Shear Bearing Capacity Tests And Computing Method Study Of Diaphragm-through Connection Of CFRT

The diaphragm-through connections have been widely used in the concrete-filled square tubular column and steel beam frame structure system in abroad,especially in Japan,with the advantages of simple construction,definite load transferring mechanism and convenient connection.In recent years,with the development of steel structure residential housing in our country,diaphragm-through connections is one of the four main typical connection between CFST column and steel beam and has been more and more applied in practical projects.Domestic and international scholars have done lots of studies on the mechanical property of diaphragm-through connections and got some significant results.However,most existing research results are main about the bending capacity and seismic performance.There is few study about the shear bearing capacity of panel zone and no design specification can be adopted in China.In this paper,the panel zone behaviour of diaphragm-through connections is deeply study by the experimental verification in combination with theoretical analysis and FEM methods.The force transfer mechanisims of panel zone of diaphragm-through connections is made certain.Simplified models and calculation formulas for shear bearing capacity of panel zone were proposed.Based on the many specially literatures,the development and research advances on the joints between CFST columns and steel beam are described,as well as the diaphragm-through connections.The background of this paper is then pointed out and the main contents are put forward.In order to investigate the shear bearing capacity of panel zone and seismic behaviour of diaphragm-through connections of concrete-filled square steel tubular column with steel beam,five exterior connections and six inner connections of diaphragm-through joint are studied by low frequency cyclic loading test.The failure character and load-displacement curves of panel zone are gained.Based on the core concrete slitting test results,the crack formation of core concrete and its development rule on the damage surface are summarized.The width of compression strut of core concrete is made clear.Three-dimensional finite element models for the diaphragm-through connections with materials nonlinear,geometric nonlinear and contact problems between the steel and the concrete is established using ANSYS software.This paper makes an elastic and plastic analysis and calculation of the specimens.The reliability of the models was validated by experimental results.Comparison analysis indicates that calculating results agree well with experimental results.Then the three dimensional finite element model of exterior and inner connections were set up and analysed.The yielding mechanism of panel zone is discussed in detail and the width of compression strut of core concrete is determined by the analysis results.The total shear bearing capacity of panel zone consists of two parts: web part of the steel tube and core concrete.The existing calculation methods for shear bearing capacity of panel zone are introduced and its deficiency is mentioned as well.Based on experimental data and finite element analysis results,the simplified computing model of steel tube web and core concrete are established for shear bearing capacity calculating.A new calculation method for shear bearing capacity of panel zone based on superposition theory was presented.Comparison analysis indicates that calculating results agree well with experimental results,which provided reliable data for diaphragm-through connections design and fabrication.