Fragility curve modifiers for dual-frame systems in various site classes incorporating nonlinear SSI effects

Abstract

The seismic response of reinforced concrete buildings depends on the interaction between the superstructure, foundation type and soil properties, making accurate fragility assessment a complex engineering challenge. This study focuses on constructing fragility curves specific to building vulnerability assessment by incorporating various damage parameters that account for soil–structure interaction effects. Using finite element analysis software, Incremental Dynamic Analysis was performed on RC building models with both fixed and flexible bases founded on varying soil conditions. Fragility curves were developed using three engineering demand parameters: maximum roof displacement, inter-storey drift and plastic energy dissipation. Findings reveal that maximum roof displacement parameter consistently yields the highest probabilities of exceedance, reaching up to 90–100% for soft soil at a PGA of 0.3 g, identifying it as the most conservative measure, while plastic energy dissipation displays the lowest probabilities (10–50% across all soil types), indicating its limitations in capturing deformation demands. To streamline vulnerability assessment for buildings incorporating the effect of supporting soil stratum, fragility modification factors are proposed to efficiently adjust existing fragility curves for incorporating SSI effects based on different damage measures and soil conditions, providing a comprehensive approach to efficient vulnerability analysis. © 2025 Korea Institute for Structural Maintenance and Inspection.