Nonlinear Behaviour Analysis Of Extended End-plate Connection In Fire

Numerical simulation of extended end-plate connection's pure steel and composite joints under fire was successfully done using FEM software ANSYS.Geometric,material and contact non-linearity was taken into account. The finite element models were validated by tests results. The influence of various parameters of joints on fire resistant capacity, failure modes and distortion were investigated by finite element analysis and theory of elasticity and plasticity. The suggestions that benefit for design were proposed. The following contents were studied in this paper.Temperature distribution, rotational capacity and failure modes of unprotected and partial protected joints were analyzed. Rotation-temperature curves and Mises stress distribution were obtained. Fire resistance and loading capacity in fire of joint can be obviously enhanced by partial protection.The influences of end-plate thickness on fire resistant capacity and degenerate rate of rotational stiffness on joints was investigated. The results show that:①When end-plate thickness is less than column flange thickness, the rotational stiffness of joints'degenerate rate descend faster with temperature rising, if end-plate thickness is thinner a lot than column flange, then the bending stiffness of end-plate and column flange doesn't match, the tensile part of endplate deviates column flange and bring about obviously plastic bending distortion, which results in bolts subjecting to eccentric tensile load and additional prying force.②If end-plate thickness is more than thickness of column flange, then any more increasing of end-plate thickness almost has no effect on rotational stiffness below 480℃, and the end-plate deformation corresponds with the column flange for the joint without stiffeners, the prying force could be ignored.③Bolts would subject larger prying force for the joint with tensile stiffener even in the condition of column flange having the same thickness with the end-plate, But the stability of column is maintained in fire. So the end-plate thickness should be equal to or more than the thickness of column flange, and the effect of tensile stiffener on bolts'distortion and column stability should be considered together.In structure, the distortion and rotation of joints which subject internal thermal axial force is less than isolated joints. So the resistant fire capacity of joints in integral structure is higher than the isolated joints. The integral effect on joint fire resistance should be considered in joint fire resistance design.Because the bottom flange temperature is always higher than the top flange, the degradation rate of resistance distortion stiffness in the tensile area of the joint in the case of subjecting hogging moment is always quicker then the case of sagging moment, its fire resistance is less than the joint subjected hogging moment. The rotation-temperature curve was obtained by research of the temperature distribution,rotational capacity of composite joint. The research indicates fire resistance of the composite joints is better than pure steel joints because of the compositive effect of reinforced slab and beam as well as integral effect.