Behavior of steel bridge girders under fire conditions

• Behavior of steel bridge girders under fire conditions is investigated.
• Results from fire tests and numerical modeling on bridge girders are presented.
• Effect of web slenderness and stiffeners on fire response of girders is quantified.
• Failure time and mode of failure in fire exposed girders is discussed.

This paper presents results from experimental and numerical studies on the fire performance of typical steel girders used in bridges. As part of experimental studies three steel–concrete composite girders were tested under simultaneous loading and fire exposure. Test variables included: load level, web slenderness, and spacing of stiffeners. Results from fire tests indicate that typical steel girders can experience failure under standard fire conditions in about 30–35 min. The time to failure and mode of failure in fire exposed steel girders is highly influenced by web slenderness, spacing of stiffeners, and type of fire exposure. Steel bridge girders fail through flexural yielding when web slenderness is around 50; however failure mode changes to web shear buckling when web slenderness in girders exceed 100. Data from fire tests is utilized to validate a finite element based numerical model for tracing the response of steel bridge girders exposed to fire. Results from numerical analysis show that the proposed finite element model is capable of tracing the response of steel bridge girders under simultaneous loading and fire conditions.