STUDY ON AXIAL COMPRESSION PERFORMANCES OF CONCRETE-ENCASED CONCRETE-FILLED STEEL-TUBE STUB COLUMNS STRENGTHENED WITH EXTERNAL STEEL FRAMES AFTER EXPOSURE TO FIRE

Based on verification of fimite element analysis results with relevant experiment data, the axial compression properties of concrete-encased concrete-filled steel tubular (CFST) stub columns at room temperatures, post-fire and strengthened with cladding steel after exposure to fire were studied.The effects of fire exposure time, intervals of batten plate and thickness of cladding steel on the bearing capacity and axial stiffness of specimens were analyzed. The results showed that strengthened with cladding steel, the bearing capacity and stiffness of the specimens were obviously improved, even exceeding the ones of specimens at room temperature. Through parameter analysis, it was found that the degree of reduction for bearing capacity of specimens had experienced a process of increasing first and then decreasing, and the effects of repaired specimens with cladding steel were gradually weakened. The bearing capacity gradually decreased with the increase of intervals of batten plates, but the reduction was small, and the stiffness of specimens was evidently affected. Increasing the thickness of the clading steel could obviously improve the bearing capacity of specimens, and improve their stiffness more significantly.