Study On Axial Compression Performance Of RC Columns After Fire Wrapped With Thin-wall Steel Tube

High temperature of fire may decrease the rigidity and ultimate bearing capacity of reinforced concrete column. A new technique can be used for repairing and strengthening the RC column after fire by wrapped reinforced concrete column with thin-walled steel tube. Due to the constraints of thin-walled steel tube, the core of the reinforced concrete is in a three-way compression state. It increases the compressive strength of the component, leading to the higher ultimate bearing capacity and deformation capacity. The steel tube itself can be used as a template of the new concrete column for easy construction. Without increasing the component size, the reinforcement technology is environment friendly, good performance and high temperature resistant.Experiments and analysis of the axial compression performance of the RC columns after fire wrapped with thin-walled steel tube are done in the paper. The main work and conclusions are as follows: 1. The axial compression tests of eight reinforced concrete columns with thin-walled steel tube after fire, two columns without fire and two columns after fire are carried out. The thickness of steel tube, strengthening mode and cross section shape were analyzed to figure out the influence on failure mode, axial bearing capacity, rigidity and ultimate deformability of the columns. The results show that:(1) The RC columns after fire wrapped with square-shape thin-walled steel tube specimens appear as drum-shaped failure, while the round-shape of strengthened specimens appear as shear failure.(2)The axial bearing capacity and axial rigidity of RC columns after fire wrapped with thin-walled steel tube may regain or even exceed the level of specimens without fire. And the ultimate deformability is larger than specimens without fire.(3)With the increase of the thickness of steel tube, the axial bearing capacity of square-shape RC columns wrapped with square-shape steel tube go up. The axial deformability increases when steel tube only works as constraints, while the axial deformability decreases when steel tube works to support the vertical load.(4)The strengthening mode has no significant influence on axial bearing capacity, while it do has an obvious influence on axial deformability. The axial deformability of steel tube working as constraints is bigger than that the steel tube supporting the vertical load.(5)The axial bearing capacity and the axial deformability of the square column wrapped with circular steel tube are bigger than the square column wrapped with square steel tube.(6)The section shape has little influence on the axial bearing capacity of RC column before fire, while it plays a major role on the axial bearing capacity of RC column wrapped with thin-walled steel tube after fire.(7) The steel tube working as constraints suffers tensile stress and it has a strong constraints on the core concrete. While the steel tube supporting the vertical load suffers compression stress and it is prone to buckling.(8) Steel performance is fully functioned to strengthening the RC column, and it can provide a stronger constraint to concrete.2. Use the superposition method to deduce the axial bearing capacity of RC column wrapped with thin-walled steel tube after fire, and compare it with the test results, design discipline at home and abroad.