Effects of sustained axial load and cooling phase on post-fire behaviour of concrete-filled steel tubular stub columns

This paper experimentally investigated the effects of pre-load and cooling phase on the residual strength and stiffness of concrete-filled steel tubular (CFT) stub columns which were heated and cooled down to room temperature under sustained axial load. CFT stub columns were axially loaded and heated to specified high temperatures in a specially built electrical furnace. After the specimens cooled down to room temperature while the axial load was kept constant, the stub columns were loaded to failure. The test results showed that the mechanical behaviour of the fire-damaged CFT stub columns with pre-load was obviously different from those without pre-load. The axial load level and the high temperature exposure had more significant effects on the stiffness of CFT stub columns than the residual strength. The sustained pre-load led to significant residual deformations of CFT stub columns during the cooling phase. Based on the test results, it is recommended that the effects of sustained axial loads and fire cooling phase should be taken into consideration in assessing the fire-damaged CFT columns.