Simple Approach for Calculating Inelastic Deflections of Simply Supported Steel Beams under Fire

A simple approach is proposed for predicting inelastic deflections of simply supported steel beams subjected to fire conditions. In this method, the same equations used for calculating elastic deflections of beams at room temperature are used with an equivalent flexural rigidity. Simplified equations for the equivalent flexural rigidity are developed using moment-curvature relationships of steel beams. The effect of creep on deflection, which is significant under fire, is implicitly accounted for in the equivalent flexural rigidity equations. The simplified method is validated with deflections predicted using the ANSYS computer program for a range of load ratios and heating rates. The proposed approach is simple enough to use in any fire-resistant design specification.