Experimental Research on the Fire Resistance of Precast-Cast-in-Place Composite Square Concrete Columns

An experimental study was conducted to evaluate the fire resistance of two full-scale precast-cast-in-place composite square concrete columns featuring a novel connection method under the ISO 834 standard fire curve. The investigation aimed to examine the differences in failure modes， axial deformation， and fire resistance limits when the core cast-in-place concrete strength was C30 （normal-strength concrete） versus C60 （high-strength concrete）. The results demonstrated that the use of high-strength core concrete led to more severe spalling. The precast square tubes provided effective thermal insulation， delaying heat transfer to the core concrete， thereby protecting it and resulting in a smaller loss of bearing capacity. Furthermore， the precast square tubes and the core concrete exhibited synergistic behavior， maintaining excellent structural integrity even at failure. The axial deformations at failure were -25.28 mm for C30 and -19.32 mm for C60， indicating an insignificant difference. However， the fire resistance limits were 121 minutes for C30 and 48 minutes for C60， revealing a significant degradation in fire resistance when high-strength concrete was used in the core. In conclusion， composite columns with normal-strength core concrete possess superior fire resistance compared to those with high-strength core concrete.