High-strength steel with a tensile strength rating of 780 N/mm2 have been developed in Japan. However, in order to make the strength of the weld equal to that of the base material, much labor and cost are required. If the welds for the column splices in the site can be done by under-match welds, the problems in welding work can be greatly reduced. This paper proposes a design method for the column splices performed by under-matching welds. We carried out bending tests of box column members with the column splice and estimated the ultimate flexural strength of column splices.
