Research On Residual Load Bearing Capacity Of Post-fire Circular Steel Tubes Under Eccentric Compression And Practical Design Method

The performance of steel structures in fire is very poor,and the load bearing capacity of steel structures can be greatly affected after fire.At present,some progress has been made in the study of the mechanical behavior of steel structures under fire,but there are few researches on their residual load bearing capacity after fire.Based on the residual stress and residual lateral deformation of eccentric compressive circular steel tubes caused by fire,calculation method of their residual load bearing capacity was studied.Then a practical method for evaluating residual load bearing capacity after fire was put forward for space grid structures composed of eccentric compressive circular steel tubes.The content mainly includes:(1)Through finite element analysis of eccentric compressive circular steel tubes in fire,the relationship between the residual lateral deformation after fire and rotational restraint stiffness ratio,end moment ratio,axial restraint stiffness ratio,maximum temperature,slenderness ratio,initial moment ratio,initial axial compression ratio was determined.An empirical formula for the calculation of the residual lateral deformation of eccentric compressive circular steel tubes after fire was obtained by regression analysis.(2)The stability of eccentric compressive circular steel tubes after fire was studied,considering the residual lateral deformation caused by fire.The reduction factor of stability coefficient and the corresponding equivalent slenderness ratio were determined for eccentric compressive circular steel tubes with different residual lateral deformation.A simplified calculation method was then proposed for the residual load bearing capacity of eccentric compressive circular steel tubes after fire.(3)A practical method for evaluating the residual load bearing capacity of space grid structures after fire was put forward.A single-layer cylindrical lattice shell was taken as a case study,the necessary reinforcement was suggested and the residual load bearing capacity was evaluated.