Modeling the Influence of Residual Stress on the Ultimate Load Conditions of Steel Frames

A generalized material model for wide-flange sections was developed based on m-p-tau plots of detailed fiber element models over a full range of moment, axial load and maximum residual stress conditions. Several different cross-sections were investigated to determine the appropriate exponent in the material model for approximating the stiffness reduction under major axis bending or minor axis bending conditions. The nonlinear material model was used as normalized tangent modulus expressions in MASTAN2 and ultimate load analyses were conducted on four benchmark frames. Using residual stress scale factor conditions of 0.6 and 1.4, the relative percent difference in the lateral load at collapse was investigated as the initial vertical load conditions were increased. The influence of residual stress was studied on three test frames with loads applied only at the beam-to-column joints and on one test frame with more realistic design conditions. Discussion is provided on the ability of the material model to approximate the stiffness reduction of wide-flange sections and on the conditions that produce an increased residual stress effect on the ultimate load capacity of steel frames.

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