Behaviour Analysis Of Flexible Steel Connections In Fire

Numerical simulation of flexible end-plates connections and fin plate shear connections under fire was successfully done using FEM software ANSYS. Geometric, material and contact non-linearity was taken into account. Finite element models were validated by tests results, Analysis of variety of parameters which have great influence on fire resistant capacity of joints had been made, and suggestions that benefit for design were proposed. Following contents were investigated in this paper:1. Non-linear finite element analysis of flexible end plate connections.Temperature distribution, rotation capacity and failure modes of flexible end plate connections in fire was investigated by numerical simulation and theory analysis. The influences factors to fire-resistant capacity were mainly investigated from four aspects of load ratio, end-plate thickness, fire condition, axial restraint.Research shows that the fire protection to column is effective in lowering the temperature of the joints, raise the critical temperature and limit time of fire-resistant. The connection's initial rotation angle increases with the load increases, while the critical temperature decreases as the load increases. with the end-plate thickness increasing, initial rotation stiffness and critical temperature of connection is increasing, on the contrary, initial rotation angle and the rate of degradation of connections'stiffness decreases, but the increase in the thickness of the end plate exacerbated stress concentration of junction between the end plate and the web Welding. The whole structure, because of effect of the internal beam axial temperature force caused by axial restraint, its deformation is smaller than isolated joints, but its critical temperature is higher. When Beams bottom flange buckling occurs, the characteristics of the connection is characteristiced by "simply supported", then, cross-deflection will increase dramatically.Composite joint of flexible end plate connections in fire was investigated by numerical simulation.2. Non-linear finite element analysis of fin plate shears connections.Joints'temperature distribution regulation, structural deform regulation, destruction process and pattern were researched in based on the consideration of structure axial restraint in the heated conditions.The factors influencing fire-resistant capacity were analyzed from following aspects, catenaries action, type of load, load size, stiffener thickness and the ratio of shear plate thickness to beam web.Research shows that elongation of the highest holes in the beam web is the main pattern of failure. The elongation increased joint flexibility, allowing larger deformations without further fracture. When connection come into the phase of larger deformations, axial force turn into the tensile force, prevent the further deform, it means that catenaries action occur. Load style and load level have a decisive impact on fire-resistant capacity. After numerical simulation, it is found that the connections with the higher ratio of concentric force in total load and higher load rate have the worse fire-resistant properties. In order to ensure the limit capacity of stiffener, it is suggested to choose thickness of stiffener as the same as beam flange. Beam web choose the same thickness as fin plate to improve the flexibility of connection. On the premise of ensuring the safty of bolt, increasing the thickness of the web appropriately could improve the connections'fire-resistant capacity.