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Developing Performance-Based Design and Assessment Methods for Self-Centering Steel Braced Frames with Controlled Rocking

A number of studies have been carried out to develop rocking steel braced frames with post-tensioning rods and replaceable fuses. However, these studies have largely focused on performing large scale testing and developing computational models to simulate their response to earthquake ground motions. In contrast, comparatively much less has been accomplished in formulating performance-based design and assessment methods that can be used by practicing engineers to implement these systems in real buildings and quantify their benefits with regards to life cycle costs and sustainability.

This project will address this need by establishing performance-based design and assessment methods for self-centering steel braced frame systems with controlled rocking. Specific objectives include (1) developing performance-based design methodologies, (2) providing recommendations for design parameters used to control the occurrence and sequence of critical limit states, (3) formulating a capacity-design criteria for the force-controlled elements and (4) developing a stochastic service-life model that can be used to quantify the benefits, in terms of life cycle costs and environmental impacts, of implementing a controlled rocking braced frame system compared to other more traditional lateral force resisting systems. 

Figure 2 Limit State Fragilities

Utilizing Remote Sensing to Assess the Implication of Tall Building Performance on the Resilience of Urban Centers (NSF Award Number 1538866)

Tall buildings have become a staple of central business districts in the United States and other parts of the world, reflecting the intersection of increased urbanization with the constraints of limited land space. Recent advancements in computational modeling and performance-based earthquake engineering are enabling improved scientific assessment of the expected seismic performance of tall buildings in terms of stakeholder-driven metrics such as the cost to repair damage from future earthquakes. However, these methodologies are based on the notion of the building as “an island”, where seismic impacts are constrained within its footprint. Whereas, recent earthquakes that have occurred around the world have highlighted the critical role of building performance in minimizing the impact on community functionality. This project aims to address this  limitation by developing and applying new methods to assess the impact of tall building performance on the resilience of dense urban centers, using downtown Los Angeles as a test-bed.

The main project tasks include (1) improving modeling and post-earthquake damage assessment by using and enhancing the only mandatory seismic instrumentation program that exists in the US, in the City of Los Angeles, (2) developing a framework that enables the study of the impact of tall buildings on the resilience of urban clusters and (3) developing tools that enhance engineering data use and visualization, creating opportunities for collaboration among scientists, engineers, social scientists, and policy makers.

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Developing a Post-Disaster Recovery Model for Residential Communities (NSF Award Number 1538747)

The goal of this project is to develop an integrated post-disaster recovery model for residential communities, which integrates robust assessments of building performance with spatial and temporal characterization of decisions, actions, and broader community factors. The three main components of the proposed research are (1) a probabilistic model for representing residential building performance limit states, such as loss of functionality, habitability, and repairability, which are explicitly linked to recovery decisions and actions, (2) quantifying the likelihoods and influences of homeowners’ decisions whether to repair, reoccupy, sell, or abandon damaged homes based on recovery-based building limit states, socio-demographic factors, neighborhood conditions, and lifeline services and (3) simulation models that capture the recovery trajectory of the housing stock and building re-occupancy. We will apply the simulation model to a large urban jurisdiction (Los Angeles County) for the purposes of evaluating the model and assessing potential policies and other interventions for enhancing recovery.

Stochastic Characterization of Aftershock Building Collapse Risk (USGS EHP Award Number G16AP00006)

While the threat posed by aftershocks is now well recognized, research to quantify the associated risk is still in its infancy, particularly with regards to integrating the time-dependent aftershock hazard with the increased vulnerability to collapse of damaged buildings. This research seeks to quantify the incremental increase in collapse risk for buildings subject to both mainshock and aftershock ground motions as compared to if they were to experience the mainshock alone. The proposed project will implement the performance-based earthquake engineering framework to assess the aftershock collapse risk of a set of reinforced concrete buildings, utilizing the Next Generation Attenuation database of recorded ground motions from mainshock-aftershock sequences in active crustal regions. Building on recent advancements in classifying and characterizing mainshock and aftershock events as well as ground motion prediction for aftershocks, the goal is to better characterize seismic hazard and its resulting effects on collapse risk.