Fire hazard in concrete bridges: review, assessment and mitigation strategies

This paper analyses the vulnerability of concrete bridges to fire through a comprehensive review and proposes strategies to overcome the fire hazard. As part of mitigation strategies, the application of advanced analysis is illustrated through developing a non-linear transient finite-element model for fire resistance evaluation of prestressed concrete bridge girders. The numerical model is validated using results from fire tests on concrete beams. The model is applied to investigate the effect of girder shape (rectangular and I-shaped sections) and strength of concrete (normal- and high-strength concretes) on the fire resistance of typical concrete bridge girders. Results from the analysis clearly show that fire resistance of high-strength concrete (HSC) girders is lower than that of normal-strength concrete (NSC) girders, which is attributed to its faster degradation of strength and stiffness with temperature. On the other hand, I-shaped girders present lower fire resistance than similar girders of rectangular cross-section due to rapid degradation of its shear capacity. This is mainly the result of slender web widths in I-shaped girders, which results in faster progression of temperatures in the web, leading to early failure under the shear limit state. This problem can be overcome by developing relevant fire mitigation strategies, such as provision of external thermal insulation on girders of critical bridges.