DISCUSSION ON RESEARCH ACTIVITY PUBLISHED AS "THE ULTIMATE STRENGTH OF REINFORCED CONCRETE COLUMNS USING HALF PRECAST SQUARE TUBE CONCRETE FORM BY CENTRIFUGAL CASTING UNDER COMPRESSION, BENDING AND SHEAR"(Kimiya HAMADA, Yasunao NAKANISHI and Koichi MINAMI, J.Struct. Constr. Eng., AIJ, No.532, 127-136, JUN., 2000)