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.

The promotion of risk-targeted hazard as the basis of seismic design internationally has increased over the past decade. Risk-targeted hazard estimates are derived through convolution of hazard curves with representative fragility functions and provide a means to target uniform risk across a region. Using risk targets also enables performance objectives of building codes that are consistent with other life risks and can include societal input into the expected performance of structures. Current design procedures using a uniform-hazard spectrum are unable to provide equal risk across the country due to variation in the shapes of hazard curves in different locations and uncertainty in structural response. In this article a framework is proposed, which can be used with national seismic hazard models, to produce risk-targeted hazard spectra for seismic design. This study extends the risk-targeted hazard framework through full quantification of epistemic uncertainty in seismic hazard and includes multiple risk targets for individual and societal risk at the building and city scales. The article describes a framework that can be used to adjust current seismic design force levels in New Zealand standards to target uniform seismic risk for buildings considering both the performance of individual buildings and the performance of cities.

A framework is proposed to assess the impact of safety cordons on the recovery of community functions after an earthquake, using high-resolution geospatial information to simulate the damage, cordons, and recovery trajectories for buildings in the affected area. Ground motion maps are developed to characterize shaking intensities for regional building-level engineering assessments of damage, repair times, and recovery times to quantify the impact of access restrictions associated with cordons around tall buildings with impaired collapse safety. The results are presented as recovery curves that quantify the cumulative loss in building functionality across the community as a function of time following an earthquake. A case study considers recovery of office space in Downtown San Francisco, following a Mw7.2 event on the San Andreas Fault. For this scenario, an average of 219 community days of office functionality are lost in the first year, representing about 60% of the total office space capacity. About one-third of the loss is attributed to access restrictions associated with cordons around older tall buildings. The proposed framework can be used to investigate the efficacy of various mitigation strategies to expedite recovery. While the most effective strategy for mitigating the overall impact of cordon restrictions is to seismically retrofit older tall buildings that trigger cordons, other less expensive preparedness measures are shown to be effective, depending on the recovery time frame of interest. Specifically, recovery preparedness measures are generally more effective when evaluated for longer-term recovery targets (e.g. recovery of function after 12 months) compared with short-term targets (e.g. recovery after 4 months).

The anticipated performance of a 4-story reinforced concrete (RC) building designed in accordance with ASCE/SEI 7, is assessed using ASCE/SEI 41. Engineering practitioners employing the performance-based seismic engineering philosophy are increasingly using ASCE/SEI 41, as the "first generation" performance-based seismic design principle, to justify the adequacy of the seismic performance of new buildings. However, ASCE/SEI 41 was developed to assess the structural performance of existing buildings. In order to compare the anticipated structural performance between ASCE 7 and ASCE 41, the seismic performance of an ASCE/SEI 7 codecompliant 4-story special RC moment frame building is assessed based on the four evaluation methodologies defined in the Tier 3 analysis of ASCE/SEI 41 for the collapse prevention structural performance level. The assessment results show that the ASCE/SEI 7 code-compliant building does not meet the collapse prevention performance level requirements in ASCE/SEI 41 for the columns in the first story when linear analyses are employed.

Performance-based seismic design (PBSD) has been recognized as a framework for designing new buildings in the United States in recent years. Various guidelines and standards have been developed to codify and document the implementation of PBSD, including “ Seismic Evaluation and Retrofit of Existing Buildings” (ASCE 41-17), the Tall Buildings Initiative’s Guidelines for Performance-Based Seismic Design of Tall Buildings (TBI Guidelines), and the Los Angeles Tall Buildings Structural Design Council’s An Alternative Procedure for Seismic Analysis and Design of Tall Buildings Located in the Los Angeles Region (LATBSDC Procedure). The main goal of these documents is to regularize the implementation of PBSD for practicing engineers. These documents were developed independently with experts from varying backgrounds and organizations and consequently have differences in several degrees from basic intent to the details of the implementation. As the main objective of PBSD is to ensure a specified building performance, these documents would be expected to provide similar recommendations for achieving a given performance objective for new buildings. This article provides a detailed comparison among each document’s implementation of PBSD for reinforced concrete buildings, with the goal of highlighting the differences among these documents and identifying provisions in which the designed building may achieve varied performance depending on the chosen standard/guideline. This comparison can help committees developing these documents to be aware of their differences, investigate the sources of their divergence, and bring these documents closer to common ground in future cycles.