The effect of fire loading on a steel frame and connection

Abstract

The objective of this paper is to investigate the behavior of steel shear connections subjected to severe fire loading conditions. A time-history transient FE analysis is used to model the fire loading. A detailed 3D FE model of an extended shear tab steel connection used in a beam-column joint is developed. The shear tab plate is welded to the web of the column and it is connected to the web of the beam by tightened bolts. The change in steel material properties such as the modulus of elasticity, yield and ultimate strength, and the coefficient of thermal expansion are considered as functions of increasing temperature resulting from fire loading. Stress-strain curves for steel at elevated temperatures are used in the model. Two cases of boundary conditions are studied: one representing a roller at the far end of the beam, another assumes that the beam is pin supported. The base of the column is maintained as a fixed support, while the upper edge of the column is free to deflect in the vertical direction as shown in Figure 2. Pre-tensioning loads are modeled to represent the tightening of the bolts. A fire curve based on tests conducted in accordance with ASTM E119, is applied to the connection and the structural members. Results show deflection, rotations, and distortion fields of the structural components for both conventional and new fire resisting steel. Mechanical and thermal plastic strain and stress fields are predicted, documenting yielding, plasticity and ultimate failure in the plate, bolts and structural members. This is a 3D nonlinear model that provides graphical and empirical results for a variety of steel connections that could be used for comparison with established experimental results if available. Design recommendations, failure limitations, and material selection and specifications can be suggested for steel connections in such fire loading.