Effect of fire exposure on residual stresses relief in welded high strength Q690 steel sections

Abstract

Welding induced residual stresses in steel sections can be reduced by high temperatures in fire conditions and thus affect the load bearing capacity and stiffness of structural steel members. This paper presents effect of high temperature exposure on residual stresses relief in welded high-strength Q690 steel sections by experimental and numerical studies. The distribution and magnitude of the residual stresses in three Q690 steel H-sections and three Q690 steel box-sections after exposure to 600 °C and 800 °C were investigated by cutting method. In the numerical studies, finite element analysis software ANSYS was employed to simulate residual stress generation and relief in the entire welding and high temperature exposure stages, including the heating and cooling phases. The predicted results of the residual stresses after an exposure to high temperature obtained by the finite element analysis agree well with the test results. Parametric studies were conducted to investigate the influence of exposed temperature, high temperature duration, and creep strain in steel on residual stresses after being exposed to high temperature. For welded Q690 steel H- sections and box-sections, equations to evaluate the corresponding residual stress reduction factor at elevated temperatures and after high temperature exposure were proposed based on the results of finite element analysis.