Performance of steel structures subjected to fire following earthquake

Includes bibliographical references.2016 Summer.Fires following earthquakes are considered sequential hazards that may occur in metropolitans with moderate-to-highly seismicity. The potential for fire ignition is elevated by various factors including damage to active and passive fire protections following a strong ground motion. In addition, damage imposed by an earthquake to transportation networks, water supply, and communication systems, could hinder the response of fire departments to the post-earthquake fire events. In addition, the simultaneous ignitions – caused by strong earthquake – might turn to mass conflagrations in the shaken area, which could lead to catastrophic scenarios including structural collapse, hazardous materials release, loss of life, and the inability to provide the emergency medical need. This has been demonstrated through various historical events including the fires following the 1906 San Francisco earthquake and the 1995 Kobe earthquakes, among others, making fire following earthquake the most dominant contributor to earthquake-induced losses in properties and lives in the United States and Japan in the last century. From a design perspective, current performance-based earthquake design philosophy allows certain degrees of damage in the structural and non-structural members of steel-framed buildings during the earthquake. The cumulative structural damages, caused by the earthquake, can reduce the load-bearing capacity of structural members in a typical steel building. In addition, potential damage to active and passive fire protections following an earthquake leaves the steel material exposed to elevated temperatures in the case of post-earthquake fire events. The combined damage to steel members and components following an earthquake combined with damage to fire protection systems can increase the vulnerability of steel buildings to withstand fire following seismic events. Therefore, there is a pressing need to quantify the performance of steel structures under fire following earthquake in moderate-to-high seismic regions. The aim of the study is to assess the performance of steel structural members and systems under the cascading hazards of earthquake and fire. The research commences with evaluation of the stability of hot-rolled W-shape steel columns subjected to the earthquake-induced lateral deformations followed by fire loads. Based on the stability analyses, equations are proposed to predict the elastic and inelastic buckling stresses in steel columns exposed to the fire following earthquake, considering a wide variety of variables. The performance of three steel moment-resisting frames – with 3, 9, and 20 stories – with reduced beam section connections is assessed under multi-story fires following a suite of earthquake records. The response of structural components – beams, columns, and critical connection details – is investigated to evaluate the demand and system-level instability under fire following earthquake. Next, a performance-based framework is established for probabilistic assessment of steel structural members and systems under the combined events of earthquake and fire. A stochastic model of the effective random variables is utilized for conducting the probabilistic performance-based analysis. This framework allows structural engineers to generate fragility of steel columns and frames under multiple-hazard of earthquake and fire. The results demonstrate that instability can be a major concern in steel structures, both on the member and system levels, under the sequential events and highlights the need to develop provisions for the design of steel structures subjected to fire following earthquake. Furthermore, a suite of recommendations is proposed for future studies based on findings in this dissertation