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About this book

This book gathers the best peer-reviewed papers presented at the Italian Concrete Days national conference, held in Lecco, Italy, on June 14-15, 2018. The conference topics encompass the aspects of design, execution, rehabilitation and control of concrete structures, with particular reference to theory and modeling, applications and realizations, materials and investigations, technology and construction techniques. The contributions amply demonstrate that today’s structural concrete applications concern not only new constructions, but more and more rehabilitation, conservation, strengthening and seismic upgrading of existing premises, and that requirements cover new aspects within the frame of sustainability, including environmental friendliness, durability, adaptability and reuse of works and / or materials. As such the book represents an invaluable, up-to-the-minute tool, providing an essential overview of structural concrete, as well as all new materials with cementitious matrices.

Table of Contents

Frontmatter

Theory and Modeling Materials

Frontmatter

Assessment of the Partial Safety Factor Related to Resistance Model Uncertainties in 2D NLFEAs of R.C. Systems

This work estimates the partial safety factor corresponding to the resistance model uncertainties in non-linear finite element method analyses (NLFEAs) of reinforced concrete structures considering various structural typologies with different behaviours and failure modes (i.e., walls, deep beams, panels). The comparison between the two-dimensional NLFE structural model results and the experimental outcomes is carried out considering the possible solution strategies available to describe the mechanical behaviour of reinforced concrete members in different software codes. Several NLFE structural models are defined for each experimental test in order to investigate the resistance model uncertainty. Then, a consistent treatment of the resistance model uncertainties is proposed following a Bayesian approach identifying the mean value and the coefficient of variation of the resistance model uncertainties. Finally, in agreement with the safety formats for NLFEAs of reinforced concrete structures, the partial safety factor is calibrated.

P. Castaldo, D. Gino, D. La Mazza, G. Bertagnoli, V. I. Carbone, G. Mancini

Robustness of 3D Base-Isolated R.C. Systems with FPS

This study evaluates the seismic robustness of 3D r.c. structures isolated with single-concave friction pendulum system (FPS) devices by computing the seismic reliability of different models related to different malfunction cases of the seismic isolators. Considering the elastic response pseudo-acceleration as the relevant random variable, the input data have been defined by means of the Latin Hypercube Sampling technique in order to develop 3D inelastic time-history analyses. In this way, bivariate structural performance curves at each level of the r.c. structural systems as well as seismic reliability-based design abacuses for the FP devices have been computed and compared in order to evaluate the robustness of the r.c. system considering different failure cases of the FP bearings. Moreover, the seismic robustness is examined by considering both a configuration equipped with beams connecting the substructure columns and a configuration without these connecting beams in order to demonstrate their effectiveness and provide useful design recommendations for base-isolated structural systems equipped with FPS.

P. Castaldo, G. Mancini, B. Palazzo

A Model for the Analysis at ULS of Corroded RC Beams

The proposed model is able to consider the interaction between bending, shear and normal forces. Some experimental tests present in the literature, where the structural behaviour of reinforced concrete beams in presence of corrosion of longitudinal and transversal rebar was investigated, were used in the present study in order to validate the proposed model. The numerical results seem to be in good agreement with the experimental ones.

A. Recupero, N. Spinella, F. Tondolo

Criteria for the Structural Analysis of Precast Buildings with Dissipative Connection Systems of Cladding Wall Panels

With reference to the connections of cladding wall panels of precast buildings, different types of dissipative devices have been recently proposed. They have been developed based on a comprehensive theoretical study and experimental verification. A problem with the method of structural analysis is still pending to allow for practical application of these devices in the design and construction of the overall building in which they are installed. In general, non-linear time-history dynamic analysis can be applied on a 3-D model inclusive of frame, panels and their connections. However, this approach is demanding and not handy for the current design practice. A linear static or modal dynamic analysis based on the response spectrum could be applied, but at present the pertinent force-reducing behaviour factor is not given by the codes. Some simplified approximate approaches are hence presented in this paper, referring in particular to a friction based dissipative device to be used both in vertical and horizontal panels and to a plastic dissipative device to be used in horizontal panels. This latter, further to new constructions, can be applied also for the retrofitting or strengthening of existing buildings.

G. Toniolo, F. Biondini, B. Dal Lago

The Effect of Infill Walls on the Structural Identification of an Existing RC Frame Building

A large number of Reinforced Concrete (RC) frames buildings containing unreinforced masonry infill walls are commonly used in structural system around the world. Earthquakes revealed that the performance of this type of buildings can be significantly affected by infill walls according their type and distribution in plane and along the height. The paper describes the experimental and analytical modal analysis of an existing RC framed building underling the influence of infill walls and partitions. An ambient vibration test was carried out and analysed by OMA; a 3D finite element model, comprehensive of infill walls and partitions, was successfully updated manually based on the in-situ test global modes. The progressive introduction of the infill walls and partitions, with the updating of their characteristics, allowed to demonstrate their essential effect on the elastic dynamic response of the structure and the necessity of their modelling to attain a reliable structural identification and model assessment.

A. De Angelis, M. R. Pecce

Influence of the Modelling Approach on the Failure Modes of RC Infilled Frames Under Seismic Actions

The influence of the masonry infills on the seismic performances of Reinforced Concrete (RC) frames is generally evaluated in analytical and numerical studies by adopting the equivalent strut model; it is based on experimental observations showing that at the onset of damage, stresses migrate to the diagonal of the panel and are transferred to the surrounding frame through the contact zones at the corners. Above the different equivalent strut models available in literature, single-strut models are generally used to evaluate the global behaviour, while multi-strut approaches are preferred to investigate on local interaction phenomena between panel and frame. In case of existing buildings, with poor transversal reinforcement of the columns, the presence of the infills can lead to pre-emptive brittle failure. The present study is aimed at evaluating the influence of the modelling approach on the evaluation of the seismic performance both in terms of global and local behaviour. Nonlinear dynamic analyses have been performed on an 8-storey infilled RC frame, following the Incremental Dynamic Analysis procedure, in order to evaluate structural performances depending on the model adopted to simulate the infills.

G. Blasi, D. Perrone, M. A. Aiello

Nonlinear Modeling Approaches for Existing Reinforced Concrete Buildings: The Case Study of De Gasperi-Battaglia School Building in Norcia

This paper reports on a collaborative activity developed as part of the DPC-ReLUIS Research Project, year 2017. It aims at comparing the results obtained by considering alternative options in the definition of the nonlinear FEM model employed in pushover analyses for seismic assessment of existing RC frames. Specifically, the RC frame structure of the De Gasperi-Battaglia school building located in Norcia, Italy, is considered as a relevant case-study. This structure has been designed in the ‘60s of the past century according to the seismic code of the time and, hence, without taking into account the principles of Capacity Design. Although the building was actually retrofitted before the 2016 Central Italian earthquake, in this paper its original configuration has been considered. The nonlinear behaviour of the frame structure has been modelled by both following alternative approaches and employing different analysis codes. Therefore, this paper proposes an overview about how different the simulation output can be as a result of different modelling and analysis choices. In doing that, the work can be relevant to practitioners, as they may be warned about the consequences of those choices in terms of seismic vulnerability evaluation.

C. Lima, M. Angiolilli, F. Barbagallo, B. Belletti, A. V. Bergami, G. Camata, C. Cantagallo, M. Di Domenico, G. Fiorentino, A. Ghersi, A. Gregori, D. Lavorato, R. Luciano, E. M. Marino, E. Martinelli, C. Nuti, P. Ricci, L. Rosati, S. Ruggieri, S. Sessa, E. Spacone, M. Terrenzi, G. Uva, F. Vecchi, G. M. Verderame

Modeling the Seismic Response of Vertical Concrete Cladding Panels

During the recent earthquakes in Northern Italy many RC precast industrial buildings were seriously damaged. Amongst different types of damage, many falls of cladding panels were occurred. Consequently, many doubts about current knowledge about their seismic behaviour have been expressed.To study the seismic response of claddings in real conditions and their influence on the system response of whole structure a series of full-scale shake table tests was performed by the University of Ljubljana in cooperation with IZIIS, Macedonia. The results of these experimental campaign were used to define and calibrate appropriate numerical models for the main structure, claddings and cladding-to-structure connections. These models are presented in the paper.

G. Menichini, T. Isaković

Seismic Strength of One-Story Precast Building Dowel Connections

Typical European precast buildings commonly show dowel beam-to-column connections which consist of vertical steel dowels, embedded in the column and passing through or inserted in holes in the beam. These connections can be characterized by two different failure modes depending on the concrete cover/dowel diameter ratio so that the failure mode involves the yielding of the dowel and the crushing of the concrete around the dowel or the concrete cover splitting in the direction of the load or in the orthogonal direction (side splitting). In this paper, beam-to-column dowel connections are designed according to the Italian seismic building code and the Eurocode 8 general principles, for a set of case-study buildings, considering different geometrical layouts for primary structure and different seismic hazard levels. Different connection configurations are also considered and the connection shear strength is estimated taking into account code and literature formulations, in order to assess their seismic performance.

M. Cimmino, G. Magliulo, G. Manfredi

FE Analysis of the Flexural Behavior of Cementitious Composites Using the Concrete Damage Plasticity Model

In this study, the structural and fracture behavior of cementitious composite beams subjected to flexural loads is experimentally and numerically investigated. Six series of mortar specimens reinforced with steel mesh layer ware cast and tested in 4–point bending. Configurations with 2, 4 or 6 mesh layers were examined to characterize the flexural response of materials. A 3D FE model was developed in ABAQUS to predict the nonlinear behavior of the beams and to simulate the evolution of fracture patterns under an increasing load. The nonlinear cracking and crushing response of the mortar was implemented by using the Concrete Damage Plasticity model. For the steel reinforcement, an elasto-plastic model with isotropic hardening was adopted. The results of the numerical analysis are discussed. Comparisons between numerical and experimental results highlight a reasonably good agreement both in term of structural response and of damage growth.

F. Aymerich, L. Fenu, G. Loi

Investigations of Shear Resistance Related to Slab Bridges in Comparison with International Design Standards, Nonlinear FE-Analysis and Results of Full-Scale Test Series

This research paper deals with different concrete slab bridges, which were built in the years 1930 to 1990 and should be used in their current mode of operation at least until the end of their expected economic lifetime or even further.The main target of this research was to display structural reserves of existing slab bridges within the context of the bridge management system nowadays and the differences of the current international standards. To ensure the quality of the results, all investigations are verified by numerical analysis.Finally the investigations pointed out that 50% of the design value of the reinforcing steel in addition to the concrete contribution according to EC 2 should be used for the verification of existing slab bridges with bent-up bars. Furthermore, with the consideration of these calculative assumptions, the normative safety of bridge structures could be achieved and many bridges are still safe to use in their mode of operation, if the maintenance conditions are adequate.

Michaela Kopp, Gerald Köck, Markus Vill

Modeling of the Shear Connection Capacity of Hybrid Steel Trussed Composite Beams

Hybrid Steel Trussed Composite Beams represent a technical solution in use in numerous countries since many years. They are able to join the advantages of prefabrication with those of cast in place structures: they are easy to manufacture, fast to realize, monolithic and with no need of formwork. The behavior of these beams has been recently topic of discussion in the scientific community because the knowledge both related to the reinforced concrete structures and that of composite constructions cannot be straightforwardly extended to this typology, which is intermediate between one and another technology. This paper provides a contribution towards a better understanding of the mechanism of transfer in the beam typologies with bottom steel plate. A FE model is set up and, subsequently, a simple design formula for the prediction of the shear capacity of the concrete-steel connection is derived and verified on the results of parametric FE analyses.

M. Latour, A. Monaco, G. Rizzano

Applications and Realizations

Frontmatter

SEACON and Resilient FRP-RC/PC Solutions: The Halls River Bridge

The SEACON project features the University of Miami (UM), the Florida Department of Transportation (FDOT), along with European partners (Politecnico di Milano) and representative of the industrial sector working toward the development of innovative material solutions to address sustainability and resilience challenges in construction. The project aims to develop sustainable concrete solutions using seawater and chloride-contaminated aggregates. An integral component involves validating Fiber Reinforced Polymers (FRP) and stainless steel (SS) as non-corrosive reinforcement for Reinforced Concrete (RC) and Prestressed Concrete (PC) applications. The Halls River Bridge (HRB) features large-scale implementation of innovative materials. It showcases the SEACON research outcomes and serves as a proof-of-concept for the validation of design philosophies to be included in the new generation of FRP design guidelines. This paper speaks about the issues of design of a non-corrosive FRP-RC/PC structure. HRB is presented as a successful case study.

M. Rossini, T. Cadenazzi, S. Nolan, A. Nanni

Design Recommendations for Foundation Slabs with Punching Shear Reinforcement

The structural performance of reinforced concrete foundation slabs or footings supporting isolated columns is often limited by the punching shear capacity in the area around the column. This can be significantly increased by using vertical punching shear reinforcement, which is typically provided under the form of tailor made stirrups or industrially produced double-headed studs. The lack of knowledge about the performance of slabs reinforced with this kind of reinforcement elements, which are not included in current EN 1992-1-1, has been the main motivation behind an experimental research program at the EPFL in Lausanne consisting in full scale laboratory tests of footings reinforced with Peikko PSB® studs. The results of this program have been used to develop design recommendations for slabs reinforced with Peikko PSB® studs that are now implemented in ETA 13/0151. The paper summarizes the main outcomes of the research project and presents practical design recommendations yielding from it.

E. Camnasio, J. Bujnak

Safety Check Procedures of Fiber Reinforced Concrete Curbs for Bridge Slabs

The construction of new curbs or the replacement of existing ones is usually due to the need of installing safety or anti-noise barriers. Recent studies, developed by the authors and proven by experimental tests, have shown the effectiveness of a new technology, based on the use of high performance fiber reinforced concrete. This technology shows several advantages: a significant reduction in execution time of the curb and of installation of barriers elements, thanks to the rapid achievement of high resistance; lack of interference between barriers anchorages and reinforcement rebars. Aim of the study is the formulation of simplified procedures for the safety check of curb-slab systems, against the action of the vehicle impact, with reference to curbs rebuilding on existing reinforced concrete bridge slabs. Finally, safety check criteria of curbs, characterized by rectangular or L-shaped cross section, are proposed, based on both global and local behaviours.

F. Di Carlo, A. Meda, Z. Rinaldi, F. Simonelli

Applications of Non-metallic Concrete Reinforcements

Initial pilot projects assessing the potential applications of non metallic concrete reinforcements date back to the end of the ‘90s. In 2001, reinforcements made with Glass Fiber Reinforced Polymers (“GFRP”) were used for the first time to realize a tunnel excavation front containing wall. This temporary application was motivated by the easiness of severing the reinforcement directly with the TBM during excavation, a technique (known as Soft-Eye) currently widely used in the field of geotechnics. Today, non-metallic concrete reinforcements for permanent applications are the focus of new interest triggered by the awareness that, due to a number of factors, the effective duration of existing concrete structures does not correspond in most cases to that of design. This paper presents some concrete structures realized in recent years with GFRP reinforcements that guarantee long term behaviour.

M. Arduini, G. Balconi

Structures of the Generali Tower in Milano – A Concrete Challenge

The form of the tower is generated by a variation in the plan of each floor, and by a continuous rotation – greater at the lower levels and decreasing towards the summit – of each storey around the centre. The functionality of the internal spaces demand that the perimeter columns be aligned with the form of the outer shell, thus requiring them to slope, each with a different inclination matching the enveloping curvature. This generates an additional, unusual phenomenon, for the tower equilibrium: the horizontal forces resulting from this angular variation produce a global torque, inducing a warping effect in the core elements. The weight of the building and the vertical loads acting on it generate both vertical and horizontal actions, encircling the core. Choosing concrete as the construction material meant great efficiency but also the need of a complex design in terms of analysis and forecast of non-linear and time dependent effects, geometry control and construction phasing.

Mauro Eugenio Giuliani

Materials and Investigations

Frontmatter

Characterization of Fabric Reinforced Cementitious Matrix (FRCM) Composites for Structural Retrofitting

Fabric Reinforced Cementitious Matrix (FRCM) composites are inorganic-matrix innovative materials often particularly suited for strengthening of masonry and concrete structures. These materials are composed of a dry grid of fibers (i.e. an open-mesh textile) embedded in an inorganic-matrix enriched with short fibers. In this paper, some mechanical tests proposed for the mechanical characterization of FRCM composites are presented and discussed. Initially, the mechanical properties of the components (matrix and dry fibers) are described. Then, tensile, debonding, and pull-out test set-ups are presented. Tensile tests are employed to obtain the FRCM stress-strain behavior and identify the main mechanical properties, whereas bond tests (debonding and pull-out) are used to evaluate the failure mode and study the bond behavior of the FRCM composite. The results of some of these experimental tests are necessary to obtain a complete assessment of the FRCM composite in accordance with the current Italian guidelines.

F. G. Carozzi, T. D’Antino, A. Gatti, G. Mantegazza, C. Poggi

Structural Behavior of RC Beams with EAF Slag as Recycled Aggregates: Numerical Versus Experimental Findings

This papers aims at investigating the structural behavior of reinforced concrete (RC) beams with electric arc furnace (EAF) slag as full replacement of coarse natural aggregates. A few real scale EAF RC beams have been experimentally investigated under four-point bending tests in order to analyze their structural behavior in terms of peak load, deflections and crack patterns in comparison with traditional RC beams without recycled aggregates. Then, a numerical investigation has been carried out through two different three-dimensional finite element procedures: the former is a conventional step-by-step incremental analysis based on a nonlinear stress-strain law for concrete in compression and a post-failure response in tension based on a smeared-crack approach; the latter is an iterative, simplified methodology based on the application of the limit analysis theory. Comparison between numerical and experimental results is discussed and the main advantages and drawbacks of the two proposed numerical procedures are outlined.

D. De Domenico, F. Faleschini, C. Pellegrino, G. Ricciardi

Experimental Assessment of Bond Characteristics in Reinforced Concrete with Electric Arc Furnace Slag

The anchorage between deformed steel bars embedded in concrete blocks has been studied for many years in literature, thus leading to a well-established knowledge on this topic. However, literature is more limited when novel kind of concretes are used, e.g. recycled concretes or electric arc furnace (EAF) slag concretes. This study deals particularly on EAF concrete, and bond between steel reinforcement was studied experimentally through pull-out tests, according to RILEM recommendations. Six series of samples were used, characterized by different aggregate type and water/cement ratio. Bond-slip relationships were analyzed, and the main bond stress characteristics were obtained. Additionally, experimental results were compared with analytical predictions, obtained with empirical formulations collected from literature. Results indicate that bond strength is enhanced when EAF slag is used as recycled coarse aggregates in relatively high-strength concrete.

Flora Faleschini, Amaia Santamaria, Mariano Aneglo Zanini, Carlo Pellegrino

Exterior RC Beam-Column Joints Made with Recycled Concrete: Experimental Behavior Under Lateral Cyclic Reversed Loading

The use of recycled materials to cast reinforced concrete structures opens to new frontiers in developing high-performances and sustainable building materials. Recently, the use of electric arc furnace (EAF) slag as artificial aggregate allowed to produce cement-based materials characterized by high mechanical strength and good durability-related properties. However, few tests were carried out in literature dealing with full scale reinforced concrete structural elements. This paper shows the results of the first experimental campaign on two real-scale exterior beam-column joints made with EAF concrete, subject to cyclic lateral load and column axial load, and failing due to shear of the panel joint and yielding of steel bars in the beam. Results are analyzed in terms of hysteretic behavior, dissipated energy, ductility, and local panel joint behavior, and compared with the ones derived for a reference specimen, made with the same concrete mix proportions.

Flora Faleschini, Mariano Angelo Zanini, Lorenzo Hofer, Carlo Pellegrino

Strain Measurement in a Reinforced Concrete Beam Using Embedded Smart Concrete Sensors

The paper is aimed at investigating the use of embedded smart concrete sensors for monitoring the strain in full-scale reinforced concrete beams. The new sensors are made of the same matrix material of the concrete elements to be monitored and can be easily embedded into structural components before casting, thus achieving a durable and distributed sensing solution for structural health monitoring purposes. The self-monitoring ability is obtained through the dispersion of nano-metric conductive carbon-based fillers which induce new piezoresistive properties. In this study, a set of smart concrete sensors was embedded on top of a simply supported reinforced concrete beam and the dynamic performance of the element was evaluated, by measuring the variation in electrical resistance of the smart concrete sensors and benchmarked against measurements carried out with traditional strain gauges. The results of such comparisons demonstrate that the new sensors are apt for strain monitoring in RC structural components.

A. D’Alessandro, A. Meoni, F. Ubertini, A. Luigi Materazzi

The Effect of Freeze-Thaw Cycles on the Mechanical Performance of RAC

The recycling of Construction and Demolition Waste (CDW) to be used as aggregates for concrete is a potential alternative to minimize the environmental impact. In cold regions, the damage caused to concrete structures by freezing and thawing is a serious problem. This study presents the results of experimental tests aimed at investigating the influence of the use of Recycled Concrete Aggregate (RCA) on concrete submitted to 150 freeze-thaw cycles. Aggregates made from laboratory-produced concrete waste were used in two size fractions (i.e., Coarse 0–4.8 to 9.5 mm and Coarse 1–9.5 to 19 mm). Concrete mixtures of normal strength and high strength were produced with only natural aggregate and mixtures with 100% RCA in each of the size fractions. The mechanical behavior and physical properties were evaluated. The results showed that, for both natural and recycled concretes, the most affected class was the normal strength class.

C. S. Rangel, M. Amario, M. Pepe, E. Martinelli, R. D. Toledo Filho

Effect of a Crystallizing Admixture on Concrete Properties: Italian Concrete Days

The present work aims at investigating the effect of a crystallizing admixture on concrete properties. Several concrete mixtures, properly prepared with different W/C ratios and different cement contents, have been compared with similar ones containing different dosages of Crystallizing admixture. The crystallizing effect of the product has been assessed and discussed both on fresh and hardened properties of the mixtures studied. Evaluations on setting time and strength development have been done on reference and trial mixes. Specific testing like the evaluation of chloride ion diffusion, accelerated carbonation testing and other tests have been performed to have an overview on all aspects on different levels of permeability. The crystallizing effect has been detected and demonstrated with a Scanning Electron Microscopy (SEM-EDS). The pictures of crystals growing into the capillary voids are intended to demonstrate the blocking effect of the cement matrix through the crystallizing compounds.

F. Longhi, F. Surico

The Effect of Calcium Sulfoaluminate Cement on the Engineering Properties of High Performance Concretes with and Without Fibers

This study investigates the effect of fully replacement of ordinary Portland cement (OPC) with calcium sulfoaluminate cement (CSA) as a sustainable binder in High Performance Concrete (HPC). In addition, the effect of introducing double hooked-end (DHE) steel fibers at fiber volume fraction of 1% was assessed. The mechanical properties of HPC were evaluated and the microstructure of the concretes was studied with scanning electron microscopy (SEM) method. The replacement of OPC with CSA cement results in an improvement in the mechanical properties of HPC particularly at later ages of curing. The addition DHE steel fibers significantly increased the engineering properties of concrete. The bond between cement matrix and steel fibers has been enhanced due to the expansive behavior of CSA cement. The SEM observations also show the significant influence of CSA cement on the microstructure of concrete by formation a rich amount of ettringite that subsequently results in an improvement in the properties of concrete.

V. Afroughsabet, S. Cattaneo, G. L. Guerrini, S. Tortelli

Seismic Retrofitting of Masonry with Fabric Reinforced Mortar

Masonry walls are particularly vulnerable against out-of-plane seismic actions. Fabric Reinforced Mortars (FRM) composites, comprising high strength fabrics applied with inorganic matrices, may be used to prevent or delay the onset of collapse mechanisms, and integrated with traditional techniques in compliance with the preservation criteria required for applications to historic structures. This work describes a shake table test carried out on two full-scale wall specimens, one made of two leaves of rubble stones and one of regular tuff blocks. The walls were subjected to out-of-plane vertical bending under seismic base motion. Natural accelerograms were applied in both horizontal and vertical direction with increasing scale factor to collapse. The walls were tested unreinforced, then repaired and strengthened with FRMs, and tested again.

S. De Santis, G. De Canio, G. de Felice, I. Roselli

Bond Behavior of FRCM Composites Applied on Concrete and Masonry

Fiber Reinforced Cementitious Matrix (FRCM) composite materials have been recently introduced in civil engineering applications for the strengthening of masonry and reinforced concrete elements. The aim of the presented experimental study is to evaluate the bond behavior of carbon and glass FRCM composite materials, in the form of bidirectional grids or unidirectional sheets, applied on different substrates by using a cementitious mortar together with an adhesion promoter. Experimental outcomes obtained on masonry using a cementitious mortar have also been compared with the results coming from the same strengthening systems applied with lime mortar. All specimens were subjected to single-lap shear tests until failure, in order to evaluate failure modes, maximum bond capacity and the whole samples behavior in terms of displacement and strain maps (thanks to Digital Image Correlation technique). Experimental outcomes highlighted the good performance of the strengthening systems tested when applied in combination with the adhesion promoter.

A. Bellini, C. Mazzotti

Confinement of Concrete with FRCM Materials

Fabric-reinforced cementitious matrix (FRCM) composites have recently enter the market as a promising, sustainable, and durable solution for the external strengthening of RC and masonry structural members. In this paper, an analytical study on the confinement of concrete with FRCM materials is presented. To this purpose, a wide database including results of compression tests performed on more than 250 concrete cylinders externally wrapped with FRCM was collected from the literature, firstly to perform an overall analysis of the efficiency of the FRCM confinement by varying some of the relevant parameters, such as: type of fiber (glass, carbon, steel, PBO or basalt) and geometry of the mesh, number of layers, composition of the inorganic matrix and compressive strength of the unconfined concrete. Then, preliminary relationships for estimating the compression strength of FRCM confined concrete were developed through best-fit techniques.

Ciro Faella, Annalisa Napoli, Roberto Realfonzo

Explosive Spalling in R/C Structures Exposed to Fire: Key Aspects in Experimental Testing

Explosive spalling in R/C members exposed to fire consists in the violent expulsion of the hottest layers of concrete, due to the combination of compressive stress and vapour pressure, with the consequent reduction of the bearing cross-section and of the structural fire resistance. Experimental tests aimed at assessing concrete spalling sensitivity can be performed at different scales, namely small, intermediate and real scale, with increasing time and cost of testing. The correct level of investigation must be defined as the right compromise between efficiency and representativeness of the real case. Starting from the comparison among different test setups at different scales, the main parameters to be considered in planning the experimental investigations will be described. On the other hand, with regards to the definition of the mix design, it will be shown how the use of different types of fibre can bring remarkable benefits against spalling.

Francesco Lo Monte, Roberto Felicetti, Alberto Meda, Anna Bortolussi

A Sensor for Embedded Stress Measure of Concrete: Testing and Material Heterogeneity Issues

Concrete is well known to be a heterogeneous material that is usually considered homogeneous only referring to a scale of several centimetres. This characteristic makes measuring stresses inside concrete a particularly difficult task. Strains can be measured using several well-known devices. Nevertheless, it is almost impossible to derive a correct estimation of the stress within a concrete structure starting from strain measures as the modulus of elasticity is variable and unknown and creep strains superimpose elastic ones. A preliminary experimental campaign performed to test a stress sensor with the dimensions of a coin to be embedded in concrete is described in the present paper. The effects external applied load are measured comparing the results of short-term loading test performed directly on the sensor and on concrete specimens

C. Anerdi, D. Gino, M. Malavisi, G. Bertagnoli

Slab STRESS – Seismic Testing of a R/C Flat Slab Structure

A research entitled Slab STRESS - Slab STructuralRESponse for European Seismic Design, within the European project SERA - H2020-INFRAIA-2016-1, is currently in progress to study the response of flat slab floors under combined gravity and lateral loads. The project is being carried out by a group of European institutions, led by the Politecnico di Milano together with EPFL Lausanne, UNOVA Lisbon and UTCB Bucharest. A real scale flat slab building will be tested at the JRC ELSA reaction wall facility in Ispra (IT). The Seismic European Code ENV 1998 for does not cover flat slab buildings, that are intensively used because of the reduction in construction costs and time, the simplicity of the geometry and possibility to increase available volumes. The paper describes the research objectives, the specimen and features of the testing program.

D. Coronelli, P. Bamonte

Reinforcement of RC Beams by Means of Mortar Liner. Experiments and Design Rules

It is commonly believed that the restoring of degraded reinforced concrete beams does not require particular precautions to ensure perfect adherence. In fact a number of researchers (e.g. Perez, Morency & Bissonnette in Concrete Repair, Rehabilitation and Retrofitting II - 2009) have shown that without adequate preparation of the substrate and without mortars with valuable characteristics it is possible neither to re-establish the original resistant capacity nor to reproduce the same stiffness of the original intact beam. Furthermore, due to the deterioration phenomena of the reinforcements, it is often necessary to intervene not only for the purposes of restoration but also for insertion of new resistant reinforcement in the same restoration. The design for this intervention is implemented assuming the perfect adherence and cross-section remain plane but these assumptions are not always achieved, with the result that the “restored” element has a greater deformability and/or a reduced resistance with respect to expectations. The document CNR DT 200-2013 has established a series of “poles” for calculation of the reinforcement of “glued” systems on healthy reinforced concrete elements, but has neglected to address the aspects related to “restoration” (which, however, are very common for this reinforcement technique) and to consider the aspects related to the transfer of stresses to the substrate-restoration interface. The absence of such control entails the risk of using a reinforcement adhering to a restoration with high properties, but which then delaminates it from the substrate earlier than expected. To understand these aspects, a substantial series of experimental data is presented in this document, processed at the BASF CC - Treviso test laboratory, on approximately forty reinforced concrete beams where the need for restoration/reinforcement by scarification and restoration of the concrete cover was simulated with mortars of different rheology and mechanical strength, with the addition of carbon FRP rods inserted in the repair mortar. The tests are then compared with the calculation regulations provided for in the current legislation in order to validate a specific calculation software that guarantees an adequate safety factor against failure.

Marco Arduini, Marco Lenotti, Andrea Nicoletti

Bond Mechanisms Between Steel Bars and Lightweight Rubberized Concrete from Waste Tyres

It is well known that the concrete industry has a strong environmental impact on our planet. First, there are the huge volumes of material needed to produce the billions of tons of concrete worldwide each year. Then there are the CO2 emissions caused during the production of Portland cement. Together with the energy requirements, water and aggregates consumption and generation of construction and demolition waste, appears evident as the concrete is not particularly environmentally friendly or compatible with the demands of sustainable development.In this context large number of papers focused on new concrete materials that would be more suitable with environmental point of view. Among these materials, one of the most discussed is rubberized concrete. Rubberized concrete is obtained by incorporating rubber particles, obtained from recycled end of life tyres, as a replacement for mineral aggregates.

F. Tondolo, M. Leone, A. P. Fantilli, M. A. Aiello

AASHTO Design Specifications for GFRP-RC Bridges: 2nd Edition

The development of a comprehensive bridge design national standard is paramount to allow for a wider and safe deployment of Glass Fiber Reinforced Polymer (GFRP) Reinforced Concrete (RC) in the transportation infrastructure. To respond to this demand, a task force of researchers, practitioners, and transportation officials lead by the University of Miami (UM), the University of South Carolina (USC), and the Florida Department of Transportation (FDOT), has developed a draft of the second edition of the Bridge Design Guide Specifications for GFRP-RC (BDGS-GFRP), now under consideration by the American Association of State Highway and Transportation Officials (AASHTO) committee T6. This paper deals with the salient contents of the document, with specific emphasis on the design of flexural members. Compared to the first edition, changes were proposed to reflect the state-of-the-art from archival literature and harmonize the design philosophy with that of other authoritative national and international standards.

M. Rossini, F. Matta, S. Nolan, W. Potter, A. Nanni

SRG for Strengthening Reinforced Concrete: From Laboratory to Field Applications

Fiber-Reinforced Cementitious Matrix (FRCM) composites are becoming a wide-spread technology for the rehabilitation and strengthening of reinforced concrete structures due to some advantages that allow them to be a suitable alternative to Fiber-Reinforced Polymer (FRP) composites. In this work, a new family of FRCM composites system made of ultra-high strength steel cords installed with inorganic mortars named Steel Reinforced Grout (SRG) is presented. This paper briefly introduces to the main properties and mechanical characteristics of SRGs, and introduces a case study on a reinforced concrete structures demonstrating the effectiveness of this strengthening solution

P. Casadei, P. Girardello

Technology and Construction Techniques

Frontmatter

GFRP Reinforcement for Segmental Linings of Mechanized Tunnels

The use of Glass Fibre Reinforced Polymer (GFRP) reinforcements is gradually spreading to replace or to integrate the traditional steel rebar for tunnels excavated with shielded TBMs and lined with precast segmental lining. The complete replacement of the steel rebar with GFRP is particularly used for segments that should be demolished after their installation, for example for cross-passages or niches realization. GFRP reinforcement cages placed on segments’ edges can play an important role to limit the number of cracks and local breakages caused by impacts and unforeseen load conditions, mainly before and during the lining installation. The analyses’ results on a 3D model, which allowed to consider the contribution of such reinforcements both during the lining erection and the service, show that they can increase the lining strength. Moreover, GFRP perimetric cages can be coupled with steel fibre reinforcement (SFRC) to increase the overall flexural and local resistance of segments. Examples of dimensioning and results of laboratory tests carried out to show the GFRP reinforcement effectiveness are reported.

A. Meda, M. Moja, E. M. Pizzarotti, G. Vago

On-Site Demonstration Project of Reinforced Concrete with Seawater

Chloride-contamination of reinforced concrete (RC) structures, whether arising from the use of chloride-contaminated raw materials or from exposure to aggressive environments, results in corrosion of traditional steel reinforcement. For this reason, design standards worldwide limit the use of chloride-contaminated materials in cement and concrete production, without considering the related advantages in saving natural resources. The SEACON project aims at demonstrating the safe utilization of seawater and salt-contaminated aggregates for sustainable concrete production when combined with corrosion resistant reinforcement. For this purpose, a demonstration was built and exposed to an aggressive environment, with the aim of proving the feasibility of using such different technology to produce RC, and collecting data to evaluate durability aspects.This paper shows the results achieved through laboratory investigations and the preliminary results of the on-site monitoring, with particular reference to the materials characterization.

F. Bertola, F. Canonico, E. Redaelli, M. Carsana, M. Gastaldi, F. Lollini, F. Torabian Isfahani, A. Nanni

Precast Segments with Sulphoaluminate Cement and GFRP Reinforcement

During tunnel excavation by means of a tunnel boring machine (TBM), the lining consists of precast structural elements, placed by the TBM during the excavation process and used as support elements during the advancing phase. The use of concrete based on sulphoaluminate binders allows the production of the elements to be speeded up, a reduction in the number of segments stacked waiting for the required strengths to be achieved and provides a more eco-sustainable process avoiding the use of steam curing. In order to verify the feasibility of the proposed solution, two full-scale tests (bending test and TBM jacks thrust test) on metro tunnel precast segments were carried out. The internal reinforcement consisted of a next-gen Glass Fibre Reinforced Polymer (GFRP) cage. The use of GFRP reinforcement, to replace traditional steel, in tunnel segments provides several advantages mainly related to durability aspects or when the use of a provisional lining is foreseen.

M. Bianchi, F. Canonico, A. Meda, S. Spagnuolo, A. Giamundo

New Punching Shear Reinforcement System for Footings and Ground Slabs

Punching shear tests on footings indicated that the inclination of compression struts is much steeper compared to flat slabs. The resulting steeper inclination of shear cracks leads to the assumption that vertically arranged punching shear reinforcement elements are less efficient in footings than in flat slabs. On that basis, a new punching shear reinforcement element with inclined bars was developed. At RWTH Aachen University, 14 punching shear tests on reinforced concrete footings including the new punching shear reinforcement elements were conducted. The test specimens partly failed inside the shear‐reinforced zone and at maximum load level. In spite of a reduction of total steel cross sectional area, the test specimens with the new punching shear elements showed a significant increase in punching shear capacity (40–50%) compared to previous test series. The new punching shear reinforcement system allows for a significant reduction of footing’s dimensions.

M. Ricker, D. Kueres, F. Häusler, D. Carminati, J. Hegger

Integral Bridges: A Construction Method to Minimize Maintenance Problems

In traditional bridges, expansion joints and supports are installed to facilitate relative displacements and prevent the occurrence of stresses induced by thermal variations. However, such devices can cause maintenance problems. On the other hand, integral bridges are structures without joints and supports where abutments, piers and deck are connected monolithically producing a complex structural and geotechnical interaction. Integral construction thus eliminates maintenance works related to the presence of connection devices. However many countries have imposed restrictive limits on the length of these structures, and this paper aims to identify the maximum length of integral bridges, in relation to the particular boundary conditions considered in the case study. The authors present a study on soil-structure interaction concerning both backfill and foundation soil, and carry out the design of some structural elements of a reinforced and prestressed concrete integral bridge, paying attention to guarantee the necessary flexibility to the structure.

Achille Devitofranceschi, Elisa Paolieri

FIB Bulletin 75 – New System Performances and Full Scale Tests

FIB Bulletin 75 recommendation has introduced improved performance requirements on corrugated plastic ducts for post-tensioning tendons and also on the entire post-tensioning system. Aim of this article is to describe and analyze critically the most important innovations introduced also with reference to previous FIB Bulletin 7. Special emphasis is given on the full scale testing program carried out recently by Tensa over its post-tensioning tendons in accordance to Annex B of FIB Bulletin 75. A supplementary testing program, made with reference to Florida Department of Transportation 2018 Construction Specifications, is also considered as a reference for further analysis.

T. Ciccone, L. Civati

Stay Cable Multi-tube Saddles, Design and Testing

Saddle systems for stay cables are at the moment one of the preferred solutions in the field of cable stayed bridge design across the world, and this trend seems to increase day by day. The most advanced systems currently available for parallel strand stay cable systems are multi-tube friction saddles, where each single strand runs into an individual pipe and the stay cable differential force is transferred by friction. The structural behaviour of a saddle device is a very complex topic involving several mutually dependent aspects. The development and validation of saddle systems is usually performed in the frame of the design assisted by testing. Full-scale tests have been carried out at the Structural Engineering Laboratory of Politecnico of Milan taking into account current developments of International Recommendations, such as FIB Bulletin 30 and PTI DC 45.1-12, with the aim of characterizing friction, fatigue and static performances of saddles.

A. Castiglioni di Caronno, T. Ciccone

The Bridge Over the Blue Nile at Mekane Selam - Ethiopia

The present paper reports the description of the construction technologies used during the building of the Blue Nile Bridge at Mekane Selam, in the Amara region in northern Ethiopia. The bridge is part of the second section of the Kombolcha–Gundewein road project, which foresee the upgrading of about 139 km of rural routes to a road in conformity with the DBST standard. The work is carried out using cantilever system with a single-cell frame section of variable height. Unique in its kind for the geographic context in which it is inscribed, the bridge is one of the first examples of prestressed concrete structure in Ethiopia, and the first with cantilever technology. Due to the seismic activity that characterizes the entire area, the design and construction of the work have been carried out in compliance with the anti-seismic regulations of the American Regulations (AASHTO), integrated with the national standards.

E. Codacci-Pisanelli, G. Minisola

Flexural Design of Elevated Slabs Made of FRC According to fib Model Code 2010: A Case Study

Elevated concrete slabs are typically used as columns/piles supported floors in multi-story buildings or industrial facilities. The need to reduce construction time and costs has favoured the use of ever more advanced materials, like Steel Fiber Reinforced Concrete, as an alternative to conventional reinforced concrete. Many research studies and on-site applications have proven that steel fibers can be successfully used to totally substitute the main flexural reinforcement generally placed in conventional reinforced concrete slabs. However, in order to ensure the required minimum structural performance both at ultimate and serviceability loading conditions, the total removal of rebars requires the use of very high steel fiber contents (>70 kg/m3). However, the use of a proper combination of fibers and conventional rebars, generally known as Hybrid Reinforced Concrete (HRC), may represent a feasible solution to get the required structural performance by minimizing, at the same time, the total amount of reinforcement (fibers+rebars).This paper focuses on the design of HRC elevated slabs according to the design provisions for FRC structures reported by the fib Model Code 2010 and recently introduced also by the Italian structural design code (NTC 2018). A simplified design procedure based on a consolidated design practice is proposed. Emphasis is given to the use of HRC for optimizing the slab reinforcement. A case study of an elevated slab made with synthetic Fiber Reinforced Concrete is used to show the effectiveness of the design procedure.

L. Facconi, A. Conforti, F. Minelli, G. Plizzari

An Innovative and Sustainable Wet Joint Between Precast Beam and Columns from the Oil & Gas

This innovative joint was conceived for the effective and sustainable construction of precast concrete pipe-rack structures in petrochemical plants. It consists in a cast-in-situ joint between precast beam and column concrete elements, featuring easy in-shop fabrication and on-site assembly, with no scaffolding and minimum formworks. The solution is characterized by high strength and ductile behaviour in the plastic range, by means of loop splices and cast-in-situ concrete with steel fibres. Experimental tests conducted on reduced-scale structures verified that the performance of the prefabricated solution during an earthquake is comparable to, if not better than, that of the corresponding cast-in-situ concrete solution, while fulfilling the American Concrete Institute requirements. This precast concrete solution economically mimics the behaviour of monolithic reinforced concrete frames and has been already successfully implemented in several pipe rack structures in remote seismic zones.

V. Colone, P. Lopriore

Backmatter

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