Ultimate shear strength of unstiffened long web panels at high temperatures

Following the collapse of the World Trade Center towers, investigating the building resistance and providing the safety of residents in case of fire have attracted the attention of engineers more than ever. In this regard, similar to buildings, gas and liquid containment structures, vehicles, planes, and vessel fuselages are examples of engineering usage which need to be designed against fire. It was shown that inelastic or elastic buckling of steel plate webs, that experience plastic buckling at normal temperatures, is a possible phenomenon at elevated temperatures owing to the deterioration of mechanical properties, i.e., a change in the failure mode, is to be expected. Therefore, regarding the importance of the issue and its application in the industry, it is necessary to investigate the behavior of the I-shaped plate girders against fire. In this research, shear behaviors of long steel plate girder web panels subjected to pure shear loading are investigated at elevated temperatures by the nonlinear finite element method. Therefore, web panel shear design relationships mentioned in AISC360-16 specification is modified to be used in fire conditions. This is achieved by direct utilization of steel stress-strain reduction factors in EN1993-1-2 at elevated temperatures. It is observed that the adopted equation of AISC360-16 for fire situations yields values that are more non-conservative such that the difference reaches almost 18%. On the other hand, AISC equations are more accurate and in the safe region for compact plates. However, these equations lead to the unsafe condition at higher slenderness values. In this regard, nonlinear finite element analysis results were employed to modify the AISC 360-16 equation for predicting the ultimate shear strength of long steel plate girder web panels by considering the strength degradation caused by high slenderness, high temperature, and initial geometrical imperfections. Comparison of the results corroborated the appropriate accuracy of the proposed equations.