Large-Scale Experimental Studies of Damage-Free Self-Centering Concentrically-Braced Frame under Seismic Loading

Conventional concentrically-braced frame (CBF) systems have limited drift capacity before brace buckling and related damage leads to deterioration in strength and stiffness. A new type of CBF is being developed which has greater drift capacity before damage and which develops less permanent (residual) drift under seismic loading. This self-centering CBF (SC-CBF) system is motivated by the goal of minimizing structural damage under seismic loading and is intended to provide significant non-linear drift capacity while limiting damage and residual drift. The fundamental lateral load behavior of the SC-CBF system is rocking on its base, which occurs when the column under tension from overturning moment decompresses and uplifts from its support. The SC-CBF is designed to decompress at the base at a selected level of lateral loading, initiating a rigid-body rotation (rocking) of the frame. Vertically-aligned post-tensioning (PT) steel resists this uplift and provides a restoring force to return the SC-CBF to its support (to re-center the system). Experimental results show that SC-CBFs can be designed to sustain no significant structural damage under the design basis earthquake and only minor structural damage under the maximum considered earthquake.