Fire hazard assessment, performance evaluation, and fire resistance enhancement of bridges

Abstract

Although the performance of bridge structures under prescriptive fire scenarios has been the subject of numerous studies, performance-based approaches are yet to be developed to achieve an efficient and economical design. This paper presents a performance-based framework that identifies bridges at high fire risk, produces realistic fire scenarios, provides an open source tool to apply the realistic fire load to the thermomechanical model and evaluate the structural performance of the bridge. It also provides guidance to improve the fire resistance of the bridge. The proposed framework is implemented by simulating the I-65 overpass fire accident in 2002, Birmingham, Alabama, USA. Firstly, fire risk of the bridge is estimated by considering various criteria such as the social and economic impact of fire, structural vulnerability, and the likelihood of fire. Secondly, a realistic fire scenario is developed using the real fire accident data by conducting computational fluid dynamics (CFD) simulations. Thirdly, the newly developed open source FSDM framework is utilised to apply the realistic fire load to the thermomechanical model and finally, the fire resistance of the bridge structure is estimated. The unprotected bridge failed after 12 min of fire exposure which is found in compliance with the actual failure time of the bridge during the accident. Further thermomechanical analyses are performed applying different thicknesses of fire protection to estimate the suitable amount of fire protection to achieve improved fire resistance. It is observed that the fire resistance of the bridge can be enhanced up to 60 min by providing a fire protection of 12 mm thickness. This framework presents an important methodology for the highway department and bridge engineers to identify bridges at high fire risk and accurately determine the amount of fire protection required to reduce the fire risk and enhance the fire resistance of these bridges.