Experimental Study On Static Behavior Of Assembled Joints Of Steel Staggered Truss To Concrete-filled Square Steel Tube Column With External Diaphragm And End-plate Connections

The assembled staggered truss structure system is one kind of structure which is easy to carry out in industrial way.The system is economical,practical and efficient,and more and more researchers are attracted by it.The performance of connections indicates to what degree a structure is pre-fabricated.The connections not only should have good mechanical properties,but also be convenient to construction,minimizing or even preventing on-site welding.Based on the above reasons,this paper studies this connection with experiment and finite element method,and the research result can provide some reference for the application of the connections.In this paper,two sets of external diaphragm and end-plate connections are designed,namely,the upper chord and below chord joints.The main parameters to be studied are the thickness of the external diaphragm,the vertical plate and the eccentricity.At the same time,a finite element model is proposed,which includes geometrical nonlinearity,material nonlinearity,contact between concrete and steel tube,progressive damage and failure of concrete and steel.The finite element model uses the element deletion technique to simulate the occurrence and development of cracks,the results corresponds with experiment very well.Based on the experimental study and the results of finite element analysis,the main factors which have significant influence on the bearing capacity of the connections are analyzed.These factors are:the thickness of the external diaphragm,the thickness of the vertical plate,the strength of concrete and the axial load ratio.Based on the yield line theory and the principle of virtual work,the bearing capacity calculation formula of the below chord is deduced.The bearing capacity of the below chord consists of two parts:the shear capacity of the external diaphragm and the moment-resisting capacity of the steel tube.Then,the formula is compared with the finite element model,showing that the formula has sufficient accuracy to meet the design requirements.