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2022 | Buch

Proceedings of the 10th International Conference on Behaviour of Steel Structures in Seismic Areas



Über dieses Buch

This volume highlights the latest advances, innovations, and applications in the field of seismic design and performance of steel structures, as presented by leading international researchers and engineers at the 10th International Conference on the Behaviour of Steel Structures in Seismic Areas (STESSA), held in Timisoara, Romania, on 25-27 May 2022. It covers a diverse range of topics such as behaviour of structural members and connections, performance of structural systems, mixed and composite structures, energy dissipation systems, self-centring and low-damage systems, assessment and retrofitting, codes and standards, light-gauge systems. The contributions, which were selected by means of a rigorous international peer-review process, present a wealth of exciting ideas that will open novel research directions and foster multidisciplinary collaboration among different specialists.



Keynote Lectures

Steel and Composite Shear Walls - Two High-Performance Lateral Force Resisting Systems

This keynote speech focuses on cyclic behavior and seismic design of steel and composite shear walls, two efficient and ductile lateral force resisting systems. First, a summary of types of steel shear walls and their seismic performance are presented. Then, recent advances on the unstiffened steel plate shear walls are discussed. Unstiffened steel plate shear walls have been studied, and their design procedures are currently in most seismic design codes. However, their use has been quite limited. The main reason is that in the current unstiffened steel plate shear walls, included in the seismic codes, such as the North American specifications and the Eurocode, quite large lateral forces are applied to the boundary columns creating significant bending moments in the columns. The other reason for reluctance in using the existing steel plate shear wall is the very high cost of the field-welded moment connections that are currently used in this system. The keynote speech will discuss innovative systems developed in recent years to eliminate both problems. The second part of the keynote speech will focus on the steel-concrete composite systems. Available cyclic tests are briefly summarized, and recent developments and innovative systems will be discussed.

Abolhassan Astaneh-Asl
Fifty Years of Severe Earthquake Experiences in Japan and the Next Direction of Steel Structures in the World

Steel is a superior structural material due to its strength and ductility. These properties are advantageous especially for seismic resistant buildings. Masonry wall structures are vulnerable to earthquakes with their heavy weight and brittleness. Having a lower fire resistant nature is critical for wooden structures. For reinforced concrete (RC) structures, it is difficult to equip seismic energy dissipating systems. The RC structures can absorb the seismic energy with their plastic deformation with cracks; however, residents do not feel at ease with cracked RC buildings by large earthquakes and do not wish for such cracks to remain inside. In spite of the superior material properties of steel, extensive damage has been observed after large earthquakes over the past 50 years. Damage tolerant structures were proposed with the development of eccentric brace frames and buckling restrained braces (BRBs) in 1970 and 1987, respectively. Nowadays, many passively controlled steel buildings using BRBs or other damping devices have been constructed. A brief history about the innovation of damage tolerant structures and recent applications in Japan are introduced.

Akira Wada
Lifetime Resilience of Bridges Under Single and Multiple Hazards: Emphasis on Earthquake and Corrosion

Design and assessment of structures have been geared towards addressing the most dominant hazard at the location of interest. In general, single hazard approaches underestimate risk. Therefore, the possibility of structures experiencing multiple independent or interacting hazards of different types during their lifetime needs to be considered. The design methodology of bridges must shift towards a more comprehensive approach of addressing multiple hazards to ensure adequate performance under different mechanical and environmental stressors. Quantification of the reliability and risk associated with damage to individual bridges under multiple hazards can help in prioritizing retrofit activities for bridges in a network. Significant advances have been accomplished in the field of earthquake engineering. However, there is a need to promote further research for developing concepts and methods in order to design resilient bridges and assess the resilience of existing bridges and bridge networks in a life-cycle context. Resilience emphasizes the impact of infrastructure damage, failure and societal recovery under extreme hazards with a low probability of occurrence and high consequences. An infrastructure system needs to include resilient and adaptive capabilities for ensuring its long-term performance. This keynote paper provides an overview of life-cycle design and assessment methodologies of bridges under multiple hazards with an emphasis on earthquake and continuous deterioration. Several important performance indicators such as risk and resilience necessary to be implemented into the practical design and assessment are introduced. Finally, the concepts and methods presented are illustrated in case studies on bridge networks under seismic and corrosion hazards.

Dan M. Frangopol, Mitsuyoshi Akiyama
Steelwork for Seismic Upgrading

The improving of the seismic performance of existing buildings is worldwide recognized as a pressing need in many earthquake prone countries. The use of steelwork may represent a satisfactory tool to fulfil this goal in effective and economical way. This paper illustrates the intervention technological systems based on steelwork, providing examples of some real application.

Federico M. Mazzolani
Development and Application of Multi-stage Steel Dampers

Yielding of steel can dissipate a substantial amount of energy, which can be used in steel dampers for mitigating seismic effect on engineering structures. However, the accumulation of cyclic plastic deformation of steel due to earthquakes may lead to low-cycle fatigue fractures of steel dampers. Though the accumulated plastic deformation capacity of steel can be increased by employing low-yielding ductile steel, plastic deformation capacity of steel is still limited.Nevertheless, the plastic deformation demands on steel dampers are various, which depend on their working range of earthquake levels. If steel dampers are required to dissipate energy in the range of earthquakes at both minor and major levels, the accumulated plastic deformation would be too large for steel dampers to accommodate. To solve this problem, the concept of multi-stage steel dampers is proposed.A multi-stage steel damper is a combination of two or even three steel dampers to effectively work in various ranges of earthquake levels. The working range can be between minor and moderate earthquake levels, between moderate and major earthquake levels, and even between major and mega earthquake levels. Since each steel damper only needs to meet the requirement on a relatively narrow range of working earthquake levels, the demands of accumulated plastic deformation can be easily met.Based on the concept of multi-stage steel dampers, the multi-stage steel beam-type dampers and brace-type dampers has been developed. The configuration and performance objectives of multi-stage steel beam-type and brace-type dampers are presented and their workability at various earthquake levels are demonstrated with experiments. The effectiveness of application of multi-stage steel beam-type and brace-type dampers in practical projects are also presented in comparison with usage of traditional dampers.

Guo-Qiang Li, Hua-Jian Jin, Meng-De Pang, Ying-Zhi Sun, Da-Zhu Hu, Fei-Fei Sun
Improving the Seismic Performance of Structural Steel Systems Through Advanced Testing

Recent earthquakes in many parts of the world have resulted in damage to the civil infrastructure, resulting in fatalities and economic loss. This experience has resulted in stake holders demanding a more resilient infrastructure and the mitigation of earthquake hazards to minimize their impact on society. Researchers have developed concepts for structural steel systems to promote resilient performance. Real-time hybrid simulation (RTHS) provides an experimental technique to meet the need to validate new concepts. RTHS enables a complete structural system, including the soil and foundation to be considered in a simulation, interaction effects and rate dependency in component and system response to be accounted for, and realistic demand imposed onto the system for prescribed hazard levels. This paper presents the concept of RTHS and developments achieved at the Lehigh NHERI Experimental Facility that have advanced RTHS to enable accurate large-scale, multidirectional simulations involving multi-natural hazards to be performed. The role that hybrid simulation has played in these developments and how its use has enabled a deeper understanding of structural system behavior under seismic and wind loading will be discussed. Examples include self-centering steel moment resisting frame systems, braced frame systems with nonlinear viscous, and tall buildings with outriggers that are outfitted with nonlinear viscous.

James Ricles

Behaviour of Structural Members

Development of an Objective Brace Fatigue Model

To dissipate energy, steel braces in concentrically braced frames are expected to sustain large deformations due to yielding in tension and global buckling in compression. During seismic events, braces can experience very large strain demands that can lead to brace rupture. Thus, characterization of behavior and evaluation of braced frame performance depends on adequately simulating force re-distributions following both buckling and fracture of the brace elements. In the past, the fatigue life of braces has been estimated by using the Coffin-Manson relationship and Miner’s rule to evaluate the accumulation of damage based on strain or deformation histories. Typically, this model for low-cycle fatigue is considered only at the material level. However, when using force-based beam-column elements, strains at the material level are nonobjective and depend on the numerical model inputs, e.g., location and number of integration points used to model the brace. Therefore, using the same fatigue model with different numerical modeling parameters for the brace does not always produce consistent results. In contrast, deformations at the element level are little affected by the numerical model inputs. An objective fatigue model based on deformations at the element level is developed to calculate damage and fracture in brace elements. Results are compared to similar fatigue models implemented at the material and section levels. The new section and element brace fatigue models have been implemented in the source code of OpenSees.

Akiri Seki, Barbara Simpson
Pre-test Numerical Modelling of Stainless Steel and Hybrid Links

Eccentrically braced steel frames have of good balance between lateral stiffness, strength and ductility, and therefore are often preferred as a seismic-resistant system. Replaceable bolted links and a dual structural configuration, consisting of eccentrically braced and moment resisting frames was proposed in the past for enhancing the structural system with re-centering capability. Further enhancement of the seismic performance is sought through adopting stainless steel links for increasing link ductility, and high-strength steel, which could reduce the link overstrength. To this end, a series of pre-test numerical investigations are performed on several link made of mild, stainless, and high-strength steel. Short links are adopted, which dissipate the seismic energy by yielding essentially in shear. Obtained numerical results indicate that existing design criteria are inappropriate for stainless and hybrid links. A new and more general criteria for the normalized link length is proposed, which explicitly accounts for the steel properties of the flanges and the web. Finite element simulations on several homogeneous and hybrid links made of mild, stainless and high strength steel proves and appropriate behaviour of links designed using the new criterion.

Anna Ene, Aurel Stratan
Experimental Investigation of Concrete-Filled Double Steel Tube Columns (CFDST) with High Performance Materials Under Monotonic and Cyclic Loading

This paper presents an experimental study on the performance of innovative Concrete-filled double steel tube (CFDST) columns with high-performance building materials under monotonic and cyclic loading. In total six stub CFDST-columns and two conventional stub concrete-filled steel tubes (CFST) were tested at Ruhr-Universität Bochum under a constant axial load with either a monotonic or a cyclic increase of lateral displacement.Focus of the paper is the comparison of the characteristic behavior of the specimen like the hysteric behavior, ductility and energy dissipation. The experimental investigations have shown that the resistances, ductility and energy dissipation of innovative CFDST is increased compared to conventional CFST-columns. The use of a high-strength inner tube did show the most benefits in terms of the resistances, while at the same time a configuration with normal-strength core materials showed better results in terms of the energy dissipation and ductility.

Dennis Witteck, Rebekka Winkler, Markus Knobloch
Modelling Stress-Strain Behaviour of Low-Yield-Point Steels

Unlike low carbon or alloy steels, low-yield-point steels are characterized with very low yield strength but very high capacity of strain hardening and deformation capacity. In order to develop their advantages in energy dissipation systems, accurate modeling of the stress-strain behavior of low-yield-point steels are imperative for structural analysis and performance evaluation. Previous experimental investigations have revealed the prominent cyclic hardening response and there generally exists an initial yield plateau. Based on these observations, a cyclic plasticity model was developed to describe the stress-strain responses under monotonic and various cyclic loadings. Both isotropic hardening and kinematic hardening were found to be nonlinear. Exponential function was used to describe the transient hardening under cyclic loading, while evolution of backstresses based on the Armstrong-Frederick rule was used to trace the significant Bauschinger effect in unloading-reloading cycles. Both isotropic and kinematic hardening rules were decomposed into short-range and long-range components to capture the stress-strain responses in yield plateau and strain-hardening regions, respectively, but using formulations of different parameters. In addition, an impermanent bounding surface in stress space and a memory surface in plastic strain space were established to correctly describe the yield plateau stress and duration. A calibration procedure by tension coupon test was established, which makes it convenient to determine model parameters in practical application. Close agreement between the experimental and the modeling stress-strain curves was obtained. Therefore, the developed cyclic plasticity model can be used for further elasto-plastic analysis of structural components or systems using low-yield-point steels to yield accurate predictions.

Fangxin Hu
Mechanical Characterization of 17-4PH Stainless Steel Manufactured by Means of Selective Laser Melting Technology

3d printing is a manufacturing process based on the addition of material layer by layer until the completion of workpieces. The rapid development of additive manufacturing, in recent years, is due to its many advantages, including material consumption and waste minimization, use of pure raw materials, low post-processing requirements, time and cost reduction, high customization of the finished product, fast prototyping, and freedom of design. So, exploiting the huge potential of these innovative technologies, it is possible to propose their application also in some fields of engineering for which they have never been considered, such as seismic and structural engineering. In fact, the most common metallic materials typically employed for those applications (steel, aluminium, titanium and nickel alloys), can be used to produce elements with outstanding structural properties by 3D printing technologies. In this aim, this paper shows the main outcomes of an experimental campaign finalized to an extensive mechanical characterisation of 17-4PH stainless steel, one of the most widely used metallic materials for Selective Laser Melting (SLM) technology. In particular, the effects of one of the main printing parameters, i.e. scanning times, on the material mechanical behaviour are evaluated by means of tensile strength tests.

Francesca Romana Andreacola, Ilaria Capasso, Giuseppe Brando
Residual Performance of Structural Steel After Cyclic Plastic Deformation and Strain Aging

The sustainability of steel construction can be improved dramatically by establishing reuse, in a new structure, steel components procured from an older structure. To achieve this goal, the residual performance of used steel must be evaluated. For seismic areas, the residual performance after experiencing an earthquake, large or small, must be quantified. Therefore, the residual performance of hot rolled I-shapes, of grades SS400, SN400B and SN490B, after plastic deformation and strain aging was examined through three test series: (I) tension coupon tests; (II) cyclic tension-and-compression coupon tests; and (III) cyclically loaded beam tests. The tests were conducted in two phases: pre loading to predetermined plastic deformation, and subsequently, after curing for 1 or 3 months at ambient temperature, loading to larger plastic deformation. The SS400 with free nitrogen content of 0.006 wt% saw substantial strain aging effects, while SN400B and SN490B with free nitrogen content of 0.003 and 0.002 wt% saw smaller effects. In the beam tests, pre-loading to ±0.02 rad resulted in up to 25% increase in yield strength but little change in maximum strength and plastic deformation capacity. Residual deformation of the beam was within geometric tolerances after cyclic loading to ±0.01 rad, but exceeded some tolerance items after cyclic loading to ±0.02 rad.

Haruka Nakagawa, Kayo Taniguchi, Shaoqi Yang, Tetsuhiro Asari, Taichiro Okazaki
Full-Scale Testing of European Steel Beams with Reduced Beam Section Under Reversed Cyclic Loading

Steel beams with reduced beam section (RBS) are often used as part of prequalified connections in seismic regions. However, RBS connections are not as common in Europe. Reasons relate to easiness in fabrication, which requires on-site welding, and the seismic performance qualification. This paper presents preliminary experimental results from a recent testing program that was conducted at the Structures Laboratory at EPFL on full-scale steel beams with RBS. The steel beam featured a European IPE profile. The test specimen discussed herein was subjected to symmetric cyclic lateral loading up to 4% rad followed by asymmetric lateral loading, which is characteristic of dynamic response prior to structural collapse. The experimental results suggest that inelastic deformations concentrated within the RBS region, as expected. The beam flange-to-steel plate complete joint penetration welds behaved satisfactory throughout the imposed lateral loading history. The test specimen did not experience flexural strength deterioration prior to 4% rad. Comparisons of the cyclic response of the test specimen with available test data from prior testing programs are also discussed.

Hiroyuki Inamasu, Dimitrios G. Lignos
Study on Quantitative Evaluation Method for Local Buckling of Flange of H-Section Steel Beam by Micro Strain Amplitude Measurement

The final purpose of this research is to establish a method for evaluating damage and residual performance of steel structural member after local buckling occurred. This paper quantitatively clarifies the change of strain amplitude caused by local buckling through analysis and discusses the possibility of its application in local buckling damage assessment. When a small shape change occurs in the steel frame member due to local buckling, the distribution of strain amplitude caused by microtremor or small earthquake would change, and it is expected that damage assessment can be made by capturing this change. When a static cyclic loading analysis using a finite element model was performed to simulate the local buckling of the H-shaped steel beam, and at the step where the load returned to zero for each loading cycle, the ratio between the strain and displacement, which we call “local stiffness,” is calculated and it was used to discuss the damage. As a result of the analysis, it was shown that the local stiffness changes as the local buckling progresses. If such changes in local stiffness can be captured by actual measurement, it is expected to lead to the establishment of damage evaluation technology.

Kaile Sun, Jun Iyama, Yoshihiro Fukushima
Fatigue Performance of the Buckling-Restrained Brace Using a Low-Yield-Point Steel Core Plate

Low-yield-point steels (LYP) have lower- and narrower-range yield strengths-, and better elongation than conventional steels. These steels are adapted to tall buildings and mid-rise buildings using seismic control devices such as buckling-restrained braces. Authors have been conducting studies to develop the buckling-restrained brace using steel mortar planks (BRBSM). In this study, we evaluate the fatigue performance of the buckling-restrained brace using a LYP core plate. First, we demonstrate the mechanical properties of LYP and the details of the buckling-restrained brace types that use them. Next, we conduct fatigue tests to examine fatigue performance using parameters such as strain amplitude and cycle frequency. Finally, we compare the maximum number of loading cycles of the buckling-restrained brace using LYP’s core plates to the ones using rolled steels used for building structure.

Makoto Nakamura, Hiroki Takizawa, Masanori Fujita, Mamoru Iwata
Mechanical Properties of Structural Steels Subjected Bending History for Reuse

In Japan, steel structure buildings, such as plants and warehouses, are demolished within approximately 30 years owing to physical, architectural, economic, or social reasons. Damages of structural steels such as plastic deformation are often caused by demolition of the building steel structures. If their performance of structural steels affected by the plastic deformation such as bending, twisting, warping are evaluated, it makes contribution to use structural steels for reuse. In this study, we focus on damages such as bending history and experimentally investigate the mechanical properties of structural steels that have been subjected to a bending and unbending process using parameters such as bending radius, bending count, thickness of structural steels. These mechanical properties such as tensile strength, yield strength, and elongation of the structural steels affected by bending history are evaluated by conducting a tensile test.

Masanori Fujita, Mamoru Iihara, Makoto Nakamura, Mamoru Iwata
Experiment on Structural Behavior of Metal Exterior Wall

In Japan, metal panels made from aluminum or steel are widely used as the exterior finishing for medium and low-rise buildings such as offices and commercial facilities. It is important to control the damage to the metal exterior wall in order to realize the continuous use of buildings after an earthquake.In this study, a cyclic loading test of metal exterior wall of the scale of one metal panel was conducted. Test parameters are the material and the thickness of the panel. From the experiment, it was found that all specimens can be used without any significant damage up to a story drift angle of 0.01rad. In addition, experimental results indicate that the slip at the bolted joint causes the metal exterior wall to non-linearize, although the slip at screw joint does not greatly affect the overall behavior. Furthermore, it was confirmed that the metal exterior wall finally exhibited the ultimate strength due to the fracture at the edge of the screw joint.

Miku Kurosawa, Shoichi Kishiki
Experiments and Modelling of Starred Angle Braces

A starred angle is a built-up shape composed of two angles joined intermittently by welded plates (stitch plates) at the heels, forming a cross-shaped section. Starred angles braces advantages include simple fabrication, easy installation on the frame, and easier clean up and maintenance. For these reasons, these braces are widely used in steel industrial construction in Chile. However, a number of these braces failed during the 2010 Maule earthquake in Chile either by local buckling, lateral torsional buckling, or connection fracture. These failures, although not yet completely explained, have made engineers steer away from the use of starred angles as braces. Six scaled specimens with the same cross section but different lengths were tested under cyclic loading of increasing amplitude. The failure modes varied depending on the slenderness of the specimen from flexural to flexural-torsional buckling. After several cycles of inelastic displacement, the specimens developed fracture in only one of the angle legs, maintaining significant tensile strength, but low residual compressive strength. No failure on the connections or stitch plates was observed. A numerical model developed by previous research for tubular and I shaped braces was adapted for starred angle braces and calibrated to represent the response of the braces, using the experimental data. This model can be used to study the performance of structural systems that include starred angle braces.

Ricardo Herrera, Robinson Guerrero, Maria A. Rodriguez
A Database for Steel Braces with Respect to Inelastic Strength and Ductility Capacity

Steel braces are efficiently and economically used in seismic prone areas. Numerous researchers conducted physical tests of steel braces subjected to cyclic loading. Some past studies developed databases for less than 100 steel braces primarily based on both of strength and ductility at certain ductility levels. The paper presents the extraction of numeric data from images on past technical papers to examine the buckling strength, ultimate strength and fracture life of the steel braces compared to the past studies. The total number of steel brace specimens for the extraction was 377. Rectangular section, rectangular hollow structural section (HSS), I-shaped, and circular HSS were used for the section of the steel braces. The maximum compressive strength observed in the physical tests was compared to member requirements refer to 5 design provisions. The ratios of the ultimate tensile strength to yield strength were in the range of 0.7–1.6. A computational approach explicitly simulating fracture life of the steel braces was re-examined to extend the range of validity.

Ryota Matsui, Zhang Yiyue, Taichiro Okazaki, Toru Takeuchi
Structural Modeling of Wide-Flange Steel Beam-Column Under Combined Loading Conditions

Generally, the strong-column-weak-beam concept is adopted for the moment-resisting frame. Two-phase design procedures must be conducted for high-rise buildings, and the strong-column-weak-beam philosophy is allowed to be checked at the floor level instead of each joint level. In this situation, the column may have a chance to form the plastic hinge. Moreover, the column may yield due to the strain hardening at the plastic hinge of the beam. Therefore, to clarify the behavior of the column under combined loading conditions, the columns’ response model is needed. Besides, when the structural engineers try to run a nonlinear-time history analysis, the columns’ mathematical modeling under the cyclic bending moment is needed. In the first step, mathematical modeling under monotonic loading is necessary to simulate. Further, the monotonic modeling can correspond to the cyclic loading’s envelope response; cyclic modeling can be constructed based on this. In this paper, a structural model for the column’s response curve under monotonic loading is proposed. From the proposed modeling, the column’s plastic deformation capacity was evaluated and compared with the test results to clarify the accuracy of the modeling. Finally, the performance curves that correspond to the plastic deformation capacity is developed. The developed performance curves are also compared with the FEA to see the correspondence.

Soya Nakatsuka, Atsushi Sato, Takuro Hayashi, Shimpei Yoshioka

Behaviour of Connections

Numerical Study of the Quasi-static Cyclic Behaviour of Blind-Bolted Connections

This paper reports on a numerical study carried out to evaluate the quasi-static cyclic response of three endplate joints using hollo-bolts and non-concrete-filled tubular columns. The present research follows an experimental program involving monotonic tests of 22 specimens, covering different sets of connections and configurations. This study introduces a numerical prevision of the behaviour of the joints’ components when subjected to both tension and shear originated by a cyclic loading, indicating that without proper reinforcement, these joints cannot be used in zones with high seismicity, given their weakness. Numerical simulations using ANSYS software are compared against the experimental monotonic tests to ensure results concordance and reliability. The purpose of this paper is to present and discuss the numerical descriptions of the main response characteristics including hysteretic loops, stiffness and strength degradation, pinching effects, energy dissipation, among other structural properties. The models indicated that the HBM20 have sufficient mechanical strength, but the column’s plasticity is too large to ensure a proper dynamic response when large moments are applied. However, due to their fast assembly and aesthetical design, new solutions are being implemented to increase the strength and resistance of these joints in order to meet the earthquake design requirements. The most relevant components of these joints that increase their structural properties are also mentioned. These findings allow having a deeper understanding of the behaviour of these connections in seismic scenarios and the results serve as a basis for a future experimental campaign dedicated to evaluate the dynamics of non-concrete-filled blind-bolted connections.

Afonso Trindade Bonina de Mesquita, Afonso Bonina de Mesquita
Data Driven Evaluation of Existing Numerical Modelling Guidelines for Semi-rigid Connections

The performance-based earthquake engineering framework requires robust numerical models to accurately quantify structural performance under different hazards, beyond the scope of conventional building codes. Predicting the nonlinear behaviour of semi-rigid (SR) steel connections can be challenging given the multitude of deforming components and failure modes. The literature comprises a number of analytical and empirical models attempting to characterize their moment-rotation behaviour. These models are generally limited in terms of applicability. This paper focuses on flush end-plate (FEP) connections that are abundantly used in construction worldwide. A comprehensive experimental data pool of 374 specimens is assembled, digitalized and processed. This data pool is used to quantify the response parameters of FEP connections, including the elastic stiffness, moment capacity and rotational ductility. The data shows that bare steel FEP connections can develop an average strength of 30% that of the beam and a considerable plastic rotation of 4% radians. The robustness of the Eurocode 3 component method, in predicting the connection’s strength and stiffness, is also assessed. The analysis highlights the loss of accuracy for the component method particularly with respect to the elastic stiffness.

Ahmed Elkady, Lam Mak
Nonlinear Numerical Assessment of Steel Reduced Beam Section Connections

Cyclic tests on Reduced Beam Section (RBS) connections made of heavy structural sections provided detailed insight into the structural behaviour, including strength, ductility, and failure modes of such configurations. The experimental results indicated that geometrical and material effects need to be carefully considered when designing welded RBS connections incorporating large steel profiles. To better interpret the experimental results, nonlinear finite element simulations are conducted for the test series, comprising four large-scale specimens with distinct sizes. It is shown that the numerical models can reproduce the overall moment-rotation curves, inelastic distribution, as well as failure modes. The findings point out the need, in relatively large sections with thick flanges, for a deeper RBS cut than currently specified in design guidance. This modification would be required to promote a response governed by extensive yielding at the RBS while reducing the excessive strain demands at the beam-column welds.

Dan V. Bompa, Teodora Bogdan, Ahmed Y. Elghazouli, Edurne Nuñez, Matthew R. Eatherthon, Roberto T. Leon
The Effect of Degree of Composite Action on RWS Connections Subject to Cyclic Loading

Concerns have been raised over the presence of concrete slab and resulting composite action in jeopardising the concept of strong column and weak beam seismic design. This comprehensive finite element analysis (FEA) aims to study the effect of the degree of composite action and other two parameters; namely, size and location of the web opening, on the performance of steel-concrete composite extended end-plate RWS connections subjected to cyclic loading. It is apparent that the degree of composite action of RWS connections is an important factor in their seismic-resistant design. In particular, the low degree of composite action in RWS connections can result in the mitigation of the bottom flange fracture damage and the crushing and cracking of the concrete slab. It is concluded that extended end-plate RWS connections can be used in retrofitting existing and in new buildings in seismic areas.

Fahad Falah Almutairi, Konstantinos Daniel Tsavdaridis
Development of Dissipative Embedded Columns Base Connections for Mitigating Column Axial Shortening

This paper proposes an innovative design concept for embedded column base (ECB) connections featuring wide flange steel columns. The developed ECB connection achieves a non-degrading hysteretic response up to lateral drift demands associated with low probability of occurrence earthquakes. Column residual axial shortening due to local buckling is also minimized. In the proposed ECB connections, the dissipative zone is shifted into the embedded portion of the steel column inside the reinforced concrete (RC) foundation. This is achieved by lowering the flexural strength of the embedded column portion by reducing the column flange width, by keeping the RC foundation elastic, and by decoupling the flexural behaviour of the steel column from that of the RC foundation through the use of a debonding material layer wrapped around the embedded column portion. Nonlinear geometric instabilities of the embedded column portion are prevented because of the surrounding concrete, which realizes a stable energy dissipation mechanism. The proposed concept is validated through large-scale quasi static testing as well as complementary finite element simulations. Both experiments and simulations demonstrate that the proposed dissipative ECB connections behave as intended. More specifically, the proposed dissipative ECB connections do not experience flexural strength deterioration of the connection up at least to 4% rads and they minimize column axial shortening.

Hiroyuki Inamasu, Albano de Castro e Sousa, Dimitrios G. Lignos
Required Strength of Column Joint of Bidirectional Steel Moment-Resisting Frames

According to current design recommendations in Japan, column joints of steel building structure are required to remain elastic under severe earthquake, even ultimate state of the structure is reached. However, the rules for designing column joint are mainly based on experience, and there is no previous research that focuses on the behaviour of column joints within bidirectional steel moment frame under severe earthquake.This paper conducted numerical analyses with steel moment-resisting frames subjected to bidirectional ground motions to investigate the behaviour and required bending strength of column joints. Firstly, from the analysis results, factors that affecting the maximum bending moment at column joint have been revealed; moreover, the shortages of current design recommendations in Japan have been figured out. Secondly, the effects of column joint yielding on the seismic response of steel moment-resisting frames under bidirectional ground motions are considered, and the required bending strength of column joint has been examined.

Iathong Chan, Yuji Koetaka
Low-Cyclic Fatigue Characteristics of Hanging Bolts Used in Building Equipment

In the 2011 Great East Japan Earthquake, it has been reported that hanging bolts of building equipment are fractured around the connection and cause damage to equipment to lose its function. The low-cyclic fatigue characteristics of hanging bolts caused by cyclic deformation has been investigated in previous studies. However, effects of relatively small loading amplitude range on the fatigue characteristics of hanging bolts are not clear. In this study, we conducted cyclic loading test focusing on the low-cyclic fatigue characteristics of hanging bolts with deformation amplitude, suspension length, and nominal diameter as parameters and clarified the fundamental structural behavior. From this cyclic loading test, it was found that the experimental values of the elastic stiffness and yield strength of the hanging bolts at initial cycle were almost the same to the calculated one. Regarding the low-cyclic fatigue characteristics of the hanging bolts, the longer suspension length brought the greater number of cycles without differences of nominal diameter. In addition, it was found that when nominal diameter was different, the elastic stiffness and yield strength were varied according to mechanics, however the number of cycles were almost the same.

Ichiro Hirano, Miku Kurosawa, Shoichi Kishiki
The Effect of Reinforcement at the Bolted Joints of Cold-Formed Steel Moment Frame Assembled by Built-Up Members

A lateral force resisting system called CFS-SBMF is specified in AISI Standard (AISI S400). In this system, C-section beams are connected to square hollow section columns by high-strength bolts to assemble the moment resisting frames (MRFs). In the previous studies, a frame type that the built-up beam and column were connected through the connecting plate by high-strength bolts was proposed, which followed the AISI CFS-SBMF system concept. As a result of full-scale testing, local deformation occurred at an early stage, and the expected structural performance was not exhibited, showing 50% of the beam capacity. To maximize the performance, reinforcement at the bolted joint region may increase the resistance of the frame. In this study, parametric FEM simulation is conducted with two reinforcement methods. These reinforcements are attached to the web and flange of the beam. Based on the results, the bolted joint resistance could be increased up to 75% of the expected performance by the reinforcement. Moreover, the appropriate dimensions for the reinforcement are considered.

Koya Tagami, Atsushi Sato
Monotonic and Cyclic Behaviour of Base-Plate Joints of Steel Storage Racks: An Experimental Study

Industrial steel storage pallet racks are commonly used in the logistic field for storing goods and products. Several typical features characterize these structures, i.e. the use of cold-formed mono-symmetric perforated columns (uprights), the presence of beam-to-column and base-plate non-linear semi-rigid joints. In addition, bracing systems are provided only in the transversal direction (cross-aisle) while in the longitudinal direction (down-aisle) the structural global response is driven only by the joints performance. Therefore, being the base-plate and beam-to-column joints the sources of racks ductility, their key role becomes even more important in case of seismic actions. The design of racks is usually based on the ‘design by testing’ approach, which requires the complete characterization of racks main components and subassemblies. In case of seismic design, tests must be performed in the cyclic regime. In this context, experimental studies were performed in the past for the cyclic characterization of beam-to-column joints. On the contrary, although the key role of base-plate joints is well recognized, the available experimental studies regarding this component are still quite limited. As a contribution to this topic, an experimental study focused on the characterization of a commercial pallet rack base-plate joint was performed at the Università di Trento. The study comprised both monotonic and cyclic tests. The present paper describes and discusses the main features and the main results of the experimental programme.

Nadia Baldassino, Martina Bernardi, Riccardo Zandonini
Experimental and Analytical Observations of the Effect of Leveling Nuts on the Stiffened Column Bases Behavior

Column base connections are designed and erected with various details to transmit the induced forces in steel moment frames to the foundation. One of the prevalent configurations is using an assembly of vertical stiffeners on exposed base plates (i.e., stiffened column bases) to reduce the required base plate thickness; nevertheless, their cyclic behavior was unknown before this study. Moreover, previous research has claimed that setting nuts and washers, also known as leveling nuts, might alter the connection load path due to the stiffer nut support rather than the grout pad. This paper examines the effects of leveling nuts on stiffened connections’ performance; experimentally and analytically. The testing program evaluates the response of four specimens with stiffened column bases to the seismic excitation. The most critical observation was the punched concrete under the foundation (approximately at the location in which bolts are placed) that led to the change in load path – and ultimately variation in behavior – compared to base connections constructed without leveling nuts. Finite Element simulations also confirm the development of the compression force in anchor rods which is attributed to leveling nuts usage. This alternative load path is not considered in the design, and bolts are solely designed for tension forces; compression is expected to be resisted by the grout pad and concrete. In summary, this study demonstrates that the location of leveling nuts dictates the connection behavior while they are only utilized for construction purposes and are not considered in the design procedure.

Niloufar Behboud, Alireza Rezaeian, Farzin Zareian
Connection Strength of Braces with Angle Steel and Channel Steel

Braced frame structures are used for low-rise steel buildings, and angle steels or channel steels are often adopted as the main seismic component. The structures are used as not only house but also emergency public shelters in event of disaster. Therefore, it is important to secure the sufficient seismic performance. However, a reconnaissance of the recent earthquake reports that the brittle fracture at the effective cross section of brace. Angle braces and channel braces have the inevitable eccentricity between the brace and gusset plate, and this detail is a disadvantage in terms of connection strength.In the present paper, connection tests of braces were carried out to clarify the effect of connection detail on strength at the connection. Specimens are braces connected to gusset plates using bolts. In these tests, the monotonic tensile loading was employed to investigate the effect of connection detail on the ultimate strength. The main parameters were cross sections of braces, the number of bolts and tension of bolts. The test results can be summarized as follows: (1) the ultimate strength basically increases in proportion to the number of bolts at the connection, regardless of the cross-sectional shape of the brace; (2) the ultimate strength of connection using more than 5 bolts does not increase compared to that of connection using 5 bolts; (3) for channel steel, the effective ratio of cross-sectional area was smaller in the braces with the width less than 150 mm.

Nobuhiko Tatsumi, Shoichi Kishiki
Preliminary Study on the Cyclic Response of Welded Joints with CHS Beams and Through-All Plates

The use of circular hollow section (CHS) members as columns of moment-resisting frames is limited by the complexity related to the realization of beam-to-column connections. Nevertheless, the recent use in the field of civil engineering of the Laser Cutting Technology (LCT) has offered the opportunity to manufacture welded connections by properly cutting the tubular profile with the imprint of the cross-section shape of the double-tee member. Such a solution is an improved alternative of the joint with the I-beam simply welded to the external surface of the hollow profile since higher flexural strength and stiffness can be provided. This type of joint has an enhanced behaviour due to the higher stiffness of the source of the deformability.To evaluate the effective contribution provided by each component, this research activity has dealt with the study of the cyclic behaviour experienced by welded connections between CHS tubes and through-all plates, since this component is intended to be representative of the actions applied on the tube by each of the beam flanges of a double-tee profile. The work comprised the accomplishment of three cyclic tests on specimens representative of realistic geometric configurations of CHS to through-all plate joints. Subsequently, a finite element model, representative of the analysed connections, has been developed and validated against the experimental results, and it has been exploited to perform numerical analyses of other 44 CHS to through-all plate configurations. The obtained force-displacement curves have been used to calibrate and predict, through analytical formulations, the parameters of the hysteretic uniaxialmaterial element belonging to the OpenSees library.

Roberto Sica, Sabatino Di Benedetto, Massimo Latour, Gianvittorio Rizzano
Evaluation of Gusset Plate Buckling Strength Using Stability Functions

A method is proposed to calculate the buckling strength of gusset plates (GPs) using stability functions. The method requires a division of GPs into sub-elements and calculation of their equivalent bending stiffness. Using these sub-elements, a GP stiffness matrix can be formulated. The elastic buckling load is the axial load that makes the determinant of this matrix equal to zero. The method is evaluated by comparing its strength predictions against the buckling load of tested GPs reported in literature and the predictions obtained using the AISC method. When the brace end of the GP was fully free or had rotational restraints, the method predicted an average of 18% and 92% respectively of the experimental values. The AISC method provided 13% and 35% of the experimental values when using effective length factors of 1.2 and 2.0 respectively.

Saul Yahdiel Vazquez-Colunga, Chin-Long Lee, Gregory MacRae
Full Plastic Strength of Circular Hollow Section Panel Zone with Large Aspect Ratio

It is well known that panel zones at beam-column joints of steel moment resisting frames may yield under strong ground motion as well as beams and columns. It is also figured out that the effect of bending moment acting on panel zones cannot be ignored, however, there were few studies regarding this topic. Then, this paper aims to clarify the effect of aspect ratio on the behavior of circular hollow-section panel zones. In this paper, cyclic loading test and finite element analysis with single panel zone specimens were conducted with varying aspect ratios, width-thickness ratio, and axial force ratio of panel zones. Experimental and numerical results showed that the effect of the width-thickness ratio on the full plastic strength was quite small, while the full plastic strength decreased as the aspect ratio increased Moreover, the plastic deformation capacity of a circular hollow-sectional panel zone with a large aspect ratio decreased as the width-thickness ratio and axial force ratio increased.

Yosuke Ashida, Yuji Koetaka, Iathong Chan
Experimental Study on Horizontal Oblique Beam-End Connections

Connections consisting of wide flange beams and square hollow section (SHS) columns with through diaphragms are commonly used in steel moment frame in Japan. Generally, it is desirable to design the beam-to-column connections so that the column and the beam are perpendicular to each other. In some cases, columns and beams are connected diagonally to gain larger space. However, the effect of such oblique beam-end connections on structural behavior remains unknown. To investigate the effect of oblique angles, the full-scale cyclic loading tests were carried out. Based on the experimental investigation, the fundamental structural behavior, plastic deformation capacity, and strain distribution at the flange of the beam-end connections considering oblique angles were discussed in this paper. The test results indicated that (i) there is no significant effect of oblique angles on the fundamental structural behavior; (ii) the effect of the different oblique angles on the deformation capacity is not affected by the cyclic loading after local buckling; (iii) the plastic deformation capacity and strain distribution of the beam end is greatly affected by the oblique angles of 30° or larger. Also, it is indicated that a large oblique angle tends to change the failure mode of the thicker beam flange.

Yuchen Liu, Shotaro Nakada, Shoichi Kishiki

Performance of Structural Systems

Effective Steel Braced Frames for Tall Building Applications in High Seismic Regions

Steel braced frames are commonly used for building structures in seismic active regions. However, steel braced frame systems are limited to low- and medium rise structures because they are prone to concentration of inelastic demand resulting from adverse P-Δ effects and lack of vertical stiffness continuity. The article introduces a modified inverted-V buckling braced frame configuration in which one of two bracing members at every level is replaced with a conventional brace designed to remain elastic and form with the beam member an elastic secondary system providing the system with positive post-yielding storey shear stiffness annihilating P-Δ effects upon yielding of the BRB members and ensuring stable seismic response for tall building applications. The anticipated behaviour and design approach of the proposed E-BRBF system is first described. The stability of the system is then verified through nonlinear response history analysis for 20-, 30- and 40-storey buildings subjected to ground motions from shallow crustal, subduction in-slab, and subduction interface earthquakes. The analysis results are compared to those obtained with conventional BRBFs. The comparison shows that the proposed E-BRBF system can significantly enhance the seismic response of tall buildings, with reduced and more evenly distributed peak storey drift demand over the structure height.

Bashar Hariri, Robert Tremblay
Numerical Response Estimations of a Frame-Spine-FLC System Prior to Experimental Dynamic Testing

Numerical modeling is widely used in structural engineering to represent buildings response under seismic loading conditions. However, even though numerical modeling is a common tool to characterize the behavior of structures, modeling uncertainties can lead to a broad range of expected response, particularly when representing the behavior of novel systems or components. Addressing different modeling choices can provide more informed insights into the response of structures, especially prior to conducting experimental tests or participating in blind prediction contests. Herein, blind response prediction of a novel steel system was conducted before testing at the E-Defense facility in Japan. The full-scale specimen consisted of a weak Moment-Resisting Frame (MRF) retrofitted with steel spines and force-limiting connections (FLC). The set of pre-test predictions involved addressing of different modeling choices to overcome the many sources of epistemic uncertainties and to provide greater confidence in the design and experimental testing program. Several models were subjected to the records specific to the testing program (Northridge Sepulveda and JMA Kobe) to estimate drift and acceleration responses. Numerical results were compared to the experimental data from the shake-table tests. Although all the models were able to represent general trends in drifts and accelerations and enabled proper development of the testing plan, peak response varied significantly depending on the modeling choices, especially those altering the system’s natural periods or those leading to different yielding patterns.

Bryam Astudillo, David Rivera, Barbara Simpson, Larry Fahnestock, Richard Sause, James Ricles, Masahiro Kurata, Taichiro Okazaki, Yohsuke Kawamata, Zhuoqi Tao, Jessica Duke, Yi Qie
Seismic Behaviour and Design of Chevron Multi‐tiered Concentrically Braced Frames

This paper investigates the possibility of using the chevron bracing configuration for multi-tiered concentrically braced frames subjected to seismic excitations. A prototype two-tiered braced frame part of a single-storey building structure was designed using three different brace force scenarios for the roof beam and the intermediate strut. Columns were designed to resist the bending expected at the maximum anticipated storey drift. The lateral response of the frame was examined through nonlinear static and dynamic analyses. For all cases studied, frame lateral deformations tend to concentrate in the first tier, where brace buckling initiated first, due to the reduced tier lateral stiffness in the brace post-buckling range. The flexural action in the intermediate struts was engaged when a reduced force was used for tension-acting braces in design, limiting nonlinear response in braces. Finally, the frames exhibited stable inelastic response with limited residual deformations, as a result of the re-centring capacity provided by the strut acting in flexure.

Christophe Comeau, Pablo Cano, Ali Imanpour, Robert Tremblay
Seismic Response of Two-Bay Steel Multi-Tiered Concentrically Braced Frames

This paper investigates the possibility of using multi-tiered concentrically braced frames in two adjacent column bays to resist seismic loads. Three prototype frames part of a single-storey building were chosen and designed using current knowledge of multi-tiered behaviour. The columns were selected to resist in-plane bending and axial loads arising from tensile yielding and compression buckling of braces in critical tiers. The lateral response of the frame was then examined using the nonlinear response history analyses under ground motion accelerations. The analyses confirmed that all frames exhibited nonuniform brace tensile yielding between tiers, which resulted in the concentration of inelastic drifts in the uppermost tiers. Peak storey drift values remained under 2.5%, although higher than the design predictions, which influenced the prediction of column in-plane bending.

Christophe Comeau, Pablo Cano, Robert Tremblay, Ali Imanpour
Performance Assessment of a Steel Wind Turbine Tower Subjected to Repeated Earthquakes

As the wind market grows rapidly and wind power plants are installed in high seismicity areas, there is the increased need for researchers and practitioners to assess the dynamic performance of Wind Turbine (WT) structures under extreme events. The present work is a preliminary attempt to quantify the performance of conventional steel WT towers under repeated earthquakes and enhance the understanding of their dynamic response. The case study is a 22 m high, 65 kW WT tower, assembled from cylindrical and conical steel sections of varying diameter and thickness. A simplified numerical model of the WT is developed in RUAUMOKO software program and subjected to five sequences of seismic events, available in the PEER strong motion database. The paper focuses on the effect of the multiplicity of earthquakes on critical response parameters, such as interstorey drift ratios and residual displacements. Incremental dynamic analyses provide estimates of the structural demand and capacity under single and multiple earthquakes of recurring periods. The findings show that repeated earthquakes significantly influence the seismic response of WT towers. Therefore, the consideration of sequences of main events and aftershocks is essential for the enhancement of the seismic resilience of WT towers.

Dionisios N. Serras, Anastasia Athanasiou
Multi-hazard Robustness Assessment of Seismic Resistant Dual Frame Concentrically Braced Frames

Present paper summarises a case study aiming to evaluate the robustness performance of a multi-story steel frame building designed for persistent and seismic design requirements. On this purpose, a reference 6-story steel building with dual inverted V bracing and moment frames was first designed. Then, the robustness performance of the structure was assessed considering extreme events that are deemed credible after an earthquake, i.e., internal gas explosion and localized fire. The structural performances were evaluated using nonlinear static and dynamic analyses. Numerical model was calibrated against experimental test data.

Dominiq Jakab, Florea Dinu, Aurel Stratan, Ioan Marginean, Dan Dubina
Data-Driven Substructuring Technique for Pseudo-Dynamic Hybrid Simulation of Steel Braced Frames

This paper proposes a new substructuring technique for hybrid simulation of steel braced frame structures under seismic loading in which a new machine learning-based model is used to predict the hysteretic response of steel braces. Corroborating numerical data is used to train the model, referred to as PI-SINDy, developed with the aid of the Prandtl-Ishlinskii hysteresis model and sparse identification algorithm. By replacing a brace part of a prototype steel buckling-restrained braced frame with the trained PI-SINDy model, a new simulation technique referred to as data-driven hybrid simulation (DDHS) is established. The accuracy of DDHS is evaluated using the nonlinear response history analysis of the prototype frame subjected to an earthquake ground motion. Compared to a baseline pure numerical model, the results show that the proposed model can accurately predict the hysteretic response of steel buckling-restrained braces.

Fardad Mokhtari, Ali Imanpour
Fragility of Steel Frames with DYBs Designed in the Framework of EC8

For a long time, the steel concentric bracing has been considered an effective structural system to sustain seismic forces. Unfortunately, today, it is widely recognized that the concentric bracing presents also serious limitations: the poor cyclic response determined by the buckling of the brace in compression and the low redundancy of the structural type. Hence, in a previous paper, the authors proposed the use of the Double-stage Yield BRB (DYB) as an alternative to the conventional steel brace. The DYB yields in tension and compression exhibiting fat hysteresis loops and large ductility capacity. In addition, yielding occurs in two stages. The double-stage yielding mitigates the lack of redundancy of the concentric bracing and promotes a global collapse mechanism. Steel frames equipped by DYBs can be designed by a procedure that is formally identical to that stipulated in Eurocode 8 for conventional braced frames. Since the cyclic response of the DYB is controlled by the ratio ρYS between first and second yield forces of the DYBs, the behaviour factor q is provided by a linear function of ρYS calibrated to fulfil the performance objectives of Eurocode 8. The goal of this paper is to investigate on the seismic fragility of steel frames equipped by DYBs characterized by different values of ρYS, by means of fragility curves.

Francesca Barbagallo, Aurelio Ghersi, Edoardo M. Marino, Dario Panarelli
Collapse Fragility Curves for Non-residential Older Single-Storey Steel Buildings

The paper describes the seismic response of non-residential single-story steel buildings designed in the decade 1980s–1990s in Italy. To this end, multiple building archetypes were designed following code regulations enforced at that time. The selected case studies are characterized by (i) a main truss system in the transverse building direction and (ii) a concentric braced system in the longitudinal building direction. Various structural schemes and two alternative brace cross section types were considered. 3D non-linear finite element models were built and analysed using OpenSees. The analysis was carried out considering the contribution of envelope panels to the seismic response by using two different types of cladding panels. Empirical fragility curves allow to highlight the role of the structural scheme, the type of envelope panels and the increasing level of the building site seismic hazard.

Gaetano Cantisani, Gaetano Della Corte
Numerical Modelling of a Three-Story Building Using a Hybrid of Mass Timber Walls with Buckling-Restrained Braces

Mass timber buildings are gaining popularity in North America as a sustainable and aesthetic alternative to traditional construction systems. However, several knowledge gaps still exist in terms of their expected seismic performance and plausible hybridizations with other materials, e.g. steel energy dissipators. This research explores the potential use of mass plywood wall panels (MPP) in spine systems using steel buckling-restrained braces (BRBs) as energy dissipators. The proposed BRB-MPP spine assembly makes up the lateral load-resisting system of a three-story mass-timber building segment that will be tested under cyclic quasi-static loading at Oregon State University. The specimen geometry and material properties result in BRBs that are shorter and of smaller core area than in most common steel structural applications. Small BRBs are prone to exhibit a hardened compressive response and fracture due to ultra-low-cycle fatigue when subjected to repeated cycles of large strain amplitude. These issues, along with the limited availability of test data, make small BRBs difficult to model. To support the experimental testing program, a material model with combined kinematic and isotropic hardening is calibrated against the available experimental data for three BRB specimens to estimate the behavior of BRBs of short length (≤3,500 mm [138 in]) and small core area (≤2,600 mm2 [4 in2]), similar to the ones designed for the test specimen. The calibrated model is used to predict the behavior of the BRB-MPP spine experiment.

Gustavo A. Araújo R., Barbara Simpson, Tu X. Ho, Gustavo F. Orozco O., Andre R. Barbosa, Arijit Sinha
Seismic Force Demands on the Foundations of Concentrically Braced Frame Systems

Concentrically braced frames (CBFs) are widely used as lateral force-resisting systems in North America. Canadian seismic design requirements for building foundations distinguish between two foundation types: capacity protected and non-capacity protected (commonly known as “rocking” foundation). For steel bracing systems such as CBFs, there are major ambiguities in how to calculate the foundation design forces, as the governing force for both foundation types is influenced by the capacity of the braces, which have an uncertain overstrength, and by the timing of braces reaching their peak force, which may or may not be simultaneous. In addition, the superstructure, foundation, and underlying soil interact in response to seismic loads, which further influences design force estimates. Therefore, there is a need to better understand the actual force demands on CBF foundations.This study considers example 2-storey and 5-storey steel frame buildings with tension-compression X-bracing, designed for Vancouver, Canada, in accordance with the 2015 National Building Code and the Canadian steel and concrete design standards. The increased drifts of the braced bay caused by foundation rotations are assessed using simplified procedures and included in the design. The buildings are analyzed using advanced numerical models in OpenSees, including brace buckling and P-Delta effects. The results obtained for fixed-base conditions are compared to those including foundation flexibility. For the latter, the effects of soil-structure interaction are represented using nonlinear spring models that can capture foundation rocking and sliding as well as the soil settlement. The results of this study confirm that the Canadian concrete standard estimates reasonably well the demands on the foundations regardless of foundation flexibility but suggest that further study is needed to verify this more reliably.

Hamid M. Madani, Lydell Wiebe, Sanda Koboevic, Peijun Guo
Potentially Plastic Zones Details in Bottom Storey Columns of Concentrically Braced Frames

The present paper is intended to illustrate the advantages and disadvantages of different structural details for the potentially plastic zones located near the bottom end of the first storey columns in concentrically braced frames. Several structural details were analysed, considering: reduced flanges cross-sections and/or transversal and longitudinal stiffeners for the bottom zone of the columns.The features of the proposed alternative details are analysed for four concentrically braced frames. The considered frames had six and respectively ten storey and were located in Bucharest, Romania. The frames had two spans of 6.0 m and the storey height was 3.5 m. Built-up I-shaped cross-sections were used for all types of structural members: braces, columns and girders. All connections among different kind of structural members, as well as the connections to the foundation were considered as fixed.Dynamic nonlinear analyses were performed for each structural configuration using acceleration records of three Vrancea earthquakes, calibrated all to a peak ground acceleration value of 0.3 times the acceleration of gravity.The maximum values of the bending moments, the axial forces and the plastic deformations in the potentially plastic zones at the bottom end of the first-storey columns were compared.The buckling resistance of first-storey columns was compared for the most unfavourable loading states recorded during dynamic nonlinear analyses.

Helmuth Köber, Ramona Marcu, Marina Stoian
Probabilistic Risk Assessment of an Existing RC Building Strengthened with Steel Bracings

Turkey is one of the earthquake-prone countries that experienced strong earthquakes in 1999. The last devastating earthquake hit Northwest part of the country, called as Marmara Earthquake, close to Istanbul. After these experienced earthquakes, various strengthening techniques have been applied to increase the seismic response of existing buildings against earthquake loads in seismically prone regions. These techniques aim to improve the lateral resistance of existing buildings by adding new elements such as steel bracing or shear walls. Braced members are one of the widely used approaches and practices for fast responses. They are used to increase the structural capacity under earthquake loads. The present study investigates a real, existing 7-story reinforced concrete (R/C) building located in Istanbul, Turkey as a case study. With seismic assessments, strengthening for existing buildings with steel bracings was evaluated. The selected building was designed according to the 1975 Turkish Seismic Code and strengthened according to the current 2007 Turkish Design Code. The construction of strengthening is currently completed, and the building is occupied in one of the high demanding regions in Istanbul, Turkey. Steel bracings were preferred to strengthen the project to gain the usage area. Strengthening with steel bracing also decreased disturbance faster than other supporting methods. The research determined the nonlinear structural behavior of a representative existing and strengthened reinforced concrete (R/C) building. Pushover curves were plotted for the existing and strengthened building models. Lateral displacements, story displacements, and plastic hinge rotations were calculated for the building. Then, probabilistic risk assessment was carried out by plotting the probability of exceedance curve for the building.

Kasim A. Korkmaz
Case Study of a Tall Building in Greece: Performance-Based Seismic Design and Assessment of Composite Coupling Beams

In the last decades many modern metropoles have embraced high-rise construction within a sustainable vertical urban development plan to accommodate the increased needs for housing and commercial needs, accounting for the limited available space. This is not valid in Greece, one of the most seismic prone countries in the Mediterranean, where the adopted urban development model was significantly different due to socio-economic and political factors that led to strictly low/mid-rise construction. Nonetheless, with the launch of Ellinikon project in the Attica region, which includes six high-rise buildings, tall buildings represent an emerging topic of interest in Greece. This paper examines the case study of a tall building in Greece, based on current US practice. For the purposes of the study, the latest LATBSDC guidelines are used and performance-based seismic design principles are applied. By means of nonlinear structural analysis software, all pertinent design parameters are investigated, and through comparative study, an assessment of composite coupling beams’ deployment is realized, highlighting their effectiveness in high-rise construction.

Konstantina Katsaveli, Evangelos Efthymiou, Sofia Gavridou
Feasibility of Strongback System in Storey Mechanism Mitigation of Steel Braced Frames

Under earthquake loading, conventional braced frames are prone to storey mechanism. To mitigate this drawback, researchers have proposed to add an alternative vertical force path to redistribute member forces among floors. Likewise the dual system, the strongback acts as a vertical elastic spine and compensates for the loss of storey shear after braces of ductile system exhibited buckling. Nevertheless, the inelastic first mode and the elastic higher vibration modes excite the strongback, which could be installed interior or exterior to the braced frame. A design method for strongback braced frame is proposed and a case study consisting of a 4-storey office building in Victoria, BC, Canada, is presented. Numerical model was developed in the OpenSees environment and results from nonlinear response history analyses, expressed in terms of interstorey drift, residual drift, and floor acceleration, are presented. The hybrid system is able to mitigate the storey mechanism and enhances the building’s safety.

Lizhu Chen, Shuaikang Wang, Anastasia Athanasiou, Lucia Tirca
Numerical Modelling of Masonry Infill Walls in Existing Steel Frames Against Experimental Results

The presence of masonry infills may significantly affect the seismic behaviour of existing steel moment-resisting frames, characterised by low lateral force resistance and inadequate energy dissipation capacity due to the lack of seismic detailing. Masonry infills may cause variation of internal force distribution along beams and columns, resulting in large local seismic demands at beam-column joints and consequently leading to soft-storey mechanisms. Several numerical models have been developed to account for the effects of masonry infills, among which the equivalent strut models were most widely used. However, it has been argued that despite its ability to capture the global response of structures, the single-strut model may not be adequate to correctly simulate the internal forces distributions in steel members. To this end, the present study investigates modelling strategies of infilled steel frames using both single- and three-strut models. The results from different modelling approaches are compared among them and with experimental tests, providing insights on the influence of the modelling strategies both at global and local levels.

Luigi Di Sarno, Jing-Ren Wu, Fabio Freddi, Fernando Gutiérrez-Urzúa, Mario D’Aniello, Stathis Bousias
Evaluation of the Seismic Behaviour of Modular Steel Moment-Resisting Frame Structures with Knee Braces

This article proposes an innovative steel modular MRF with knee brace elements for seismic applications called Moment-Resisting Knee Braced Frame (MKF). In this system, conventional MRF beam-to-column connections are replaced with a combination of simple beam-to-column connections, rigid beam-to-beam stub connections and knee brace elements. The proposed system eliminates CJP welds and adopts shop-welded, field-bolted assemblies. Furthermore, the lateral stiffness of the structure is expected to increase as a result of the application of knee elements. A 5-storey office building comprising the proposed system on the exterior walls is selected and studied. The frame is analysed using the Performance Based Plastic Design (PBPD) approach and designed as per the Canadian steel design standard. Nonlinear static and response history analyses are carried out to evaluate the seismic response of the proposed system and examine the validity of the analysis and design approaches. The results reveal that the proposed system offers a reliable seismic performance and can be a viable alternative to conventional MRFs. It is also found that the PBPD approach leads to a realistic representation of structural performance by utilizing the plastic capacity of structural components.

Mahdi Mokhtari, Ali Imanpour
Design, Analysis and Assessment of MRFs Equipped with FREEDAM Connections and Designed by TPMC: Comparison with Traditional Connections

Moment Resisting Frames were designed according to the Theory of Plastic Mechanism Control specialized for use in the Ductility Classes proposed in the new Eurocode 8 namely DC2 and DC3. These frames are equipped with both traditional haunched connections, analysed in the framework of the RFCS founded EqualJoints Plus research project, and FREEDAM joints analysed in the framework of the RFCS founded FREEDAM Plus. The seismic performances of the structures are investigated by both pushover and nonlinear dynamic analyses.

Maria Maglio, Rosario Montuori, Elide Nastri, Vincenzo Piluso
Pinned and Fixed Connections in “2 Storey X-Braced” Frames

The main objective of the present paper is to point out the influence of fixed and pinned connections, for diagonals and beams, on the seismic behaviour of concentrically braced frames. Three constructive configurations were considered for two concentrically “2 storey X-braced” frames with six and ten storey, having two spans of 6.0 m and a storey height of 3.5 m.In the first constructive configuration, fixed connections were used for all kind of structural elements. In the second configuration, pinned connections were considered at the ends of the diagonals and fixed connections were used for the beams. In the third configuration, pinned connections were considered for both diagonals and beams.Each distinct constructive configuration was subjected to dynamic nonlinear analyses using Vrancea acceleration records, calibrated to a peak ground acceleration value of about 0.3 times the acceleration of gravity. The behaviour of the different frame configurations during these analyses was compared (the extreme values for base shear forces and horizontal floor displacements, the amount of dissipated energy, the maximum inelastic deformations and member forces recorded during the analyses). The steel consumption was estimated for all analysed constructive variants.

Marina Stoian, Helmuth Köber, Ramona Marcu
Preliminary Results from Shake Table Tests of the FUTURE Mock-Up

The EC8 design rules and requirements for steel moment-resisting frames (MRFs) mainly address far-field seismic scenarios. However, there are specific issues to account for Near Fault (NF) strong motions that may increase inelastic demand on structural steel members and joints. The latter are usually designed or qualified for far-field earthquakes. Also, the drift displacement is often characterized by severe unidirectional concentration. Another aspect influencing the design of MRFs is the limitation of interstorey drifts, which is often rather restrictive, thus penalizing the design of steel MRFs. The use of ductile energy-efficient claddings can be beneficial to relax the drift limitations, thus allowing to optimize the structural design, reducing the constructional costs, and encouraging the use of more sustainable solutions. To investigate these aspects, an experimental testing program has been planned within the FUTURE project, funded in the framework of the H2020-INFRAIA SERA program. In this project, comprehensive shake table tests were carried out on a two-storey one-bay mock-up equipped with different types of beam-to-column joints and extra ductile non-structural components. This paper illustrates the preliminary experimental results obtained on the bare steel frame equipped with two different types of detachable joints.

Mario D’Aniello, Roberto Tartaglia, Raffaele Landolfo, Luigi Di Sarno, Alain Le Maoult, Giuseppe Rastiello
Seismic Performance of Industrial Component Supporting Steel Structures – Past Damages, Current Design Practice and Recent Experimental Tests

Past earthquakes showcased the vulnerability of industrial facilities equipped with complex process technologies, when serious damage of equipment caused an expensive loss of production and release of hazardous substances in facilities posed a danger to society and the environment. Nevertheless, the design of industrial plants is not properly addressed in current codes and guidelines, as they do not consider typical characteristics such as the dynamic interaction between supporting structure and supported components and thus the effect of seismic response of installations on the response of the structure and vice versa. Many more of such specific characteristics exist, which are apparently different to regular, building-like structures and demand for a different handling of industrial structures and components. The incomplete normative situation for the seismic design of industrial facilities was the starting point for the execution of the SPIF project (Seismic Performance of Multi-Component Systems in Special Risk Industrial Facilities) within the framework of the European H2020 - SERA funding scheme (Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe). The current paper sheds a light on following aspects: (i) seismic design and particularities of industrial steel structures; (ii) seismic performance and failure modes of industrial steel structures during past earthquakes; (iii) the current situation concerning existing seismic design codes tailored to industrial structures and the obvious need for such guidelines; (iv) brief description of the SERA-SPIF project.

Marius Pinkawa, Cristian Vulcu, Benno Hoffmeister
Seismic Performance of Steel Multi-tiered Buckling-Restrained Braced Frames in Canada

This paper examines the seismic response of steel Multi-Tiered Buckling-Restrained Braced Frames (MT-BRBFs). A two-tiered BRBF part of a tall single-story building is designed per the current Canadian steel design standard seismic provisions. A nonlinear numerical model of the frame is developed, followed by nonlinear static and dynamic analyses to assess its global and local response, including tier drifts, Buckling-Restrained Brace (BRB) forces, and column demands. The results obtained from the analyses indicate that the non-uniform drift response due to the difference between the BRB’s strength in compression and tension imposes in-plane bending demands on the columns, which in combination with axial compression forces could result in column instability and should be considered in the design of the MT-BRBF columns.

Moad Bani, Ali Imanpour
Seismic Performance of Dual-Concentrically Braced Frames with Slim-Floor Beam-to-Column Joints

Due to architectural advantages and, more recently demonstrated, to the applicability to seismic design, the slim-floor moment-resisting beam-to-column joints could be an efficient solution to mid- and high-rise structures. The integration of the slim-floor beam into relatively tall steel and composite structures designed to withstand inertial forces caused by seismic action was achieved on a two-dimensional Dual-Concentrically Braced Frame system. The central focus of the study is the seismic performance evaluation of this frame with nonlinear static and dynamic analyses. The analyses’ results evidenced an adequate seismic performance, proof of which were the following: damage sustained at each Limit State, progressive development of plastic mechanisms, limited inter-storey drifts and maximum joint rotation demand lower than experimentally proven. These results demonstrate the possibility of using slim-floor beam-to-column joints in seismic-resistant structures.

Rafaela Don, Cristian Vulcu, Adrian Ciutina, Aurel Stratan
Seismic Resistant Configurations for Concentrically Braced Frames

The present paper intends to point out some features of different bracing configurations used frequently in concentrically braced frames located in seismic areas. Four concentrically braced frames with six and ten storeys (eight in total) were sized for the same seismic action evaluated according to the prescriptions of EN 1998-1:2004 and the in charge Romanian seismic design code. Four concentrically bracing configurations frequently used in seismic resistant structures were analysed: ascending bracing, descending bracing, X bracing and “2 storey - X” bracing. All analysed frames had two spans of 6.0 m and a storey height of 3.5 m.The behaviour of the frames during dynamic nonlinear analyses was compared. Three base excitations of Vrancea earthquakes were considered, recorded in or around Bucharest at 04.03.1977; 31.08.1986 and 30.05.1990. All considered acceleration records were calibrated to a peak ground acceleration value of about 0.3 times the acceleration of gravity. Damping was taken into account using the Rayleigh procedure.The history of the formation of plastic hinges was observed. The maximum values for axial forces, bending moments and inelastic deformations recorded in different member types, the extreme values of horizontal displacements and base shear forces were compared. Another objective was the comparison of the estimated steel consumption.

Ramona Marcu, Helmuth Köber
Seismic Response of a Large-Scale Steel Structure with Dissipative Double Split Tee Connections

The brittle fracture experienced by the welds of full-strength joints belonging to steel moment-resisting-frames (MRFs) during the earthquakes of Northridge (1994) and Kobe (1995) represented a turning point in the seismic design of steel structures. In fact, after these events, different strategies have been proposed to solve this drawback. The use of the so-called Reduced Beam Section (RBS) strategy is one of the most popular solutions to reduce the stress concentration in the welds by weakening the beam ends into areas located sufficiently far from the column. Other solutions are based on the adoption of partial strength joints, which provide the benefit to allow the concentration of damage into connection elements which can be easily substituted after a severe seismic event.Within this framework, the adoption of double split T-stub joints is very promising as demonstrated in previous experimental, numerical and analytical works. These connections can be designed according to capacity design principles assuring that the weakest connection elements are the T-stubs, which can be properly designed to assure adequate ductility and energy dissipation capacity. The work presented in this paper follows previous experimental works on subassemblies and aims to assess the behaviour of real scale structures equipped with this particular joint typology. Specifically, the work presented in this paper regards a pseudo-dynamic test campaign performed on a two-storey steel building equipped with dissipative double split Tee joints. The paper discusses the main outcomes of the experiments.

Sabatino Di Benedetto, Antonella Bianca Francavilla, Massimo Latour, Vincenzo Piluso, Gianvittorio Rizzano

Mixed and Composite Structures

Development of Effective Designs for Composite Bridges in Seismic Areas

The design and construction of steel-concrete composite bridges using prefabricated modules offers a wide range of advantages, especially considering situations with tight completion times or challenging crossings. Transportation and manoeuvre activities are facilitated by using modules, which do not exceed the gauge requirements. Steel girders may be divided into segments and welded on site. Smart design provides easy assembling of the deck modules. VTR®, VFT® and VFT-WIB® are solutions for composite bridges using a high degree of prefabrication, proposing different technologies.The VTR® system uses steel box girders in longitudinal direction as main girders, the deck is made of prefabricated concrete cross beams and pre-slabs. All modules are connected via additional reinforcement and in situ concrete at the joints.VFT® and VFT-WIB® are systems using prefabricated composite girders typically made of reinforced concrete and halved hot rolled profiles or welded steel plates. The shear connection is achieved through composite dowels, created by a cut along the web of the steel section according to a specific geometry.Such systems of composite bridges can be successfully applied in seismic areas. These solutions have been developed in practice as a modern method of bridge construction by introducing them into frame-type structural systems, integral and semi-integral bridges, which offer a number of advantages both in terms of structural behaviour to static and dynamic actions and in terms of reduced lifetime maintenance costs. This paper presents briefly the description of these system and case studies for VTR® bridges.

Edward Petzek, Daniel Grecea, George Ispăşoiu, Alexandru Țurcan, Guido Retter
Numerical Study on Seismic Performance of High-Strength CFST Frame Structure with Aluminium Alloy Core Assembled Buckling-Restrained Braces

In this paper, a high-strength CFST-steel beam frame structure with aluminium alloy core assembled buckling restrained braces (HSC-SB-ALAB) was proposed and the brief design method for HSC-SB-ALAB were introduced. To study the influence of high-strength materials and ALAB on the seismic performance of the structure, four 10-story CFST-steel beam structures were designed with material strength and ALAB as variables. The numerical models of the four structures were established by OpenSees, and modal analysis, static elastic-plastic analysis, and dynamic time history analysis were carried out for them. The results indicate that high-strength materials and ALAB could significantly reduce the torsional effect of the structure. In the process of HSC-SB-ALAB failure, ALAB first yielded and began to dissipate energy, then the plastic hinge first appeared in some beams, and few plastic hinges appeared in columns until the later stage, which indicated that HSC-SB-ALAB has the expected yield mechanism. Under seismic load, HSC-SB-ALAB had the highest bearing capacity, and its inter-story drift ratio and story shear were the minimum of the four models. At the same time, HSC-SB-ALAB had the least damage and milder stiffness degradation. It was verified that HSC-SB-ALAB improved the seismic performance of CFST-steel beam frame structures, and the effect of high-strength materials was greater than ALAB.

Guochang Li, Lirong Wei
Seismic Behaviour Improvement of Steel-Concrete Composite Frames Based on Steel Spiral-Confined Slabs

The use of continuous spiral reinforcements can be an efficient solution for the seismic performance improvement of reinforced concrete members. Several literature studies confirm their positive confinement effects especially for concrete columns, where typical benefits take the form of enhanced ductility and energy dissipation capacity.In this paper, the attention is focused on steel-concrete composite frames, where the study of both joint and slab detailing can involve several design challenges. Steel spirals are thus introduced for the seismic reinforcement of concrete slabs. Based on literature documents and a set of parametric Finite Element (FE) numerical analyses, selected configurations of technical interest are explored. As a first key step, the compressive response of concrete slabs with confining steel spirals is discussed, with a focus on local and global effects.

Nicola Troiano, Marco Fasan, Chiara Bedon, Claudio Amadio
Slim-Floor Beam-to-Column Joints for Seismic-Resistant Structures: Design Approach and Detailing

This article presents the main steps of the design methodology developed for slim-floor beam-to-column joints, which were previously experimentally tested and numerically analysed. The design procedure and the detailing of the joints are part of an extensive study which incorporates experimental tests, numerical investigations, and global analyses on structural systems (i.e., MRFs/D-CBFs). Based on the experimental and numerical results obtained, the aim of the design procedure is to promote the development of a ductile mechanism within the intended dissipative zone of the slim-floor beam and to maintain the beam-to-column connection in the elastic range, as it was experimentally demonstrated. To achieve the design strategy, several steps and recommendations are proposed. Among these, the most important are related to the joint detailing and the use of a Reduced Beam Section (RBS) – or more accurately formulated a Reduced Flange Section (RFS) – at the lower steel plate/flange.

Rafaela Don, Cristian Vulcu, Adrian Ciutina, Aurel Stratan
Comparative Study on the Behaviour of Composite Steel-Concrete Shear Walls Under Lateral Loads

The research focused on the solutions to create performant elements for seismic resisting structures has increased in the last decade. Different hybrid solutions that have composite steel-concrete structural shear walls with steel encased profiles (CSRCW) were studied. The benefits of this structural system include high performance characteristics in terms of ultimate loads, deformations capacity and ductility. The paper presents a comparative study on the behaviour of CSRCW, both solid and with centred openings. The study is based on the theoretical and experimental results obtained on steel-concrete composite elements 1:3 scale, tested in laboratory under cyclic lateral loads. All specimens were tested under constant vertical load and cyclically increasing horizontal (lateral) loads. The tests were performed until failure. The comparative study is focused on the main parameters: maximum load bearing capacity, stress and strain distribution in structural components, cracking patterns, deformation and degradation capacity. The conclusions indicate that the composite solution of steel concrete shear walls, lately addressed also as “hybrid”, with or without openings, could offer enhanced load bearing capacity, energy absorption and relatively gradual stiffness degradation.

Viorel Todea, Daniel Dan, Valeriu Stoian, Sorin-Codruț Floruț, Dan-Adrian Popescu
The Seismic Behaviour of Composite Steel-Concrete Coupled Walls with Centred Openings

The structural system composed by composite steel-concrete shear walls (CSW) represents one of the recommended solutions for resisting structures placed in seismic areas. The system is able to provide high strength and limited displacements that successfully fulfil the requirements of earthquake resisting structures. The CSCSW are made of one reinforced concrete web panel which has embedded on the edges different types of steel profiles, with the purpose to improve the behaviour of the conventional reinforced concrete structural walls and to solve some technological issues on the boundary regions, such as reinforcement congestion. In practice, the CSCSW, either exterior or interior, need centred or staggered openings along the height of the structure, due to architectural or functional requirements. In the last decade the solution of solid composite walls without openings was investigated but there is a lack of information about the behaviour of such CSCSW with openings. This paper presents the experimental results on the behaviour of composite steel-concrete coupled shear walls with central openings. The specimens have partially embedded steel profiles on the edges and conventionally reinforced coupling-beams. The influence of different composite connections and the performance of the reinforced concrete with steel fibres in the overall seismic behaviour were studied. The failure modes, strength, stiffness and cracking analysis of the tested specimens are discussed herein. From the experimental tests, it was found that the ductility of the walls could significantly be improved if the traditionally reinforced concrete material is replaced by fibre reinforced concrete using hooked steel fibres.

Viorel Todea, Daniel Dan, Valeriu Stoian, Sorin-Codruț Floruț, Dan-Adrian Popescu
Yielding Mode Classification of Composite Beam-Square Hollow Section Column Subassemblies Under Bidirectional Loading

It is well known that not only beams and columns but also panel zones in steel moment-resisting frames (MRFs) can yield under strong ground motions. In order to understand the yielding parts of the MRFs (hereafter, the yielding mode), a past study has proposed a method of classifying the yielding mode of a cruciform plane frame with elastic-perfectly plastic material properties. This method determines that one component among beams, columns and panel zones can yield, however for the MRFs with actual material properties, multiple components may yield.This paper discusses the modified yielding mode classification for the MRFs with actual material properties. The targeting steel MRFs are three-dimensional cruciform subassemblies that consist of square hollow section columns and H-shaped beams, including composite beams. To validate the modified yielding mode classification, a finite element analysis of the subassemblies under cyclic bidirectional horizontal loading is conducted. As a result, it is clarified that the modified yielding mode classification is valid regardless of the loading direction, value of the axial force of columns, and the presence of the floor slab.

Yandong Wang, Yuji Koetaka

Energy Dissipation Systems

Dual System for Enhanced Seismic Performance of Friction-Sliding Braced Frames

Pall friction dampers (PFD) installed in braced frames have been shown to exhibit large energy dissipation. Nevertheless, in high-risk seismic zones, the Friction-Sliding Braced Frame (FSBF) is prone to large residual interstorey drifts (RISD) and weak-storey mechanism formation. To solve this drawback, a backup moment resisting frame (MRF) was added in parallel to the FSBF and the system is analysed as dual (D-FSBF). Considering a force-based design approach, the dual system was evaluated for the assumptions that the backup MRF’s columns have fixed-bases and the damper’s stroke length allows interstorey drifts within the code limit. In this paper, the failure hierarchy criteria is defined and the parameters analysed are the MRF’s base fixity condition and the PFD’s stroke length, as well as, their effects on the global seismic response. Results from nonlinear response history analyses using OpenSees demonstrated that the D-FSBF with a fixed-base MRF encountered undesirable MRF column failure caused by increased moment demand at the bottom floor. Conversely, when pinned-base MRF is employed, the D-FSBF system subjected to earthquake loads is able to achieve the failure hierarchy. However, the seismic response of D-FSBF at design level is unaffected by the MRF base connection flexibility.

Derek Millichamp, Lucia Tirca
The Influence of the U-Shaped Damper Configuration on the Seismic Performance of Steel Building Frames

The effects of the configuration of the U-shaped damper system on the seismic performance of steel frames are investigated in this paper. Two different configurations are considered for this purpose. First one is the common classical application of U-shaped devices with the aid of chevron bracing systems, where the bracing systems have the supporting role, and the second is the particular type of bending dissipative braces (BDBs) including U elements, which has been recently proposed and tested by the authors. For this purpose, steel moment resisting frames with the mentioned damper systems are designed by using the available design techniques. Then, the detailed structural models are developed in the OpenSees platform to perform nonlinear time history analyses. The behaviour of the building frames under different ground motion records is evaluated and the corresponding results compared each other. Both far-filed and near-fault earthquake records are selected for the nonlinear time history analyses in order to capture the effects of the record types on the structural response. At the end, the economic efficiency of the different configurations is discussed. The final results have shown that the use of BDB increases the structural rigidity more than in case of the classical configuration of chevron braces with U elements. It can be also observed that the installation of BDB is cheaper than the classical one.

Federico M. Mazzolani, Farshad Taiyari
Cyclic Behaviour of Steel Shear Walls with Beam-Only Connection Shear Panels

Steel plate shear walls (SPSWs) with beam-only-connection provide a ductile behavior and reduce damage of columns when subjected to horizontal shear loads. In this study, the effectiveness SPSW with beam-only-connection on failure modes of three-story shear walls with two different types of beam-to-column connections is numerically investigated. The parametric studies are focused on the web plate slenderness and gap between columns. To achieve this aim, a finite element method for simulation and validation has been calibrated according to the recent experimental investigations. Therefore, two different gaps which were constant in the web plate length are selected. In addition, a solid shear panel is chosen as a reference study to compare the numerical results in terms of failure modes and structural behavior. The numerical results illustrated that the maximum shear strength, initial stiffness and energy-dissipating capacity of computational specimens are affected by changing the web plate slenderness and gap between the columns. Finally, the specimen which has improved the failure modes of shear walls is suggested.

Hadi Monsef Ahmadi, Gianfranco De Matteis
Effectiveness of Perforated Shear Panels for Improving the Failure Modes of Beam-to-Column Connections in Steel Shear Walls

Steel plate shear walls with combinations of shear panels, boundary elements, and beam-to-column connections are able to absorb and dissipate incoming seismic energy through the different yielding mechanism of the shear panels. Perforated shear panels have been introduced as a viable alternative in many structural applications. The cyclic performance of perforated shear panels on the failure modes in the boundary components of three-story shear walls with two different types of beam-to-column connections (shear and moment resisting) is numerically studied in this study. To achieve the main goals, several experimental recent activities are simulated and validated using the finite element method by ABAQUS. Therefore, two types of perforated shear panels, one of which was perforated according to recent experimental suggestions subjected to cyclic loading, are selected. The numerical results of the computational specimens are compared in terms of maximum shear strength, initial stiffness, failure modes, and energy-dissipating capacity. Finally, the perforated shear panel which has reduced the failure modes of the boundary components of steel shear walls is suggested.

Hadi Monsef Ahmadi, Gianfranco De Matteis, Federico M. Mazzolani
Seismic Performance of SDOF System with a Negative Stiffness-Inerter System

The seismic mitigation performance of the negative stiffness-inerter system (NSIS) is investigated by frequency-domain analysis and time-history analysis. In the NSIS, the inerter is connected with a dashpot and a negative stiffness (NS) spring in parallel, which amplifies the stroke of the dashpot. Therefore, the inerter and the NS provide a significant damping magnification effect, and this feature is desired for reducing the structural responses effectively when subjected to earthquakes. The closed-form expressions of optimal parameters for an uncontrolled SDOF system with NSIS are proposed by the “fixed point” method. Then, the performance of NSIS is evaluated under actual earthquakes. Results show that the optimal NSIS can substantially reduce the displacement and acceleration responses of the SDOF system simultaneously under far-field earthquakes. For instance, the seismic responses for most structural period ranges can be reduced by 20%–55%. Besides, the seismic mitigation capacity of the inerter system (IS), the negative stiffness amplifying damper (NSAD), and the NSIS are compared, and these three systems utilize the optimal parameters. The results show that when the structural period is smaller than one sec, the displacement responses of NSIS are 20% less than the IS and 11.1% less than the NSAD. And, the acceleration reduction ability of the NSIS is better than the IS but worse than the NSAD.

Jia-qi Yang, Fei-Fei Sun
Development of a Hybrid Base Isolation-Tuned Mass Damper Inerter System (BI-TMDI) for Seismic Protection of Steel Structures

In this conference paper, the performance of a hybrid base isolation-tuned mass damper inerter (BI-TMDI) system for seismic protection of steel structures was examined. It is anticipated that the displacement concentration issue at the base isolation floor which is characterized in the literature can be solved by using a TMDI. Firstly, the notion and configuration of the novel system were introduced. In particular, the BI was made of rubber bearings equipped with steel plates. To ensure the load carrying performance of the hybrid bearings, compression tests of the prototype specimens were conducted to examine the static loading carrying performance of the bearing. Subsequently, finite element model (FEM) of specimens were developed to reproduce the behaviour of the specimens. The reasonable correlation between the test results and numerical data confirmed the adequacy of the modelling technique. Based on the verified numerical modelling, a parametric study was further carried out to examine the static stiffness of the bearing and the influential parameters, and design recommendations were proposed. To confirm the rationality of the proposed bearing system, a prototype steel structure based on multi-degree-of-freedom (MDOF) analogy was developed, and the hybrid BI-TMDI was installed in the structure. The potential of the proposed system was confirmed by nonlinear dynamic analysis subjected to earthquake motions.

Jing Bian, Lin Wang, Ke Ke, Yonghui Chen, Lingyang Chen
Friction Rotational Link for Seismic Dissipation in Steel Frames

A novel seismic dissipater for steel beam to column joints, termed the Friction Rotational Link (FRL), is described. It comprises two fixed plates welded to an end plate, which is bolted to the column flange, and two plates each with circular arch slotted holes, termed external slotted plates and bolted to the beam web. Thin disks are placed between the fixed and external slotted plates to provide stable energy dissipation. All these plates are clamped by high strength bolts. In FRLs energy is dissipated when the slotted plates rotate relatively to the fixed plates. Quasi-static testing of 8 FRLs was undertaken using A325 bolts and disks with Brinell hardness of 91 – 533BH, such as aluminium, brass, steel, and tempered steel. It is shown the FLR hysteresis loop is rectangular. The FRL strength reduced between runs, and it is dependent on the hardness ratio, which is the ratio between the disk hardness and the slotted plate hardness. For high hardness ratios of 2.9, such as for tempered steel disks, the FRL strength was low and almost constant. For hardness ratios of unity, such as for steel disks, the strength was high with an increasing trend. It is also shown the reduction in FRL strength between runs is due to bolt tension loss caused by the degradation of the disks and the slotted plates surfaces (rotational interfaces). Two types of degradation of rotational interfaces were observed: abrasive for steel disks, and adhesive for aluminium, copper, and tempered steel disks. While in the abrasive degradation, the rotational interfaces are abraded producing high bolt tension loss, in the adhesive rotational mechanism, the rotational interfaces are only smoothly degraded producing low bolt tension loss.

José Christian Chanchí Golondrino, Gregory MacRae, José Luis Duque Sierra
Effects of Prying Forces on the Hysteretic Behaviour of Asymmetric Friction Connections (AFCs)

Asymmetric Friction Connections (AFCs) are used to dissipate seismic energy. The AFC hysteresis loop shape has been described as rectangular. However, recently, testing of AFCs with long slotted plates (i.e., 200 mm slot length), showed the hysteresis loop is trapezoidal. This paper proposes an AFC sliding mechanism that explains such trapezoidal hysteresis loop shape. A simple AFC elastic model performed in MASTAN 2 was used to verify the proposed mechanism. It is shown the trapezoidal hysteresis loop shape is produced by prying forces developed between the slotted and fixed plates and at the AFC clamped zone. While in some areas of the AFC clamped zone, the prying forces move the fixed and slotted plates apart, in other areas of the AFC clamped zone, they increase the interface force between these plates. As a net result of this mechanism, the friction resistance of the AFC increases. The proposed mechanism agrees well with experimental data for AFCs with Bisalloy 500 shims.

José Christian Chanchí Golondrino, Gregory MacRae, Geoffrey Rodgers
Seismic Design of Steel Moment Resisting Frames with Fluid Viscous Dampers Using Optimization

In this paper, an optimization approach for the design of moment-resisting frames (MRFs) with nonlinear fluid viscous dampers (FVDs) is presented. The objective of the optimization is to minimize the cost function, considered the cost of steel and dampers. The topology and properties of the dampers and the cross-section properties of each element are considered as design variables. The expected loss of the building is considered as a performance constraint, where the PEER framework is utilized. The structural response is evaluated using nonlinear time history analysis (NTHA), accounting for both the nonlinear behavior of the frame elements and dampers. The optimization process relies on a first-order optimization approach; the adjoint sensitivity analysis is adopted to derive the gradients of the problem efficiently; Discrete material optimization (DMO) functions are utilized to achieve a practical initial design. The numerical example shows the efficiency of the proposed method, where the elements and dampers are simultaneously optimized.

Ohad Idels, Oren Lavan
Seismic Performance and Rehabilitation of the Solca Hospital Main Buildings After the 2016 Pedernales Earthquake

The Solca Hospital in Guayaquil is located approximately 160 miles from the epicenter of the Mw 7.8 April 16, 2016 Pedernales Earthquake. The hospital is composed of several moment resistant reinforced concrete frame buildings some of them constructed at the beginning of the 1980s. The medical activities of the Solca Hospital are mainly dedicated to the treatment of cancer. During the shaking, some of the buildings experienced various degrees of damage that forced to close several sections of the hospital. After the earthquake, some buildings of the hospital went through a systematic process that included post-earthquake inspections, evaluations, and structural rehabilitation. This work presents the studies performed by the authors in order to seismically rehabilitate these buildings. First, a general description of the buildings is presented. Second, the seismic damage observed in each structure is reported. Then, the paper describes the field and the analytical studies performed in order to determine the cause of the damages. Finally, the paper includes a description of the seismic rehabilitation strategies proposed for each building. The selected strategies consisted of the addition of a combination of frames with buckling restrained braces (BRBFs) and eccentrically braced frames (EBFs). The analyses performed in the rehabilitated structures showed that these systems incorporate redundancy, stiffness, ductility, strength, and capacity to dissipate energy with controlled structural and nonstructural damage.

Pedro P. Rojas, Rodrigo Retamales, Eduardo Miranda, Martha Caballero, José Barros, Leandro García
Controlling Drift Demands in Steel Moment Resisting Frames at Frequent Earthquakes Using Tuned Mass Dampers

A tuned mass damper (TMD) is a device consisting of a mass, a spring, and a damper attached to a structure to reduce its dynamic response. The TMD concept was first applied at the beginning of the 20th century to reduce the rolling motion of ships and ship hull vibrations. Although currently they are mainly used to reduce wind-induced oscillations in buildings, there are also applications to reduce the response of the building under seismic action. Plastic deformations induced in the structural elements during strong earthquakes modify the dynamic characteristics of the structure, which makes the behaviour of the TMD system during seismic action more complex than in the case of wind, where the structure remains elastic. Often, the performance requirement that dictates the design of a building structure is the limitation of drifts induced by frequent earthquakes or by wind. Although the TMD may not be practical in reducing the structural response under larger earthquakes, it may represent a convenient solution for limiting non-structural damage under frequent earthquakes. To investigate this possibility, a steel moment resisting frame equipped with a sliding TMD system is designed and analysed using nonlinear response history analyses. The advantages, disadvantages, and effectiveness of TMD systems in reducing structural response in frequent and design-level earthquakes are investigated.

Toma Florin Voica, Aurel Stratan

Self-centring and Low-Damage Systems

Optimization Based Seismic Design of Self-centering Concentrically Braced Frames

This paper presents a design approach for multiple rocking Self-Centering concentrically Braced Frames (SC-CBFs) using a zero-order optimization framework. The objective of the design is to minimize the construction cost of the SC-CBF while satisfying performance constraints. The design space includes the properties of the rocking sections while the elements of the structural system are indirectly considered. In addition, the optimization problem is formulated to eliminate unnecessary rocking sections. Due to the nonlinearity of the optimization problem, an iterative procedure is adopted. Each iteration includes a set of new candidate designs of the system which are a product of the optimization algorithm used. The response of each design is computed using a nonlinear time history analysis (NLTHA) utilizing the Mixed Lagrangian Formalism (MLF). MLF has been shown as an efficient numerical scheme for this type of problem. The proposed methodology has been applied for the seismic design of SC-CBFs with multiple rocking sections. The results show that the optimized structures satisfy the predefined allowable performance levels with reduced construction costs.

Ameer Marzok, Oren Lavan
Design of Low-Rise Controlled Rocking Braced Frames for Life Cycle Costs

Controlled rocking braced frames (CRBFs) are being developed as a seismic force resisting system with promising structural performance and minimal residual drift. Allowing CRBFs to uplift and rock while controlling their response with energy dissipation devices and post-tensioning strands can reduce structural losses and provide self-centring behaviour to avoid residual drifts. Previous studies have shown that even CRBFs designed with a large response modification factor (R) have high drift capacity and low collapse probability. To complement CRBFs’ excellent structural performance, it is also necessary to consider the demands on nonstructural components, which may account for more than 80% of the building’s investment. In this study, three- and six-story CRBFs with different R factors are designed and loss assessment analysis is performed. The results show that less than 30% of losses were due to structural damage, including complete building loss due to collapse or excessive residual drift. Conversely, acceleration-sensitive structural components accounted for a substantial percentage of the damage in buildings with CRBFs. In all cases, the total annualized repair cost was small relative to the initial construction cost of the building.

Amir Banihashemi, Lydell Wiebe
Design and Analysis of Damage-Free Self-centring Links for Seismic-Resilient Eccentrically Braced Frames

Earthquake resilient steel frames, such as Self-Centring Moment Resisting Frames (SC-MRFs) or Concentrically Braced Frames (SC-CBFs), have been widely studied during the past few years while little attention has been paid to the development of self-centring solutions based on Eccentrically Braced Frames (EBFs). The present paper investigates a possible solution for damage-free self-centring EBFs relying on the use of a damage-free self-centring devices as seismic link. The device uses post-tensioned high-strength steel bars with disks springs to control the self-centring behaviour and friction devices to dissipate seismic energy. A four-storey EBF is designed according to the Eurocode 8 and the third storey of the structure is extracted to investigate the behaviour of a sub-assembly upgraded with the proposed seismic device. A 3D nonlinear finite element model of the device is developed in ABAQUS to evaluate the local behaviour. The results of the conventional and upgraded systems are compared, showing the effectiveness of the solution.

Annarosa Lettieri, Massimo Latour, Leo Kauntz Moderini, Fabio Freddi, Gianvittorio Rizzano
Comparison of the Seismic Performance of Conventional Moment Resisting Frames and Innovative Dissipative Replaceable Link Frames

The Dissipative Replaceable Link Frame (DRLF) is an innovative lateral load resisting system, recently developed, investigated, and further optimized in the European research projects FUSEIS, MATCH, INNOSEIS and DISSIPABLE. The system consists of two strong columns, which are rigidly interconnected by several horizontal beams, forming a vertical VIERENDEEL beam. The interconnecting beams are attached by bolted end-plate connections, making them easily detachable. These links are separated from the slab; consequently, they do not take part in the gravity load bearing function. The dissipative replaceable links being the only intended spots of inelastic action and therefore energy dissipation act as replaceable seismic fuses during a strong earthquake. After such an event, exchanging the beam links is foreseen to restore the structure to its undamaged pre-earthquake conditions quickly. Thus, the structure must possess sufficient re-centring capabilities. Recently an improvement of the initial DRLF system has been introduced within the DISSIPABLE research project: i.e. DRLF’s joined by means of strong coupling beams, forming a Coupled Dissipative Replaceable Link Frame (CDRLF). These coupling beams are not intended to dissipate energy, but instead should remain elastic, in order to provide a source of re-centring. In this paper the basic concept of the DRLF and CDRLF is introduced and demonstrated by applying it to the design of a typical low- and mid-rise office building. The case study includes also two traditional Moment Resisting Frames (MRF). A rough cost comparison is made based on steel consumption, and the seismic performance of both strategies is investigated via non-linear static analyses. In comparison to MRF’s it is shown, how the CDRLF approach is better suited for modern performance driven seismic design, focusing on reparability and cost effectiveness.

Cristian Vulcu, Marius Pinkawa, Benno Hoffmeister
Pseudo-dynamic Testing of a Large-Scale Steel Building with Innovative Column Base Connections: Design and Numerical Simulations

In the last two decades, increasing efforts have been devoted to the definition of innovative seismic design philosophies, with the aim of reducing seismic induced direct and indirect losses. Among others, beam-to-column connections equipped with friction devices have emerged as an effective solution to dissipate the seismic input energy while also enhancing the damage-free behaviour of steel Moment Resisting Frames (MRFs). Additionally, recent numerical studies have demonstrated the benefits deriving from the replacement of conventional full-strength column bases (CBs) with innovative damage-free and self-centring CBs, for both damage and residual drifts reductions of low-rise MRFs. Within this framework, an experimental campaign has been planned on a two-storey one-bay large-scale case-study MRF equipped with damage-free self-centring CBs. The present paper illustrates the preparatory work required for the design of the specimen, the test setup, and the Pseudo-Dynamic test procedures, and aims at foreseeing the response that will be observed during the experimental test by advanced numerical simulations in OpenSees. Non-linear time history analyses have been performed considering ground motion records scaled to several intensity levels. The preliminary numerical results provide useful information for the selection of the accelerograms to be used during the tests and on the expected response of the structure.

Elena Elettore, Fabio Freddi, Massimo Latour, Gianvittorio Rizzano
Parametric Study and Finite Element Modelling of Damage-Free Self-centring Column Bases with Different Structural Properties

Many recent research studies have focused on the development of innovative seismic-resilient structural systems to reduce repair costs and downtime in the aftermath of severe earthquake events. In this regard, dealing with steel Moment Resisting Frames (MRFs), recent experimental and numerical studies have demonstrated the benefits deriving from the replacement of conventional full-strength column bases (CBs) with innovative damage-free and self-centring CBs, for both damage and residual drifts reductions. Although several technologies have been conceived, studied, and experimentally tested in this direction, only a few research studies investigated the significant properties of the connections influencing the self-centring capability of these systems. Focusing on a damage-free self-centring steel CB previously investigated by the authors, the present study performs a parametric analysis to evaluate the influence of some design parameters on the seismic performance of steel Moment Resisting Frames (MRFs). Three CB configurations belonging to different case-study MRFs are investigated. Finite element (FE) models of the CB configurations have been designed and developed in the ABAQUS, considering sixteen different cases for each configuration. The FE analysis confirms the effectiveness of the theoretical design methodology and provides additional insights to improve the design requirements.

Elena Elettore, Fabio Freddi, Massimo Latour, Gianvittorio Rizzano
Low-Cost Self-Centering Composite Structural Frame Systems for Highly-Resilient Buildings

This paper presents the experimental results of an ongoing research project to develop a low-cost self-centering structural frame system. In the proposed system, shear is transferred through a slotted shear tab connection, and flexure is transferred through buckling restrained struts embedded in the floor slab above the beam and a seat angle below the beam. Post-tensioned strands in the floor slab engage with the strut to re-center the moment frame during lateral motion. A full-scale prototype of the proposed system was subjected to a quasi-static fully-reversed cyclic loading protocol. The results showed that the system was able to achieve the required story drift for a moderately ductile steel moment frame. The strength and stiffness were higher in one direction, however. The beam was isolated from column rotation up to 3% story drift. After 4% story drift, the gap between the slab and the column was insufficient to prevent the strut tabs from ramming into the slab. Several aspects of the frame contributed to the flexural strength. The results suggest that the proposed system is viable for seismic areas, but details of the system need to be refined before implementation.

Emma Kratz-Bailey, Johnn Judd
Slab Effects on Rocking Frame Performance

The response of a rocking frame with and without slab affects is described. The 3-storey 2D steel rocking frame has friction tension-only “GripNGrab” (GNG) devices. It was found that the effect of the slab reduced the displacements of the short period frame considered, especially at high levels of shaking. Also, the response became less sensitive to GNG tooth pitch, and to GNG stiffness, when the slab was considered. However, the increase in base shear was 300% in the case studied and permanent displacements resulted due to slab yielding.

Kiran Rangwani, Gregory MacRae, Geoffrey Rodgers, Hossein Soleimankhani
Frame-Spine System with Force-Limiting Connections for Low-Damage Seismic-Resilient Buildings

A novel structural system is being investigated collaboratively – by an international team including three U.S. universities, two Japanese universities and two major experimental research labs – as a means to protect essential facilities, such as hospitals, where damage to the building and its contents and occupant injuries must be prevented and where continuity of operation is imperative during large earthquakes. The new system employs practical structural components, including (1) flexible steel moment frames, (2) stiff steel elastic spines and (3) force-limiting connections (FLC) that connect the frames to the spines, to economically control building response and prevent damaging levels of displacement and acceleration. The moment frames serve as the economical primary element of the system to resist a significant proportion of the lateral load, dissipate energy through controlled nonlinear response and provide persistent positive lateral stiffness. The spines distribute response evenly over the height of the building and prevent story mechanisms, and the FLCs reduce higher-mode effects and provide supplemental energy dissipation. The Frame-Spine-FLC System development is focusing on new construction, but it also has potential for use in seismic retrofit of deficient existing buildings. This paper provides an overview of the ongoing research project, including selected FLC cyclic test results and a description of the full-scale shake-table testing of a building with the Frame-Spine-FLC System, which represents a hospital facility and includes realistic nonstructural components and medical equipment.

Larry Fahnestock, Richard Sause, James Ricles, Barbara Simpson, Masahiro Kurata, Taichiro Okazaki, Yohsuke Kawamata, Zhuoqi Tao, Jessica Duke, David Rivera, Bryam Astudillo, Yi Qie
Application and Optimization of Ring Spring Dampers for Seismic Design

The application of ring spring dampers in seismic design and strengthening/rehabilitation of civil structures is almost unknown and poorly investigated. Ring spring dampers are extremely robust, heat-resistant, durable, and have almost no maintenance requirements. Through an innovative design, they combine self-centering characteristics with a high seismic energy absorption capacity. Preloading gives them the typical flag-shaped force-deformation hysteresis curve, which can very efficiently absorb seismic energy in a structure, independently of the deformation velocity (non-viscous damping). Due to these properties, a structure with ring spring dampers can withstand seismic loads with little or no damage. The springs themselves also remain free of damage.The objective of this paper is to give an overview of the behavior of ring spring dampers, which are used as braces that will be activated in case of a seismic event. The resulting behavior of structures is discussed based on the analytical and numerical investigation of the equivalent stiffness and damping of the dampers. By the special combination of ring spring dampers with additional parts, the braces can be designed to resist seismic forces and absorb the resulting energy in both the tension and compression directions. Several structural and spring design parameters (structural and spring layout, spring type, spring composition, etc.) determine the overall seismic performance of the structure.The main influencing factors on the stiffness and damping of the ring springs were identified and investigated and their use for design purposes was elaborated. Generally, high initial stiffness and a high preload have a positive effect.By applying ring spring dampers, masses and cross-sections can be reduced. The dimensioning and practical applicability of ring spring dampers used as bracing units has been proven in several projects.

Lukas Helm, Hamid Sadegh-Azar, Lars Jahnel, Hauke Jandrey
Seismic Performance of Steel Beam-To-Column Joint with Replaceable Buckling-Restrained Energy Dissipation Fuses

This paper proposes a new seismic resilient steel beam-to-column joint using replaceable buckling-restrained energy dissipation fuse plates. Such a joint consists of a column tree where the beam stud is welded to the column in shop, and a midportion beam connected to the stud beam on site by using fuse plates, C-shaped shear tabs and high-strength bolts. The C-shaped shear tabs are used to connect beam webs and transfer the shear force while the fuse plates to connect beam flanges and transfer the bending moment. Specifically, the C-shaped shear tabs and beam flanges provide out-of-plane restraints for fuse plates to guarantee stable development of both moment strength and energy dissipation capacity, and the damaged fuse plates can be replaced after earthquakes. Three full-scale joint specimens were tested under cyclic loading to study their seismic behaviour and resilience. Test results showed that this kind of joint was able to shift the plastic damage from the beam-to-column welded connection to the replaceable fuse plates while the beam and column were basically elastic. Based on a comparative analysis, flat fuse plates (FP) and C-shaped shear tabs with the stiffener are recommended to ensure the easy repairability of the joint even after a large story drift. The repaired joint developed nearly identical seismic performance as the original one. This new joint provides an alternative solution, which is both economical and effective, for seismic resilient steel structures.

Peng Chen, Fangxin Hu, Jianrong Pan, Zhan Wang
Studies on Moment-Resisting Fuse Link Beam-To-Column Connection for Seismic Resilient Steel Moment Frame Buildings

This paper presents the details of numerical investigations on exterior beam-to-column joint sub-assemblage, using a fuse link connection, under cyclic loading. The fuse link beam-to-column connection is developed to act as structural fuse in the event of strong earthquakes, thereby preventing collapse of buildings to ensure occupant safety and also enables rehabilitation of such buildings after a strong earthquake. The fuse link connection consists of two fuse links, which connect the beam to the column flanges and one standard shear tab, which connects the beam web and column flange. The developed connection confines the inelasticity within the fuse links and limits damage in the primary members, standard shear tab and the connecting bolts. To demonstrate the behaviour of the developed fuse link connection, numerical studies are carried out on exterior fuse link beam-to-column joint sub-assemblages. Numerical model is validated using results of full-scale experimental investigations, with focus on both global and local component’s behaviour, to demonstrate the efficiency of developed models. Further, it is demonstrated that the inelastic actions are concentrated only in the fuse links as envisaged at the design stage.

Saravanan Murugesan, Rupen Goswami, Palani Gadyam Somasundaram
The Optimised Sliding Hinge Joint (OSHJ): Overview and First Application to a Project

The Optimised Sliding Hinge Joint (OSHJ) is based on a significant enhancement of the Sliding Hinge Joint (SHJ) originally created for Moment Resisting Steel Framed (MRSF) buildings. The traditional SHJ offered a significant advance over traditional rigid moment frames but had a limitation of suffering post-earthquake loss of strength and stiffness. This response meant that during subsequent events, a building’s lateral bracing system could experience increased displacements and have increased potential for damage. Post-shaking this could result in post-event residual drift and make the building too flexible for subsequent lateral loading from wind or earthquake. The OSHJ addresses these weaknesses recognised during testing and research carried out over the last fifteen years.The OSHJ presents a significant step forward in the seismic behaviour with the creation of a connection that deserves the moniker of a “low damage” steel-framed joint. The OSHJ enhances protection provided to buildings from suffering structural damage during large earthquakes. In subsequent aftershocks the joint continues to respond without significant loss of stiffness and facilitates building recentring.This paper outlines the OSHJ characteristics followed by reporting its first implementation in three multi-storey buildings in Hamilton, New Zealand, as a result of a collaboration between AUT, UoA, Beca, and other industrial parties.

Shahab Ramhormozian, Charles Clifton, Sean Gledhill
Replaceable Brace Modules for Concentrically Braced Frames: Test Results from Substructure with Moment-Resisting Beam-Column Connections

In current practice for concentrically braced frames (CBFs), a gusset plate is typically used to join the brace to the frame elements. Using a linear clearance to accommodate the out-of-plane deformation of the buckling brace can have negative implications for both construction and seismic performance. An alternative connection approach, intended to be more seismically resilient, has recently been developed based on a replaceable brace module (RBM). This connection uses shop welded/field bolted connections to facilitate erection and make the brace replaceable by confining all damage to the RBM.This paper presents results from 70%-scale testing of a concentrically braced frame with RBMs and moment-resisting beam-column connections. The experimental program consisted of two phases. In Phase I, the frame was subjected to quasi-static cyclic loading up to brace fracture. In Phase II, the damaged RBMs were replaced with new RBMs, and the behaviour of the frame was investigated under the same loading protocol. The tests demonstrate that the frame performance was at least equivalent to what would be expected with more traditional connections, while also allowing site welding to be avoided, brace buckling to be limited to the in-plane direction, and the brace modules to be easily replaced. The moment-resisting beam-column connections functioned as intended, with minimal damage up to brace fracture during the first tests, and similar behaviour during the Phase II tests with replaced RBMs. In this way, the testing demonstrated the viability of the proposed new approach to detailing concentrically braced frames to facilitate more rapid repair.

Vahid Mohsenzadeh, Lydell Wiebe
Seismic Behavior of a Hybrid Moment-Resisting Frame with Replaceable Energy Dissipation Angles

The primary focus of this research was the targeted replaceability in steel moment-resisting frames. For this purpose, a hybrid moment-resisting frame with replaceable energy dissipation angles (HMRF-REDA) is proposed with the advantage of cost-effective and easy replacement work. The system consists of energy dissipation bays (EDBs) equipped with fuse connections and recentering bays (RBs) made of high strength steel (HSS). The fuse connections are located in beams of EDBs with connection plates at the top flange and steel angles at the bottom flange. Inelasticity is expected to be restrained in the angles during a wide deformation range, allowing repair by replacing the angles. In this research, shaking table tests were performed to investigate the seismic performance of the HMRF systems and in particular, the on-site fuse replacement feasibility in a complete structural system. The specimen was comprised of two parallel one-second scaled, three-story hybrid moment-resisting frames designed with fuse connections. The results demonstrated that HMRF-REDA exhibited a multi-stage yielding sequence with damage restricted to the fuse elements for the expected deformation range. The HSS frame members were able to fully recenter the structure that experienced an inner-story drift up to 0.0235 rad. Two on-site fuse replacement operations were implemented within the complete structural systems and proved to be feasible and easy to operate. The fuse replaced frame model achieved a similar subsequent elastic and inelastic performance when it experienced a preceding drift up to 0.0184 rad.

Xiuzhang He, Yiyi Chen

Assessment and Retrofitting

A New Seismic Coating System for Requalification of Existing Constructions

The current trend in the retrofit of existing buildings is to think mainly to environmental aspects, giving few attention to seismic issues. Contrary, recent EU’s policies in this field are based on integrated approaches able to improve both energy and earthquake performances of the existing built-up. Therefore, the so-called seismic coats have been launched on the building market. In this framework, the design of a new envelope system, named DUO SYSTEM, for seismic-environmental requalification of existing constructions made of masonry or reinforced concrete is presented and illustrated in the present paper. The novel seismic-environmental coating system is composed of a cold-formed aluminium framed structure equipped with a shear wall system, represented by either OSB panels or aluminium alloy trapezoidal sheeting, which are designed according to the Sheeting Braced Design theory. In the current work, firstly, the novel seismic coat has been presented by detailing all its components. Secondly, the anti-seismic solutions based on OSB shear walls have been used for upgrading two existing school buildings, one made of masonry and the other made of reinforced concrete. Finally, the comparisons of performances of examined buildings before and after the intervention have been made to evaluate the benefits provided by the proposed coating system under seismic and environmental viewpoints.

Antonio Formisano
Vulnerability Curves of Existing Italian Industrial Steel Buildings Designed Without Seismic Criteria

The Italian earthquakes of the last 15 years highlighted the significant seismic vulnerability of industrial buildings, which represent structural typologies at high risk due to their noteworthy exposure. The paper concerns a parametric study on a class of Italian existing industrial steel buildings designed before 1980 without anti-seismic criteria. The choice of the specific class of warehouses is based on field surveys carried out filling the CARTIS-GL form in the municipality of Cercola, within the district of Naples. These buildings, having different geometrical dimensions, represent one of the most common steel industrial structures widespread in the Italian territory in those years. Five families of structural models, placed into different geographical areas, are designed with the calculation methods of the reference time. The seismic behaviour of the investigated industrial buildings is investigated through non-linear static analyses. The results allow to plot vulnerability curves to be compared to seismic fragility curves derived from literature research. The comparison among curves is useful to estimate the effectiveness of the literature studies, as well as to evaluate the seismic damages suffered by investigated structures under different earthquake levels.

Antonio Formisano, Emilia Meglio, Gianmaria Di Lorenzo, Raffaele Landolfo
The Use of Steel in the Functional-Structural Rehabilitation of the Prince Caracciolo of Avellino Building in Naples

The paper presents the functional and structural rehabilitation of an historical masonry building located in the old town of Naples, which is an UNESCO World Heritage Site. The building was initially built in the 16th century as monastery and in the 17th century it was achieved by the Prince Caracciolo of Avellino family, who made major modifications. The building has a rectangular plan with a length of about 50 m and width of about 10 m. It has 6 stories, one of which is below the street level; the pitched roof reaches a maximum height of about 26 m. Before the renovation intervention the building was very much degraded, presenting widespread cracks in the masonry walls and vaults and deteriorated wooden floors. The rehabilitation was dedicated on one hand to the retrofit of existing vertical and horizontal structures, on the other hand to adapt the building to the new use, as a Foundation of Contemporary Art. The paper briefly describes the state of the construction before the intervention and its recovery and transformation, with particular reference to the structural aspects, highlighting the versatility, compatibility and efficiency of retrofitting solutions based on steel in the masonry built cultural heritage.

Beatrice Faggiano, Luigi Fiorino, Vincenzo Macillo, Giulia Bonelli, Claudio Rossi, Federico M. Mazzolani
Seismic Upgrading of an Existing Steel Structure Using Inverted Y-braces

The paper describes an application of steel eccentric bracing with vertical shear link (inverted Y-bracing) for seismic retrofitting of an existing school building. The building is located in a little village of a high seismic zone in Italy. The existing structure presented several structural defects and irregularities which required an “ad hoc” intervention of seismic upgrading for both gravity and earthquake loads. The proposed technical solution, also in agreement with the new seismic regulations, improves the seismic performance, increasing stiffness and resistance, as well as global ductility, of the lateral-force resisting system. The upgraded structure allowed satisfaction of current minimum Italian code requirements, evaluated by means of static nonlinear analysis. The paper highlights general design concepts, while also providing some details about capacity design of connections between the newly added structural elements and the existing structure. Global modelling issues and connection design offer perspectives on research needs for this type of applications.

Federico M. Mazzolani, Gaetano Della Corte, Gaetano Cantisani
Design of Metal Shear Panels for Seismic Protection of RC Buildings

Many studies in literature proved the excellent hysteretic behaviour of metal shear panels that exhibited large ductility and energy dissipation capacity under cyclic loading. The lack of standardized design procedures has seriously limited their use for seismic retrofitting of RC buildings. This paper develops a passive control design method for RC structures added with metal shear panels. The simplified method is based on a single-degree-of-freedom idealization and an optimum equivalent stiffness distribution to arrange the metal shear panels over the height of the building. The design method is validated through implementation in two different building cases. Its effectiveness is demonstrated through nonlinear dynamic analyses focusing on the effects of the cyclic behaviour of the metal shear panels.

Gianfranco de Matteis, Massimiliano Ferraioli, Rocco Raimo, Angelo Lavino, Pasquale Bencivenga
On the Use of Steel Exoskeletons for Seismic Retrofit of Existing RC Buildings: A Case Study

Since the ‘80s the use of steel external additive structures is considered one of the most suitable techniques for seismic retrofit of existing RC structures with low dissipative capacity. This structural typology, called exoskeleton, made its first appearance in 2000s in the Japanese and American codes dealing with structural rehabilitation issues. Nowadays, exoskeletons can be implemented without interrupting the building use and they are also used for the integrated retrofit of the building systems. In the present work, after the typological classification of steel exoskeletons in families and the definition of their key project parameters, the application of these systems to the case study of the primary school P. Santini in Loro Piceno, a district of Macerata, has been shown for illustrative purpose.

Gianmaria Di Lorenzo, Agustina Di Filippo, Antonio Formisano, Raffaele Landolfo
Retrofitting Solution for an Existing Steel Frame Structure Sensitive to Global Torsion

The present paper shows a retrofitting solution for the steel structure of an existing hotel building, located in Tulcea County, Romania. The building has three storey and a curved layout, which makes the structure sensitive to global torsional effects. The constructed area of the building is about 2000 m2. The central bay of the structure on transverse direction is 12.7 m, while the average length of the eight bays is about 4.5 m. The bottom storey height is 3.8 m and the current storey height is 5.5 m. The infrastructure consists in a network of foundation beams placed under all columns of the steel structure. The existing steel structure, designed in 2011, has some major deficiencies: sensitivity of the structure to global torsion; insufficient lateral stiffness, when subjected to horizontal seismic loads; unappropriated configuration of the connections among different structural elements; large floor deformations under gravitational loads; quite large floor vibrations could be noticed, when someone was dancing or jumping on the floors. The proposed retrofitting solution, consisted in introducing additional eccentrically connected braces, on both main directions of the existing structure.

Helmuth Köber, Sebastian Ștefănescu, Antonio Andrei Cristian
Retrofit of a RC Building Against Seismic and Progressive Collapse Using Steel Bracing and Cabling

The retrofit of a RC hospital building using low impact strengthening techniques based on steel bracing and cabling is illustrated in the paper. A preliminary investigation of the seismic performance capability of the building has been made, in such a way to address the possibility to improve the earthquake protection together with structural robustness. Out of the possible low impact structural solutions, the ones relying on steel concentric braces and catenary cables have been considered and analyzed in detail. The proposed solutions are critically examined as to parameters like ease of implementation, global impact on the construction, and intervention reversibility. Both seismic and progressive collapse resisting capacity of the retrofitted building are assessed and discussed based on nonlinear static and dynamic analyses.

Massimiliano Ferraioli, Angelo Lavino, Alberto Mandara
Seismic and Progressive Collapse Retrofit of a Steel Braced Frame Office Building

A case study is presented in this paper dealing with a steel braced frame office building located in Southern Italy and designed for gravity loads only. The building, erected in the early ‘60s, is investigated to assess its behavior with regard to both seismic and progressive collapse performance. At the same time, some possible retrofit strategies are outlined. To this aim, the results of both linear and nonlinear static and dynamic analyses are presented and discussed considering different column removal scenarios. Then, an integrated design procedure involving both robustness and seismic safety is developed using steel-braced frames and mega-truss outriggers. In this context, both seismic and progressive collapse performances after retrofit are investigated.

Massimiliano Ferraioli, Angelo Lavino, Crescenzo Capasso, Alberto Mandara
Design of Buckling Restrained Damper for Retrofit of Steel Truss Bridge

The seismic design codes have been revised whenever severe damage was observed in the aftermath of a seismic event. The seismic resistance of quite a few existing bridges may not be satisfactory for the current seismic design codes. Retrofit is needed for those bridges. To this end, the application of the device of the buckling restrained bracing (BRB) to a steel truss bridge as a damper (BRD) is explored. A parametric study on the seismic performance of the truss bridge with the BRD is conducted by changing the length and the cross-sectional area of the yielding core of the BRD. The numerical results by the nonlinear dynamic analysis show that the BRD surely improves the seismic performance of the bridge. It is found that a shorter length tends to work better and a larger cross-sectional area enhances the safety. The study concludes that an appropriate design of the BRD would help steel truss bridge stay intact even under a rather large seismic loading.

Namkhainyambuu Enkhbold, Purevdorj Sosorburam, Eiki Yamaguchi
Application of Buckling Restrained Damper to Steel Arch Bridge

The seismic resistance of quite a few existing bridges may not be satisfactory for the current seismic design codes in Japan. Retrofit is needed for those bridges. To this end, the application of the device of the buckling restrained bracing (BRB) to a steel arch bridge as a damper (BRD) is explored. An arch bridge model based on the existing bridge is studied. A road is located on the top of the arch bridge. The nonlinear dynamic finite element analysis indicates that several vertical and diagonal members of the arch bridge are possibly damaged under large seismic loads. BRDs are installed to the girder on the top of the arch bridge to reduce the overall horizontal movement. A parametric study on the seismic performance of the arch bridge with the BRDs is then conducted by changing the length and the cross-sectional area of the yielding core of the BRD. The damage is indeed reduced by the BRDs. Yet even the best values of the parameters cannot save all the arch members: some vertical members are still possibly damaged, undergoing column buckling. Then more BRDs are installed to prevent such vertical members from buckling, connecting the joint in the middle part of the vertical member and the joint at the bottom of the adjacent vertical member. The numerical analysis shows that the buckling of those vertical members can then be avoided.

Purevdorj Sosorburam, Eiki Yamaguchi, Namkhainyambuu Enkhbold
Seismic Assessment of Beam-To-Column Joints for a Non-conforming MRF Existing Structure

The present work is focused on seismic assessment and retrofit of the beam-to-column joints of an existing non-conforming steel building. Refined finite element analyses were performed to investigate the performance of the existing beam-to-column joints under monotonic and cyclic loading conditions as well as the effectiveness of different strengthening interventions. The main features of these joints are the continuity of beams and hollow square columns interrupted at each level and connected by a bolted flange that is strengthened by fillet welds to the tapered flanges of the beams. The results of the finite element simulations show that the existing joints of the examined building exhibit very poor seismic behaviour, mainly due to failure of the welds. On the contrary, the strengthened joints have enhanced response. The comparison between the response of the unreinforced and the various retrofitted joints is described, and the best solutions in terms of both cyclic behaviour and technological feasibility are subsequently identified.

Roberto Tartaglia, Aldo Milone, Mario D’Aniello, Attilio De Martino, Raffaele Landolfo
Seismic Assessment and Strengthening of an Existing Industrial Building

Nowadays, the development of rapid and low-impact structural rehabilitation strategies and techniques is very topical. These prerogatives are essential for the seismic retrofit of industrial buildings, for which the seismic retrofit solution should be selected also accounting for the impact of the interventions on the productive activities. Therefore, a retrofit solution that allows to increase the structural capacity without interfering with the industries production could be preferred with respect to canonical retrofit solutions. In this framework, the aim of the present work is to investigate the efficiency of orthogonal steel exoskeletons for the retrofitting of a steel single-storey industrial building. The investigated case study has poor lateral stiffness and strength. Following a specific design methodology, the various elements of the system were designed, and their efficiency was assessed by means of a non-linear static procedure. Moreover, a local retrofit of the truss to column connections of the MFRs was performed and investigated by means of FEM analysis.

Roberto Tartaglia, Alessandro Prota, Aldo Milone, Gianmaria Di Lorenzo, Raffaele Landolfo
Simplified Rules for the Evaluation of Moment Resisting Frames and Concentrically Braced Frames Seismic Performances

Recent earthquakes have highlighted the need for a prompt classification of the built heritage in terms of seismic vulnerability. The capacity of a structure can be assessed through nonlinear analysis, requiring onerous numerical procedures. Therefore, a simplified procedure for the evaluation of the seismic performance of steel Moment Resisting Frames (MRFs) and Concentrically Braced Frames (CBFs) not resorting to any static or dynamic non-linear analysis seems to be useful in everyday practise or the aftermath of a seismic event. The proposed performance-based method has been set up by a wide parametric analysis on several MRFs and CBFs. The design procedure has been developed according to 3 different approaches: the first is Theory of Plastic Mechanism Control (TPMC) ensuring the design of structures showing global collapse mechanism, the second is based on the Eurocode 8 requirements while the third is a design only for horizontal loads (not resorting to rules aimed at the mechanism control).

Rosario Montuori, Elide Nastri, Vincenzo Piluso, Paolo Todisco
Numerical Study on Seismic Repair by Re-tightening Turnbuckle Braces

Gymnasium is one of the most important facilities used as an evacuation centre during a disaster in Japan. So securing the earthquake resistant of such structure is important. For gymnasiums, tension-only brace is an important for seismic member. It is thought that the gymnasium can be used early after disaster by repairing the braces.This paper focuses on the seismic repair by re-tightening turnbuckle braces. The dynamic response analysis using single-degree-of-freedom system was conducted to investigate the safety against aftershocks and the effectiveness of repair. The findings obtained from the dynamic analysis are summarized as follows: (1) the maximum story drift ratio does not increase when the aftershock’s PGV is less than 20% of the mainshocks or less than 20 cm/s; (2) it is not needed to consider the increase of the maximum story drift ratio because almost all the aftershock’s PGVs are less than 20% of the mainshocks; (3) the number of turnbuckle braces that exert the effectiveness of repair can be obtained by using the equations proposed in this study.

Shotaro Nakada, Shoichi Kishiki

Codes and Standards

Evaluation of the Canadian Seismic Design Provisions for Wide-Flange Columns in Steel Moment-Resisting Frames

This paper evaluates the stability design requirements set by the 2019 Canadian steel design standard for steel moment-resisting frame columns with base flexural plastic hinging through the finite element analysis of square and deep wide-flange columns that are part of a five-story building subjected to ground motion accelerations. The results showed significant local buckling and strength deterioration of deep slender columns compared to square sections, however the new web slenderness limit h/tw = 37 appears to limit strength deterioration and column axial shortening within acceptable ranges at axial loads around 0.15AFy. No columns experienced member buckling even though none of the deep, slender columns met the global slenderness ratio limit Lb/ry = 50 specified by the standard, suggesting the limit may be overly conservative and can be relaxed.

Abrar Islam, Ali Imanpour
Revision of Eurocode 8: Features Common to All Materials

The revision of Eurocode 8 is under way. The paper summarizes aspects of the revised rules common to all materials, like new format for the seismic action, enlarged sections on pushover analysis and the redefinition of the ductility classes with limits of applicability in terms of seismic action per structural systems and materials fitting better with the real seismic capacity of each structural type. The range of application of the former lower class DCL is increased for some systems while a class DC2 intermediate between the former DCL and DCM is introduced for more economical design. The revision improves the structural logic of requirements, taking for instance into consideration the force amplification in columns which exists after formation of a first plastic zone.

André Plumier
Mitigation of Soft Storey Failure: A New Criteria

The definition of ductility classes DC of Eurocode 8 has been modified in the on-going revision process. DC1, without objective of plastic deformation capacity or energy dissipation capacity, is equivalent to the former DCL, on the contrary of DC3 which, like former DCM and DCH, requires those characteristics and imposes for moment resisting frames the “weak beams-strong columns” criteria. In DC2, the latter is not imposed, but soft storey failures have to be mitigated anyway; local overstrength capacity, deformation capacity and energy dissipation capacity are required; the control of the global plastic capacity is made through limitation of drift and of second order effects and, for moment resisting frames, by the respect, at each storey level, of a criteria showing that the storey possess the energy dissipation potential required for stability. The basis of this criteria is explained in the paper.

André Plumier
Seismic Behaviour of Steel MRFs Designed According to EN1998-1(2005) and prEN1998-1-2(2020)

This study aims at evaluating the capacity of steel moment frame (MRF) structures at collapse limit state designed according to the current version and next release of Eurocode 8. To this purpose, the framework of performance-based earthquake engineering according to PEER is adopted. The collapse intensity and subsequently the mean annual rate of collapse are computed as an index of comparison. The structural assessment is carried out by means of nonlinear static and dynamic analyses on 2D models developed using “OpenSees”. The results show that the incoming version of the EC8 allows exploiting the inherent ductility of the structure, while having the same collapse risk as the frame designed in accordance with the current version of EC8.

Arash Poursadrollah, Roberto Tartaglia, Mario D’Aniello, Raffaele Landolfo
Ductility Classes in prEN 1998-1. Comparative Analysis on Eccentrically Braced Frames

During severe earthquakes, it is desirable for a structure to be able to undergo significant plastic deformations and to develop a plastic mechanism. Codes usually manage this plastic behaviour ability of structures using ductility classes. The future version of the European code EN 1998-1, defines three such classes, DC1, DC2 and DC3, which are different from DCL, DCM and DCH that are used nowadays in the present version. The behaviour factor q is better managed in this future version and the difference in requirements among the three ductility classes is more accurately expressed. Under these circumstances, numerical testing of the new requirements is necessary. The present paper focuses on differences that can be noticed when designing eccentrically braced frames according to the three new approaches. An eccentrically braced frame with short links was considered. Three solutions were obtained for the cross-sections of members, using the requirements defined for DC1, DC2 and DC3. As the “mathematical” procedure is put to test, the influence of the designer’s skills was minimised as much as possible. All three structures were designed based on resistance requirements. The material consumption and the post-elastic behaviour were observed for each one of the three structural solution and comparisons are presented.

Bogdan Cătălin Ștefănescu
FEMA P-695 Verification of Seismic Design Coefficients for Mid-to-High-Rise Hybrid Coupled Core Wall Systems

FEMA P-695 is a framework that allows verification of the appropriateness of the seismic design coefficients (namely, the overstrength factor, the seismic reduction factor, and the displacement amplification factor) by means of a statistical approach that ultimately provides a pass/fail evaluation of the coefficients for the building prototypes considered. The study presented in this paper focuses on coupled core wall systems using steel coupling beams, with the goal of demonstrating that these systems can be designed using less conservative coefficients than those currently prescribed. A secondary goal of this study is to demonstrate that these systems can also be designed for heights in excess of the current limitations provided in the ASCE 7-16 standard. The study presented consists of a large number of archetype structures, differing by height, floor plate dimensions, amount of vertical forces applied, and fundamental frequencies. Each of the archetype structures is subject to a suite of 22 near-field acceleration records, and for each record an incremental dynamic analysis is performed. The results of thousands of nonlinear dynamic analyses are summarized in this paper, showing that hybrid coupled core wall systems can be safely designed using the largest seismic reduction coefficient currently allowed (R = 8), without a correspondingly unduly large overstrength factor and displacement amplification factor. The paper provides some information on the design approach for these systems, as well as a summary of all analyses performed, highlighting which of the archetypes are less likely to perform well under the conditions investigated. In conclusion, the paper shows that a FEMA P-695 verification of coupled core wall system supports the use of a higher seismic reduction factor for buildings in excess of the height limitation currently in ASCE 7-16.

Dennis Bartole, Yao Ding, Gian Andrea Rassati, James Swanson
A Strength Amplification Factor to Counterbalance P–∆ Effects in Steel Moment Resisting Frames

The importance of P–Δ effects is generally modest in the elastic range of behaviour. However, it becomes significant when the structure experiences large plastic deformations. Seismic codes indicate that P–Δ effects may be counterbalanced through an increase in the lateral strength required by a first order analysis. The expressions suggested in codes for this amplification factor are simplistic and often criticized by researchers. Hence, the paper proposes a formulation of the strength amplification factor, which is alternative to those of seismic codes. This formulation is a generalization of the one derived in the past by the authors based on the numerical response of SDOF systems.To validate the proposed formulation, steel moment resisting frames characterized by different sensitivity to P–Δ effects are considered. Each structure is designed taking into account P–Δ effects in keeping with provisions of seismic codes or according to the proposed strength amplification factor. To comment on the effectiveness of the proposal, the nonlinear seismic response of these structures is determined by nonlinear static analysis. The increase in size of the cross-sections required to counterbalance P–Δ effects is also determined to compare the costs of structures designed according to the proposed and existing formulations.

Francesca Barbagallo, Melina Bosco, Aurelio Ghersi, Pier Paolo Rossi
Seismic Performance of Steel MRFs Designed to the Provisions of the Latest Draft Eurocode 8: Case Studies

Various improvements have been proposed to the seismic code Eurocode 8 in recent years. In its current state, the norm under revision has been expanded in content and structure. Modifications in the definition of ductility classes, behaviour factors, inter-storey drift sensitivity (ISDS) coefficient, the local hierarchy criteria, and the design rules for medium (DC2) and high ductility class (DC3) structures are a few of the notable changes to be mentioned for the design of steel moment-resisting frames (MRFs).In MRFs, which are highly susceptible to lateral deformations, design is often governed by stability requirements in the verification of the significant damage limit state. This leads to the use of heavier sections in members to meet the lateral stiffness demand. In the computation of ISDS, the draft code takes advantage of the design over-strength ratio and the material variability in the dissipative zones. This paper aims to study and compare seismic designs of MRFs using the revised specific rules for steel design in the new code which is now at a working draft level. The flexibility achieved due to the mentioned considerations is first studied through case study frames. Once designed, the performance of these frames is examined through non-linear analyses using OpenSees.

Melaku Seyoum Lemma, Carlos Rebelo, Luís Simões Silva
Prediction of the Bending Moments in Columns of Concentrically Braced Frames in the Chevron Configuration

Several studies have shown that the application rules of the capacity design principle suggested for chevron braced frames are often not effective in preventing yielding or buckling of the columns of the braced frame. Indeed, the design procedures available in literature or in seismic codes either neglect or significantly underestimate bending moments in columns.These bending moments are negligible when braces are in the elastic range of behaviour, but they may become significant because of concentration of the interstorey displacement demand when the braced frame overcomes its elastic range of behaviour and braces of a few stories experience large inelastic deformations. The high values of bending moments undermine the seismic performance of concentrically braced frames if yielding or buckling of the columns occurs prior to the full exploitation of the ductility capacity of braces.A simple procedure has been recently proposed by the authors to estimate the bending moments in columns of braced frames at the achievement of the ductility capacity of braces. In this paper, the abovementioned procedure is applied to predict bending moments in columns of concentrically braced frames in the chevron configuration designed according to different design procedures available in literature. To assess the effectiveness of the procedure, the predicted values of bending moments are compared to those obtained by nonlinear dynamic analyses with reference to peak ground accelerations leading the structure to either significant damage or near collapse limit state.

Melina Bosco, Andrea Floridia, Edoardo Marino, Pier Paolo Rossi
Seismic Design of Steel Frames by Improved Direct Displacement-Based Design Method

An improved direct displacement-based design approach for seismic design of plane steel moment-resisting frames is presented. The improvement stems from the use of a multi-degree-of-freedom equivalent system rather than the original direct displacement-based design method’s single-degree-of-freedom equivalent system. As a result, higher modes and P-Δ effects are evaluated more prudently. The suggested approach utilizes deformation-dependent equivalent modal damping ratios and design modal displacements, which correspond to the first few significant modes, as a function of target inter-storey drift ratios accounting for different performance levels. After combining a-compatible with various damping ratios-displacement design spectrum with the equivalent modal damping ratios and design modal displacements, one may calculate the necessary modal periods, stiffnesses and shear forces at the base. Through a modal combination rule, the base shear is computed and properly distributed to all storey levels. Via a numerical example of a 15 storey moment resisting frame, the benefits of the proposed method are highlighted.

Nicos A. Kalapodis, Edmond V. Muho, Dimitri E. Beskos
Proposal of Seismic Coefficient and Estimate for Horizontal Sliding for Steel Tanks by Backward Seismic Analysis (BSA) Method

Large steel tanks used for oil storage, petrochemical industry and for processing plants have frequently suffered repeated damages in largest earthquakes observed in the world and Chile 1960–1985–2007 and 2010 also in Alaska 1964 and other cities of United States (1933–1995). In most cases when tanks were anchored, they performed a good structural response with repairable damages to return to operation in reasonable periods of time, confirming that the effective use of anchors, helps to prevent buckling effect called “elephant foot” or “horizontal sliding”. Based upon the observation of real behavior of steel tanks in large earthquakes, the proposed methodology aims to reduce the tanks damage and structural stability, through seismic coefficient for tanks with safe slenderness ratios design ranges for imperfections in the shell and estimates of horizontal coseismic sliding of unanchored tanks in subduction zones. The proposed methodology is based upon the BSA method, developed by the authors in previous works (Pineda & Saragoni) considering the Chilean high seismicity, demonstrating that there is no direct correlation between the theoretical and the observed models, given that the characteristic non-vibratory inertial effect of mega-subduction earthquakes with simultaneous high ground accelerations is not considered in the design codes. The analyses encompass the seismic behavior of 382 tanks in operation during the last 80 years, which were mainly designed by different editions of the API650 standard with the appendix E. This proposal is essential to modify the main design codes for steel tanks.

Patricio Pineda, Rodolfo Saragoni
Seismic Design of Foundations for Steel-Framed Buildings: A Canadian Perspective

Provisions for the seismic design of foundations have changed significantly in recent editions of Canadian codes and standards. Considering that the foundations are constructed using reinforced concrete, these requirements were developed mainly based on Canadian studies of the seismic response of RC shear walls. Hence, they may be less adapted to steel braced frame systems and the particularities of their seismic behaviour and design, such as a distributed yielding mechanism and a differentiation between the nominal and probable capacities of ductile elements. This may lead to overly conservative design estimates of the demands on foundations and the total building drifts, adversely affecting not only the foundations themselves by increasing their size and cost, but also the choice of steel as the material for the seismic force resisting system.This paper presents an overview of Canadian provisions for the seismic design of foundations and critically assesses their applicability to the foundations of steel concentrically braced frames. The design procedure is illustrated with the example of 3-storey steel buildings with X-type tension-compression bracing, located in Vancouver and Montreal and designed following the National Building Code of Canada and the associated editions of the concrete and steel design standards. The seismic response is examined using nonlinear time history analysis, where a numerical model developed in OpenSees integrates inelastic frame behaviour and nonlinear soil response. The results clearly demonstrate the shortcomings of current foundation design procedures when applied to steel frames. Possible solutions to overcome these limitations with an improved design methodology are discussed.

Sanda Koboevic, Ushanthan Murugananthan, Angel Reyes-Fernandez, Hamid M. Madani, Lydell Wiebe

Light-Gauge Systems

A Case for Rethinking ASCE 41 Performance-Based Assessment Criteria for Cold-Formed Steel

The objective of this paper is to evaluate the impact of applying the ASCE 41-17 performance-based design provisions on a 2-story building previously designed and tested during the CFS-NEES research project. The latest version of the American Society of Civil Engineers Standard 41 (ASCE 41-17) incorporates new provisions for the assessment of cold-formed steel (CFS) systems. These provisions include component acceptance criteria derived from a database of available experimental data. Though the new set of criteria was rigorously developed, how these criteria would score a newly-designed CFS building is not well understood. Given that the vast majority of CFS buildings are designed using linear procedures, particular interest is given to comparing the linear procedures for new design (i.e., using ASCE 7–16) versus the linear procedures for existing building assessment (i.e., using ASCE 41). Findings show that although the 2-story building withstood shake table tests with intensities greater than the maximum considered earthquake, the ASCE 41 assessment indicates the building’s shear walls are deficient. This highlights a disconnect between ASCE 41 and new building design per ASCE 7. To help resolve this disconnect, practical ways to account for system overstrength should be considered in future editions of ASCE 41.

Matthew S. Speicher, Zhidong Zhang, Benjamin W. Schafer
An Overview of Studies of the Response of a Typical Steel Light-Gauge Housing System

In recent years, the use of light housing structural solutions made of cold-formed steel (CFS) members is becoming increasingly popular. Among the main advantages of these systems, the lightweight is the one that makes them attractive and competitive in seismic areas if compared to the more traditional solutions. The complex behaviour of cold-formed profiles, of sub-assemblages and of the whole system make difficult to adopt a purely theoretical approach for their design. Therefore, a mixed approach that combines experimental tests and numerical simulations is usually adopted.The University of Trento was involved in a research project aimed to develop an industrialized housing system made of CFS members. With the aim to have a holistic comprehension of the performance of these building systems, a suitable number of experimental tests and numerical simulations were performed ranging from the single component to the entire building. In detail, the local behaviours of the single components (i.e. member, connections, sheathing, and steel deck), the in-plane behaviour of shear walls and of floor systems and finally the response of the entire building were investigated under quasi static and seismic actions. The paper presents an overview of the whole project and of the main findings.

Nadia Baldassino, Riccardo Zandonini, Marco Zordan
Shake Table Tests to Examine the Seismic Performance of Prefabricated Steel Unit Houses

Shake table tests were conducted to examine the seismic performance of prefabricated steel unit houses, which are modular steel frames comprising four corner columns and light-gauge steel beams that can be assembled vertically and horizontally as needed. The product of interest has the shorter beam shop welded to the column, and the longer beam connected to the column using a slip-critical bolted connection. Three specimens were constructed, each comprising 4 unit-house units connected vertically and horizontally, furbished with external wall panels. The JMA Kobe record, whose intensity is twofold greater than Japanese code requirements, produced a maximum story drift of 0.029 to 0.045 rad. After experiencing this motion twice, structural damage was observed in the short-side frame: weld fracture in the lower beam, local buckling of the upper beam, and bending of column base plates. In the long-side frame, much of the inelastic energy was dissipated by repeated slipping of the bolted connections. At story drifts larger than 0.01 rad, the wall panels supplied as much lateral stiffness and strength as the structural system. Overall, the tests demonstrated excellent performance of the unit house beyond the current Japanese code requirements for ordinary, non-temporary buildings.

Ryosuke Matsuda, Taichiro Okazaki, Takuya Nagae, Tomohiro Matsumiya, Yoshikazu Kanzaki, Takahiro Fukui, Toshihiko Iijima, Yoshiro Kiriyama, Koichi Kajiwara
Upright Base Connection Impact on Structural Design of Steel Storage Rack Systems in Seismic Zones

The paper presents the investigation of the seismic behaviour of a particular configuration of a cold-formed steel storage racking system. The seismic study is focusing on the comparison of the behaviour of the same rack structural system under same loading conditions, same seismic loading but different upright base connection. The reference structure is considered with perfect pinned column base without uplifting possibility. Then, the influence on the behaviour of the structure is evaluated, introducing in the structural model the base plate uplift stiffness. The rack structural response is evaluated using nonlinear time history analysis. Results are expressed in terms of the magnitude of the base reaction forces, maximum sway deformation and variation of the fundamental eigen period of the rack structure. The performed nonlinear time history analyses confirms that dealing only with base plate uplift has a significant influence on the global response of the steel storage racking system hit by cross-aisle seismic action.

Zsolt Nagy, Annabella Sánduly
Proceedings of the 10th International Conference on Behaviour of Steel Structures in Seismic Areas
herausgegeben von
Prof. Federico M. Mazzolani
Prof. Dan Dubina
Prof. Aurel Stratan
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