Seismic behavior of concrete-filled double-skin thin-walled steel box columns stiffened with PBL

Concrete-filled double-skin thin-walled steel box (CFDTSB) columns stiffened with PBL are a new type of columns formed by setting longitudinal ribs on an inner wall of outer and inner steel boxes of CFDTSB columns. Quasi-static tests on one CFDTSB column without PBL and two CFDTSB columns stiffened with PBL were carried out to investigate their seismic performance. The damage modes, hysteresis curves, envelope curves and strain distribution on outer steel boxes of different specimens were compared and analyzed. Then, FE models of CFDTSB columns stiffened with PBL and without PBL were established and parametric analysis was conducted to investigate the effects of cross-sectional hollow ratio, thickness of outer steel boxes and height of PBL ribs. At last, calculation methods for load bearing capacity of the two types of columns were proposed. It is found that, the arranging of PBL ribs significantly improves the local buckling of outer steel boxes, enables steel boxes to fully participate in bearing the axial load and bending moment, and enhances the interaction between steel boxes and sandwich concrete, so the bearing capacity, deformation capacity, and energy dissipation capacity of CFDTSB columns stiffened with PBL are improved a lot, compared with CFDTSB columns without PBL. That is to say, the seismic behavior of CFDTSB columns stiffened with PBL is good. The proposed method could consider the local buckling of steel boxes, steel-concrete interaction and effect of PBL ribs on them rationally, thus predicting the load-carrying capacity of the two types of columns.