Bi-directional shake table tests of a modular steel building with orthogonal buckling restrained braced frames

The experimental performance of a full-scale three-story steel building, referred to as the Modular Test Bed Building (MTB²), subjected to earthquake motions while configured with orthogonal Buckling Restrained Braced Frames (BRBFs) is presented. The MTB² was designed and built such that select components would remain elastic to facilitate their reuse in future shake table tests of structural and non-structural components and systems. In the configuration presented herein, BRBFs are used as the lateral force resisting system (LFRS) in both orthogonal directions. The building was subjected to multiple earthquake input motions of increasing intensity under uni-directional (1D) and bi-directional (2D) excitations. Robust response of the BRBFs was observed, controlling the transient maximum drift ratio to 0.75% and the residual drift ratio to a maximum of 0.05%. The maximum BRB tensile strain reached 4.8 times the yield strain. Assessment of BRB fatigue performance showed minimal damage and was consistent with visual observations. This study reinforced the AISC 341–22 requirement that corner columns, which are part of intersecting orthogonal BRBFs, should be designed considering 100% of the seismic force in both directions. In general, based on the experimental results from three different input ground motions, this requirement may be conservative depending on the particular motion. No damage to columns, beams, connections or gusset plates was observed, which demonstrates that similarly designed buildings with intersecting orthogonal BRBFs are expected to be seismically resilient.