Development and axial behavior of precast concrete wrapped square steel tube columns

Conventional thin-walled square steel tube columns are vulnerable to local buckling, carbon steel is susceptible to corrosion, and complicated fireproof measures increase the maintenance expenditures. As a result, a novel composite component, namely precast concrete wrapped square steel tube (PCWST) column is developed in this study. Seven PCWST columns subjected to axial compression load were investigated experimentally with different width-to-thickness ratios, specimen sizes, types and configurations of shear connectors in comparison to three square steel tube columns. The distinctive behavior of PCWST columns and square steel tube columns included failure modes, axial load-axial shortening responses, stiffness, buckling respond, load-carrying capacity and ductility were compared. Based on experimental results, nonlinear finite element (FE) models with full detailing were established and validated. Meanwhile, a simplified formula for predicting the load-carrying capacity of PCWST columns was proposed. Tested and simulated results show that steel tube and reinforced concrete (RC) encasement worked together for PCWST columns, and the head studs and the developed kinked rebars can enhance their interaction. The existing of RC encasement dramatically improves stiffness and load-carrying capacity, and it also delays the occurrence of local buckling of steel tubes.