Experimental investigation of residual stresses in thin-walled welded H-sections after fire exposure

Residual stresses can have a significant effect on the stiffness of steel members. Residual stresses in welded H-shaped sections at room temperature have been widely studied. However, little information is available on residual stresses in steel members after fire exposure. Fire exposure affects the magnitude and distribution of residual stresses due to plastic deformation and creep in steel at elevated temperatures. This paper presents the results of an experimental investigation on post-fire residual stresses in thin-walled welded H-shaped sections, both for mild Q235 steel with a nominal yield stress of 235 MPa and high strength Q460 steel with a nominal yield stress of 460 MPa. Five Q235 steel H-sections and five Q460 steel H-sections were investigated. Residual stresses at ambient condition were also measured as a baseline. Specimens were heated to 200 °C, 400 °C, 600 °C and 800 °C and residual stresses were measured after the temperature of specimens reached the target temperature and cooled down to room temperature. It was found that the residual stresses after fire exposure decrease significantly with increase of specimen temperature. Based on these experiments, recommendations are provided for the distribution and reduction in magnitude of residual stresses after fire exposure.