT) programme, the results of a series of 27 double shear bond tests on NSM FRP strengthened concrete. Aim of this project is to investigate the feasibility of the adopted test method and to investigate the mechanism of bond between NSM reinforcement and substrate material. Experimental results confirm the efficiency and re-liability of the test method and the bond effectiveness of the NSM technique for strengthening RC members.

A. Palmieri, S. Matthys

Bond Strength of BFRP Bars to Basalt Fiber Reinforced High-Strength Concrete

In order to study the bonding characteristic of the BFRP(Basalt Fiber Reinforced Plastics for short) bars and the basalt fiber reinforced high-strength concrete, we embedded the BFRP bar into the cubic concrete specimen which mixed the element of the basalt fiber sized 150mm×150mm×150mm. The diameter of the BFRP bars used for experiment were differentiated into 10mm, 14mm and 18mm. The BFRP bonding length was differentiated into 40mm, 70mm and 100mm. The basalt fiber volume content of high-strength concrete was differentiated into 0%, 0.1%, 0.15% and 0.2%. By changing the diameter of the BFRP, the bonding length of the BFRP and the basalt fiber volume content of the basalt fiber reinforced high-strength concrete, we can research the bonding capacity between the BFRP and the basalt fiber reinforced high-strength concrete. The experimental results indicate that the average bonding strength decreased while the bonding length increased and it become weaker while the diameter of the BFRP was bigger, and we have the best effect of the bonding strength when its fiber content was 0.2% comparing with three kinds of fiber content.

Qiaowei Bi, Hui Wang

Bond Strength of FRP Rebar to Concrete: Effect of Concrete Confinement

According to ACI 440.1R-06, the presence of transverse reinforcement does not affect the bond strength of fiber reinforced polymer (FRP) rebar to concrete. This conclusion was based on a limited number of data (19 confined beam tests) available in literature at the time. In the present study, 177 beam bond test data, failed by concrete splitting, was collected to investigate the effect of concrete confinement on the bond strength with FRP rebar. Of these 177 beam-type specimens, 105 specimens had transverse reinforcement. It was observed that the presence of transverse reinforcement increased the bond strength of FRP rebar to concrete by 10%–15%, which eventually decreases the development length needed for attaining the tensile strength of FRP rebar. A linear regression was performed on the collected data to develop an equation to determine the bond strength of FRP rebar to concrete in presence of transverse reinforcement and the equation was compared with the ACI 440.1R-06 equation and the experimental results. Based on the analysis, it was found that the proposed equation is in good agreement with the experimental results and it yields a better estimate of bond strength than the ACI 440.1R-06 equation.

Shahriar Quayyum, Ahmad Rteil

Bond Strength of Fiber Reinforced Polymer (FRP) Bars in Autoclaved Aerated Concrete (AAC)

The use of fiber reinforced polymer (FRP) composites is significantly growing in civil engineering works where maintenance cost of structure is concerned. They have excellent properties on highly corrosion resistance, high strength and lightweight. This research studies bond strength of autoclaved aerated concrete (AAC) reinforced with FRP bars. It is compared with autoclaved aerated concrete reinforced with mild steel bars. The concentric pullout method is implemented in order to find the bond strength. The bond strength including the mode of failure and bond strength is studied with varying type, surface treatment and embed-ment length of reinforcing bars. The result reveals that bond strength is found increased with embedment length. In particular, sand -coated Carbon fiber bar gives the most promising results with the highest bond strength in synthetic fiber bars.

B. Israngkura Na Ayudhya, Y. Ungkoon

Bond Mechanism of Carbon Fiber Reinforced Polymer Grid to Concrete

Carbon Fiber Reinforced Polymer (CFRP) Grid provides alternative reinforcing material for concrete structural elements. To implement its use for different structure applications, this paper summarize a research under taken to study the bond properties of CFRP Grid to concrete. The research includes an experimental program consist of eight specially designed specimens, each consist of two concrete blocks, used to apply pure tension loads to the CFRP Grid using hydraulic jacks. The specimens included different embedment length of the CFRP Grid with and without transverse wires. The experimental program included also four one way reinforced concrete slabs with different spliced lengths at mid span to determine the effective development lengths of the CFRP Grid subject to flexural stresses. Research funding provided general design guideline for the use of these types of grids as reinforcements for concrete structures.

L. Ding, S. Rizkalla, G. Wu, Z. S. Wu

Confinement of Concrete by FRP in Compression

Frontmatter

Effect of Geometric Discontinuities on FRP Strain Efficiency in FRP-Confined Circular Concrete-Filled Steel Tubes

The confinement of concrete columns using FRP jackets/wraps has become a popular retrofitting technique. More recently, the benefit of FRP confinement of concrete-filled steel tubes has been also explored by researchers. Failure of such FRP-wrapped concrete-filled steel tubes is usually governed by rupture of the FRP in the hoop direction. However, the observed FRP hoop strain at failure is typically lower than the ultimate strain in a flat coupon test. Many factors contribute to this phenomenon, one of which is the geometrical discontinuities at the ends of FRP wraps. This paper examines the effect of these geometrical discontinuities on the hoop rupture strain of FRP wraps. Detailed finite element (FE) analyses conducted using both linear elastic and elastic-perfectly plastic adhesive constitutive models are presented. Comparison between the FE predictions and available test results shows that the strain efficiency predicted by FE analysis using an elastic-perfectly plastic adhesive model are in reasonable overall agreement with the test results.

S. Q. Li, J. F. Chen, L. A. Bisby, Y. M. Hu, J. G. Teng

The Ultimate Condition of FRP Confined Concrete Columns: New Experimental Observations and Insights

A large body of research is available on FRP confinement of concrete. Many hundreds of tests have been performed and dozens of empirical models are available. However, some of the key mechanics of FRP wrapped concrete are still not understood. Research is needed to understand, quantify, and rationally account for the hoop strain variation in FRP wraps at failure; since failure is fundamentally defined by hoop rupture of the FRP in tension. In this paper, a digital image analysis technique is used to quantify the variation of axial and hoop strain over the surface of FRP wrapped concrete cylinders. Tests on FRP wrapped cylinders of varying aspect ratio are presented to study factors influencing strain variability. The first ever quantified statistical description of hoop strain variability is provided, and the consequences of this variability are discussed.

Luke A. Bisby, Tim J. Stratford

Bearing Strength of CFRP Confined Concrete

Concrete sections may be subjected to compressive loads in a concentrated part of the total area. The bearing strength of concrete is related to the compressive strength and the ratio of the total surface area to load bearing area (known as bearing ratio). The bearing strength of concrete can be increased by providing external lateral confinement. This paper reports and discusses the results of experimental investigations into the bearing strength of laterally confined concrete, using Carbon Fibre Reinforced Polymer (CFRP). The parameters of the investigations included the bearing ratio (2, 4 and 6) and bearing shape (square and circular). Results demonstrated the bearing strength of concrete is increased by up to 74% through CFRP confinement. It was found the shape of the bearing area had marginal influence on the bearing strength of concrete.

Craig A. Scheffers, R. Sri Ravindrarajah, Rhesa Reinaldy

Confinement Behaviour of Eccentrically Loaded RCC Columns Using FRP Sheets

The use of Fiber Reinforced Polymer (FRP) confined reinforced concrete columns are increasing rapidly for new construction as well as rebuilding of concrete structures. Design of these FRP confined concrete columns requires an accurate estimate of the performance enhancement due to the confinement mechanism. Therefore, key issue is to develop a confinement model, which relates the confined concrete strength with the unconfined concrete strength. In the present study, a 3-D finite element model of FRP confined reinforced concrete column under axial and eccentric loading has been developed. The finite element model was developed using the finite element software, ANSYS. Different important parameters have been studied in the present paper: namely, unconfined concrete strength, thickness, orthotropic properties and orientation of FRP layers. The present study has focused on some interesting aspects of these parameters on the confinement effectiveness and has also generated many new results for future reference.

Anupam Chakrabarti

Concrete Column Confinement with Mechanism-Based Composite Bistable Structures

The application of fiber reinforced polymer (FRP) composites in civil engineering has advanced drastically in recent years, especially in the area of retrofitting concrete bridge columns. However, composite’s non-ductile (brittle) behavior is one of the concerns that have yet to be fully addressed. The objective of this research is to investigate a mechanism-based bistable composite structure as the wrapping system to improve the confinement in concrete columns. It consists of energy-absorbing “links”, main link and waiting link with the former being the primary load carrier and the latter as the secondary after the main link fails. A series of testing on cylindrical concrete members wrapped with the bistable structure made of hybrid carbon and glass FRP were conducted to investigate the effect of link geometry on the behavior. The results showed that a controlled failure was achieved in the structure and the ductility and energy absorption were enhanced. The effectiveness of the confinement was found to be affected by the number of links and the energy absorption relied on the size of the links.

C. Wan, C. Quon, L. Cheng

Confined Circular and Square R.C. Sections: an Analytical Model for the Prediction of Ultimate Strength

An analytical model is proposed for the prediction of ultimate strength of square sections confined by FRP. Since the model considers the corner radius influence, circular sections are automatically included as a particular case. The simplified model has been tested against a set of experimental values available in the literature: the comparison was satisfactory and its accuracy is discussed. The performance of the model is validated in terms of average absolute error and its standard deviation. The model is based on a revision of the classical strength criterion proposed by Ottosen.

Nicola Nisticò, Giorgio Monti, Valentino Lovo

Stress-Strain Modeling of Rectangular Concrete Columns Confined by FRP Jacket

The stress-strain behavior of fiber reinforced polymer (FRP)-confined concrete under axial compression has been extensively studied. However, most of the existing models deal with circular and square columns. This paper presents a unified stress-strain model for rectangular, square and circular concrete columns confined by FRP jackets. The model is based on a large database that includes both data from the authors’ own tests and those collected from the literature. A difficult task for the stress-strain modeling is the determination of the ultimate strain for which existing models present a larger scattering of results. Different models for the prediction of the ultimate stress and strain of FRP-confined concrete are reviewed, and more accurate expres-sions are proposed. The proposed stress-strain model is compared with other existing models, which shows a reasonable agreement with the experimental results and an improved performance.

Youyi Wei, Yufei Wu

Axial Behavior of FRP Jacketed Extended Rectangular Members Constructed with Low Strength Concrete

While extensive experimental data is present on the axial behavior of FRP jacketed concrete members with circular cross-section, only few data is available for the members with square and rectangular cross-sections. Furthermore, the data is particularly scarce for extended rectangular cross-sections, where the cross-sectional aspect ratio is over two. In addition, most of the existing codes and/or guidelines limit the cross-sectional aspect ratio with 1.5–2.0 due to significantly reduced efficiency of FRP confinement beyond these cross-sectional aspect ratios. In this study, specimens with the cross-sectional aspect ratio of 3.0 are tested under axial compression by using a displacement-ontrolled 000 kN-capacity Instron testing system. While keeping the thickness of external FRP jacket same in all specimens, the arrangement of FRP sheets, which are used in the form of cross-ties are changed. The concrete quality of the specimens is intentionally poor for representing existing weak structural members. Experimental results showed that the efficiency of FRP jacketing was quite high for the extended rectangular cross-sections in case of low strength concrete. In addition, the efficiency of FRP jacketing could further be increased by the use of additional FRP sheets in the form of cross-ties. In the analytical part, the increased efficiency of the FRP jacketing due to presence of FRP cross-ties is explained using the concept of efficiently confined cross-section developed before for concrete confined with steel rectilinear stirrups and cross-ties.

Dogan Akgun, Cem Demir, Alper Ilki

Nonlinear Micromechanics-Based Finite Element Analysis of FRP-Rapped Concrete Columns Subjected to Axial Load

In this research work, new modifications for the microplane constitutive law are first presented to precisely simulate concrete behaviour under various levels of lateral confinement pressure. A key feature of the suggested formula is to make the microplane theory valid to represent concrete behaviour under both low and high lateral confining pressures. An analysis is then carried out using two different numerical procedures. The first procedure is the use of a three-dimensional finite element analysis with the modified microplane formulations as a user-supplied subroutine into the FE commercial software ADINA to model the concrete behaviour under various stress and strain histories. Here, the sub-objective is to validate the formulated microplane approach that is proposed in the first phase of the research program. In the second analysis; the confinement behaviour is simulated using an in-house code. The code uses the proposed formulations for the microplane theory to represent the concrete characteristics to predict the stress—strain relationships of FRP-wrapped concrete columns up to failure. An accurate equation correlating the axial stiffness of the FRP laminates and the lateral strain of the concrete columns to the confining pressure is incorporated in the in-house code. The two analyses give almost the same predictions, with minor discrepancies due to some numerical aspects. An experimental program consisting of testing thirty eight concrete cylinders under various lateral confinement pressures is carried out to assess the accuracy of the numerical predictions. In the experimental program, the lateral pressure is designed to give almost the same lateral confinement behaviour as that resulting from applying FRP sheets. The numerical predictions are finally compared to experimental results for FRP-wrapped and un-wrapped concrete columns under various levels of lateral pressure. This paper gives an overview for the whole research program with a special emphasis on the theoretical part.

Abdel Baky, Demers, Yahiaoui, Neale

Compressive Strength of Concrete Cylinders Confined with CFRP Wraps

It is well established that the confinement of concrete with fiber reinforced polymers (FRP) composites can lead to a significant increase in both the compressive strength and ultimate strain of concrete. Most of the studies focused on normal-strength concretes with strengths in the range of 35 to 60 MPa, and research on FRP-confined low-strength concrete has been very limited. This paper presents the results of an experimental study on the compressive strengths of FRP-confined concrete cylinders with unconfined concrete strength in the range of 21 MPa. Different confinement schemes were used to determine the effect of schemes on the compressive strength of concrete. All the cylinders were tested in uniaxial compression to determine the load carrying capacities of the confined and unconfined cylinders. Compressive strength of FRP-confined concrete was enhanced in all confinement schemes indicating that confinement of concrete using CFRP strips is an ef-ficient method to improve strength of concrete.

A. R. Khan, N. S. Zafar

Procedure for the Statistical Determination of the Design FRP-Confined Concrete Strength

Worldwide research has now reached a level of integration where an effort towards the harmonization of procedures is absolutely needed. Such harmonization may regard, for example, the various steps that lead to the definition of capacity models to be included in design codes, specifically: definition of the test setup, quantities to be measured, identification of the basic variables influencing the phenomenon, distinction between average values and other fractiles, disaggregation of the model in different parts accounting for me-chanics, fine-tuning and randomnesses, and, finally, assessment of the model against the experimental results. Test results and ensuing model developed according to this procedure would naturally lend themselves to be easily shared among the scientific community and would facilitate the task of calibrating the partial coeffi-cients, with the ambitious aim of attaining a uniform reliability level among all capacity equations. This paper, based on previous author works, proposes the application of a procedure for the development of capacity design equations to the capacity model of concrete confined with FRP. The procedure has been applied, with some improving, to a new capacity model proposal and to the one included in the Italian Instructions CNR DT 200–2004. The comparison has the aim of evaluating the uncertainties of the assumed model (both of the me-chanical model and of the basic variables) to obtain a constant level of structural reliability and to outline the implication that a not very well calibrated equation could have in the definition of the characteristic value.

Giorgio Monti, Nicola Nisticò, Valentino Lovo, Silvia Alessandri, Silvia Santini

Performance Evaluation of SFRP-Confined Circular Concrete Columns

This paper presents the results of an experimental investigation that evaluates the effectiveness of using Steel Fibre Reinforced Polymer (SFRP) sheets to confine small-scale plain concrete circular columns. Different parameters were investigated including: number of SFRP layers (1, 2, and 3) and concrete compressive strength (25, 30, and 35 MPa). A total of thirty-five circular specimens (150 mm diameter × 300 mm height) were tested and divided into three groups according to concrete compressive strength. In each group, two/three specimens were tested without wrapping for comparison purposes, and two/three specimens for each number of layers. The specimens were tested under monotonic concentric uni-axial compressive load. Results showed that SFRP confinement improved the performance of the concrete cylinders in terms of axial strength, stress-strain behaviour, and ductility.

Mohammad A. Mashrik, Raafat El-Hacha, Khoa Tran

Mechanical Behavior of Concrete Columns Confined by Laterally Pre-Tensioned FRP

This paper presents the results of an experimental investigation of concrete columns confined by a wound pre-tensioned carbon filament yarn. Yarn winding equipment was developed in the Institute of Polymer Mechanics with the ability to set the desired pre-tension force and thereby producing confined concrete specimens with different initial lateral pressure. It is shown that initial lateral pressure increases the axial stress at which intense internal cracking of the concrete develops.

E. Zīle, V. Tamužs, M. Daugevičius

Effect of CFRP and GFRP Confinement on Behavior of Square Lightweight Concrete Specimens

For improving of the structural properties of lightweight concrete, confinement by Fiber Reinforced Polymer (FRP) can be used. Effect of Fiber Reinforced Polymer on confined lightweight concrete elements is one of the most important research fields. In this study, behavior of confined and unconfined lightweight concrete specimens under uniaxial loading has been discussed. For decreasing of stress concentration and to prevent the fiber from being folded, corners of specimens were chamfered to a radius of 5 to 25 mm. The Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP) were used to confine lightweight concrete specimens. The stress-strain curve of specimens is compared. The result was shown that, Confinement of specimens with CFRP has more ultimate strength than the specimens confined with GFRP.

A. Vatani Oskouei, M. Pirgholi Kivi, S. Taghipour Boroujeni

Confinement of Concrete Piles with FRP

Precast piles are typically reinforced with steel spiral to provide confinement for the concrete core to increase the load carrying capacity as well as ductility of the pile. Confinement is particularly critical within the top region of the pile to resist the impact forces during driving. Due to direct exposure of piles to soils and harsh minerals, corrosion of outer spiral can compromise the long-term durability of typical piles. Since carbon fiber reinforced polymer (CFRP) materials are non-corrosive, they provide a promising alternative to the spiral steel for precast piles. This paper summarizes test results of an experimental program undertaken to evaluate the performance of specially designed CFRP Grid to replace the steel spirals for piles. Seven short columns, representing a 914 mm long section at the top of a pile were tested up to failure to study the effectiveness of the proposed CFRP Grid as reinforcement for confinement.

Hatem M. Seliem, Lining Ding, Sami Rizkalla

Three-Dimensional Finite Element Model for FRP-Confined Circular Concrete Cylinders under Axial Compression

This paper presents a 3D FE model for FRP-confined circular concrete cylinders based on a plastic-damage constitutive model for concrete recently proposed by Yu et al. (2010b). This 3D model is capable of modeling deformation non-uniformity in the axial direction due to factors such as end restraints. Numerical results obtained using the FE model for FRP-confined cylinders with end restraints or with a vertical gap in the FRP jacket conform to expected trends although their quantitative accuracy awaits confirmation by laboratory tests. This FE model has the potential for extension to more general cases of FRP-confined concrete columns (e.g. rectangular concrete columns) and can provide a useful tool for the exploration of confinement mechanisms in the development of simple stress-strain models for design use.

Q. G. Xiao, J. G. Teng, T. Yu, L. Lam

Numerical Analysis of Rectangular Reinforced Concrete Columns Confined with FRP Jacket under Eccentric Loading

The present paper is devoted to investigate the behavior of square RC columns confined with FRP wraps using ANSYS software. A total of four prisms of size 150mm×300mm×500mm and 210mm×210mm×500mm were simulated by the FE model and the results were compared with the experimental test results reported in literature. Very good agreement was found between the model results and the test results. Therefore, the model was validated. As predicted, it was found that the effectiveness of FRP jackets under eccentric loads is reduced in comparison with concentric loads. In the next step, the interaction diagrams of axial force and bending moment for columns confined with FRP wrap was obtained from the model results. They were compared with the interaction diagrams proposed by the design guideline of ACI 440.2R-08. It was found that the load carrying capacities resulted from the model are generally higher than those recommended by ACI 440.2R-08.

M. Hajsadeghi, F. J. Alaee

Flexural Strengthening of Concrete Beams and Slabs

Frontmatter

Flexural Strengthening of Reinforced Concrete Beams with Textile Reinforced Concrete (TRC)

Carbon-epoxy composite materials are of considerable interest for reinforcement, but they need to be improved and have constraints, particularly in terms of cost and criteria of sustainable development. Such alternatives as textile reinforced concrete (TRC) should be seriously considered as substitutes for traditional composite materials. It is in this background that this study aims to explore the feasibility and assess the mechanical performance of reinforced beams in bending. This work focuses on the mechanical feasibility of such solutions by comparing them with traditional solutions such as CFRP and NSM (deformation rate rein-forcement, cracking density, ultimate load, degradation level... etc.) on the basis of an experimental campaign based on 5 beams tested under four point bending. Finally we will try to adapt, supplemented where appropri-ate, CFRP predictive models in the case of the TRC and assess their degree of relevance.

Si Larbi Amir, Contamine Raphael, Ferrier Emmanuel, Hamelin Patrice

The Flexural Behavior of Beams Strengthened with FRP Grid and ECC

Engineered Cementitious Composite (ECC) is a new kind of random short fiber reinforced cementitious composite with ultra high ductility. Unlike common FRC, ECC is developed by optimizing the microstructure of the composite which exhibits tensile strain-hardening behavior with strain capacity more than 3%, yet the fiber content is typically 2% by volume or less. The flexural behavior of concrete beams reinforced with CFRP grid (named NEFMAC) and ECC is studied in this paper. The behavior of concrete beams reinforced with ECC-NEFMAC is compared with the behavior of a beam reinforced with steel and carbon fiber sheet. The research investigates their flexural behavior including pre-cracking state, cracking pattern and width, deflections, ultimate capacities and strains, and the mode of failure. The information obtained throughout this investigation is valuable for future field application and development of design guidelines for ECC and FRP grids.

Ding Yi, Chen Xiaobing, Chen Wenyong

Comparison of Different Repairing Techniques Used for Rehabilitation of Initially Cracked RCC Beams

This paper presents the comparison of different repairing techniques commonly used for cracked RCC beams. Five RCC beams (each 3 meter × 225 mm × 300 mm) designed as under-reinforced beams were cast, cured and tested by two-point loading. One beam was loaded up to failure and treated as “control beam”. Its failure load was noted and deflections were regularly measured by deflection gauges installed at middle and quarter points. Other four beams were loaded up to three-fourth of the failure load of control beam or otherwise up to the development of initial cracks. These beams were then repaired by using four different repair techniques i.e., ferrocement layer, section enlargeent, cement grouting and epoxy injection. When repair process was over, the four repaired beams were tested again and loaded up to their ultimate loads. Again deflections were noted and overall performance of beams was examined. Results were analyzed and disscussed to have a comparison between four methods used in terms of strength and ductility performance. However it was concluded that all patterns used were able to restore or enhance the original structural capacity of cracked sections of beams.

Liaqat A. Qureshi, Kamran A. Qureshi, Tahir Sultan, Jahangeer Munir

Analysis on Mechanical Behavior of RC Beams Strengthened with Inorganic Adhesive CFRP Sheets

The failure modes, ultimate states, flexural strength and shear capacity of reinforced concrete(RC) beams strengthened with inorganic adhesive carbon-fiber-reinforced-polymer(CFRP) sheets were separately discussed based the experimental results. The influences of CFRP sheet amount, anchor condition and steel reinforcement ratio on the flexural strength, and the effects of CFRP sheet amount, CFRP sheet layer, shear span/depth ratio and concrete strength on the shear capacity were analyzed. The results show that debonding failures are prevalent in the RC beams strengthened with inorganic adhesive CFRP sheets; the maximum effective tensile strain of the CFRP sheet is about 0.005; the flexural strength is increased due to the bottom CFRP sheets; the shear capacity is improved for the lateral U type CFRP sheets. Finally, practical calculation formulae for the flexural strength and shear capacity of RC beams strengthened with the inorganic adhesive CFRP sheets are established, which are found good agreement with test results with reasonable reliability.

Xin Zhang, Shibin Li, Liluan Yang, Xiangfei Kong

Experimental Study of Concrete Beams Strengthened with CFRP Sheets under Simulated Vehicles Loads

Five reinforced concrete (RC) beams with epoxy-bonded carbon fiber reinforced polymer (CFRP) sheets were loaded symmetrically with sinusoidal dynamic loads simulating vehicles loads. One sustained loaded RC beam strengthened with externally bonded CFRP sheets and two control RC beams were experimentally investigated. Variables considered in this experimental program included compressive strength of the concrete, reinforcement ratio, bonded length, and load range. The experimental program included two parts: dynamic test and static test. Application of CFRP sheets to the bottom of five RC beams was conducted under dynamic loads and then the static test began after 174,000 dynamic cycles. The results demonstrate the feasibility of rehabilitating and strengthening damaged RC beams with CFRP sheets while the beams are under simulating vehicles loads. The static test program shows that the application of CFRP to RC beams results in increased strength and enhanced performance.

Wenwei Wang, Guofan Zhao, Chengkui Huang

A Systematic Study of Rehabilitation of Reinforced Concrete T-beam Structures Using Externally Bonded FRP Composites

This paper describes a synthesis of findings pertaining to rehabilitation of concrete T-beam bridges with externally bonded FRP composites from a Pennsylvania Department of Transportation District 3 (PennDOT D3) project, with the purpose of answering common questions of concern mainly by state Department of Transportation (DOT) engineers and officials. A method for selecting applicable candidate bridges for suitability of repair with externally bonded FRP composites is described. With this classification, a candidate bridge was selected for a contract repair project. Field and laboratory testing of existing and repaired bridge materials is described. Structural analysis was based on AASHTO specifications. Finite Element (FE) model-ing was performed. Current ACI 440.2R-08 design guidelines were used. Supporting full-scale lab studies were conducted. Results were used to develop draft PennDOT design standards and construction specifica-tions and to apply “lessons learned” to the design and constructability of nearly 1,000 concrete T-beam bridges in Pennsylvania, USA.

J. F. Davalos, A. Chen, I. Ray, A. Justice

Basalt FRPs for Strengthening of RC Members

The use of FRPs to enhance the structural performance of RC members represents today’s common practice. This is mainly due to their high strength to weight ratio, corrosion resistance or ease of application. However, given the current circumstances, the construction industry is in need of a more viable alternative to the commonly used glass and carbon fibres. Hence, the paper discusses two experimental programmes investigating the use of relatively new basalt fibres for strengthening of both compression and flexural members. Application of shear strips in strengthening of an RC beam (University of Sheffield) has shown that even a small amount of basalt FRPs can successfully increase the ultimate load capacity as well as provide anchorage and reduce the brittleness of plate end debonding. Testing of FRP confined concrete cylinders (Magnel Laboratory) has proven basalt to be 14% more effective than glass, yielding an average compressive strength increase of 84% when compared to the unconfined cylinders.

A. Serbescu, M. Guadagnini, K. Pilakoutas, A. Palmieri, S. Matthys

Load-Carrying Capacity of Flexural Reinforced PC Beams with Pretensioned AFRP Sheet

To develop a rational flexural reinforcing method for prestressed concrete (PC) beams with pretensioned Aramid Fiber Reinforced Polymer sheet (AFRPs), the new anchoring method is proposed. It is the concept of this method to rationally disperse the concentrated anchoring stress due to bonding the cross-directional AFRPs in the anchorage areas and to gradually relax the high strain caused at the ends of sheet due to applying the high-strain type epoxy-resin in the areas. Its applicability was confirmed by conducting static four-point loading test of the PC beams reinforced by means of the proposed method. From this study, following results were obtained: 1) applying the proposed anchoring method, predetermined pretensioning force of the sheet can be perfectly introduced into the beams without any mechanical anchoring devices; 2) the cracking and yielding loads, and the ultimate load of the PC beams can be upgraded due to bonding pretensioned AFRPs.

Y. Kurihashi, N. Kishi, A. M. Ali, H. Mikami

Flexural Performance of RC Beams Strengthened with Prestressed AFRP Sheets: Part I. Experiments

A experimental study of flexural performance of reinforced concrete beams (RC) using prestressed aramid fiber reinforced plastic (AFRP) sheets with permanent anchor was conducted. The number of AFRP sheet layers on beams varied from 1 to 3 and the prestress level varied from 0.45 to 0.65. Based on the experimental study of seven beams, the beams strengthened with prestressed AFRP sheets were compared with the beams strengthened with un-prestressed AFRP sheets in flexural properties of cracking moment, yield moment, ulti-mate moment and flexural stiffness. The experimental results show that, compared with the un-strengthened control beams, the flexural performance of beams strengthened with un-prestressed AFRP sheets were enhanced, and that of beams strengthened with prestressed AFRP sheets were further improved, validating the efficiency of prestressed AFRP sheet retrofit.

Zong-cai Deng, Rui Xiao

Flexural Performance of RC Beams Strengthened with Prestressed AFRP Sheets: Part II. Theoretical Analysis

The flexural performance of reinforced concrete beams (RC) strengthened by prestressed aramid fiber reinforced plastic (AFRP) sheets with permanent anchor have been tested and shown in companion paper (Deng & Xiao 2010). Based on sectional analysis, the formulas for calculating the bearing capacity of beams strengthened with prestressed AFRP sheets were established in this paper. By these formulas, the theoretic results of cracking, yield and ultimate moments and its corresponding deflections at these points were derived and compared with the experimental test results of beams. The comparison analysis show that, the analytical results of tested RC beams are in coincidence with the experimental results.

Zong-cai Deng, Rui Xiao

Numerical Simulation on Flexural Reinforcing Effects of AFRP Sheet for Damaged RC Girders

In order to rationally evaluate the reinforcing effects of Aramid fiber reinforced polymer (AFRP) sheet on damaged reinforced concrete (RC) girders, a 3D nonlinear FE analysis method was proposed. Here, firstly assuming the FRP sheet elements to be dummy, pre-analysis was conducted for numerically realizing the damaged situation of the girder. After that, the girder reinforced by bonding FRP sheet on the tension-side surface was analyzed by substituting the dummy elements into FRP sheet ones. In this analysis, the discontinuities of cracks, bond slip, and delamination of sheet were also considered by using interface elements. Its applicability was confirmed comparing with the experimental results.

N. Kishi, M. Komuro, H. Mikami

A Study on the Applicability of ECE Technique on Chloride Contaminated Concrete Retrofitted with FRP Strips

The objective of this study is to evaluate whether the Electrochemical Chloride Extraction (ECE) technique, which has been proven to be an effective tool for removing chloride ions for regular concrete structures, can be effectively used for Fiber-Reinforced Polymer (FRP) repaired concrete structures. FRP retrofit for deteriorated concrete structures is a highly successful practice, but alone it does not address the corrosion at its source: accumulated chloride ions from environmental sources such as de-icing salts. A total of 28 beams were tested, with testing variables including intermittent vs. continuous ECE techniques, different FRP repairing schemes, and applying ECE before and after FRP repair. Parameters monitored during the study included chloride content, pH value around the steel, and current resistance and density. The effectiveness of ECE was determined by changes in chloride levels and the pH value around the steel.

Matthew Anderson, Indrajit Ray, An Chen, Julio Davalos

Finite Element Modeling of RC Beams Strengthened in Flexure with Prestressed NSM CFRP Strips

This paper presents the results from Finite Element Modeling (FEM) of reinforced concrete (RC) beams strengthened in flexure with prestressed Near-Surface Mounted (NSM) Carbon Fiber Reinforced Polymer (CFRP) strips. A total of four large-scale (5.15 m long) RC beams tested at University of Calgary are modeled with ANSYS program. The beams are simply supported with rectangular cross section strengthened with CFRP strips, mounted in one groove in the concrete on the tension side of the beams, using various prestressing levels (0%, 20%, 40% and 60% of the ultimate tensile strength of the CFRP strip). The beams were tested under four-point bending. Comparison between numerical and experimental results shows a good correlation in terms of load-deflection curve at mid-span, strain profile along the CFRP strip at cracking, yielding and ultimate loads, and type of failure mode.

Hamid Y. Omran, Raafat El-Hacha

Advances of Finite Element Analysis for FRP Concrete Beams

In this paper, the advances of finite element methods and analyses for FRP reinforced and strengthened concrete beams in last two decades are reviewed to present a state of the art of the research of numerical analysis and modelling of FRP composite concrete beams. Future research on finite element analysis of FRP composite beams is also presented.

Y. X. Zhang, Xiaoshan Lin

Nonlinear Finite Element Analysis of Composite Steel/FRP-Reinforced Concrete Beams Using a New Beam Element

In this paper, a simple and computation effective one-dimensional two-node beam element is developed based on the Timoshenko’s beam functions and layered approach for nonlinear finite element analysis of structural behaviour of composite steel/FRP-reinforced concrete beams. Both geometric nonlinearity and material nonlinearity are accounted for in the nonlinear finite element model, and Timoshenko’s composite beam functions are employed to represent the transverse displacement and rotation of the element. The agreement of the computed results for steel and FRP reinforced concrete beams with those obtained from experimental study and other numerical analysis demonstrate the efficiency and accuracy of the proposed element model.

Xiaoshan Lin, Y. X. Zhang

Non-Bolted Anchorage Systems for CFRP Laminates Applied for Strengthening of RC Slabs

The anchorage of carbon fibre reinforced polymer (CFRP) laminates used for improving bending capacity of RC slabs is one of the governing factors for their effectiveness. Many investigations are indicating that one of the main modes of failure for CFRP strengthened slabs and decks is via failure of the anchorage of the laminates. Existing systems for improving the anchorage via attaching steel bolts are effective but expensive and time consuming.

The proposed work is investigating the opportunity to use non-bolted anchorage systems which could achieve faster, easier and less expensive improvement of the anchorage in comparison with bolted anchorage systems. The attempt for developing new anchoring systems is based on the idea for redistribution of the stresses in the laminates and the adjacent concrete at the zone of the anchorage.

Four types of anchorage systems for CFRP laminates are used. The laminates are applied on reduced scale RC plints loaded on bending and reflecting unidirectional strengthening of RC slabs. The results indicate opportunity to increase the anchoring capacity of the laminates using similar materials as for initial strengthening. Analysis of the experimental results and comparison with corresponding approaches suggested from other authors is offered.

Ted Donchev, Parviz Nabi

Arching Action in Laterally Restrained GFRP Reinforced Slabs

Expansive corrosion in steel reinforcement significantly reduces the design life and durability of concrete structures. Glass Fibre Reinforced Polymer (GFRP) reinforcement is a more durable alternative to steel reinforcement and has higher strength to weight ratio than steel. Replacing conventional steel with GFRP reinforcement can be highly beneficial. FRP reinforcement can be successfully used in laterally restrained slabs due to enhanced strength above the flexural capacity and increased stiffness as a result of arching action. This paper discusses the tests carried out on three full scale concrete slabs strips reinforced with GFRP bars.

G. Tharmarajah, Susan E. Taylor, Desmond Robinson, David J. Cleland

Flexural Strengthening of RC Continuous Beams Using Hybrid FRP Sheets

Due to linear stress—strain characteristics of FRP up to failure, the ductility of plated members and their ability to redistribute moment is less than that of unplated RC beams. Hybrid FRP laminates, which consist of a combination of either carbon and glass fibers, changes the behavior of the material to a non-linear behavior. Although many in situ RC beams are of continuous construction, there has been very little research into the behavior of such beams with external reinforcement. This paper presents an experimental program conducted to study the behaviour of RC two-span beams strengthened with hybrid carbon and glass reinforced polymer sheets (HCG). The program consists of a total of six continuous beams with overall dimensions equal to 250×150×6000 mm. The test results showed that using the HCG for strengthening the continuous RC beams lead to significantly increase of bearing capacity, ductility and moment redistribution ratio compared to strengthened beams with CFRP or GFRP.

Habib Akbarzadeh, A. A. Maghsoudi

Comparative Study of Deflection Equations for FRP RC Beams

The mechanical and bond characteristics of Fibre Reinforced Polymers (FRP) used as internal reinforcement for Reinforced Concrete (RC) elements result in larger deflections and crack widths compared to the conventional steel RC elements. Consequently, serviceability requirements may govern the design of such members. In the last 20 years, several approaches and codes of practice have been published to predict the theoretical deflection of FRP RC elements.

This paper analyses and examines the experimental deflection results of 145 concrete beams reinforced with FRP bars tested by several researchers, and compares their values with the theoretical values of 10 different approaches and design codes. All of the beam specimens were tested under a four point bending configuration and presented different reinforcement ratios and mechanical and bond properties of the FRP bars.

The objective of the paper is to investigate the suitability of the different approaches at different states of loading under the serviceability range. A statistical analysis is performed to evaluate the goodness of fit of each approach. The influence of several parameters as the level of load, the reinforcement ratio, or the modular ratio is analyzed and compared.

I. Vilanova, C. Barris, Ll. Torres, C. Miàs, M. Baena, V. O. García

Experimental Study on Deformation Recovery and Residual Strength of FRP RC Beams

Many researches on behavior of the structures which were externally strengthened with FRPs have been conducted. However, researches on time-dependent behavior have not been conducted yet. In order to provide improved serviceability to reinforced concrete (RC) members strengthened with FRPs, the behavior of RC structures strengthened with FRPs under sustained loads should be investigated. This paper presents a series of long-term deflection, deformation-recovery and residual strength experiments. For the long-term experiments, three RC beams were fabricated and two of the beams were strengthened with a carbon FRP(CFRP) plate and a glass FRP(GFRP) plate respectively. The beams were placed under sustained load for about 550 days and unloaded. After unloading, static flexural experiments were carried out. As the result, CFRP showed better performance in terms of deflection and strains of rebars and CFRP plate. Moreover, CFRP showed higher deformation recovery and residual strength than the other beams.

M. H. Oh, S. N. Hong, T. W. Kim, J. Cui, S. K. Park

Shear Strengthening of Concrete Beams

Frontmatter

Influence of the Concrete Properties in the Effectiveness of the NSM CFRP Laminates for the Shear Strengthening of RC Beams

The New Surface Mounted (NSM) technique was applied to increase the shear resistance of Reinforced Concrete (RC) beams. For this purpose, laminates of Carbon Fiber Reinforced Polymer (CFRP) were introduced into thin slits made on the concrete cover of the lateral faces of the beams to be strengthened. In the present paper the influence of concrete strength on the effectiveness of the NSM technique is assessed by an experimental program. From the obtained results it can be concluded that the NSM shear strengthening technique with CFRP laminates is still effective in RC beams with low concrete strength. However, as minimum is the concrete strength as less effective is the NSM technique.

Salvador Dias, Joaquim Barros

Experimental Tests on FRP Shear Retrofitted RC Beams

The paper presents the results of experimental tests on two reinforced concrete beams retrofitted by means of FRP strips. Both beams have been removed from the structure of one of the older r.c. buildings in Rome, built up at the beginning of XX century. The experimental tests are carried out in the Laboratory of the Department of Structures at the University of Roma Tre. Before retrofitting, preliminary tests are performed in order to evaluate the homogeneity and the mechanical characteristics of concrete, and elastic tests (shear/bending tests) in order to evaluate the original state of the beams. After retrofitting, failure tests (shear/bending tests) on the beams togheter with compressive tests on concrete and tension tests on rebars are carried out. All performed tests demonstrate the capability of repairing and retrofitting on r.c. structures of modest quality, moreover revealing some aspects due to the fragile behaviour of carbon fibers.

Camillo Nuti, Silvia Santini, Lorena Sguerri

Influence of Transverse Steel on the Performance of RC T-Beams Strengthened in Shear with GFRP Strips

The need for structural rehabilitation of concrete structures all over the world is well established and a large amount of research is devoted in this area. Though a large volume of research is directed towards the flexural behaviour of beams, works on the effect of GFRP strips strengthened on shear are relatively sparse. The present paper focuses on the study of the effect of transverse steel on the performance against shear and modes of failure of simply supported RC T-beams strengthened in shear with GFRP strips. RC T-beams of 2.5 m span are cast at the structural laboratory of IIT, Kharagpur, and are tested with shear reinforcement and GFRP strips in U-shape around the web, and side bonded with orientation of the GFRP strips at 90° and 45° with the horizontal axis of the beam. All the beams are tested on a 300 T UTM. The experimental results clearly indicate the advantage of using externally applied epoxy bonded GFRP system to restore or increase the shear capacity of RC T-beams. It is also observed that the combination of configuration of GFRP strips and transverse steel is an important factor to gain the shear capacity and the ductility.

K. C. Panda, S. V. Barai, S. K. Bhattacharyya

Shear Design Equations for Concrete Girders Strengthened with FRP

Fiber Reinforced Polymer (FRP) systems have emerged as one of the most promising and widely accepted methods of strengthening concrete structures. FRP strengthening systems may consist of carbon (CFRP), glass (GFRP), or aramid (AFRP) fibers. The acceptance and utilization of such strengthening techniques depends on the availability of reliable design guidelines. Shear strengthening with externally bonded FRP is still under investigation and the results obtained thus far are scarce and sometimes controversial. In this study, predictions by the existing analytical models developed for externally bonded FRP shear reinforcements were evaluated and compared to experimental results available in the literature. The results of this investigation show that the models are not reliable for predicting the shear strengthening effect of externally bonded FRPs in a majority of cases. Results from full-scale testing and a comprehensive collection of data from the literature were used in the development and calibration of new design equations which give better predictions of the FRP contribution to shear resistance. This paper presents the results and final recommendations of this study.

M. S. Murphy, A. Belarbi, D. Kuchma

The Shear Behavior of Beams Strengthened with FRP Grid

In this paper, the shear behavior of concrete beam reinforced with FRP grid is studied for the first time and is compared with the behavior of beams reinforced with steel and CFRP sheet respectively. The results show that the beams strengthened with FRP grid have good shear behavior both increasing shear capacity and controlling of crack width.

Wenyong Chen, Xiaobing Chen, Ding Yi

Efficiency of RC T-Section Beams Shear Strengthening with NSM FRP Reinforcement

The paper analyzes an efficiency of a near-surface mounted (NSM) fiber reinforced polymers (FRP) technique for shear strengthening of reinforced concrete (RC) beams. A review of existing research shows that a number of experimental tests and engineering practice in this field is extremely limited. However, the first results have been very promising and aroused interest of the worldwide FRP community. Based on published test results, the paper provides a comparative study of failure modes, FRP strain efficiency and shear strength enhancement. The efficiency of the NSM shear strengthening is discussed in aspect of the following parameters: shape of the beam’s cross-section, beam’s dimensions, internal shear steel reinforcement percentage, type, cross-section, inclination and spacing of the NSM FRP reinforcement along the beam’s axis and the concrete strength.

Renata Kotynia

Mechanical Model to Simulate the NSM FRP Strips Shear Strength Contribution to RC Beams

A three dimensional mechanical model has been recently developed to simulate the Near Surface Mounted (NSM) Fibre Reinforced Polymer (FRP) strips shear strength contribution to Reinforced Concrete (RC) beams throughout the entire loading process, as function of the Critical Diagonal Crack (CDC) opening angle. It was developed by fulfilling equilibrium, kinematic compatibility and constitutive laws of both intervening materials and bond between them. It takes into consideration all of possible failure modes that can affect the behaviour, at ultimate, of a single NSM strip, namely: loss of bond (debonding), semi-conical concrete tensile fracture, rupture of the strip itself and a mixed shallow-semi-cone-plus-debonding failure. Besides, it allows the interaction among adjacent strips to be accounted for. The numerical results, in terms of both shear strength contribution and predicted cracking scenario are presented and compared with experimental evidence regarding some of the most recent experimental programs. From that comparison, a satisfactory level of prediction accuracy, regardless of the main parameters such as concrete mechanical properties, amount and inclination of strips, arises. The main findings, as well as the influence of some of the main intervening parameters, are shown.

Vincenzo Bianco, J. A. O. Barros, Giorgio Monti

Shear Strengthening of RC Beams by Means of NSM FRP Strips: Constitutive Law of a Single Strip

The need to provide a rational explanation to the observed peculiar failure mode affecting the behaviour, at ultimate, of a Reinforced Concrete (RC) beam strengthened in shear by Near Surface Mounted (NSM) Fibre Reinforced Polymer (FRP) strips, led the authors to develop a comprehensive numerical model for simulating the NSM shear strength contribution to RC beams throughout the entire loading process as function of the Critical Diagonal Crack (CDC) opening angle. That model was respectful of equilibrium, kinematic compati-bility and constitutive laws. Despite its high level of prediction accuracy, taking into account all of the possible failure modes, as well as the interaction among adjacent strips, that model resulted relatively complex to be easily implemented in a practitioners-addressed building regulations code. Yet, it can be conveniently simplified into a more user-friendly and closed-form design formula. Crucial point of that simplification is the development of a reliable constitutive analytical law providing the single strip strength as function of the imposed end slip. This paper presents the modelling strategy adopted to determine that constitutive law, as well as its final analytical expression.

Vincenzo Bianco, Giorgio Monti, J. A. O. Barros

Size Effects in Reinforced Concrete Beams Strengthened with CFRP Straps

A carbon fibre reinforced polymer (CFRP) strap system has been identified as a promising method for retrofitting existing reinforced concrete (RC) structures. The CFRP straps, which can be prestressed, act as additional transverse reinforcement and have been shown to increase the shear capacity of RC beams. Since the straps are unbonded, the strap strain consists of any initial prestrain plus an additional strain due to crack opening. Hence, in a retrofitted beam, there are two potential sources of size effects: within the base RC structure; and that inherent in the unbonded strap system. RC beams with low transverse reinforcement ratios have been found to exhibit a reduction in capacity with increasing depth. In strengthened beams, the crack opening strap strain decreases with increasing beam depth and the initial prestrain becomes of increasing importance. The potential interaction between the two sources of size effects presents difficulties when assessing the overall beam behaviour.

Levingshan Augusthus Nelson, Janet M. Lees

Shear Capacity of Flexural Strengthened Reinforced Concrete Structures with CFRP Materials

By enlarging the flexural capacity of reinforced concrete structures with externally bonded CRFP materials the shear behavior is also affected. To evaluate this effect shear tests on flexural strengthened reinforced concrete beams were carried out. Half of the tests were done with externally bonded CFRP-strips and the other half with near surface mounted reinforcement. Based on these tests and the EC2 approach for the shear force was checked.

Wolfgang Finckh, Konrad Zilch

Strengthening of Concrete Columns, Walls and Frames

Frontmatter

Emergency Retrofit for Damaged RC Columns by Fiber Belts Prestressing and Plywoods

After a strong earthquake attacks to a building, damaged structural members such as columns should have sufficient vertical resistance to sustain gravity loads to rescue residents or move equipments. The rehabilitation of a damaged building is called “Emergency Seismic Retrofit” hereafter. Previous experimental investigations have demonstrated by utilizing high-strength steel bar prestressing or aramid fiber belt prestressing, seismic performances of shear-damaged RC columns significantly improved. In following the previous investigations on emergency seismic retrofit of shear-damaged RC columns, in this study a new approach is proposed regarding economic consideration and easy operation. In this method the polypropylene belts are used instead of aramid fiber belts, plywoods instead of steel plates, and customarily-fabricated ratchet buckles instead of specially-fabricated couplers. Experimental results exhibited efficiency of the pro-posed approach for emergency seismic retrofit of shear-damaged RC columns.

N. Kyoda, T. Yamakawa, K. Nakada, P. Javadi, A. Nagahama

Seismic Retrofitting by FRP Jacketing and Prediction Method of Ultimate Deformation

In this study, a method to predict the ultimate deformation is developed for reinforced concrete columns under seismic loading. The proposed sectional analysis or fiber model was combined with the truss mechanism approach in order to predict strength and deformation for both pre-peak and post-peak behavior. The proposed model is more effective at predicting the load deformation response of FRP-jacketed RC columns and shows that the fiber with a high rupture strain can provide good ultimate ductility.

T. Jirawattanasomkul, D. Anggawidjaja, T. Ueda

Seismic Performance of FRP-Confined Circular RC Columns

To investigate the seismic performance of FRP-confined circular RC columns with high axial compression ratio, six third-scaled columns confined with Carbon Fiber-reinforced Polymer (CFRP) at plastic hinge region and two control columns were tested under constant axial load and cyclic lateral force. The maximum axial compression ratio (P/

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A

g

) was 0.65 and the shear span ratio was 3.5. Test results demonstrated marked improvement in the ductility and energy dissipation of the columns due to CFRP wrapping at plastic hinge region. The study also found that the contribution of hoops to confining effect should not be ignored under the condition of high axial compression ratio. To accurately simulate the seismic performance and obtain the hysteretic shear-deformation curves of FRP-confined columns, a nonlinear analytical procedure was developed using fiber model based on OpenSees (Open System for Earthquake Engineering Simulation). A stress-strain model which considers the confining effects of both the internal hoops and external CFRP jacketing was used. The analytical results indicated that inclusion of the both confining effects results in better simulation of the test results from this and other studies. But, if the axial compression ratio is less than 0.3, the analytical results are not affected even considering the contributions of hoops. The lateral loading capacity of columns begins to decrease when the axial compression ratio exceeds 0.6 and when the length of wrapped CFRP at the plastic hinge region exceeds 1.2D (D is the diameter of columns), the seismic performance could be improved to a level equivalent to fully wrapped columns.

Z. Y. Wang, D. Y. Wang, S. A. Sheikh, J. T. Liu

Cyclic Behaviour of FRP Confined RC Rectangular Columns with High Aspect Ratio

This paper presents an experimental study undertaken to investigate the seismic behavior of square and rectangular RC columns confined with FRP or strengthened with FRP wraps and longitudinal steel profiles. Test results aim to explore the influence on the column performance of relevant parameters, such as: concrete strength, longitudinal steel reinforcement of the member (smooth or deformed rebars), type of strengthening system (FRP confinement w/ or w/o steel profiles); axial load levels; number of FRP layers used for columns jacketing. In particular, results form tests on rectangular columns are reported herein.

A. Napoli, B. Nunziata, R. Realfonzo

Numerical Simulation of FRP-Jacketed RC Columns Subjected to Cyclic Loading

This paper presents a study that forms part of an ongoing project on the seismic retrofit of reinforced concrete (RC) structures with fibre-reinforced polymer (FRP). In this study, a stress-strain model for FRP-confined concrete subjected to cyclic loading was implemented into OpenSees to support the performance-based design of FRP jackets for the seismic retrofit of RC columns/structures. Initial results from the numerical column model for two test columns show that the predicted responses are in close agreement with the test responses.

J. G. Teng, J. Y. Lu, L. Lam, Q. G. Xiao

Concrete Column Shape Modification with FRP and Expansive Cement Concrete

Fibre Reinforced Polymer (FRP) composites are an effective material for confining circular concrete columns. FRP confinement for square and rectangular columns is less effective due to stress concentrations at the sharp corners and loss of the membrane effect. Shape modification using post-tensioning of FRP shells through expansive cement concrete is described. In the field, shape modification can be achieved by utilizing pre-fabricated FRP shells as the permanent forms. An analytical model is briefly introduced to predict results of the experiments regarding the enhanced stress-strain behaviour of FRP-confined concrete. The confinement model and shape modification technique with FRP shells and expansive cement concrete are used in simulations of seismic rehabilitation of square columns for existing reinforced concrete bridges and are compared to in-situ tests of square columns with bonded FRP jackets.

Zihan Yan, Chris P. Pantelides, Jeffrey B. Duffin

Flexural Behavior of Concrete Columns Strengthened with Near Surface Mounted FRP Bars

Using composite materials for repairing and strengthening of concrete structures, specifically reinforced concrete (RC) columns, has continuously increased during past few years. Fiber reinforced polymer (FRP) is one of the different types of these materials, which can be used by either wrapping or near surface mounted (NSM) methods, in order to improve the confinement effects and the flexural capacity of RC columns. In this study, concrete column specimens, strengthened with near surface mounted FRP bars, were modeled in computer program, using finite element analysis. The behaviors of these columns were then analyzed under monotonic and cyclic lateral loads with constant axial compressive loads. The analytical results were compared to the results obtained from experimental observations on specimens with the same geometry and loading conditions and they were in good agreement. Since the anchorage of FRP bars in column’s foundation is an important factor to prevent premature failure, an additional parametric study on the specimens was done to find the optimal development length of FRP reinforcement in the foundation.

F. Danesh, B. Baradaran Noveiri

Use Near Surface Mounted FRP Rods for Flexural Retrofitting of RC Columns

Near surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement is one of the latest and most promising strengthening techniques for reinforced concrete (RC) structures. This technique based on bonding carbon or glass fiber reinforced polymer (CFRP or GFRP) bars (rods or laminate strips) into pre-cut grooves on the concrete cover of the elements to strength. In this work, a strengthening technique based on near surface mounted (NSM) carbon fiber rods is used to improve the flexural capacity of columns subjected to bending and compression. We describe the strengthening technique and report the experimental results in the strengthening process. The results obtained in series of reinforced concrete columns, subjected to combined constant axial compression and lateral cyclic loading, show that a significant increase on the load carrying capacity and flexural resistance can be achieved by using the NSM technique.

Mehdi Sarafraz, Fakhreddin Danesh

Effect of FRP Strengthening on the Behavior of Shear Walls with Opening

In recent decades, Fiber Reinforced Polymer (FRP) strengthening of concrete members is known as a unanimously acceptable method. An example of a proper application of this method is strengthening of shear walls with openings using FRP strips around them, especially at corners with high stress concentration, where FRP strips keep cracks closed and prevent brittle shear failure to the edges. The efficiency of FRP strengthening on shear walls and around the openings was examined in the current study using finite element (FE) software (ABAQUS). Available laboratory test results on concrete shear walls under lateral loads were used to calibrate the software and verify its application. Then, boundaries of the openings in the wall strengthened with FRP composites in different configurations and nonlinearly were analysed. The results showed considerable effectiveness of FRP strengthening on the overall behaviour of the walls with opening.

M. Asfa, D. Mostofinejad, N. Abdoli

Seismic Assessment of FRP-Retrofitted RC Frames Using Pushover Analysis Considering Strain Softening of Concrete

Seismic actions cause unacceptable levels of damage in existing RC buildings. Existing buildings designed to earlier codes have insufficient lateral resistance, exhibit lower strength and ductility, which induce a global failure mechanism to the structure. Under these circumstances, “weak-column strong-beam” behaviour dominated the buildings which may lead to the formation of local hinges in the column and so strengthening becomes necessary. In this paper, seismic behaviour of retrofitted RC frames using FRP at joints and steel braces are investigated. For this, moment curvature of the FRP-retrofitted joints are captured by FE analysis considering strain softening of concrete and then pushover analysis for all frames are carried out. Ductility, behaviour factor and performance points of two, four and eight stories frames are then evaluated. The results show that FRP-retrofitting technique can better improve the seismic performance of eight storey frame than steel braces but in low-rise frames, both techniques are beneficial.

S. S. Mahini, S. A. Hadigheh, M. R. Maheri

Seismic Performance Analysis of FRP Reinforced Concrete Frame Structure

Based on the experimental study for seismic performance of FRP reinforced concrete beam-column joints, two-storey two-span plane frames were taken for examples, in which the static elastoplastic analysis (the pushover method) was carried on the joints of the FRP strengthened concrete frames, and then the comparative analysis was made on seismic performance of RFP strengthened frame structure through the calculated pushover curve, the distribution of plastic hinges, the target displacement and other parameters. The result showed that effective reinforcement for the beam-column joints may obviously improve overall seismic performance of frame structures.

Yaping Peng, Ming Ma, Guang Dong

The Anchorage Behavior of FRP EBR in the Plastic Zone of RC Beams

In this paper the bond behavior of external FRP reinforcement anchored in an high stressed zone of RC beams has been investigated under monotonic and cyclic actions. The detailed study of the experimental strain distributions along the FRP strengthening has evidenced a progressive damage of bond at increasing the cycles and the influence of steel yielding propagation under both monotonic and cyclic load histories.

Francesca Ceroni, Marisa Pecce, Fabio A. Bibbò

Application of FRP for Punching Shear Retrofit of Concrete Slab-Column Connections

Fibre reinforced plastic, FRP, shear bolt system has been recently developed at the University of Waterloo, Canada. The system can be used to protect existing reinforced concrete slabs against brittle and sudden punching shear failure. The retrofit procedure requires drilling small holes in a slab around the perimeter of a column, inserting bolts into the holes and anchoring the bolts at both external surfaces of the slab. Many existing reinforced concrete slabs had been built without any shear reinforcements. Also, many of these slabs are in corrosive environments, e.g. in parking garages where the use of de-icing salts accelerates reinforcement corrosion and concrete deterioration. Therefore, FRP is an ideal material to be used for such retrofit. The challenge, however, has been the development of mechanical end anchorages for FRP rods that is efficient, aesthetic, cost effective, and that can be applied on-site. In the presented research six isolated slab-column specimens were constructed representing interior slab-column connections in a continuous flat plate slab system. The specimens were subjected to simulated gravity and gravity plus seismic loadings. A new anchorage technique for the FRP rods was developed, which is based on crimping the rod ends with the aluminum fittings. Using this approach, fairly large loads can be resisted by the end-fittings. The developed FRP bolts worked very well improving the performance of the slab-column connections and showing the benefits of using FRP in punching shear retrofit of reinforced concrete slabs.

Maria Anna Polak, Nicholas Lawler

Beam-to-Column Connection of a Precast Concrete Frame Strengthened by NSM CFRP Strips

This paper presents results of experimental tests of a concrete frame with emphasis on the connections strengthening assessment. The tests were conducted in a small scale frame composed of precast columns and beam. Initially there were pinned connections between the beam and columns. The frame was loaded in two points of the beam until a beam cracking had been observed. The connections were strengthened by em-bedding CFRP strips in the lateral concrete cover. The frame was loaded again until failure which had occurred by splitting concrete edge in the connection region. It was observed that the strengthened connection exhibited semi-rigid behavior and provided significant reduction in the beam midspan deflection.

T. de C. C. S. da Fonseca, S. F. de Almeida, J. B. de Hanai

Strengthening of Steel Structure

Frontmatter

Treatment of Steel Surfaces for Effective Adhesive Bonding

In the FRP strengthening of steel structures, cohesion failure in the adhesive is the preferred mode of debonding failure at FRP-to-steel interfaces so that the design theory can be established based on the properties of the adhesive. In this paper, results from a systematic experimental study are presented to examine the effects of steel surface treatment and adhesive properties on the adhesion strength between steel and adhesive. The test results show that adhesion failure can be avoided if the steel surface is grit-blasted prior to bonding and the treated surface can be characterised using three key surface parameters.

J. G. Teng, D. Fernando, T. Yu, X. L. Zhao

Effect of Surface Preparation on the Strength of FRP-to-Mild Steel and FRP-to-Stainless Steel Joints

A detailed understanding of the strength and behaviour of the bond between fibre-reinforced polymer (FRP) composites to metals is an ongoing field of research. The many different geometrical and material parameters make for extensive research demands. This paper in turn reports a series of tests on the shear strength and behaviour of FRP-to metal joints in which the main test parameters, which have received limited attention to date, consists of (i) type of metal (i.e. non-galvanised mild steel and stainless steel), and (ii) surface preparation technique (i.e. different mechanical abrasion methods). All specimens are loaded in displacement control which enables the failure process to be followed and identification of different failure modes to be made. The results enable the effectiveness of different surface preparation techniques upon the bond of FRP to different types of metals to be made.

S. J. Kim, S. T. Smith, B. Young

Modeling of Steel Beams Strengthened with CFRP Strips Including Bond-Slip Properties

This paper presents a modeling approach to predict the flexural behavior of steel beams strengthened with carbon fiber reinforced polymer (CFRP) strips. The beams, W150×18, are simply supported and monotonically loaded until failure occurs. To examine the effect of CFRP-strengthening, selected beams are intentionally damaged by creating a notch at the tension flange. A three-dimensional finite element analysis is conducted, including bond-slip properties at the CFRP-steel interface. The CFRP-strengthening results in im-proved load-carrying capacity of the damaged beam and reduces strain localization near the damage.

Yail J. Kim, Kent A. Harries

Temperature Effect on Adhesively Bonded CFRP and Steel Double Strap Joints

Steel/CFRP double-strap joints adhesive-bonded by epoxy were tested in tension under different temperatures ranging between 20°C and 60°C. Effective bond length was experimentally determined at 20°C first. Specimens, varied with the effective, half and twice the effective bond length and with one or three carbon fibre layers, were examined under the specified temperature range. It was found that the ultimate load and the joint stiffness of all specimens decreased significantly at temperatures near to Tg. Based on the kinetic modeling of glass transition of adhesive, a mechanism-based model was proposed to describe the strength and stiffness degradation of steel/CFRP double strap joints at elevated temperatures, and the modeling results were validated by the corresponding experimental measurements. In addition, it demonstrated that the effec-tive bond length is increased with temperature.

Tien C. Nguyen, Yu Bai, Xiao-Ling Zhao, M. R. Bambach, Riadh Al-Mahaidi

Repairing Method for the Steel Members by CFRP Strand Sheets

The steel structure is corroded by various mechanisms, and thus its performance decreases. As a repairing method of the corroded steel member, a method in which carbon fiber sheets is bonded to the steel member with glue has been studied. In recent years, as more efficient repairing method using FRP materials, the strand sheet method which has high mass per unit area has been developed. The purpose of this study is to propose the repairing method for corroded steel member by using the strand sheets. In order to confirm a reinforcing effect, the tensile and flexural tests using steel plates and girders reinforced with strand sheets were performed. Test results showed effectiveness of strand sheets for the reinforcement of the steel members.

Y. Hidekuma, A. Kobayashi, A. Tateishi, M. Nagai, T. Miyashita

Temperature Effects in Adhesively Bonded FRP Strengthening Applied to Steel Beams: Experimental Observations

FRP plates can be used to strengthen a steel beam in flexure, but this method relies critically upon the adhesive used to bond the FRP plate to the existing steel member. When the temperature of the strengthened beam is increased, differential thermal expansion occurs between the steel and FRP. In addition, the glass transition temperature of a typical two-part ambient-cure epoxy adhesive is typically between about 50°C and 65°C, and the stiffness and strength of the adhesive will decrease at temperatures somewhat below the glass transition temperature. This paper reports tests conducted on steel beams strengthened with CFRP plates and ambient-cure epoxy adhesive. Load was applied to the beams in four-point bending, and the temperature of the strengthening was then increased until failure occurred. Slip deformations were directly observed across the adhesive joint, giving an indication of the performance of the strengthening at elevated temperatures. The consequences of this preliminary study upon the design of externally-bonded FRP strengthening for steel structures are discussed.

Tim J. Stratford, Luke A. Bisby

Experimental Study on Bond Behaviour between UHM CFRP Laminate and Steel

The technique of strengthening steel structures with carbon fibre reinforced polymer (CFRP) has attracted growing attention in research field as well as in practice. A newly developed CFRP laminate with a modulus of 460GPa makes it possible to increase the elastic behaviour of strengthened steel structures. A series of tension tests were carried out with double-strap joints using different types of adhesives and bond lengths. Full range bond behaviour including bond strength, effective bond length, stress distribution and derived bond-slip relations at different locations along the bond line are presented in this paper.

Chao Wu, Xiao-Ling Zhao, Riadh Al-Mahaidi, Wen Hui Duan

Static Behavior of Tension Steel Plate Strengthened with Pre-Stressed CFRP Laminates

An experimental and analytical study was conducted to investigate the static performance of steel plates strengthened with pre-stressed CFRP (carbon fiber-reinforced polymer) in uni-axial tension. A linear elastic theoretical model was presented to predict the stress distribution of reinforced specimens. Static testing was performed on the double edge notched specimens strengthened by CFRP laminates at different pre-stressing levels. The theoretically predicted results were in good agreement with the experimental results. The results show that pre-stressed CFRP laminates had a large impact on the specimen’s strength but resulted only in a moderate increase of its stiffness. An eccentricity due to pre-stressing was observed leading to bending effects which result in a non-uniform stress distribution. The test results indicated that the long-term pre-stress losses due to static and fatigue loading were slight because of the excellent mechanical properties of CFRP laminates. Therefore, the total pre-stress losses could be simplified as the short-term pre-stress losses with considering a safe factor.

Huawen Ye, Shizhong Qiang, Christian König, Robin Plum, Thomas Ummenhofer

Fatigue Life Prediction of Steel Beams Strengthened with a Carbon Fibre Composite Plate

There are many applications in metallic beams strengthened with a bonded carbon fibre reinforced polymer (CFRP) plate in recent years. The fatigue performance of the retrofitted beams in a bridge must be considered. In this study, steel beams strengthened with a bonded CFRP plate were tested under fatigue loading. Both crack-free fatigue life and crack propagation life were considered. In accordance with the test results, the relationship between the peak interfacial stresses and the cyclic number to crack initiation in the bonding layer was obtained to predict the crack-free fatigue life. The relationship between the CFRP peeling rate and the energy release rate was obtained to predict the crack propagation life. In addition, based on the findings obtained from the previous and present studies on adhesive bonding in the retrofitted beams, some design suggestions for steel beams strengthened by bonded CFRP plates are proposed.

Jun Deng

Tests on CFRP Repaired Welded Thin-Walled Cross-Beam Connections

Cracked cross-beam connections made of thin-walled rectangular hollow sections (RHS) are repaired with carbon fibre reinforced polymer (CFRP) composites and constant amplitude fatigue experiments are conducted on the repaired specimens. In the previous pilot test on a T-connection of square hollow sections (SHS), early debonding happened in the corner region due to peeling effect. In this study, circumferential or transverse restraining CFRP patches are applied in the corner region which prevent early debonding and lead to significant increase in fatigue life. Furthermore, the addition of strengthening steel plates has further increased the flexural stiffness and fatigue life of the cracked specimens.

Zhi-Gang Xiao, Xiao-Ling Zhao, Le-Wei Tong

Fatigue Behavior of CFRP Repaired Non-Load Carrying Cruciform Welded Joints

In recent years, large amount of research has been conducted on carbon fibre reinforced polymer (CFRP) strengthening of steel members. There is very limited work on CFRP strengthening of welded connections. This paper reports an experimental study on the use of CFRP sheets to rehabilitate non-load carrying cruciform welded joints subjected to fatigue loading. Failure modes and corresponding fatigue lives were rec-orded during tests. Thereafter, series of numerical analyses were performed to understand the effects of weld toe radius, layer of CFRP sheets and Young’s modulus of reinforced materials on local stress concentration at weld toe. It was found that fatigue life of such welded connections can be enhanced by CFRP sheets. A para-metric study was also carried out. It was found that the weld toe radius and the number of CFRP layers are the key parameters influencing the stress concentration factors of such joint.

Tao Chen, Xianglin Gu, Xiaoling Zhao

Tests on CFRP Strengthened Aluminium RHS Subject to End Bearing Force

Web crippling of thin-walled members is often observed at loading or reaction points where concentrated forces exist. This paper reports an investigation on using CFRP (carbon fiber reinforced polymer) strengthening technique to improve the web crippling capacity of aluminium RHS (rectangular hollow section). Several types of strengthening technique were adopted in this project. They include applying CFRP plates outside or/and inside the RHS. A series of laboratory tests were conducted. Significant increase in load carrying capacity was obtained. The test results are also compared with those for cold-formed steel RHS strengthened by CFRP.

Xiao-Ling Zhao, Phaon Phiphat

Lateral Torsional Buckling of Steel I-Beam Retrofitted Using FRP Sheets: Analytical Solution and Optimization

This paper presents an analytical investigation on lateral stability of steel metal beam which is retrofitted using FRP patch. The methodology is based on implementing total potential energy and Rayleigh Ritz method. The laminate theory including first order shear deformation is included in this study. The linear elasticity solution is considered for determining of buckling critical load. The compound beam is assumed a simply supported under pure bending. Some combinations of FRP sheets on single or both sides of flanges and web are applied as different cases of section retrofitting in order to investigate the effectiveness of strengthening pattern on the lateral torsional buckling of the metal beam. The FRP sheet can be extended to the total or partial length, full or partial patch, of the beam. In each case, parametric study with variation of fiber orientation is examined to find out the optimum fiber direction for design purposes. The results of this study would be benefitted for retrofitting of existing steel bridges which many of them are exposed to the harsh environment.

M. Z. Kabir, A. E. Seif

Experimental Study on Behavior of FRP Anti-Buckling Strengthening Steel Members

This paper puts forward a thought of a FRP (Fiber Reinforced Polymer) anti-buckling strengthening of steel members. Through compression tests of 14 specimens, the influence of slenderness ratio, binding (filled or not filled), fillers, as well as connection methods to the core steel compression performance was studied. The results show that the reinforcement changes the ultimate failure mode of the specimen, and increases the ultimate bearing capacity and ductility to varying degrees. It is worthy of further research and has the value of promotion in practice.

Sawulet Bekey, Feng Peng, Ye Lieping

Effects of FRP Reinforcements on the Buckling and Reduced Stiffness Criteria of Compressed Steel Cylinders

FRP laminated reinforced steel cylinders under compression have been studied in this paper. The effects of the thickness and fibre orientation of reinforcements as well as initial geometric imperfections on the buckling load carrying capacity and the associated buckling modes have been made clear through three kinds of analytical procedures; the conventional linear eigenvalue buckling analysis, the reduced stiffness buckling analysis and the fully nonlinear numerical experiments. These multiple treatments suggest obtaining valuable information for the design of FRP based hybrid structural elements having the complex buckling collapse behavior.

Seishi Yamada, Krishna Kumar Bhetwal, Masayuki Yanagida, Yukihiro Matsumoto

Numerical Simulation of Prestressed CFRP Plate Strengthened Steel-Concrete Composite Girders

This paper presents the results of Finite Element (FE) modeling of flexural behavior of steel-concrete composite girders strengthened with prestressed Carbon Fiber Reinforced Polymer (CFRP) plate. To the best knowledge of the authors, this is the first numerical modeling of such application with prestress available in the literature The level of prestressing that is used to validate the model is 12% of the ultimate tensile strength of the CFRP plate and it is based on the results of an experimental study conducted at University of Calgary on the same large-scale beam tested in bending under monotonic static loading. Comparison shows a very good agreement between the numerical and the experimental results. After validation of the model, a parametric study using different prestressing levels is conducted and the effects of increasing the prestress level on ductility index, yield and ultimate loads are presented.

Pouya Zangeneh, Hamid Y. Omran, Raafat El-Hacha

Experimental Study on Fatigue Behavior of I-Steel Beam Strengthened with Different FRP Plates

Fatigue experiments of eight I-steel beams strengthened with different fiber reinforced polymer (FRP) plates are presented in this paper. The experimental results show that, (1) under the principle of equivalent axial tensile stiffness of different types of FRP plates, the fatigue life of strengthened steel beam could increased by 3.33-5.26 times over un-strengthened steel beam, while the fatigue life of steel beam strengthened with welding steel plate increased by 1.74 times; (2) Application of FRP plates can significantly reduce the crack growth rate, prolong the fatigue life and even change the fatigue failure mode of I-steel beams compared with welding steel plates; (3) The CFRP plate with high modulus was found to be the most efficient strengthening way; (4) It was also observed that the interfaces treating method and the plate configuration have considerable influence on the fatigue life.

Gang Wu, Haiyang Liu, Zhishen Wu, Haitao Wang

Strengthening of Masonry and Timber Structures

Frontmatter

Experimental Study on Seismic Behavior before and after Retrofitting of Masonry Walls Using FRP Laminates

Masonry buildings are the most common and seismically vulnerable structures in the rural areas of China. However, 2008 Sichuan earthquake has showed that failure of masonry walls is one of the major causes of material damage and loss of human life due to seismic events. Therefore, this work presents an experimental program that investigates in-plane seismic behaviour of common types of shale masonry shear walls before and after retrofitting using fibre-reinforced polymers (FRP). The motivation of the present work is associated with the important influence that the FRP introduce as an effective and affordable retrofitting technique for masonry members. To achieve this goal, a total of four half-scale shale masonry walls, two walls with door opening and the other two are solid, were subjected to combined uniformly distributed constant vertical load and incrementally increased in-plane lateral load. This paper analyzed the general behaviour of the shear walls before and after retrofitting based on lateral load-top displacement curves and the action of the FRP laminates to masonry shear walls. The test results indicated that the FRP system remarkably increases the lateral load ca-pacity of retrofitted walls. Moreover, during the later loading stages, FRP Sheets were effective in enhancing the stiffness of retrofitted walls.

Asal Salih Oday, Li Yingmin, Mohammad Agha Houssam

Strengthening of Masonry Structures Using FRP — Experimental Research

The article deals with the problems of the failure mechanism and the load-bearing capacity of masonry barrel vault structures and masonry columns strengthened with fabric of carbon fibres. The executed experimental research of the effect of strengthening segmental barrel vaults and masonry columns by carbon fabric showed a prominent growth in the ultimate bearing capacity and ductility of barrel vault structures and masonry columns. The application of carbon fabric (CFRP) in the vault area exposed to tensile stresses limited not only the appearance and development of characteristic tensile cracks at these vault cross-sections, but also significantly increased the vault stability against buckling. The position of strengthening elements — the carbon fabric (CFRP) — affected the failure mechanism of the masonry vaults and masonry columns.

J. Witzany, T. Cejka, R. Zigler

Improvement of Transverse Connection of Masonry Walls through AFRP Bars

An innovative method to connect existing orthogonal masonry walls through aramidic FRP bars is presented. The proposed technique has the objective of mobilizing and maximizing the collaboration of intersecting structural elements, thus increasing the overall strength and stiffness of masonry buildings under horizontal forces. The method was experimentally tested to prove its applicability and effectiveness.

M. Menegotto, G. Monti, S. Salvini, M. Vailati

FRP-to-Softwood Joints: Experimental Investigation

A proper understanding of the interfacial behaviour between timber and bonded fibre-reinforced polymer (FRP) composites will assist in the rational and optimal design of FRP strengthening works for timber structures. To enhance this understanding, a series of single-lap FRP-to-timber joint shear tests are reported herein in which the strength of the bond between the FRP and timber is examined. The shear tests are conducted on softwood (Pine) which has been strengthened with carbon FRP with the main test variables being the FRP bond length and the growth characteristics of the timber. Extensive strain gauging of the FRP has enabled the onset and propagation of debonding cracks to be monitored. An effective bond length is identified, however, the results also show that timber is a variable material which requires continued investigation.

J. Wan, S. T. Smith, P. Z. Qiao

Backmatter

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