Numerical Assessment of Connections with Reduced Beam Sections under Fire Following an Earthquake Using Continuously Updated Boundary Condition

Abstract

The occurrence of fires following an earthquake in steel structures is an important scenario that can threaten the integrity of structural systems. Structural loss due to such combined events has been observed and reported. Despite such evidence, minimal studies have been conducted on the combined effects of the hazards on steel structures or any type of structures for that matter. The aim of this paper is to provide insight into the local behavior of reduced beam section connections during fire following earthquakes when representative time-dependent boundary conditions are utilized to simulate the restraint provided by the surrounding frame during the fire. This is achieved through investigating the response of two beam-column subassemblies designed for the Los Angeles region using 3D nonlinear finite element analyses. The models are developed and analyzed under several representative loading scenarios with continuously updated boundary conditions that characterize the nonlinear stiffness of the remainder of the frame. The results are presented and their implications discussed to protect against the hazard of fire following earthquakes in steel moment frames with reduced beam sections. BACKGROUNDThe occurrence of fires igniting during and immediately following a seismic event represents an important design scenario that should be taken into consideration. Building concentration and construction type, weather conditions and other factors can combine to create a situation in which fire following an earthquake is the principal cause of damage. Some examples include the 1906 San Francisco earthquake, where the losses due to fire were estimated to be ten times larger than that due to the seismic action, the 1923 Tokyo earthquake which was estimated to have 77% of building loses caused by fire, and the 1995 Kobe (Japan) in which the fire destroyed over 150,000 buildings. Structures that have been exposed to earthquakeinduced damage are particularly vulnerable to the effects of fire loading and the combination of events represents a unique scenario that is not often considered during the design process. This study investigates the effect of fire following earthquake on the response of reduced beam section (RBS) connections.

Overview of fire following earthquake: historical events and community responses

“…The results show that the frame stays stable during fire; however, softening of the beam at elevated temperatures, at regions that reach bending capacity during seismic loading, increases the frame flexibility to sideway deflections and increases drift demands on the frame. Mahmoud and Turbert (2014) studied the behavior of reduced beam section connections (a special type of connection design) during FFE. Their study models beam-column subassemblies using 3D nonlinear finite element analyses.…”