Multi-hazard fire vulnerability assessment and resilience quantification

Abstract

The increasing frequency and severity of multi-hazard events, particularly those involving fire and seismic loading, pose significant challenges to the resilience of structural systems. Fire following an earthquake, concurrent fire-seismic events, and fire following earthquakes with aftershocks introduce complex degradation mechanisms that compromise material properties, structural stability, and load-bearing capacity. Traditional design methodologies often treat these hazards in isolation, failing to capture their interdependent effects on structural behavior. This dissertation advances the field of multi-hazard vulnerability assessment by integrating fire-inclusive material modeling, probabilistic fragility analysis, and resilience quantification to improve performance-based design strategies. A central contribution of this research is the development of advanced nonlinear material models for steel and concrete under fire and cyclic loading conditions. These models capture critical thermal-mechanical interactions, including strain reversal effects, cyclic degradation, and temperature-dependent stress-strain behavior. The study introduces a bilinear-quadratic cyclic model for steel, incorporating plastic strain accumulation to enhance predictive accuracy under sequential and concurrent dynamic loading conditions. For concrete, a modified Mander’s model is extended to account for high-temperature degradation, including spalling, stiffness reduction, and progressive strength deterioration. These material models are validated through numerical simulations and experimental data to ensure their reliability in hazard assessments. Building upon these material formulations, a multi-hazard fragility assessment framework is developed to quantify the probability of structural failure under fire and seismic loading conditions. Probabilistic fragility curves are generated using finite element reliability using MATLAB method, incorporating uncertainty in fire intensity, seismic ground motion, and structural parameters. Case studies examine the fragility of reinforced concrete (RC) structures under various hazard sequences, including fire-following-earthquake, fire following earthquake with aftershock, and concurrent fire-seismic loading. Results highlight significant reductions in structural capacity due to fire-induced stiffness degradation, yield strength reduction, and progressive material failure mechanisms. To extend the utility of fragility analysis, this research introduces a resilience index as a computational metric for quantifying post-hazard structural performance. This index integrates fragility-based failure probabilities with structural damage states, providing an analytical tool for assessing recovery potential and structural adaptability under multi-hazard exposure. The framework demonstrates how elevated temperatures and cyclic loading interactions exacerbate structural vulnerabilities, reinforcing the need for multi-hazard-inclusive design approaches. The findings of this research contribute to the advancement of fire-aware fragility modeling and performance-based multi-hazard assessment, providing engineers, policymakers, and researchers with quantitative tools for designing resilient infrastructure in fire-prone and seismic regions. The proposed methodologies and models enhance the accuracy of multi-hazard structural performance predictions, bridging critical gaps in current hazard assessment frameworks.