Mechanical Behavior Of Concrete Filled Steel Tubular Column-Prestressed Concrete Beam Joint

Finite element numerical simulation is carried out for the concrete filled steel tubular column-prestressed concrete beam joint to study its static performance and seismic performance.The main work and conclusions are as follows:1)Nonlinear finite element analysis(FEA)was conducted for the composite joints.The FEA model considered both geometrical and material nonlinearity,interaction and connection between steel and concrete,residual stress and initial imperfection,etc.Prestress is simulates by falling temperature method.The accuracy of the FEA model was verified by extensive experimental results.2)Based on the ABAQUS finite element model,the mechanism of the concrete-filled steel tubular column to prestressed concrete beam planar connection is studied deeply.The damage development of the frame beam is analyzed systematically.The internal forces,deformation distribution and stress development of the components of the joints(such as brackets,shear rings,ring plates,bolts,etc.)are analyzed in detail.The results show that the common joints are the bending failure of the frame beam,and the prestressed joints are the bending shear failure of the frame beam.The shear failure of the common joints and the prestressing joints occurs on the frame beam,which satisfies the design requirements of "strong nodes and components".3)The static stress mechanism of the concrete prestressed joint and the non-prestressed(ie,ordinary)joint of the concrete-filled steel tubular column and the four beams is studied deeply and the prestressing parameters are analyzed.The results show that the failure mode and the force transfer mechanism of the unprestressed joint and the prestressed joint are the same.The damage occurs at the position of the beam near the beam,which satisfies the design requirements of "strong node,weak component".From the analysis of prestressing parameters,it can be seen that the application of prestressing can significantly improve the cracking load of the joint,the yield load of the upper longitudinal reinforcement,the yield load of the upper leg,the yield load of the lower leg and the yield load of the second row of intermediate bolts,However,with the increase of the prestressing value,the increase of the yield value of each component is gradually reduced.Put forward the optimization design recommendations of the brackets.4)The load-displacement hysteresis curves of the concrete-filled steel tubular column-reinforced concrete beam under cyclic loading are studied.A comprehensive parametric study was conducted.Influences of the parameters on the joint behaviour were analyzed.The parameters included:prestressing force,column axial compression ratio.The internal forces,stress and strain distribution at different characteristic points on the force versus deformation relations were investigated.The results showed that the load versus deflection curves were plump and stable strength and stiffness degradations were observed under cyclic loading.It is concluded that this kind of joints had a favorable hysteresis characteristic.The increase of the axial compression ratio has a negative effect on the ductility of the joints,but the pre-stress has little effect on the ductility coefficient.