Research On Fire Resistance Of Cast Steel Joints

Cast steel joints have been widely used in large space steel structures because of their good plasticity,toughness,weldability,beautiful and smooth transition shape.With the construction of large space steel structures,the fire resistance and design methods of the structures have become a hot issue concerned by domestic and foreign scholars.It is particularly important to do research on the fire resistance of the joints,which is the key area in the structures.The research on static,seismic and fatigue resistance of cast steel joints at room temperature has made some achievements,but the research on fire resistance is still scarce.In this thesis,the fire resistance of three forks joints in tree-like structures and Xtype joints in single-layer latticed shell structures is numerically simulated by thermalmechanical coupling analysis method.The behavior response of cast steel joints under fire is studied,which includes temperature rising characteristics,deformation characteristics,failure mode,critical temperature and fire-resistant time of the joints.It provides a reference for the fire resistance design of cast steel joints in practical engineering.The main contents and results of this paper are as follows:(1)In this thesis,the fire resistance of three forks cast steel joints used in tree structure is studied.Firstly,the effects of geometric parameters such as pipe diameter ratio,angle between supervisor and branch pipe,diameter to thickness ratio,chamfer radius on the heating process are analyzed.Then the geometrical parameters,axial force ratio and bending moment ratio of the joints are analyzed in detail under three load conditions: axial force alone,bending moment alone,and the combined action of the axial force and bending moment.And the effects of different parameters on the joint fire resistance are obtained.(2)In this thesis,the fire resistance of X-type cast steel joints in single-layer latticed shell structures is studied.Firstly,the effects of geometric parameters such as the angle of branch pipe,the ratio of diameter to thickness and the ratio of stiffening plate thickness to pipe wall thickness on the heating process are respectively analyzed.After that,the geometric parameters,moment ratio and axial force ratio of the joints are analyzed in detail under the load conditions of in-plane bending moment and out-of-plane bending moment,and the effects of different parameters on the joint anti-fire performance are obtained.(3)This thesis summarizes the results of the numerical analysis of fire resistance performance of two kinds of nodes,fitting out the practical formula of critical temperature and fire-resistant time of the joints under different load condition.In order to improve the fire resistance,this paper provides some suggestions for the design of cast steel joints.