Behavior of steel box bridge girders subjected to hydrocarbon fire and bending-torsion coupled loading

This paper presents an experimental together with numerical investigation on behavior of steel box bridge girders under hydrocarbon (HC) fire and bending-torsion coupled loading conditions. Four test bridge girders fabricated utilizing single-box configured with twin-chamber supporting thin concrete slabs, taking into consideration sectional features and loading methods, were simultaneously subjected to HC fire exposure and bending-torsion coupled loading to analyze thermal and structural response. A numerical model established through program ANSYS, validated dependent on measured data generated from fire tests, was used to conduct a parametric analysis. Results show that significant discrepancies of temperature occur in mid-web and side-web of test bridge girders exposed to HC fire. Steel top flange has a significant influence on heat accumulation and transfer inside steel box, escape of water vapour in concrete slab and also fire resistance of steel box bridge girders. Deflection difference in transverse section of test bridge girders subjected to bending-torsion coupled loading gradually become predominant with fire exposure time. Test bridge girders without steel top flange experience a wide longitudinal crack in concrete slabs instead of excessive flexural deflection through entire fire exposure duration. Increasing longitudinal stiffeners in mid-web and bottom flange can effectively enhance fire resistance of steel box bridge girders. Timely evacuation of applied loads enforced on bridge girders during fire exposure can greatly delay deflection progression. The post-fire residual bearing capacity in test bridge girders can recover more than 80 % of initial bearing capacity after HC fire exposure. The experienced maximum temperature and fire exposure time has a predominant influence on post-fire recovery ability of steel box bridge girders under ventilation cooling conditions.