Bidirectional Loading Response of Square-HSS Columns and Panel Zones Measured in Shake-Table Tests of a 10-Story Steel Building

A series of shake-table tests on a nearly full-scale, 10-story steel moment-resisting frame with buckling-restrained braces (BRBs) was conducted at the E-Defense shake-table facility in Japan in February 2023. The specimen was subjected to the Japan Meteorological Agency Kobe motion recorded from the 1995 Kobe earthquake, scaled from 25% to 100%. Yielding of the interior columns and column panel zones was expected from the relative proportions of the columns and beams. At one of the interior grid points, responses of such interior columns, panel zones, BRBs, and connecting beams were measured to understand the interaction between the members under a real, dynamic loading environment. During the 100% motion, the specimen yielded in the 1st to 8th stories, developing maximum story drift ratios of 0.021 rad and 0.017 rad in the two orthogonal directions. As expected, the column and panel zones in the interior grid point yielded under biaxial forces, while the connecting beams remained elastic. Methods to estimate the panel-zone shear force and strength were devised to match the measured responses. A two-dimensional (2D) numerical model of BRB-to-beam-to-column joints was calibrated to match the measured column inflection points and panel-zone deformation. Time history analysis of the frame using the calibrated model reproduced the experimental results with acceptable consistency.