Empirical seismic fragility assessment and optimal risk mitigation of building contents

Abstract

Building contents proved challenging in performance-based earthquake engineering frameworks because of the data scarcity. Despite the content seismic losses in the past two decades, the overall effectiveness of restrainers to contents has not been thoroughly investigated. This paper aims to provide a detailed analysis for assessing content damage, loss, and protection to better understand content risk and performance. In this paper, analytical fragility functions for rigid block-type contents are developed based on nonlinear time history analysis of four dynamic models to represent freestanding and anchored building contents with elastic-brittle restrainers considering multiple failure modes. The effectiveness of restrainers is quantified by the improvement of the fragility median. A simplified expression is proposed to estimate content lognormal fragility parameters based on a wide range of variables' correlation between contents' characteristics and restraint strength. The proposed simplified expression is adopted in FEMA P-58 loss assessment framework through a case study of a 4-story light-frame wood office building to estimate content dollar loss. To further investigate content risk mitigation, we used a quantitative loss assessment for multiple mitigation scenarios by anchoring different content types such as heavy, expensive, electrical, furniture, or glassware. It is found that elastic-brittle restrainers are more effective for rigid systems than flexible systems, and decision-makers should design restrainers based on a combination of block-like content and restrainer characteristics for efficient protection and life safety. For the case study, anchoring expensive components was the optimal mitigation scenario, which resulted in a 74% reduction in the average annual losses compared to freestanding contents.