Steel braces perform effectively against horizontal forces. However, because of inferior energy absorbing capacities due to buckling, steel braces are not often used in tall buildings which might be subjected to dynamic forces corresponding to earthquake excitation in Japan. With this in mind, a new composite steel brace called an unbonded brace has been developed. The unbonded brace which is restrained by a reinforced concrete cover or steel tube which prevents buckling without changing rigidity by providing insulation between steel braces and reinforced concrete covers. The purpose of this paper is to investigate the stiffness requirement of the reinforced concrete cover if it is not fail until the steel brace attain its yield strength.
