Abstract
In order to improve the quality of repair welding for existing steel bridges, the effect of residual stress relaxation of welded part by heat treatment with a sheet-type portable heater was investigated through the experiment and analysis on box welded out-of-plane gusset joints. The thermal history required for heat treatment was controlled with high accuracy. The welding residual stress around the yield stress could be relaxed by the heat treatment. The stress relaxation mechanism was elucidated by the thermal elastic plastic analysis considering the high temperature creep characteristics. The fatigue life in the low stress range (100MPa) of joints of which the residual stress was relaxed became twice as long as that of the joints as welded.
