Experimental study on evolution of residual stress in welded box-sections after high temperature exposure

Presence of residual stresses can significantly influence the stiffness and fatigue life of steel structures. The extent of residual stress that develops in welded box-shaped sections at room temperature is extensively studied. However, there is limited data on the development of residual stresses after fire exposure. Such fire exposure has great influence on the residual stress distribution due to temperature induced plastic deformation and creep strains in steel. In order to provide benchmark data for the theoretical models and post-fire design recommendations, this paper presents results from an experimental investigation on the post-fire residual stresses in welded box-shaped sections. The tests are carried out by sectioning method, and two types of commonly used steels, mild Q235 steel with a nominal yield stress of 235MPa and high strength Q460 steel with a nominal yield stress of 460MPa are considered. The residual stresses were evaluated after exposing the specimens to 200℃, 400℃, 600℃ and 800℃and cooling down to room temperature. Data from the tests clear show that the residual stresses decrease significantly with increase in specimen temperature. Further, results from the tests are utilized to propose simplified relations for temperature induced residual stresses in welded box-section of Q235 and Q460 steels.