Maximum Considered Earthquake Research Articles

Multiple performance objective design for a sliding isolator with variable curvature

Thanks to its variable mechanical properties, the sliding isolator with variable curvature (SIVC) has recently attracted significant attention in seismic isolation research. Nevertheless, designing an SIVC is a challenging task, as it usually involves more design parameters than a conventional sliding isolator. To expedite the application of SIVCs, this study proposes a systematic design method that enables SIVCs to achieve multiple performance objectives corresponding to dual earthquake levels. The method comprises linear and nonlinear design stages. During the linear design stage, the linearized isolator parameters that comply with the design-basis-earthquake (DBE) and maximum-considered-earthquake (MCE) seismic demands specified in a design code are determined. Subsequently, in the nonlinear design stage, the isolator geometric parameters are determined based on the linearized parameters. While the linear design procedure is generic and applicable to all types of SIVCs, the derived formulas for determining the isolator geometric parameters in the nonlinear design stage are tailored for the polynomial friction pendulum isolator (PFPI). Finally, the proposed method is demonstrated by implementing a PFPI design for a 5-story reinforced-concrete (RC) building. The effectiveness of the proposed design method is validated through dynamic analysis of a hysteretic structural model representing the RC building with two different types of PFPIs subjected to 23 spectrum-compatible ground motions. The results demonstrate that, despite their different mechanical features, both types of PFPIs can accomplish the “preset” DBE and MCE design objectives. Additionally, the simulated results highlight the advantages of using different types of PFPIs.

Development and validation analysis of a steel-lead hybrid dual-yield BRB for multi-stage seismic energy dissipation

To address the limitations inherent in conventional all-steel buckling restrained braces (BRBs) that maintain elastic behavior and lack seismic energy dissipation during frequent earthquakes (FEs), this study proposes a novel approach of combining lead dampers with BRB, forming the development of steel-lead hybrid dual-yield BRB (or simply dual-yield BRB). Integrating lead material into the dual-yield BRB harnesses its dynamic recrystallization capacity, allowing the lead dampers to yield and efficiently dissipate seismic energy during FEs via well-designed configurations. This study delineates the approach for connecting lead dampers to BRBs and performs comparative quasi-static tests on dual-yield BRBs and conventional BRBs. Key observations from the laboratory tests confirmed that lead dampers experience earlier failure compared to inner cores. Dual-yield BRB exhibited significantly lower initial displacement requirements for energy dissipation than conventional BRB, demonstrating a hexagonal hysteretic curve, trilinear behavior in the skeleton curve, and superior overall energy dissipation capacity at small displacements. The feasible strategy of refined numerical simulations was initially validated based on experimental results. Subsequently, to enhance analysis efficiency, simplified models using truss elements were developed and endorsed. Elasto-plastic time history analyses were performed on benchmark models of 9-story steel frames, considering scenarios with no bracing, conventional BRBs, and dual-yield BRBs, exposed to FEs and maximum considered earthquakes (MCEs). Various parameters, including component forces, structural displacement and damping underwent thorough examination. These findings underscore the exceptional seismic performance and energy dissipation abilities of dual-yield BRBs, solidifying them as a valuable addition to earthquake-resistant structural systems.

Seismic assessment of the in‐plane/out‐of‐plane interaction of masonry infills in a two‐storey RC building subjected to bi‐directional shaking table tests

AbstractThis paper presents a series of shaking table tests conducted on a 60%‐scaled two‐storey infilled reinforced concrete building. The main parameters include the presence of openings in the masonry infills and the effect of bi‐directional dynamic shaking to the latter. The building was subjected to four different levels of shaking intensity, ranging up to the Maximum Considered Earthquake (MCE), equivalent to 150% of the design earthquake. The study focuses on and evaluates the damage caused by combined in‐ and out‐of‐plane shaking. Under the design level earthquake, the second‐storey infill walls with openings were severely damaged, with near‐collapse of a masonry pier. For the fully infilled direction without openings instead, diagonal cracking as well as out‐of‐plane inclination of the infill wall in the second storey were observed. Due to the interaction between the two loading directions and the direct adverse effect of the in‐plane damage on the out‐of‐plane resistance of the infills, the out‐of‐plane collapse of 3/4 of the second storey masonry infill occurred during the MCE. The reported damage observations on the masonry‐infills with or without openings provide further insights on the vulnerability of non‐seismically designed reinforced concrete buildings. Additionally, the seismic performance of the structure is assessed using further structural response quantities recorded during testing, including floor accelerations, inter‐storey drifts, base shear forces and reductions in natural frequency. Future testing will focus on investigating the effectiveness of retrofitting measures in improving the connection between the infill and frame, reducing in‐plane damage, and preventing out‐of‐plane failure of the infills.

Seismic design and performance evaluation of steel braced frames with post-tensioned and disc-spring-based self-centering buckling-restrained braces

In this study, we focus on two types of self-centering buckling-restrained braces (SC-BRBs), which are post-tensioned (PT) SC-BRB and disc-spring-based SC-BRB, and develop a seismic design method for steel braced frames with these braces according to the displacement-based design theory. The whole independent parameters that describe the hysteretic behavior of the SC-BRBs are first determined. Then nonlinear time history analysis (NLTHA) is conducted to explore the effects of these hysteretic parameters on the ductility demands of the nonlinear single-degree-of-freedom (SDOF) system. Based on the analysis results, a ductility demand spectral model is developed, followed by a nonlinear displacement ratio spectral model. Subsequently, the seismic design procedure for SC-BRB frames is proposed based on the two spectral models. Finally, a total of 24 six-story steel frames with the two types of SC-BRBs, two target inter-story drifts, and different parameter combinations are designed at the maximum considered earthquake (MCE) level. The pushover analysis and NLTHA results indicate that a smaller strength ratio β and a larger initial stiffness ratio αs are beneficial for reducing the base shear and obtain an economical design when the designed frames achieve the same target inter-story drift. Considering the initial stiffness of the SC-BRBs is highly sensitive to machining errors, it is recommended that the value of β be taken within 0.25 to reduce the influence of the initial stiffness uncertainty of the braces on seismic design results. Moreover, controlling β within 0.25 also helps to reduce the higher-mode effect and peak floor acceleration responses of the designed structures effectively.

Seismic Performance Assessment of Composite Frame–High-Strength Steel Plate Wall Core Tube Resilient Structural System

Against the backdrop of China’s continuous promotion of green and low-carbon transformation and the development of construction industrialization, high-strength composite structural systems have significant development prospects. However, their research and application in the field of construction are insufficient. In response to this issue, the study proposes a new high-performance structural system, namely the composite frame–high-strength steel plate wall core tube resilient structural system, which includes a core tube composed of double steel plate concrete composite shear walls and replaceable energy dissipation coupling beams, as well as composite frames. The highest strength grades of the steel plate and concrete used in the composite walls of the core tube are Q550 and C100, respectively. Using a 200 m building as an example, this study designs and establishes models for this high-performance structure and a conventional reinforced concrete frame–core tube structure. Subsequently, the dynamic elastoplastic time history analysis and seismic resilience assessment of structures are conducted under design basis earthquakes (DBEs), maximum considered earthquakes (MCEs), and extremely rare earthquakes (EREs). Research has shown that, compared to conventional structures, the thickness of shear walls of new high-performance structures can be effectively reduced, which helps decrease the self-weight of the structure and improve the available space in buildings. Additionally, high-performance structures exhibit a better performance in controlling the story drift ratio, lower plastic damage and overall stiffness degradation of the structure, and better seismic performance. The seismic resilience of the high-performance structure has been significantly enhanced, especially in terms of minimizing casualties, thereby better ensuring the safety of people’s lives and property.

A two-level performance-based plastic design method for multi-story steel frames with double-yielding systems

The performance-based seismic design (PBSD) is usually conducted under design basis earthquakes (DBE), and then, the performance of the designed structures is examined under maximum considered earthquakes (MCE). As a result, it is challenging to simultaneously satisfy the performance targets associated with the DBE and MCE levels. To this end, this study proposes a two-level performance-based plastic design (PBPD) method. The fused steel frames exhibiting trilinear capacity curves are selected as the example structures. The peak interstory drift ratios under the DBE and MCE levels are defined as the performance targets and they are explicitly utilized at the beginning of the design procedure. The expressions of two energy modification factors are first obtained by establishing energy balance equations for single-degree-of-freedom (SDOF) systems under the DBE and MCE levels, respectively. Nonlinear time history analyses (NLTHA) for SDOF systems with various trilinear capacity curves are conducted to derive necessary design parameters. The versatility and flexibility of this design method are achieved by enabling both the primary and secondary yielding systems to yield under the DBE level. To demonstrate and validate the proposed design method, a six-story benchmark steel frame equipped with idealized metallic yielding damping braces is selected and designed with two sets of performance targets. The nonlinear static and NLTHA results proved that the designed structures can simultaneously meet the prescribed performance targets under both DBE and MCE levels.

Seismic Performance Evaluation and Comparative Study of Reinforced Concrete Building on a Sloped Terrain with Regular Building by Considering the Effect of URM Infill Walls

This paper focuses on the seismic vulnerabilities of multi-storey buildings in hilly regions like Sikkim and Uttarakhand, where rapid construction is driven by population growth and tourism. The study particularly evaluates step-back buildings on hilly slopes, comparing their vulnerability to standard buildings on flat terrain. Using non-linear analysis to assess structural aspects like displacement and storey drift ratio, the research examines the performance of these buildings in both uphill and downhill orientations against typical three-storey and six-storey structures, respectively. The findings indicate that step-back buildings, especially those without infill walls, are more susceptible to seismic damage. For instance, on the uphill side, a step-back building shows a mean drift ratio 15.11% greater in the X direction and 4.57% greater in the Y direction compared to a three-storey regular building (3SR). This vulnerability is exacerbated when infill walls are absent, with mean drift ratios in step-back buildings being 74.75% and 33% higher in the X and Y directions, respectively. Moreover, at a seismic acceleration of 0.36 g, the mean displacement of a step-back building is 83% greater in the X direction and 51% greater in the Y direction than those with infill walls (SBIN), underscoring the significant role of infill walls in enhancing earthquake resilience. The study also highlights that short columns in step-back buildings are particularly prone to severe damage, especially just above the uppermost foundation level. While infill walls offer substantial mitigation of damage at the Design Basis Earthquake (DBE) level, at the Maximum Considered Earthquake (MCE) level, step-back buildings still endure severe damage compared to regular buildings with infill walls. Consequently, the research establishes that step-back buildings demonstrate greater vulnerability at DBE levels without infill walls and are more susceptible to damage than flat terrain buildings at MCE levels, emphasizing the need for careful design and reinforcement strategies in earthquake-prone hilly areas.

Parametric Investigation of Self-Centering Prestressed Concrete Frame Structures with Variable Friction Dampers

To enhance the structural stiffness and energy-dissipating capacity after the decompression of beam-to-column connections for self-centering prestressed concrete (SCPC) frames, this study presents the seismic performance of a new type of SCPC frame with variable friction dampers (VFDs). The structure is characterized by a third stiffness and a variable energy-dissipating capacity. A 5-story and an 8-story VFD-SCPC frame were selected as the analytical cases, and their numerical models were built based on OpenSees 3.3.0 finite-element software. Sixteen ground-motion records were selected as excitations for the analyses, and the influence of the second stiffness and the third stiffness for the VFD-SCPC connections, as well as the second activation for VFD, on the seismic performance of the structures, was studied. The results showed that increasing the stiffness (number) of prestressed strands and their distance to the center of the beam section can obviously increase the second stiffness of the structures, thus decreasing their displacement, while the distribution mode of inter-story drift along the building’s height cannot be changed. Increasing the third stiffness of the connections (the angle of slope sliding parts and the stiffness for the combination of disc springs) can effectively reduce the deformation of the structures under MCE (maximum-considered earthquakes) seismic levels and improve the energy-dissipation capacity of structures significantly. The premature secondary activation of VFD can enhance the loading capacity and energy-dissipation capacity of structures under both DBE (design-basis earthquakes) and MCE seismic levels, and reduce the inter-story drift of structures effectively.

Behavior of Anchors Embedded in Concrete Damaged by the Maximum Considered Earthquake: An Experimental Study

The article presents experimental tests carried out to investigate the effect of crack width (0.4, 0.8, 1.5, and 3.0 mm) on the behavior of anchor bolts under static and dynamic loading. Ultimate loads for anchors reached 220 kN depending on the anchor type, the diameter, and the crack opening width. Mechanical and bonded anchors were studied as the most frequently used anchor types. Two states of concrete, resulting from the design earthquake and the maximum considered earthquake, were simulated in the course of the experiments. Within the framework of the study, dependencies between the bearing capacity and stiffness of anchorages, on the one hand, and the level of concrete damage, on the other hand, were identified for different types of anchors. The data, generated in the course of the study, were used to identify the types of anchorages recommended for embedment in seismic areas. Plasticity coefficients and seismic load reduction coefficients were determined for different types of anchors and levels of concrete damage as a result of experimental studies. Reduction coefficients can be contributed to the design of anchorages embedded in seismic areas.

System-level seismic fragility of high-speed railway track-bridge system with component-replaceable U-shaped combined steel damper

A component-replaceable U-shaped combined steel damper (UCSD) was presented as an energy dissipation device to mitigate the seismic damage of high-speed railway track-bridge system (HSRTBS). The energy-dissipation modules inside the UCSD can be replaced by removing the high-tensile bolts. A low cyclic test of the energy dissipation module was carried out. Parametric analysis of the UCSD with varying U-shaped plate thicknesses was conducted using finite element analysis, including 8, 10, 12, 14, and 16 mm. To study the effect of the UCSD on HSRTBS under near-fault ground motions, twenty-eight near-fault records recommended by FEMA-P695 were selected, and the UCSD was installed adjacent to bearings in HSRTBS. Component-level fragility curves of HSRTBS with UCSDs with the different thicknesses of U-shaped plates were compared. To comprehensively and efficiently evaluate the contribution of the UCSDs on HSRTBS, system-level fragility curves were obtained by the product of the conditional marginal (PCM) method. Results indicate that the UCSD exhibits excellent hysteresis performance and energy dissipation capacity, improving with the U-shaped plate. At the maximum considered earthquakes (MCE) level, the exceeding probability of complete damage of the system is reduced from 100 % to 95 %, 79 %, 57 %, 35 %, and 20 % respectively after adding UCSDs in five different U-shaped plate thicknesses. This reveals that the proposed UCSD can effectively mitigate HSRTBS seismic damage under near-fault motions, progressively improving with increased U-shaped plate thickness.

Reliability analysis of two archetype RC buildings with hysteretic dampers

The manuscript deals with a study on the performance/reliability analysis of steel hysteretic dampers designed for the seismic retrofit of RC frame structures at the Basic Design Earthquake, BDE (characterized by a 10 % probability of being exceeded over the reference lifespan, VR) for higher hazard levels, represented by a Maximum Considered Earthquake, MCE, with either 5 %/VR or 2.5 %/VR exceedance probabilities. Indeed, seismic codes prescribe that anti-seismic devices designed to satisfy the performance requirements at the BDE must be able to resist earthquakes of higher intensity. Therefore, γ-factors amplifying the design displacement or force must be considered for the design of the device capacity.The objective of the study consists in evaluating the over-demand caused on the steel dampers incorporated in dissipative bracing systems when passing from the BDE to the two higher hazard levels, and comparing this over-demand to the values of the corresponding γ-factors proposed in current codes. Dampers with various ductility factors are considered to include the majority of current hysteretic devices.The amplification factors recommended in the codes for hysteretic dampers are shown to be not suitable for guaranteeing the damper reliability; moreover, a dependence of the reliability of the retrofitted structures upon the ductility of the damped braces is highlighted.

Enhancing seismic performance of buckling-restrained brace frames equipped with innovative bracing systems

Nowadays, to improve the performance of conventional bracing systems, in which, buckling in the pressure loads is the main disadvantage, the buckling-restrained brace (BRB) is introduced as a solution. In this study, the performance of the BRB system was improved with innovative lateral-resisting systems of double-stage yield buckling-restrained brace (DYB), and a combination of DYB improved with shape memory alloy (SMA) materials (DYBSMA). The proposed systems have been verified and implemented in the 2- to 12-story elevation steel buckling-restrained brace frames (BRBFs). To evaluate their effects on the seismic performance, two types of analysis including nonlinear dynamic analysis (NDA) and incremental dynamic analysis (IDA) were performed considering design-based earthquakes (DBE) and maximum considered earthquakes (MCE) levels for far-field ground motions. The results showed that the BRB system in all BRBFs had the highest values of residual drift ratio (RDRMed) demands, while implementing innovative DYBSMA can considerably reduce the values of RDRMed compared to other lateral-resisting systems. In addition, under MCE level, the BRB-DYBSMA system had lower values of the interstory drift ratio (IDRMed) and RDRMed demands (e.g., the IDRMed reduced by 79.67% and 18.5% compared to BRB and DYB systems, respectively), and can be introduced as the best lateral-resisting system. Therefore, the proposed BRB-DYBSMA system can effectively reduce the IDRMed and RDRMed demands, as result, higher performance levels can be achieved, as well as, the collapse probability occurrence over 1 and 50 years impressively decreased.

Effect of pulse on fragility curves of buckling-restrained braced frames

To investigate the effect of presence of the pulse in earthquake motions on the vulnerability of buckling-restrained braced frames (BRBFs), this technical note uses pulse-like ground motions (original records) and their residual parts obtained by extracting the pulse via wavelet analysis, as input vibrations. Conducting the numerical simulation of 4, 8, 12, and 15-storey BRBFs, their responses to the scaled original and residual motions are recorded using incremental dynamic analysis (IDA). Accordingly, the seismic performance of BRBFs is generally evaluated, and fragility curves are developed at collapse prevention (CP), life safety (LS), and immediate occupancy (IO) performance levels. The results indicate that a maximum difference of about 25%–30% may occur between the fragility curves due to the original and residual parts of ground motions at the maximum considered earthquake (MCE) intensity level for 8, 12, and 15-storey BRBFs, so that the original records lead to a severe damage in comparison with the residual ones. Also, the original records increase the probability by 20% on average compared to the residual records at the LS level for the considered BRBFs.

Evaluation of the Seismic Performance of Single-Plate Metallic Slit Dampers Using Experimental and Numerical Data

Passive energy dissipation systems and devices are helpful in mitigating the danger of earthquake damage to structures. Metallic slit dampers (MSDs) are one of the most efficient and cost-effective solutions for decreasing seismic energy intake. The potential importance of MSDs in managing vibrations and limiting structural fatigue continues to grow as research advances and new materials and designs are introduced. This study evaluated the seismic performance of single-plate MSDs (SPMSDs) through a combination of numerical simulation and assessment of experimental results. ABAQUS software was used to create an assembly consisting of endplates, bolts, and SPMSDs. A real-world earthquake scenario was simulated using cyclic loads based on ASCE/SEI standards, and displacement-measuring devices such as strain gauges and LVDT were employed to record the behavior of the SPMSDs. The results of the experiment are used to assess the compliance of the SPMSDs and discuss their behavior as they undergo minimum and maximum displacements due to minimum and maximum applied forces. The energy dissipation capabilities of the dampers are presented by analyzing and comparing the area of their hysteresis loops, equivalent viscous damping, and their damping ratios. Actual failure modes are identified and shown to describe the limitations and potential vulnerability of the dampers. The relative error between the lowest and greatest recorded forces from experimental data and numerical simulation ranges from 4.4% to 5.7% for SPMSD 1 and from 1.6% to 2.1% for SPMSD 2, respectively. These deviation values represent a satisfactory level of precision, demonstrating that the numerical simulation accurately predicts the actual performance and behavior of the dampers when subjected to cyclic stress. The topology optimization performed in this study yielded an improved geometry of the SPMSD suited for a corresponding maximum considered earthquake (MCER) displacement of ±33 mm. This research also suggests practical implementations of the investigated and improved SPMSDs.

SMA-braced steel frames influenced by temperature: Practical modelling strategy and probabilistic performance assessment

This study presents a practical and efficient modelling approach for shape memory alloy (SMA)-braced steel frames under various temperatures, and examines their probabilistic performance affected by temperature. A one-dimensional constitutive model is developed in OpenSees to capture the superelasticity (SE), partial SE, shape memory effect (SME), and permanent yielding behaviors of SMA elements subjected to varying temperatures. The proposed modelling approach is partly validated against an experimental study newly conducted in the present work. The material-level investigation is followed by a comprehensive probabilistic performance assessment of a typical steel frame employing SMA-based self-centering braces (SMA-SCBs), where a practical and realistic modelling strategy for the SMA-SCB is developed to capture the degradation behavior, especially at low temperatures. Seismic risk assessment is conducted to evaluate the collapse resistance and resilience performance of the considered structures, with the influence of temperature highlighted. Among other important findings, it is shown that the decrease in environment temperature significantly increases the peak inter-story drift (PID) and residual inter-story drift (RID) responses. Under the maximum considered earthquake (MCE), the probability of collapse increases from 2.7% to 19.7% when the temperature decreases from 30 °C to −15 °C. From a self-centering capability point of view, the probabilistic of exceedance of 0.5% RID threshold soars from negligible to nearly 100%, considering the same temperature variation. The study highlights the fact that temperature plays a significant role in the annual rate of exceedance of all damage states, and warns that the idealized flag-shaped modelling approach for SMA components is extremely unsafe at low temperatures.

Hybrid simulation test and seismic assessment of CFDST moment resisting frame

Concrete filled double skin steel tubular (CFDST) moment resisting frame is an effective structural system owing to the higher strength to weight ratio and better fire performance compared with traditional concrete filled steel tubular (CFST) structures. This paper aims to analyze the seismic response of assembled CFDST moment resisting frame with blind bolted joints by the hybrid simulation test and numerical approaches. A prototype CFDST moment resisting frame was designed and its numerical model was established by Opensees software. After the validation of the numerical model, typical failure modes and dynamic response of the CFDST moment resisting frame observed from the hybrid simulation test were detected and discussed under maximum-considered earthquake (MCE) and 2MCE levels (2 times MCE level), respectively. Detailed behavior of the columns and joints were analyzed for the prototype building. It verified that a large portion of energy was dissipated by the joints under seismic loads. Subsequently, parametric analyses were performed to study the influence of joint stiffness on the global behavior of CFDST moment resisting frames by the endurance time method. The energy dissipated by the columns and joints were investigated in detail, indicating that the energy dissipated by the joints was more than 70% of the total hysteretic energy of the frame under earthquakes. It indicated that decreasing the joint stiffness was beneficial for the joint to dissipate more energy and for protecting the column from being damaged. It also generalized that decreasing the joint stiffness had a positive contribution to the uniform story drift distribution and would not always increase the maximum story drift. The analysis results verified that the CFDST moment resisting frame exhibited excellent seismic behavior and activated the application of CFDST moment resisting in engineering practice.

Full‐scale shaking table test and numerical analysis of structural frames with SMA cable‐restrained base isolation

AbstractRestrainer is a promising solution for deformation control of isolated systems. The present study comprehensively discusses the behavior, design and potential application of a novel superelastic shape memory alloy (SMA) cable‐restrained laminated natural rubber (SMA‐LNR) bearing. The study commences with a brief introduction of the working principle, and then a quasi‐static test on an individual bearing specimen is presented. A full‐scale shaking table test is subsequently presented, followed by a comprehensive parametric study, leading to preliminary design recommendations. The quasi‐static test shows a two‐stage behavior exhibited by the individual SMA‐LNR bearing, that is, linear flexible behavior at small displacements and restraining stage beyond initial gap. Under dynamic excitations, the SMA cables swayed smoothly with the shear deformation of the bearings, and experienced fracture beyond the maximum considered earthquake (MCE). The restraining effect is strengthened with increasing number of SMA cables, but this is accompanied by an increase in the acceleration response of the superstructure. An earlier engagement of the SMA cables, that is, smaller initial gap, leads to decreases in the bearing deformation. The acceleration responses of the superstructure and the maximum cable strain are not very sensitive to the initial gap. Using an overly small number of SMA cables has limited beneficial effect on bearing deformation control, and may even increase the deformation under certain excitations; therefore, a lower‐bound restraining force offered by SMA cables should be given to ensure an unconditional positive bearing deformation control. Two normalized design parameters and their recommended values are finally proposed to facilitate practical design.

Development of Risk-targeted Seismic Hazard Maps for Low-rise and Mid-rise Reinforced Concrete Buildings in the Philippines

The seismic hazard maps of the Philippines provide spectral acceleration mean values that describe the probability of occurrence of area-specific ground motion hazards due to earthquakes in the country. However other countries have progressed from developing hazard maps to risk-targeted maps that include information on the probability of collapse of buildings. This is the research gap that this study aims to bridge and, thus, developed maps of risk-targeted ground motions (RTGM) for the Philippines using the City of Manila as the area of focus. The maps will be created using the procedure suggested in ASCE 7-16 in obtaining the risk-targeted maximum considered earthquake (MCER). The probabilistic MCER will be created using the information obtained from the seismic hazard and the generic fragility curve that will represent the performance of buildings during a maximum considered earthquake (MCE) event. In this study, the seismic hazards were obtained using the same procedure, decision-making, and empirical formula as the one used in developing the Spectral Acceleration Maps of the Philippines (SAM PH). While the generic fragility curve was described by a function with a lognormal standard deviation, β, of 0.7. With a considered risk level of 1% probability of collapse in 50 yr, the developed RTGM maps are presented in this study. In the analysis of results, the probabilistic MCER is lesser than the MCE level spectral accelerations in the majority of the area in Manila due to the influence of the building’s collapse capacity for stiff soil profiles. The opposite can be seen in softer soil profiles. However, the final MCER values are slightly larger than the MCE values due to the application of the directivity factors.

Performance-based seismic design of self-centering steel moment frames with SMA-bolted connections

This paper proposes a performance-based seismic design (PBSD) method for self-centering moment-resisting frames with shape memory alloy (SMA)-bolted endplate connections. PBSD can be used to achieve different performance objectives, resulting in several benefits, such as cost-effectiveness and customization of the design. This study develops a PBSD framework by establishing a relationship between the fundamental period, ductility demand, and seismic force reduction factor and using an energy-balanced concept. The design method is facilitated using an artificial neural network (ANN)-based predictive tool and an efficient experimentally-validated phenomenological model for SMA-bolted endplate connections. Maximum drift and ductility ratios are adopted as performance objectives. Two 3- and 6-story prototype frames are designed and evaluated to illustrate the proposed PBSD method. The seismic response and collapse safety of the prototype frames at different shaking intensities are evaluated. The results show that the prototype frames designed using the proposed PBSD framework meet the prescribed design objectives and the collapse safety requirements in FEMA P695. The illustrative examples confirm that the designed moment frames possess the intended self-centering capability with negligible residual deformations as low as 0.05% at the maximum considered earthquake (MCE) hazard level. The results also confirm that the designed frames exhibit uniform drift distribution along their height.

Seismic fragility and loss estimation of self-centering steel braced frames under mainshock-aftershock sequences

This paper highlights the importance of considering local component failure of self-centering braces (SCBs) when examining the seismic fragility and economic performance of emerging self-centering steel braced frames, with a particular focus on the influence of mainshock-aftershock (MS-AS) sequences. The design and modelling of the prototype buildings are first presented, where the failure mechanism and simulation technique for single-core and dual-core SCBs are explained. Seismic fragility analysis and economic loss evaluation are subsequently conducted, where the damage state, component fragility, and repair cost of the considered braces are comprehensively discussed. The study confirms that MS-AS sequences have a pronounced influence on various performances of the structures. Under the maximum considered earthquake (MCE), the probabilities of collapse for structures with single-core and dual-core SCBs (structures S-SCF and D-SCF) increase from 18% to 28% and from 10% to 16%, respectively, when aftershock is additionally considered. MS-AS sequences have a small influence on the peak absolute floor acceleration of both structures. When aftershock is additionally considered, the probabilities of exceedance of the 0.5% residual inter-story drift threshold increase from 25% to 31% and from 16% to 19%, respectively, for structures S-SCF and D-SCF; the 50% percentile loss ratio of the two structures increases from 0.09 to 0.16 and from 0.08 to 0.11, respectively; and the expected losses over a 50-year period of the two structures are increased by 25.7% and 22.9%, respectively. Apart from the non-negligible influence of MS-AS sequences, the importance of appropriate modelling of tendon fracture is also highlighted.