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This paper presents experimental and numerical investigations on the characteristics of residual stresses generated by induction heating (IH) on 12 mm thick steel plates. IH at 250 • C and 350 • C provided high tensile residual stresses in the heating field but high compressive stresses away from the heating field. The double heating case generated higher compressive residual stresses-around 200 MPa-than the single heating case because of the superposition of the compressive residual stresses. It will be expected to improve the fatigue performance of welded joints when IH is applied for repair work on existing steel structural members susceptible to fatigue damage. Numerical simulation models for predicting residual stresses by IH were proposed by adopting the body heat flux input and the surface heat flux input. They will be beneficial for identifying the optimum heating conditions, such as the target temperature and the heating field, for applying IH to the actual repair work of the steel structural members.

A series of fundamental experimental investigation was conducted in order to examine the effect of PWHT by sheet-type ceramic heater on the residual stress, deformation and compressive behavior of non-stiffened welded box columns. The sheet-type ceramic heater was able to control the required temperature history for PWHT with high accuracy. The welding-induced tensile and compressive residual stresses of the specimens were reduced by 90% and 76% respectively with PWHT. Besides, PWHT could reduce the welding-induced out-of-plane deformation by 22%. It was revealed that the PWHT specimens had a slight higher stiffness than the As-welded specimens when applying monotonic static compressive load on both As-welded and PWHT specimens. They could also enhance the ultimate compressive load capacity about 32% of that of the As-welded specimens. The effectiveness of PWHT with the sheet-type ceramic heater could be confirmed.

To improve the fatigue life of welded joints in steel bridges, a series of experimental and analytical investigations was conducted on a method of welding residual stress reduction by local heating with an induction heating (IH) device. The IH coil of 110 mm x 40 mm was installed around the fillet weld and heated to 350 °C. The tensile residual stress of about 340 MPa was reduced to under 30 MPa. The local heating experiment was simulated by the thermal elasto-plastic analysis to examine the mechanism of residual stress reduction. A four-point bending fatigue experiment was conducted. The fatigue life of the locally heated joints became two to five times longer than that of the joints without heating under the applied stress conditions of 70 to 100 MPa.