Research On Measures To Improve Collapse Resistance Of Concrete Filled Square Steel Tubular Column H-beam Joint

The damage of vertical load-bearing components in building structures under extreme loads leads to the progressive collapse of structures,which often causes heavy casualties and economic losses.At present,more and more attention has been paid to the collapse resistance of structures in the process of structural design.The joint is the key component of the structure,and its robustness is directly related to the collapse resistance of the structure.Therefore,In this paper,the numerical simulation research method is adopted,and the research object is the joint of square CFST column and H-shaped beam.In order to improve the mechanical properties of the joints under the condition of progressive collapse of the central column failure,the following works are carried out.（1）Referring to two examples of beam column joint collapse performance test in the existing literature,the finite element model of the specimen is established with the help of the nonlinear finite element software ABAQUS,the failure process of the specimen is simulated by using the explicit dynamic analysis method,so as to verify the feasibility of the finite element simulation method,which provides a strong support for further research using similar methods.（2）Considering material damage and bolt preload,the failure process of the joint of square CFST column and H-shaped beam under the condition of central column failure is simulated based on the component removal method.The failure mode,bearing capacity development,beam section stress development in the core area,internal force and resistance development of the joint are analyzed.It is found that the joint has intermittent failure at the beam column connection,and the beam is mainly flexural in the stage of small deformation The force is mainly provided by the beam mechanism.With the increase of the displacement of the central column,the neutral axis moves upward,and the beam transits from the bending state to the tensile state.The later resistance is completely provided by the catenary mechanism.（3）By weakening the flange or web of square CFST column and H-shaped beam joint,it is found that the ductility of the joint is enhanced after weakening,which is conducive to the development of catenary mechanism.Both measures can significantly improve the mechanical properties of the joint under collapse conditions.On this basis,the weakening parameters are studied,and a reasonable range of values is given.（4）Four ways are used to strengthen the joints,such as increasing the material strength of steel beam,increasing the thickness of lower flange,adding cover plate and haunching at the end of beam.It is found that all four methods can effectively improve the mechanical properties of the joints under the collapse condition,especially the addition of cover plate and beam end armpit.The influence of the geometric parameters of the cover plate and the angle between the armpit and flange on the mechanical properties of the joint is studied,and the suggestions are given.