Seismic Force-resisting Systems Research Articles

Seismic Collapse Risk Assessment and Fragility Analysis of Reinforced Masonry Core Walls with Boundary Elements Using the FEMA P695 Methodology

In the past, the primary objective of structural design codes was centred around ensuring human life safety, with a strong focus on preventing structural collapse. This approach predominantly relied on force- or strength-based criteria as the basis for design. Nevertheless, a notable shift has occurred recently, transitioning the design philosophy from 'strength' towards a 'performance'-based approach. This shift signifies a growing recognition that strength and performance are not identical. However, to adopt the performance-based seismic design approach, it is essential to develop precise models for estimating damage and potential losses associated with various seismic force-resisting systems (SFRSs). Fragility functions are widely interpreted among the most prevalent damage and loss models. They establish a crucial link between specific demand parameters and the likelihood of exceeding various damage states. Although reinforced masonry (RM) structures have recently gained popularity, the seismic design of mid- to high-rise RM structures is still challenging because it requires a reliable SFRS capable of providing the needed ductility and capacity. Therefore, the main objective of this study is to evaluate the key seismic performance parameters (i.e., system overstrength and ductility) and to perform a collapse capacity risk assessment of reinforced masonry core walls with boundary elements (RMCW+BEs) as the main SFRS in RM structures. The current study utilizes the applied element method (AEM) implemented in the Extreme Loading for Structures software (ELS) to model three RM structures with various heights (10-, 15-, and 20-story buildings). Nonlinear pseudo- static pushover analysis was performed to quantify the ductility and overstrength of the proposed RM system following the FEMA P695 guidelines. In addition, an incremental dynamic analysis (IDA) was carried out to assess the seismic collapse risk of RMCW+BEs by generating system-level-based fragility curves. The results showed that the proposed RM system provides the needed ductility, overstrength and deformation capacity for a ductile SFRS for typical mid- and high-rise RM buildings. Furthermore, the developed collapse fragility curves verified excellent seismic performance, negligible collapse probability values and high reserved collapse capacity at the maximum considered earthquake (MCE) design level. The findings of this study significantly contribute toward adopting RMCW+BEs as an effective SFRS for typical RM buildings in the next generations of North American masonry design standards.

Seismic Collapse Risk Assessment and Fragility Analysis of Reinforced Masonry Core Walls with Boundary Elements Using the FEMA P695 Methodology

In the past, the primary objective of structural design codes was centred around ensuring human life safety, with a strong focus on preventing structural collapse. This approach predominantly relied on force- or strength-based criteria as the basis for design. Nevertheless, a notable shift has occurred recently, transitioning the design philosophy from 'strength' towards a 'performance'-based approach. This shift signifies a growing recognition that strength and performance are not identical. However, to adopt the performance-based seismic design approach, it is essential to develop precise models for estimating damage and potential losses associated with various seismic force-resisting systems (SFRSs). Fragility functions are widely interpreted among the most prevalent damage and loss models. They establish a crucial link between specific demand parameters and the likelihood of exceeding various damage states. Although reinforced masonry (RM) structures have recently gained popularity, the seismic design of mid- to high-rise RM structures is still challenging because it requires a reliable SFRS capable of providing the needed ductility and capacity. Therefore, the main objective of this study is to evaluate the key seismic performance parameters (i.e., system overstrength and ductility) and to perform a collapse capacity risk assessment of reinforced masonry core walls with boundary elements (RMCW+BEs) as the main SFRS in RM structures. The current study utilizes the applied element method (AEM) implemented in the Extreme Loading for Structures software (ELS) to model three RM structures with various heights (10-, 15-, and 20-story buildings). Nonlinear pseudo- static pushover analysis was performed to quantify the ductility and overstrength of the proposed RM system following the FEMA P695 guidelines. In addition, an incremental dynamic analysis (IDA) was carried out to assess the seismic collapse risk of RMCW+BEs by generating system-level-based fragility curves. The results showed that the proposed RM system provides the needed ductility, overstrength and deformation capacity for a ductile SFRS for typical mid- and high-rise RM buildings. Furthermore, the developed collapse fragility curves verified excellent seismic performance, negligible collapse probability values and high reserved collapse capacity at the maximum considered earthquake (MCE) design level. The findings of this study significantly contribute toward adopting RMCW+BEs as an effective SFRS for typical RM buildings in the next generations of North American masonry design standards.

Seismic evaluation of post-tensioned precast concrete frames with non-grouted fuse-type dissipaters under successive excitations

In recent years, demands for mitigating structural damage and post-earthquake repair costs have spurred considerable research on self-centering seismic force-resisting systems. This study evaluates the Post-tensioned Precast concrete Frame with non-grouted fuse-type Dissipaters (PPFD) through experimental and numerical methods. Quasi-static tests were conducted on a one-bay, single-story PPFD to investigate its seismic response. The tested PPFD was shown to effectively control damage to concrete components and limit residual displacements; imperfections at the beam-column interface joint had a negative effect on the initial stiffness and self-centering performance of the PPFD. Parametric analyses were then performed to discuss the force and deformation responses of the beam-column joint in the PPFD with dissipaters solely beneath the beam. A design method for the PPFD was developed based on the formulas derived and verified from the parametric analyses. Nonlinear dynamic analyses were then employed to evaluate prototype designed multi-story PPFDs subjected to individual earthquakes in addition to mainshock-aftershock sequences. The findings indicated that both configurations of PPFD, with dissipaters either symmetrically arranged on the beam or located exclusively below the beam, exhibited comparable maximum inter-story drifts and significantly smaller residual inter-story drifts than a comparable reinforced concrete frame. Moreover, the PPFD demonstrated only a minor increase in both the maximum and residual inter-story drifts when subjected to aftershocks, compared to a much larger increase for the reinforced concrete frame.

Vulnerability assessment of tall isolated steel building under variable earthquake hazard levels using endurance time method

ABSTRACT In this research, the superstructure behavior in isolated structures has been studied based on their ductility. For this purpose, three tall structures isolated by triple friction pendulum isolators (TFPI) have been designed. The ductility of superstructures is different due to their different seismic force-resisting systems. The performance of the structures has been evaluated by endurance time (ET) method. This method significantly reduces nonlinear dynamic analysis time by optimizing the number of desired earthquake records to one to three endurance time excitation functions (ETEFs). Additionally, the seismic response of structures under different earthquake hazard levels can be achieved by this method. Results show that the change in ratio of the isolator period to the superstructure period (TI/TS) can affect floor acceleration, TFPI displacement and interstory drift ratio (IDR). However, TFPI displacement and IDR are also sensitive to the type of superstructure system, whether it is a braced frame or a moment frame. Moreover, there is a possibility of entering the collapse phase of structural components in tall isolated structures with braced or moment frame which are designed by linear static and spectral methods, under an earthquake with a return period equal to the earthquake hazard level considered in the design step.

Case studies on the seismic resilience of reinforced concrete shear wall buildings and steel dual concentrically braced buildings

This paper investigates various performance measures to assess the seismic resilience of low-to-high-rise multistory RC shear wall and steel dual concentrically braced buildings as dual seismic force-resisting systems in California. The performance measures include the risk of structural collapse, earthquake-induced repair costs, life-cycle cost, repair times, and seismic resilience. Six buildings, consisting of five-, 10-, and 15-story configurations, were selected and analyzed using the response spectrum method. The design of these buildings followed the provisions of ASCE/SEI 7-16, ACI 318-14, and AISC 341-16. To accurately simulate the structural behavior, nonlinear numerical models of the buildings were developed in the OpenSees software. Response history analyses were conducted to evaluate the dynamic behavior of each building until structural collapse, considering far-field ground motion records from FEMA P-695. The study also utilized a probabilistic building-specific loss assessment methodology provided in FEMA P-58 guideline, which explicitly accounts for the main sources of variability related to earthquake hazards and structural response. In general, the results of the probabilistic seismic performance assessment demonstrated that the code-compliant steel dual concentrically braced buildings performed poorly compared to the RC shear wall buildings, regardless of the number of stories. Specifically, the steel dual concentrically braced buildings exhibited a lower resilience index, especially in the case of low-rise buildings (i.e., five-story) during strong earthquake events.

Comparative analyses of reinforced masonry and reinforced concrete shear walls with different end configurations: Seismic performance and economic assessment

Recent research has been demonstrating that fully-grouted reinforced masonry (RM) shear walls possess high ductile capacity levels that resulted in excellent performance under seismic loading. Considering the results of these studies, the current ductility modification factors assigned to such shear walls in relevant building codes and design standards are excessively conservative compared to the corresponding higher values assigned to their reinforced concrete (RC) counterparts. These conservative factors are mainly attributed to the lack of research studies that have been conducted to present direct comparisons between the performance of the two seismic force-resisting systems. To address this current knowledge gap and guide future editions of their relevant design standards based on experimental and analytical evidence, the objective of the current study is to show detailed comparative analyses between the performance of several RC and RM shear walls with different end configurations when both wall systems are subjected to similar seismic demands. These analyses also include a comprehensive economic assessment to equip practicing engineers and other relevant stakeholders with detailed comparisons between the two wall systems in terms of their construction costs. In this respect, six half-scaled RC shear walls were compared to three half-scaled RM shear walls, where all nine walls were tested under a quasi-static cyclic fully-reversed loading. The six RC shear walls were tested in two phases, where each phase consisted of three different wall types (i.e., rectangular, flanged, and boundary element walls) that had identical dimensions to their RM counterparts. To allow for direct comparison between the walls, Phase I RC walls with low vertical reinforcement ratios had similar lateral strength capacities as the RM walls, whereas Phase II RC walls with high vertical reinforcement ratios had similar ultimate curvature values as the RM walls. The comparison results are presented in the current study in terms of the crack patterns, load–displacement envelopes, curvature profiles, and wall displacements. Displacement ductility values, normalized periods, and equivalent viscous damping ratios are also presented for the nine walls. Finally, an economic assessment is performed to compare the walls in terms of their total rebar weights and approximate construction costs. The results demonstrate that RM shear walls can achieve an enhanced seismic performance similar to that of RC shear walls if the former walls are well-detailed (e.g., adequate confinement). Such an enhanced performance of RM shear walls is also coupled with low construction costs when compared to their RC counterparts. The current study enlarges the database of results that will facilitate assigning effective seismic performance metrics (e.g., ductility-related force modification factors) for RM shear wall buildings in future editions of building codes and design standards.

Structural Performance of Buildings with Tension-Only Braced Frame Under Seismic Loading

In accordance with SNI 1726-2019, structures with tension-only braced frames (ToBF) can be used as seismic force-resisting systems for seismic design category (SDC) A to C, with a height of up to 10m. Limited study was done on this subject, hence a numerical study was conducted to better understand the structural performance. The models studied were of regular structures of SDC D, varying in height. The analyses used modal response spectrum analysis (MRSA) for design, and linear response history analysis (LRHA) to evaluate the response. Finally, pushover analyses were conducted to determine the structural performance levels. The study shows that structural design can be done for all models using MRSA, satisfying all requirements. When evaluated using LRHA, results reveal that requirements were not satisfied for structures with heights exceeding 10m. Analysis when reviewed using pushover analysis, results show that the performance levels for all buildings are Immediate Occupancy. However, for models with height exceeding 10m, first yielding occurs at a lower base shear than the design base shear, indicating that the value of R used may not be adequate. Further review reveals that the ToBF can be used as a seismic force-resisting system, with proper design and arrangements.

Key Factors that Affect the Behavior of Steel Beams and Columns in Special Moment Frames

Steel Special Moment Frames (SMFs) are favored seismic force-resisting systems due to their architectural flexibility and high ductility. While shallow columns (section depth less than 356 mm) were commonly used in these systems before the Northridge earthquake, deeper columns (section depth greater than 356 mm) have become more popular in recent years to meet code-enforced story drift requirements economically. However, limited research exists on the hinging behavior of deep columns under axial compression and cyclic drift. Since deep columns exhibit larger slenderness ratios and are more susceptible to local and global buckling, understanding their behavior is crucial. This study investigates the behavior of fifteen four-story steel SMFs using finite element program simulations, focusing on four key factors affecting frame behavior: 1) Column bracing, 2) Beam bracing, 3) Column stiffening, and 4) Strong Column Weak Beam (SCWB) ratio. The influence of axial force level and column section properties is also examined. Results demonstrate that deep columns may experience local and/or global instabilities at relatively low story drift levels. Findings suggest that SMF performance can be enhanced by bracing deep columns at the top and bottom levels of beam flanges and adding stiffeners to the columns' web. Controlling column shortening by increasing the SCWB ratio is also recommended.

Experimental parametric study of perforated steel plate fuses for mass timber seismic force resisting systems

The lack of practical connections with reliable desired energy dissipation capacity as the main components of a seismic force resisting system (SFRS) is a major obstacle in using mass timber in tall buildings located in seismically active regions. A common method to dissipate seismic energy in timber structures is through the yielding of steel material found in the mechanical connections. Under the induced seismic motions, these dissipative connections are intended to yield while the rest of the structure remains intact with minimum damage. In this research, the focus is on the use of perforated steel plate as a dissipating energy device and a seismic fuse. Previous tests have demonstrated the potential use of perforated steel plates as seismic fuses in mass timber SFRS and confirmed their scalability and predictability. Despite promising results under monotonic loading, their behavior under cyclic loading can be improved. This paper presents an experimental parametric study investigating the effects of the number of rows, shape, and size of perforations, the steel plate thickness, and the steel link size on the mechanical performance of the perforated plates. The obtained hysteresis responses and envelope curves are compared. It is found that the ellipse and stagger patterns possess the largest ultimate displacement and stiffness, respectively. In addition, no significant enhancement in the ultimate deformation was observed in the cyclic response of the fuse, beyond three rows of perforations. Within the range of the configurations considered, the reduced ultimate deformation under cyclic loading remains a technical challenge that needs to be addressed if this type of seismic fuse is to be installed in SFRS. The results will assist with the design of future test programs on full-size mass timber connections consisting of such fuses.

Development of small-scale buckling-restrained brace analog for physical experiments of structural systems

Experimental testing is critical for evaluating the performance of novel structural systems. However, the cost of full-scale testing can be limiting. Small-scale testing provides a lower cost alternative that can produce reliable data if each component of the scaled model is properly developed. Given their stable hysteretic behavior, buckling-restrained braces (BRBs) are featured in several seismic force-resisting systems. The design of typical BRBs involves an axially yielding steel core that is prevented from buckling by a concrete casing. Designs for adaptable and easy-to-implement small-scale BRBs that can be included in structural testing have not been established. In this work, a small-scale BRB analog is developed that utilizes a core steel yielding plate that is prevented from buckling by a pair of steel casing plates. A flexural yielding mechanism is employed in the small-scale BRB analog, which allows for practical dimensions and the ability to independently tune brace stiffness and strength. Prototype braces were fabricated and validated through quasi-static cyclic testing in which they exhibited the full and stable hysteretic behavior characteristic of BRBs. To aid in the use of this BRB analog by others, numerical results were utilized to generate empirical equations that relate the strength and stiffness of the scaled BRB to the archetypical geometry of the core plate. Given its ability to deliver a stable hysteretic performance, the wide range of strength and stiffnesses that it can provide, and its easy reusability, the developed device is a good choice for experiments where a small-scale BRB analog is needed.

Methodology for determination of seismic force modification factors in Canada: Performance-based unified procedure

The National Building Code of Canada (NBC) employs seismic force modification factors (i.e. ductility-related factor, Rd, and an overstrength-related factor, Ro) for different Seismic Force Resisting Systems (SFRSs), which, since 2005, are largely based on engineering judgment and qualitative comparisons of seismic response characteristics of different SFRSs. Currently, there is no unified procedure in Canada for systematically quantifying these values, which has potentially led to perceived inconsistent levels of performance between buildings built with different SFRSs. While some research has been carried out in Canada to quantitatively evaluate the seismic response of different SFRSs using the FEMA P695 methodology with some modifications, inconsistencies exist among different research works. Moreover, the number of archetypes developed in these studies was limited, due to the computationally laborious incremental dynamic analysis (IDA) step in FEMA P695. Therefore, there is a need for a consistent and efficient methodology for structural performance assessment of different SFRSs in Canada. The proposed performance-based unified (PBU) procedure is to systematically quantify Rd and Ro factors for different SFRSs in the NBC. The PBU procedure is designed to be a performance-based approach (vs the risk-based approach of FEMA P695). In addition, our procedure is devised to optimize the number of archetypes through a two-level screening procedure using a nonlinear pushover and time history analyses before running the IDA. To validate the PBU procedure, we developed 21 different concrete moment frame archetypes covering various key parameters. The results verify the efficiency of the screening feature of the PBU procedure by a significant reduction in the number of archetypes requiring IDA.

Dynamic response of a Single-Degree-of-Freedom system containing Phase Transforming Cellular Materials

Repeatable superelastic behavior is a much sought after attribute in the field of earthquake engineering. Phase Transforming Cellular Materials (PXCMs) are architected materials that exhibit superelastic force–deformation behavior. PXCMs can be designed to exhibit nearly perfect elasto-plastic behavior, meaning they can undergo large deformations at nearly constant force. Moreover, PXCMs can return to their original configuration without permanent deformation on removal of the external load. The viability of integrating PXCMs in Seismic Force Resisting Systems (SFRS) of structures was investigated through dynamic testing of a simple Single-Degree-of-Freedom (SDOF) PXCM system. The response of the SDOF PXCM system was also compared with the response of systems constructed using traditional materials such as reinforced concrete. The tests and comparisons showed that 1) PXCMs are capable of exhibiting nonlinear behavior without accumulating damage when subjected to dynamic loads, and 2) PXCM systems are likely to displace less than similar systems constructed using traditional materials. Hence, it was concluded that PXCMs can supplement existing building materials to enhance the overall seismic performance of a structure.

Development of Near-Field Earthquake Loading Protocols for the Steel Moment Connections in Iran

Steel moment frame buildings are widely used in Iran and around the world. The observations from major earthquakes underscored the importance of the beam-to-column connections in seismic force-resisting systems and their influence on such building’s performance. Since the most catastrophic earthquakes that occurred in Iran contained the characteristics of near-field earthquakes, hence understanding the behavior of these connections under such earthquakes is needed. This study proposed loading protocols for special steel moment-resisting frame systems under near-field earthquakes in Iran. Each of them had 23 damage half-cycles with a maximum inter-story drift of 0.065 radians. The proposed loading protocols were compared numerically to each other. The most influential one was chosen as the main loading protocol since it has the most destructive effect on the connection. The main loading protocol showed a faster rate of increase in the plastic strain and imposed the highest amount of dissipated energy at a former loading stage compared to other near-field earthquake loading protocols related to other countries such as SAC and Fang et al.

Seismic performance of modular steel buildings (MSBs) equipped with resilient slip friction joints (RSFJs)

Modular construction is becoming a prevalent technique combining off-site construction and on-site assembly to provide fast, reliable and high-quality permanent buildings. The modular method is a good alternative to traditional on-site construction when the layout consists of repetitive units such as hotels and multifamily dwellings, and when the construction schedule is tight. The dynamic performance of Modular Steel Buildings (MSBs) has not yet been fully studied, and a limited number of investigations on the nonlinear dynamic behavior of MSBs showed that they are susceptible to damage during strong ground motions. This paper considers the use of a self-centering energy dissipation device, called Resilient Slip Friction Joint (RSFJ), in MSBs to avoid seismic damage, enable immediate occupancy, and reduce the repair costs after a severe earthquake event. Two different configurations of RSFJs (namely tension-compression and tension-only configurations) were introduced to Seismic Force Resisting Systems (SFRSs) of 6- and 12-story MSBs. This study presents a step-by-step design procedure by following the capacity design for RSFJs in accordance to National Building Code of Canada (NBCC). The dynamic performances of both configurations were evaluated by performing bi-directional Nonlinear Time History Analysis (NLTHA). In addition to global response of MSBs, component level maximum demands of RSFJs were assessed to shed a light on the overall performance of MSBs under three different hazard levels. It was shown that low- and mid-rise MSBs can efficiently be equipped with RSFJ to mitigate earthquake-induced vibrations and minimize the damage to the structural members.

Nonlinear static and dynamic behaviors assessment of self-centering post-tensioned concrete wall with multiple-slit device

Conventional seismic force-resisting systems usually experience significant structural damage, and repairing such buildings is not economical. A new type of seismic force-resisting system is self-centering Post-Tensioned Concrete Wall (PT-CW), in which vertical Post-Tensioned (PT) cables supply the return force of the structure to its initial state. This study is dedicated to investigate the seismic behavior of the self-centering PT-CW system using nonlinear static, cyclic, and response history analyses. The loading and design of the studied buildings are performed in the 3D model, then one of the frames is selected and the nonlinear analyses are done in OpenSees software. In order to increase the absorption energy of PT-CW, a Multi-Slit Device (MSD) is employed. For this purpose, three systems including PT-CW with Energy Dissipators (ED) bars, PT-CW with MSD, and traditional Concrete Shear Wall (CSW) are modeled in Opensees software. These seismic force-resisting systems are applied into three, six, and ten-story buildings. To validate the proposed models, the results of an experimental study are applied. Then, the nonlinear responses of the introduced models are numerically obtained as well. Accordingly, the PT-CW with MSD has more ductility and less strength drop than the other two systems. Finally, ten far-field earthquake records are selected and scaled with the ASCE spectrum to implement NRH analysis. As a result, it is observed that the story drift of the PT-CW with MSD under the applied earthquake records is almost uniform and less than the PT-CW with ED bars.

Seismic performance of controlled-rocking concentrically braced frames designed by the equivalent energy procedure

Recent earthquakes in New Zealand and Japan showed that structures designed according to modern building codes might suffer significant damages with hefty financial and social losses. The primary reason lies in the seismic design approach, where most seismic force resisting systems (SFRS) were designed to prevent structures from collapse during strong earthquake shaking, without considering the damage and the usability of the structure after an earthquake. In this paper, a controlled rocking-concentrically braced frame (CR-CBF) is proposed. CR-CBF is a fused structural system that uses a combination of post-tensioned tendons (PTs) and energy dissipation devices (EDs) to create a controlled-rocking mechanism to minimize structural repair costs and down time after a strong earthquake. PTs are placed in the structure to provide the restoring forces and to minimize any residual deformation in the structure, while EDs are placed at the base of a structure to dissipate the earthquake energy. To ensure the CR-CBF can achieve high performance, two (CR-CBF) prototypes with different heights are designed using the novel equivalent energy design procedure (EEDP). The EEDP procedure allows designers to select different performance objectives at different shaking intensities. The results of nonlinear dynamic analyses of the CR-CBFs show that CR-CBFs have superior seismic performances as intended and can be efficiently designed using EEDP. Finally, the seismic performance of CR-CBF against collapse is assessed using incremental dynamic analysis (IDA) outlined in the FEMA-P695 methodology. The results show that the CR-CBFs designed by EEDP have sufficient safety against collapse, hence it can be used as an efficient seismic force resisting system.

A novel floor-isolated re-centering system for prefabricated modular mass timber construction – Concept development and preliminary evaluation

Prefabricated modular mass timber (MT) construction provides a resource-efficient, consistent-quality, and eco-friendly solution for the building industry. Connections that facilitate the assembly of prefabricated modules to form the final structure usually do not possess the characteristics needed for performance of these systems in high seismic zones. In this study, a novel seismic force resisting system called FIRMOCS that incorporates floor-isolation and re-centering techniques, is proposed for the prefabricated modular MT construction. Finite element models of the Floor Isolated Re-entering Modular Construction System (FIRMOCS) and of regular modular construction Seismic Force Resisting Systems (SFRS) were developed in ABAQUS, a general-purpose finite element program. The seismic performance of the regular prefabricated modular MT SFRS and that of FIRMOC systems was evaluated using nonlinear dynamic time-history analysis along the principles of the National Building Code of Canada. The preliminary results showed that FIRMOC Systems significantly reduced the seismic demand on the prefabricated modular MT construction, thus leading to improved seismic response. Using the proposed novel SFRS, an efficient and resilient prefabricated modular MT construction solutions can be achieved in high seismic zones.

Reliability of displacement capacity prediction models for reinforced concrete block shear walls

Reinforced concrete block (masonry) shear wall construction presents an economic solution for seismic resistant low- and mid-rise buildings throughout North America. In this respect, wall displacements are output, based on wall characteristics, when force-based seismic design approaches are used. In displacement-based seismic design approaches, however, target displacements are the key input needed for wall design. As large displacement demands develop within the building seismic force resisting systems (SFRS), inelastic strain, curvature, and rotation demands are expected within specific wall zones, idealized as equivalent plastic hinges. In this study, eight different models are utilized to predict the maximum displacement capacities of reinforced concrete block shear walls (RCBSW). The experimental results of 81 RCBSW have been used to evaluate the reliability of the eight models. According to the analysis performed in this study, none of the eight models was found to be reliable in terms of predicting the maximum displacement capacity when compared to the corresponding experimental results. In an attempt to further improve the predictability of these models, calibration coefficients are introduced and the corresponding improved results are re-assessed. Based on its better capability of capturing the experimental results, one of these calibrated models is selected to further investigate the influence of altering the wall design characteristics on their maximum displacement capacities. Overall, this study aims at improving RCBSW-SFRS displacement capacity prediction models, thus contributing to the efforts towards adopting displacement-based design provisions in future seismic codes.

Experimental seismic behavior of a two-story CLT platform building

Cross-laminated timber (CLT) manufacturing and construction has been steadily growing since its inception in Europe in the 1990s. In the US, the growth of the CLT adoption is inhibited by the lack of codified design provisions for CLT in high seismic regions. This led to a multi-year study conducted by Colorado State University to investigate suitable seismic design parameters of CLT shear wall systems. This paper presents the results from a series of shake-table tests featuring a full-scale two-story mass-timber building utilizing CLT Seismic Force Resisting Systems (SFRS). The building was designed using an R- factor equal to 4.0 under the equivalent lateral force procedure specifications of the ASCE 7-16 Standard. The test program included three phases with different wall configurations, reflecting different wall panel aspect ratios and the existence of transverse CLT walls. Test results indicate that the code-level life safety objective was achieved in all test configurations. The addition of transverse walls did not affect the ability of the panels to rock, and improved the performance of the building structural system.

Seismic fatigue behavior of in-plane deformational metallic energy dissipating devices

The metallic energy dissipating devices (MEDDs) have been developed to mitigate structural damage in the manner that they mainly dissipate seismic input energy rather than typical structural components. Of MEDDs, in-plane deformational metallic energy dissipating devices (IPMDs) are widely used to seismic force-resisting systems (SFRSs) in moderate and low-seismicity regions which are expected to relatively small seismic deformation demands since they effectively dissipate seismic energy throughout the yielding at small displacements obtained from relatively high initial lateral stiffness. However, IPMDs could be fractured due to their small deformation capacities and low-resistance to low-cycle fatigue failures. Even if potential problems of IPMDs exist, a current seismic code requires only a few tests of five-full-reversal cycles with a displacement amplitude expected at a very rare strong earthquake and does not provide specific requirements that can remove concern about such fatigue failures under strong earthquake. In this reason, the low-cycle fatigue behavior of IPMDs installed in SFRSs needs to be discussed in depth. To address this, this study performs nonlinear dynamic analyses of prototype SFRSs employing MEDDs and investigates fatigue damage states of MEDDs based on the strain-based approach. The analytic results show that the more rigorous requirements are required to ensure the target collapse probability under the maximum considered earthquakes (MCEs) and, in turn, to guarantee the seismic performance of structures employing MEDDs with preventing their low-cycle fatigue failures.