In 2007, the building standard law of Japan was revised and a specification of column overdesign factor (COF) was added in case of square tube columns. This research deals with existing non-conformed steel buildings using STKR columns according to being not satisfied with the specification of COF. In this paper, firstly, a practical investigation of existing steel buildings is conducted to the conformance to the specifications of current allowable stress design. As a result, it is clarified that a lot of buildings are not satisfied with the specification of COF. Next, previous researches of reinforcements to increase column overdesign factor are reviewed, and finally, some kinds of reinforcements for column are proposed based on the practical investigation.
