Hybrid Testing of the Stiff Rocking Core Seismic Rehabilitation Technique

The use of a stiff rocking core (SRC) has been proposed as a seismic rehabilitation technique to mitigate soft-story response in low-rise to midrise steel concentrically braced frame (CBF) structures. This technique uses a stiff, elastic “spine” to provide corrective lateral forces at the onset of soft-story response but otherwise remains passive for the first mode vibration response. Yielding link element can also be incorporated in the SRC-to-structure connection to dissipate energy and reduce overall building drift. An experimental testing program was performed to investigate the fundamental behaviors of the SRC rehabilitation technique applied to two approximately 1/3-scale prototype CBFs representative of modern and older design practices. Hybrid testing methods were used to simulate building dynamics, the influence of gravity framing, and response of upper stories for a midrise prototype building. Each prototype frame was subjected to two seismic ground motions to evaluate cumulative damage followed by quasi-static cyclic testing to failure. The results from these tests indicate that the SRC is effective at mitigating soft-story response by vertically redistributing lateral demands throughout the structure.