Fire behavior of composite steel truss bridge girders: numerical investigation and design strategies

Abstract Fire pose more severe threat to steel truss bridge girders as compared to common steel plate and box bridge girders. To deeply clarify failure mechanism of fire exposed steel truss bridge girders, this paper presents an investigation on fire performance of composite steel truss bridge girders simultaneously subjected to structural loadings and hydrocarbon fires. A numerical model, developed using the computer program ANSYS, is validated dependent on fire test to trace fire behavior of a typical through-type composite steel truss bridge girders under different hydrocarbon fire exposure conditions. The analysis is applied to evaluate influence of potential fire exposure scenarios occurred in bridge structures, including fire exposure lanes on bridge deck and fire exposure length beneath bridge, on temperature and structural response in steel truss bridge girders. The results shows that fire exposure lanes on bridge decks and fire exposure length beneath bridge has a significant influence on fire performance of steel truss bridge girders. Fire exposure on all lanes and side lanes can cut down fire resistance highly as compared to fire exposure on mid-lanes. The composite steel truss bridge girders exhibit special multi-hinge failure modes when fire exposure under bridge. Further, the composite steel truss bridge girders exposed to side-lane fire exhibit significant transverse torsional deformation. The established failure criteria dependent on structural deflection limit states, chord deformation and strength can be applied to evaluate fire resistance of actual composite steel truss bridge girders under realistic fire exposure scenarios. Limiting the minimum clearance of passage on bridge deck and increasing fire protection measures in upper portion of trusses can effectively improve fire resistance of through-type composite steel truss bridge girders. Some predominant design strategies closely related to oil tanker trucks traversing composite steel truss bridge girders are proposed to minimize probability of fire incidents on bridge and keep integrity of structure in the case of fire to the maximum extent possible.