For TMCP steel of high-rise building frame, an electroslag welding (ESW), which is welding with high heat input, is adopted for the joints between interior diaphragms and plates of steel box columns. Recently, structural steel become to thicker and corresponding higher heat input. The problem is the softening of the heat affected zone(HAZ) of the ESW; the softening is inevitable due to coarsening of grains by TMCP, and the softening may result in lower ESW joint strength than that of estimated by base material strength. In order to quantitatively grasp the influence of HAZ softening part on joint strength, experimental investigation and analysis were carried out.
