Challenges in Evaluating Seismic Collapse Risk for RC Buildings

Jin Zhou,Zhelun Zhang,Tessa Williams,Sashi K Kunnath

doi:10.1186/s40069-021-00463-y

Abstract

The development of fragility functions that express the probability of collapse of a building as a function of some ground motion intensity measure is an effective tool to assess seismic vulnerability of structures. However, a number of factors ranging from ground motion selection to modeling decisions can influence the quantification of collapse probability. A methodical investigation was carried out to examine the effects of component modeling and ground motion selection in establishing demand and collapse risk of a typical reinforced concrete frame building. The primary system considered in this study is a modern 6-story RC moment frame building that was designed to current code provisions in a seismically active region. Both concentrated and distributed plasticity beam–column elements were used to model the building frame and several options were considered in constitutive modeling for both options. Incremental dynamic analyses (IDA) were carried out using two suites of ground motions—the first set comprised site-dependent ground motions, while the second set was a compilation of hazard-consistent motions using the conditional scenario spectra approach. Findings from the study highlight the influence of modeling decisions and ground motion selection in the development of seismic collapse fragility functions and the characterization of risk for various demand levels.

Highlights

Partial or complete collapse of building structures results in casualties as well as direct and indirect economic losses following an earthquake
7 Conclusion The effects of ground motion selection and choice of element and material modeling parameters on establishing collapse fragility functions and assessing demand risk were evaluated for a mid-rise code-compliant RC building
The conditional scenario spectra (CSS) approach, which is an enhancement of the Conditional Spectra (CS) method incorporating spectra with assigned rates of occurrence that reproduce the hazard at the site over a period range, resulted in lower collapse probabilities than Incremental dynamic analyses (IDA), where the selected ground motion (GM) were based on site characteristics and an additional criterion for the composition of pulse-like motions in the GM set

Summary

Introduction

Partial or complete collapse of building structures results in casualties as well as direct and indirect economic losses following an earthquake. Because of the diverse consequences of structural collapse, many recent studies have focused on the collapse safety of buildings in high seismic zones. Typically expressed as a function of a selected ground motion intensity measure (IM), are gaining popularity as a tool to quantify the likelihood of structural collapse during an earthquake. Haselton et al (2011) and Liel et al (2011) examined the collapse safety of over fifty ductile and nonductile RC moment frame buildings through the development of fragility functions. Fragility functions are typically predicated on a ground motion IM, such as peak ground acceleration (PGA) or spectral acceleration at a given period. An efficient IM should result in a relatively small variability of the structural demand measure given IM, and a sufficient IM should render the selected demand measure to be conditionally independent of earthquake magnitude and source-to-site distance. Enhanced intensity measures would be needed for taller buildings, where higher modes contribute significantly to the system response

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