Experimental and numerical studies of a controlled rocking steel frame with buckling-restrained columns

A non-uplifting rocking steel frame with buckling-restrained columns (RSFB) is formed by replacing two side columns in the bottom story of a steel concentrically braced frame with two buckling-restrained columns (BRCs). During major earthquakes, the BRCs first yield to dissipate energy while the other part of the system remains elastic and rotates around the bottom of the middle column to control structural deformation. A pseudo-static test was conducted on the earthquake-resilient RSFB, observing larger out-of-plane deformation occurred in the RSFB first story and the embedment portions of BRCs due to the failure of the out-of-plane restraints. The results indicate that the RSFB needs a stronger out-of-plane restraint to ensure structural performance. A design suggestion for the out-of-plane restraint is subsequently provided. A multi-scale finite element model was established in ABAQUS and validated by the test results, and simulation analyses of the test specimen with full out-of-plane restraints were conducted. The simulation results of this model showed that the hysteresis curve is full under cyclic loads, the lateral drifts are uniformly distributed along the structural height, and the plastic deformation is mainly concentrated in the BRCs energy dissipating portion, implying that the proposed RSFB can yield excellent seismic performance, as expected. Finally, the influences of the BRC embedment lengths on the structural performance and out-of-plane deformation were studied to enhance the out-of-plane stability of the RSFB without full out-of-plane restraints.