Gusset plate connections for naturally buckling braces

A naturally buckling brace (NBB) is a steel brace that consists of a high-strength and low-yielding steel channel arranged in parallel with eccentricity acting along the brace length. To enhance the feasibility of NBB fabrication, three connecting design details of the NBB are proposed: (1) gusset plate (GP) connections for connecting the brace to the steel frame; (2) bolting connections to tie the two channels together; and (3) steel block, knife plate, or angle connections to apply eccentricity along the brace length at the NBB ends. Four brace specimens were subjected to cyclic quasi-static loading to evaluate the proposed configurations. Although GPs provided some rotational restraint, the new design maintained all the advantages of the original concept, especially until 2% story drift, whereas rupture of neither the brace nor the GP occurred up to 4% story drift. A simple design equation for estimating the postyielding stiffness is proposed. The equation is reasonable for the range of slenderness between 40 and 70 and for the ratio of strength between the two channels from 3 to 5.