Seismic Collapse Risk Assessment of Low-Aspect-Ratio Reinforced Concrete Shear Walls Using the FEMA P695 Methodology

Abstract

Several recent research studies have demonstrated that the seismic performance of low-aspect-ratio reinforced concrete (RC) shear walls (i.e., defined herein as walls with height-to-length ratios less than 2) has not been yet adequately quantified to allow for robust risk assessment. This is mainly attributed to the complex nonlinear flexure/shear interaction behavior of such walls, along with their wide spectrum of possible design parameters, leading to major discrepancies in their seismic performance. Despite this unique behavior, most building codes and design standards do not assign distinctive seismic performance factors for such walls. To address this, the main objective of the current study is to propose seismic performance factors for low-aspect-ratio RC shear walls when different wall geometrical configurations and design parameters (e.g., aspect ratios, axial load levels, and seismic design categories) are adopted. These factors are evaluated against the acceptance criteria of the FEMA P695 methodology for Quantification of Building Seismic Performance Factors. In this respect, a numerical model was developed and experimentally validated to simulate the seismic response of 36 low-aspect-ratio RC shear wall archetypes. The model was utilized to perform nonlinear static and dynamic analyses, and collapse fragility curves were then generated to assess the collapse risk of such wall archetypes following the FEMA P695 methodology. According to the methodology, the proposed seismic performance factors were assessed by quantifying the ratio between the median collapse intensity and the intensity of the maximum considered earthquake (MCE). The results showed that R factors of 2.0 and 3.0 for special low-aspect-ratio RC walls with low and high axial load levels, respectively, can limit the probability of collapse under the MCE and are subsequently able to meet the FEMA P695 acceptance criteria.