Pushover Testing of Damaged Sub-Standard Three-Story Concentrically Braced Steel Frame with Stiff Rocking Core

A rehabilitated 1/3 scale sub-standard three-story concentrically braced frame (3NCBF) was subjected to uni-directional uniform drift pushover loading after the completion of hybrid seismic testing. Cyclic loading to failure was not performed on this specimen because out-of-plane twisting observed during hybrid seismic testing threatened to damage critical test setup components required for the remaining experiments. Actuators attached to the 3NCBF specimen at each floor elevation were retracted to impose a uniform drift to acquire data on the ultimate strength and failure mechanism of this rehabilitated frame.

The 3NCBF specimen was designed using forces obtained from a 1959 SEAOC equivalent lateral force procedure (ELFP), and several connection details were purposely under designed based on a survey of older steel construction. The stiff rocking core (SRC) rehabilitation frame was attached to the 3NCBF specimen at each floor elevation using fixed-pinned links designed to dissipate energy through yielding in flexure. The SRC allows lateral forces to redistribute along the height of the frame as strength and stiffness degrade due to damage in the braces. This prevents the formation of a soft-story collapse mechanism commonly observed in older steel construction.