Seismic performance of steel frames with controlled buckling mechanisms in knee braces

• Important experimental information on structural performance of effective knee-braced frames was presented.
• Improved brace member design using controlled buckling mechanism was proposed and validated.
• Improved design for knee brace to beam connection was proposed.
• Effect of buckling mode on structural performance was evaluated.
• Parameter for finite element simulation of frame strength was proposed and validated.

This study experimentally evaluates the seismic performance of knee braced moment resisting frame (KBRF) systems. A series of cyclic load tests were performed on the special moment resisting frame (SMRF) and KBRF systems with in-plane and out-of-plane controlled buckling mechanisms in the knee braces. It was found from the test results that the strength and energy dissipation capacity of the KBRFs was significantly enhanced regardless of whether the knee braces buckled in the in-place or out-of-plane direction. Further test result comparisons demonstrated that the allowable drift at which the knee braces reached the buckling stage was higher for KBRF frames equipped with in-plane buckling braces. It is therefore suggested that braces with in-plane buckling modes be adopted for greater earthquake resistance in KBRF frame structure designs.