Research On Mechanical Performance Of Concrete-filled Centrifugal Precast Concrete Square Tube Columns And Steel Beam-Column Connections

The precast reinforced concrete column-steel beam(RCS)mixed structure combines the advantages of steel and concrete structures,and gives full play to the structural behavior of these two materials,which is an efficient and economical structural form.It has broad application prospects in the field of fabricated buildings.In this study,a new type of concrete-filled centrifugal precast concrete square tube column-steel beam(CFCPSTS)precast mixed frame system was proposed.Through the combination of experimental research,finite element simulation and theoretical analysis,the mechanical performance of concrete-filled centrifugal precast concrete square tube columns and steel beam-column connections were systematically and deeply investigated.The main research work and results of this thesis are as follows:(1)The shear test of eight square hollow precast concrete tube(HPCT)columns and twelve squre concrete-filled precast concrete tube(CFPCT)columns was conducted.The failure mode,crack propagation,bearing capacity,ductility and deformation behavior were analyzed,and the shear mechanism of the CFPCT column was revealed.The results show that the failure modes of the HPCT and CFPCT columns were shear-compression failure.No bond damage between the precast and filled concrete was observed,and the CFPCT column exhibited good integrity behavior.For CFPCT columns,the presence of filled concrete retarded the development of the column damage,which not only improved the bearing capacity,but also significantly improved the ductility and deformability,and its shear behavior was siginificantly improved compared to HPCT columns.(2)Based on the truss-arch model theory,the calculation formulas for the shear capacity of HPCT and CFPCT columns were proposed,and the calculated results agree well with the test results.Hence,the ultimate shear capacity of a HPCT column or CFPCT column with a shear-compression failure mode can be calculated by the formula proposed in this thesis.Furthermore,when using the formulas to design the shear capacity of the column,it is recommended that the strength of high-strength stirrups should not exceed 500 MPa(the corresponding strength design value does not exceed 415 MPa)to ensure that the crack width meets the limits of the crack width under serviceability limit states.(3)The cyclic loading test of seven squre CFPCT columns was conducted.The failure mode,hysteretic behavior,bearing capacity,ductility,stiffness degradation and energy dissipation were analyzed.The damage evolution process of CFPCT column was analyzed by cumulative damage model,and the calculation method of plastic hinge length of column was discussed.The results show that the CFPCT columns were subjected to compression-flexural damage.No bond damage between the precast and filled concrete was observed,and the column exhibited good integrity behavior.High-strength stirrups have a good restraining effect on the internal concrete.The CFPCT column has moderate to high levels of ductility and exhibited excellent ductility behavior.(4)Based on the ultimate strength theory,a simplified calculation fumula for predicting the bending capacity of CFPCT columns was proposed,and the calculated results agree well with the test results.In addition,the three-fold line skeleton curve model and restoring force model were developed by using the test fitting method.The proposed model can better reflect the hysteretic behavior of the CFPCT column.(5)The cyclic loading test of six square CFPCT column-steel beam joints was performed.The failure mode,hysteretic behavior,bearing capacity,energy dissipation and deformation composition were analyzed,and the shear mechanism of the joint was revealed.The results show that the failure mode of the joints was the failure of joint region,including the shear failure of joint region and the local damage of the concrete at the upper and lower ends of the joint.The shear failure of joint region is the main cause of the failure of the connection.The main factors affecting the bearing capacity of the joint are the thickness of the steel tube,the strength of the precast and filled concrete,and the axial load and the extension height of the steel tube have little effect on it.Increasing the extension height of the steel tube improves the ductility and effectively reduces the rigid body rotation of joint region.(6)Based on the superposition theory,a calcaulation formula for predicating the shear capacity of the joints was proposed.The comparison with the test results shows that the calculated results agree well with the test results.According to the research results of this thesis,some suggestions for the design of CFCPSTS precast mixed frame structure were put forward,which provided a design basis for practical projects.