Study On Seismic Behavior Of Assembled Concrete Columns Connected With Steel Joints

Joint connection is the key technology of assembly building.Its performance has an important impact on the overall reliability of the structure and the realization of the design concept of "equivalent cast-in-place".Most of the existing precast concrete frame column-column joints adopt cast-in-place concrete method in beam-column joint area,which has many wet operations,difficult construction quality and long construction period.In this paper,a kind of frame column-column connection is proposed,that is steel joints connect precast concrete columns,and nuts are fastened between the steel joints welded on the longitudinal bars of the upper column and the longitudinal bars extending on the surface of the lower column.Through the low-cycle reciprocating loading test of full-scale specimens and the finite element simulation,the seismic performance of steel-joint assembled columns is evaluated to verify the same integral cast-in-place columns in engineering application,and the bearing capacity of the joints and the checking method of the strength of steel joints are analyzed.The specific research work and results of this paper are as follows:(1)Through the low-cycle reciprocating loading test of the whole cast-in-place column and the assembled concrete column connected with steel joints,the test phenomena and failure modes of the specimens,as well as the seismic performance indexes such as hysteresis curve,skeleton curve,rigidity degradation,bearing capacity attenuation,and the strain development law of steel bar and steel plate and the deformation performance of the column body are obtained.The test results show that bending failure occurs at the bottom of the whole cast-in-place column and the assembled column.The bearing capacity of the assembled concrete column with steel joints is slightly higher than that of the whole cast-in-place column,and the ductility and energy dissipation capacity are comparable to those of the whole cast-in-place column.The effective transfer of reinforcement stress,the horizontal deformation and plastic hinge bending deformation of the whole cast-in-place column and the assembly column are basically the same,and the steel joint connection of the assembly column remains intact during the loading process.(2)In this paper,the finite element software ABAQUS is used to simulate the assembled concrete column with steel joints.The damage-plasticity model is used in the constitutive model of concrete and the double-folded line model is used in the steel constitutive model.Based on the good agreement between the finite element analysis results and the test results,the parametric analysis was carried out.The effects of the axial compression ratio,the height of the steel joints and the shear resistance measures of the joints on the mechanical properties of the assembled columns with steel joints were analyzed.The analysis results show that the seismic performance of the assembled column can reach the same level as that of the whole cast-in-place column under high axial compression ratio when the position of the steel joint is above 0.9 m from the bottom of the column.In engineering application,it is suggested that the steel joint should be set at the distance of 1.2 m from the bottom of the column.(3)According to the stress condition of steel joints and relevant specifications,the strength checking method of steel joints and the shear bearing capacity calculation formula of prefabricated column joints are put forward.Combined with the experience of specimen making,the design and key points of assembly column with steel joints are put forward,which provides theoretical basis and reference for engineering application.