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Canada’s 2020 national seismic hazard model (CSHM 2020) provides hazard estimates for interface Cascadia Subduction Zone (CSZ) earthquakes in southwestern Canada using four ground motion models (GMMs) with equal weights. Two out of the four GMMs were derived using data primarily from subduction earthquakes in Japan so their use in CSHM 2020 includes a “Japan-to-Cascadia” factor to account for local site conditions. Despite this regional factor, the GMMs do not explicitly consider the amplification effects from the Georgia sedimentary basin below Metro Vancouver. This study benchmarks ground motion shaking from a suite of 30 physics-based simulations of M9 CSZ earthquakes, which explicitly account for basin effects for periods exceeding 1 s, to corresponding estimates from interface GMMs in CSHM 2020. Using this comparison, this study proposes site-specific and period-dependent basin amplification factors for a range of sites located within the Georgia sedimentary basin. The average basin amplification factors at the deepest basin location reach values as high as 2.24 and 6.29 at a 2 s period with respect to basin-edge and outside-basin reference locations, respectively. We evaluate the proposed factors by comparing them against long-period amplifications observed in empirical strong motion recordings from the 2001 M6.8 Nisqually earthquake. A framework to incorporate the proposed basin amplification factors in the calculation of CSHM 2020 uniform hazard spectra (UHS) is also proposed. The modified UHS ordinates at the deepest basin location reach values that are 58% to 271% higher, at a 2 s period, than non-basin UHS estimates when amplification factors are calculated with respect to basin-edge and outside-basin reference locations, respectively.

Past earthquakes have illustrated the impacts of reduced hospital functionality due to physical damage resulting in a health service deficit immediately after a major seismic event. In this article, a methodology was developed to quantify the deficit in health care anticipated due to a loss of functionality of a hospital emergency department (ED) and a surge in demand due to regional damage in an earthquake scenario. Earthquake-induced patient arrivals were calculated using multi-severity casualty estimation for the catchment area of the hospital. The surge in patients (demand) was then compared to the ability of the hospital to treat patients (capacity) based on anticipated functionality. Nonlinear response history analysis of the hospital building was performed using simplified structural models, and the structural and non-structural component damage was estimated based on FEMA P-58. Expected damage was linked to the post-earthquake functionality of the ED service areas on each floor by incorporating the fault-tree analysis method. Finally, discrete event simulation was used to evaluate the ED surge capacity, providing hospital performance metrics, such as wait times (WTs) and length of stay (LOS) for patients of ranging acuity. A case study of a hospital in the City of Vancouver subjected to an Mw9.0 Cascadia Subduction Zone scenario earthquake was presented. Emergency rooms (ERs) were identified as the ED bottleneck during the emergency response. The mean ER WT exceeded its limit of 2 h and reached up to 17 h in the most unfavorable simulation. Likewise, the mean LOS nearly doubled from 6.5 to 12 h, also exceeding the established target of 10 h. The deployment of field hospitals for less severe patients as an emergency plan to mitigate the ED overcrowding was also analyzed to demonstrate that the methodology can be used as a decision support tool to improve healthcare disaster planning.

While modern seismic design codes intend to ensure life-safety in extreme earthquakes, policy-makers are moving toward performance objectives stated in terms of acceptable recovery times. This article describes a framework to probabilistically model the post-earthquake recovery of buildings and provide quantitative seismic performance measures, expressed in terms of downtime, that are useful for decision-making. Downtime estimates include the time for mobilizing resources after an earthquake and conduct necessary repairs. The proposed framework advances the well-established Federal Emergency Management Agency (FEMA) P-58 and Resilience-based Earthquake Design initiative (REDi) methodologies by modeling temporal building recovery trajectories to target recovery states, such as stability, shelter-in-place, reoccupancy, and functional recovery. The shelter-in-place recovery state accounts for relaxed post-earthquake habitability standards, in contrast with the reoccupancy recovery state that relates to pre-event habitability criteria. Analogous to safety-based codes, which specify a threshold for the probability of collapse under a given ground motion shaking intensity, this framework permits evaluating the probability of a building not achieving a target recovery state, for example, shelter-in-place, immediately after an earthquake, or, alternatively, the probability of achieving a target recovery state, for example, functional recovery, within a specified time frame. The proposed framework is implemented to evaluate a modern 12-story residential reinforced concrete shear wall building in Seattle, WA. The assessment results indicate that under a functional-level earthquake (roughly equivalent to ground motion shaking with a return period of 475 years), the probability of not achieving shelter-in-place immediately after the earthquake is 22%, and the probability of downtime to functional recovery exceeding 4 months is 88%, which far exceeds acceptable thresholds suggested in the 2015 National Earthquake Hazards Reductions Program (NEHRP) guidelines and FEMA P-2090.

Current building code requirements for seismic design are primarily intended to minimize life-safety risks due to structural damage under extreme earthquakes. While tall buildings designed under current standards are expected to achieve the life-safety goal, this study estimates that they may require up to 7.5 months of repair to return to functionality after a design-level earthquake (roughly equivalent to ground motion shaking with a 10% probability of exceedance in 50 years), and over 1 year after a risk-targeted maximum considered earthquake (roughly equivalent to ground motion shaking with a 2%–4% chance of exceedance in 50 years). These long downtimes, which correspond to median predictions, far exceed recovery goals for major employers and other recovery-critical uses and can have disproportionately harmful effects on businesses and residents. To address such extensive downtime risks, we evaluate the impact of recovery-based design guidelines for reducing recovery times through (1) more stringent drift limits under expected ground motions and (2) measures to mitigate externalities that impede recovery. The results suggest that by combining these strategies, expected recovery times following a design-level earthquake can be reduced to roughly 1 month, and to 2 months following a risk-targeted maximum considered earthquake. These findings are illustrated for an archetype 42-story reinforced concrete shear wall residential building and a 40-story steel buckling-restrained braced frame office building in San Francisco, CA.

This study benchmarks the performance of older existing tall steel moment resisting frame buildings designed following historic code-prescriptive requirements (1973 Uniform Building Code) against modern design standards (2015 International Building Code). The comparison is based on seismic risk assessments of alternative designs of a 50-story archetype office building, located at a site in San Francisco, CA. The mean annual frequency collapse risk of the 1973 building is 28 times greater than the equivalent 2015 building (28 × 10−4 versus 1 × 10−4), or approximately 13% versus 0.5% probability of collapse in 50 years. The average annual economic loss (based on cost of repair) is 65% higher for the 1973 as compared to the 2015 building (0.66% versus 0.40% of building replacement cost). The average annual downtime to re-occupancy for the 1973 building is 72% longer (8.1 vs 4.7 days) and to functional recovery is about 100% longer (10.4 vs 5.0 days). Building performance evaluations at the design basis earthquake (DBE) and the maximum considered earthquake (MCE) shaking intensities further suggest that 1970s tall steel moment frames have much higher risks of collapse under extreme ground motions and risks of damage and building closure in moderate earthquakes. Furthermore, while modern building code requirements provide acceptable seismic collapse safety, they do not necessarily ensure a level of damage control to assure a swift recovery after a damaging earthquake due to extensive downtime. A set of vulnerability functions are proposed for both archetype buildings considered in the assessment.

Tall residential RC shear wall buildings (RCSW), which are predominant in Metro Vancouver, have the potential to experience large magnitude earthquakes generated by the Cascadia Subduction ...

In recent years, a novel type of hybrid coupled wall (HCW), which consists of reinforced concrete (RC) wall piers and replaceable steel coupling beams (RSCBs), has been proposed for enhancing the seismic resilience of high-rise buildings. This paper presents the assessment of the seismic performance of an 11-story building located in a highly seismic area and designed per modern Chinese codes. The building adopts the frame-shear wall interacting system. For comparison, two cases are considered: one using the novel hybrid coupled walls and another using conventional RC coupled walls (RCW). The dynamic response of the buildings under high intensities of ground motion shaking is obtained from nonlinear dynamic analysis in OpenSees. The seismic performance, expressed in terms of repair cost and time, is assessed based on the FEMA P-58 method. The results indicate that most of the damage is concentrated in the coupling beams and nonstructural components. The use of novel HCWs instead of conventional RCWs results in maximum interstory drifts up to 24.5% lower in the HCW building than the RCW building when subjected to a maximum considered earthquake (MCE) intensity. Novel HCWs result in a reduction of 50.8% and 60.5% in the median building repair cost and time, respectively, under MCE, due to less damage to coupling beams and RC frames and easy replacement of RSCBs after a damaging earthquake. It is also noted that HCWs have limited influence on the peak floor accelerations, and thus the repair cost and time for acceleration-sensitive non-structural components are similar for both the HCW building and the RCW building.

The Pacific Northwest has the potential to experience large-magnitude earthquakes generated by the Cascadia Subduction Zone, which is located approximately 100 km from the city of Seattle. Tall buildings in Seattle are particularly vulnerable to these earthquakes because the city lies above a deep sedimentary basin, which can amplify the intensity of earthquake ground motions at long periods. This paper evaluates the response of an archetype 1970s 50-story steel moment-resisting frame office building in Seattle under 30 simulated scenarios of a magnitude-9 (M9) Cascadia Subduction Zone earthquake with explicit consideration of basin effects. The archetype is assumed to have fracture-prone welded connections consistent with those identified following the 1994 Northridge earthquake. The probability of collapse conditioned on the occurrence of the M9 scenarios, which have a return period of approximately 500 years, is 30%. The annualized collapse risk of the archetype building is also assessed considering all sources (i.e., crustral, intraslab and interface earthquakes) that contribute to the seismic hazard through a multiple stripe analysis procedure. The results indicate a 50-year collapse risk of 6.9% when basin effects are neglected and 10.5% when basin effects are considered. These results exceed the 1% in 50-year target implicit in modern seismic design standards by a factor of 10. These high collapse risks are largely driven by (i) deep sedimentary basin effects and (ii) the expected brittle behavior of fracture-prone welded beam-to-column connections. The simulations of the performance of the building under the M9 scenarios outside of the basin or with ductile beam-to-column connections result in a negligible probability of collapse.

This paper describes the post-earthquake safety assessments conducted by the European Union Civil Protection Team (EUCPT) following the Mw 7.8 Ecuador earthquake of April 16, 2016. The mission of the structural engineers within the EUCPT took place from April 22 to May 7, 2016. Several activities were performed: (i) rapid post-earthquake safety evaluations of buildings, (ii) demolition verification, (iii) safe road access, and (iv) detailed post-earthquake safety assessments of critical buildings. Despite the small number of structural experts, more than 1000 buildings were inspected in Portoviejo and approximately 150 in Pedernales. Several lessons were identified during this mission, including the need of embedding local experts in foreign teams and the importance of having preparedness programs on post-earthquake assessment both for technicians and emergency managers. The efforts of the EUCPT benefitted largely from a Disaster Risk Reduction (DRR) pilot project which was underway at the time of the earthquake. While the project was not yet completed, such investment in DRR benefitted the disaster response efforts, even in areas which were not directly involved in the program.

Summary This study assesses the seismic performance of a hybrid coupled wall (HCW) system with replaceable steel coupling beams (RSCBs) at four intensities of ground motion shaking. The performance of the HCW system is benchmarked against the traditional reinforced concrete coupled wall (RCW). Nonlinear numerical models are developed in OpenSees for a representative wall elevation in a prototype 11-story building designed per modern Chinese codes. Performance is assessed via nonlinear dynamic analysis. The results indicate that both systems can adequately meet code defined objectives in terms of global and component behavior. Behavior of the two systems is consistent under service level earthquakes, whereas under more extreme events, the HCW system illustrates enhanced performance over the RCW system resulting in peak interstory drifts up to 31% lower in the HCW than the RCW. Larger drifts in the RCW are because of reduced coupling action induced by stiffness degradation of RC coupling beams, whereas the stable hysteretic responses and overstrength of RSCBs benefit post-yield behavior of the HCW. Under extreme events, the maximum beam rotations of the RSCBs are up to 42% smaller than those of the RC coupling beams. Moderate to severe damage is expected in the RC coupling beams, whereas the RSCBs sustain damage to the slab above the beam and possible web buckling of shear links. The assessment illustrates the benefits of the HCW with RSCBs over the RCW system, because of easy replacement of the shear links as opposed to costly and time-consuming repairs of RC coupling beams. Copyright © 2016 John Wiley & Sons, Ltd.

The authors propose a new tuned viscous mass damper (TVMD) coupled wall system for use in high-rise buildings. In this novel structural system, the TVMDs are arranged in a zig-zag configuration to couple wall piers in order to control both lateral inter-story drifts and floor accelerations. This novel structural system is used in this study to investigate the seismic performance of a 15-story prototype building. A nonlinear finite element model of the TVMD coupled wall (TCW system) is developed via the opensource finite element analysis software OpenSees. The TVMD is modeled by means of a newly compiled element named InertiaTruss, and the behavior of the coupled wall is simulated using a well-established multi-layer shell element approach. The seismic behavior of this novel TCW system is compared with walls coupled with conventional reinforced concrete beams (RCW system) and with viscous dampers (VCW system). The results indicate that, with a proper tuning design, seismic response parameters such as inter-story drift and floor acceleration are reduced by up to 16% and 28%, respectively, in the TCW system compared to the RCW system. The TCW system also shows better control of floor acceleration than the VCW system, though drifts are comparable. The force demands in the TVMD-to-wall joints are small due to the benefit of the TVMD zig-zag configuration. The analysis results also indicate that the effect of detuning in this new system is insignificant even when subjected to severe motions.

In areas of high seismicity in the United States, the design of many existing tall buildings followed guidelines that do not provide an explicit understanding of performance during major earthquakes. This paper presents an assessment of the seismic performance of existing tall buildings and strategies for increased resilience for a case study city, San Francisco, where an archetype tall building is designed based on an inventory of the existing tall building stock. A 40-story moment-resisting frame system is selected as a representative tall building. The archetype building is rectangular in plan and represents the state of design and construction practice from the mid-1970s to the mid-1980s. Nonlinear response history analysis (NLRHA) are conducted with ground motions representative of the design earthquake hazard level defined in current building codes, with explicit consideration of near-fault directivity effects. Mean transient interstory drifts and story accelerations under the 10% in 50-year...