Flexural performance of prestressed concrete I-shaped bridge girders exposed to hydrocarbon fire

Abstract

This study examines the flexural performance of identical I-shaped bridge girders with different prestressing arrangements and methods under fire conditions. A finite element model was developed to simulate the temperature evolution in the bridge girders exposed to fire. Temperature data from the model were used to assess the degradation in the ultimate strength of prestressing strands, as well as the reduction in flexural strength and the subsequent rating factor of both girders over time. The results reveal that the flexural capacity of the post-tensioned girder remained relatively stable for the first 90 minutes of fire exposure but gradually decreased thereafter. In contrast, the flexural strength of the pre-tensioned girder degraded more rapidly than that of the post-tensioned girder. Specifically, the pre-tensioned girder lost up to 51% of its initial flexural capacity, while the post-tensioned girder only lost 26% after four hours of exposure to a hydrocarbon fire. Additionally, the pre-tensioned girder lost its ability to carry the design live load after 100 minutes of fire exposure, whereas the post-tensioned girder retained this capacity for 190 minutes. The findings highlight that the prestressing arrangement is a crucial factor influencing the degradation of flexural capacity in prestressed girders under fire. Pre-tensioned girders, with strands located near the soffits, are significantly more vulnerable to strength loss compared to post-tensioned girders, which have cables positioned farther from the soffit.  Additionally, fire intensity plays a critical role in determining the extent of degradation in the flexural strength of prestressed concrete bridge girders under fire conditions.