Effect of shear on stability of steel girders under fire conditions

In current practice, failure in beams under fire conditions is evaluated based on flexural limit state without any consideration to shear effects. However in certain scenarios, fire exposed beams and girders can experience temperature induced sectional instability due to shear rather than flexural effects. This paper presents a three-dimensional nonlinear finite element model for evaluating behavior of fire exposed steel girders. This model, developed in ANSYS, is capable of predicting fire response of steel girders taking into consideration flexural, shear and deflection limit states. The validated model is utilized to study different conditions under which shear parameters dominate the response of fire exposed steel girders. Results from numerical studies show that shear capacity can degrade at a higher rate than flexural capacity under certain loading scenarios and hence, failure can result from shear effects prior to that due to flexure. In addition, web slenderness and reserve shear capacity are also found to influence the onset of sectional instability in fire exposed steel girders.