This article presents an approach for investigating performance of prestressed concrete box bridge girders under hydrocarbon fire exposure. A three-dimensional nonlinear finite element model, developed in computer program ANSYS, is utilized to analyze the response of prestressed concrete box bridge girders under combined effects of fire exposure duration and simultaneous structural loading. The model validation is performed using a scaled prestressed concrete box girder exposed to ISO834 fire in furnace. Subsequently, the validated model is used to investigate fire performance of prestressed concrete box bridge girders through taking into consideration some variables, namely concrete cover thickness to prestressing strands, prestress degree, load level, fire exposure length, and position. Through a case study, results from numerical analysis show that concrete cover thickness to prestressing strands and load level has significant effect on fire resistance of prestressed concrete box bridge girders. Increasing prestress degree in prestressing strands can speed up the progression of deflection (sudden collapse) in prestressed concrete box bridge girder toward the final fire exposure stage. Reducing fire exposure length or preventing fire exposure on mid-span zone can highly enhance the fire resistance of simply supported prestressed concrete box bridge girders. Failure of prestressed concrete box bridge girder, under hydrocarbon fire exposure conditions, is governed by rate of deflection failure criterion in particular cases.

Double-layer steel truss continuous girders are prone to significant temperature stress, deviation, torsion, and warping, thus causing adverse temperature structural responses, and also affecting the safety and durability of bridge structures. This paper presents an investigation on time-dependent characteristics in the temperature field and temperature response of double-layer steel truss continuous bridge girders, fully considering the shielding effect subjected to different solar radiation angles during the high-temperature season. The time-dependent thermal boundary conditions and support conditions provided for the steel truss bridge structure were determined. Subsequently, a thermal analysis model for the entire structure of double-layer steel truss continuous girders was established to attain the temperature distribution law. The research results show that significant differences occur in the position and temperature difference of temperature gradients exhibited in the vertical, horizontal, and longitudinal directions in the double-layer steel truss bridge structure. The temperature distribution pattern within the chord section is mainly influenced by the environmental temperature and solar radiation intensity, along with the heat exchange between different panels. Thereafter, a validated temperature gradient formula for the component section has been proposed. The time-dependent laws in structural displacement, stress, and rotation angle under daily temperature cycling conditions have been revealed, thereby providing a theoretical basis for the life cycle construction and safety maintenance of double-layer steel truss structure bridges.

This paper presents a detailed investigation in to fire resistance along with failure mode in continuous steel-concrete composite twin I-shaped bridge girders under different localized fire through considering fire severity and fire exposure positions namely; mid-span zone in one of the two span, hogging moment zone and side-support zone. A 3-D finite element (FE) model, built utilizing the computer program ANSYS, is used to track structural fire performance in a typical two span of continuous composite twin I-shaped bridge girders (fabricated with twin I-shaped plates supporting a concrete slab) dependent on thermomechanical coupled analysis. The model validation is undertook through comparison of temperature and deflection response attained from a scaled composite single I-shaped girder tested exposed to ISO834 fire. The numerical analysis results show that the developed model can be favorably used to analyze the behavior and failure mode of continuous steel-concrete composite twin I-shaped bridge girders during entire range of fire exposure. Fire severity and fire exposure positions present critical influence in to the fire resistance of continuous composite bridge girders. Fire exposure prevention on hogging moment zone can significantly extend failure time of continuous girders, and further hold back progressive structural collapse. Web buckling based failure criterion can be applicable to calculate fire resistance of realistic continuous girders under simultaneous structural loading together with localized fire. Continuous composite bridge girders subjected to localized fire present highly significant local deformation response in the fire exposed bridge girder span.