Analysis on local thermal critical buckling of square concrete filled steel short tubular under axial compression

Based on the small deflection bending theory of thin plate, inference analysis on the local thermal buckling of steel plate of CFST columns was conducted with the method of energy. Critical buckling coefficient under axial load and thermal load coupled situation has been deduced as well as critical buckling temperature formula. Meanwhile, the relationships between the critical buckling load at room temperature and axial load with thermal load under coupled field of steel plate were deduced. The results show that the Young’s Modulus of steel tube under fire has no effect on critical buckling temperature change. The width to thickness ratio is the main influence factor on critical buckling coefficient and critical buckling temperature change，thus the limit of width to thickness ratio has been suggested in the paper. Based on the critical buckling coefficient, the minimum value of length-width ratio can be calculated and used in the design of steel plate’s thermal buckling.