Mechanical properties of cross-shaped built-in lattice circular CFST short columns after fire

This paper describes four short built-in lattice circular concrete-filled steel tube (LCCFST) columns and four cross-shaped equal-strength reinforced concrete (ESRC) short columns. The initial stiffness, load-bearing capacity, ductility, and energy dissipation capacity of the specimens after different heating times (0 min, 60 min, 90 min, and 120 min) were analyzed. The results showed that both types of specimens exposed to fire after water spray cooling failed in the same way as the specimens unexposed to fire, i.e., by oblique shear failure. By extending the heating time, the load-bearing capacity of both specimens decreased constantly. The ductility and initial axial compression stiffness of the cross-shaped LCCFST short columns tended to initially increase and then decrease, while those of the cross-shaped ESRC short columns tended to decrease continuously. All specimens showed an increase in energy dissipation after exposure to fire, and the cross-shaped LCCFST short columns in particular performed better during the transition from the peak load to the failure load. Then, a strength reduction factor of concrete outside the steel tubes after water spray cooling was introduced and a load-bearing capacity formula of short cross-shaped lattice CFST columns was put forward. •Experimental, FE and theoretical studies of the built-in LCCFST cruciform column under actual fire sprinkler conditions are conducted.•FEM modeling method for the temperature field of the built-in LCCFST cruciform column is provided.•A simplified formula for calculating the residual loading-bearing capacity of the built-in LCCFST cruciform column after water cooling is proposed.•The experimental study of mechanical properties of ES-RC cruciform column after water cooling exposed to fire is carried out.