PURPOSE: To make unnecessary diaphragms and electroslag welding, by a method wherein set-up steel members, in each of which a horizontal piece and a vertical piece are set-up in the shape of a letter L or T, are placed on the inside of each surface of a tubular steel column, and circular rings each are placed in the tubular steel column so as to cover the protrusions composed of the steel members.

CONSTITUTION: L-shaped set-up steel members 3, in each of which a horizontal piece 3a and a vertical piece 3b are set-up in the shape of a letter L, are placed on the inside of each surface of a tubular steel column 1 and at the position opposed to each flange of structural steel beams 2. Each circular ring 4 is fitted extending over the top ends of the steel members and concrete 5 is filled up. Therefore, force from the structural steel beams 2 can be smoothly transmitted to the column 1 through the steel members 3, the circular rings 4 and the concrete 5. In this way, diaphragms and electroslag welding for joining the diaphragms and the tubular steel column together are made unnecessary, and the toughness of parts welded by a large amount of heat inputted can be prevented from lowering.