Research On The Static And Seismic Behavior Of Circular Tubed RC Column To RC Beam Joints

Tubed reinforced concrete(TRC)columns are being widely used in engineering structures in recent years.As the key link of structures,it is very necessary to investigate the performance of TRC column to beam joints.This paper evaluated the static and seismic behavior of circular TRC column to reinforced concrete(RC)beam joints through both experimental and numerical methods.The main research works are summarized as follows:(1)Four circular TRC column to RC beam joints,as well as two reference circular TRC short columns,were tested to failure under axial compression.The failure modes,load-carrying capacities,load-displacement curves and load-tube stress curves of the specimens were analyzed to investigate the influence of joint types,arrangement of orthogonal beams.The test results could provide a basis for the theoretical analysis.(2)A finite element(FE)model,which is suitable for the analysis of circular TRC columns,was proposed in this paper.An estimation method for predicting the effective confining pressure of the steel tube on the core concrete for different load conditions was also proposed.Moreover,to simulate the plastic behavior of core concrete,an equivalent stress-strain relationship for FE model,was proposed after modification of Mander's model for confined concrete.The influences of the main parameters such as boundary conditions,bond and friction on the axial load behavior of the specimens were investigated.Values of the key parameters in the FE model were specified.The numerical predictions of the FE model shown good agreement with the test results,thus the reasonableness and reliability of the FE model were validated.(3)The openings on the circular hollow section(for the joints with tube partially through the joint region)or the gaps between joints tube and column tubes(for the joints with hoop-tube)allow the beam reinforcement to be continuous,thus the shear transfer capacity at the beam-end interfaces of the two type joints is discontinuous.Based on the analysis and comparison of existing theoretical models,design guidelines and specifications,the formulas for predicting the shear transfer capacities of these interfaces and design recommendations were proposed.For the joints proposed in this paper,the openings of tubes would impair the axial load-bearing capacities of the joints.To investigate the influence of the openings,the simplified models for the three type joints were proposed.Based on the numerical and analytical results,the strengthening method that according to the comparison of the effective confining pressures on concrete of different regions were proposed.(4)A total of eleven circular TRC column to RC beam joints were tested under combined constant axial compression and lateral cyclic load to investigate their seismic behavior.These joints include one specimen with stirrups,four specimens with tube partially through the joint region(Type A),two specimens with ring ribs(Type B),and four specimens with hoop-tubes(Type C).The mechanical analyses of the test process and failure modes were conducted.The influences of the variable parameters on the ultimate strength,energy dissipation capacity,ductility,etc.,were also investigated.The lateral displacement of the column top of each specimen was decomposed and analyzed.Moreover,the stress analysis about the longitudinal rebar of concrete beam,the joint tubes and ring ribs were carried out to study the mechanical mechanism.(5)Based on the test results,parameter analysis about the hysteretic behavior of the three type joints was conducted by FE models.The influences of the variable parameters were further clarified.A confined diagonal concrete compression strut model was proposed,and the equations for predicting the shear contribution of diagonal concrete compression strut and joint steel tube were derived according to the confined diagonal concrete compression strut model.Furthermore,the derived equations were modified by conception analysis,tests,and FE results.Finally,the equations for calculating the shear strength of the three type joins were proposed,and the predicted results obtained from the theoretical models shown good agreement compare with test and FE results.