Influence Of Internal Defects Of Semi Grouting Sleeve Connection On Seismic Performance Of Assembled Monolithic Columns

Assembling integral concrete frame structure is one of the main directions of the development of building industrialization.The safety and reliability of the connection of each component of the frame directly affect the development of the prefabricated building.At present,the sleeve grouting connection of concrete frame structure is widely used in China.Due to the errors in the accuracy of the reserved reinforcement position and the difficulty in the quality control of grouting,the performance of the connection may be affected.In view of this,this paper studies the changes of the tensile properties of the sleeve connection and the seismic performance of the assembled monolithic column caused by the connection defects of the semi grouted sleeve as follows:(1)Based on the analysis of grouting defects caused by sleeve grouting construction and their causes,21 semi grouting sleeve connectors with different degrees of grouting defects were made.Through one-way tensile test,this paper studies the influence of grouting defects on the bearing capacity and failure mode of the specimens.The result shows that when connection defect is less than or equal to 30%,the reinforcement of the semi grouting sleeve connection breaks,the yield strength and tensile strength meet the requirements of the code,the load displacement curve of the test piece is basically the same as that of the reinforcement,and the connection defect has almost no effect on the connection performance of the test piece;When connection defects are 40%and 45%of the specimens,the reinforcement will be pulled out,and the deformation will be larger under the same load.For the flawless specimen,the average bond stress of the specimen is 20.05mpa,only 59.9%of the ultimate bond strength,indicating that the semi grouting sleeve connection has a large safety reserve.(2)One cast-in-place concrete column and four assembled integral concrete columns with grouting sleeve connecting reinforcement are designed and manufactured for low cycle reciprocating load test.Among them,the assembled test pieces include one group of flawless columns(ZP)and three groups of assembled integral columns(ZP10,ZP20,ZP30)with 10%,20%and 30%connection defects respectively.The test results show that both the cast-in-place column and the assembled integral column are damaged by bending,the concrete crushing area of the four corners of the cast-in-place column is larger,and the crack development is more sufficient;The grouting layer of the assembled integral column is easy to be pulled apart,and the concrete cracks on the upper part of the sleeve develop more closely;the larger the connection defects in the sleeve,the less the cracks on the prefabricated column body,and the less the cracks develop.The assembled integral column without defect has good seismic energy dissipation capacity,but its seismic performance is weaker than that of cast-in-place column.The existence of connection defects will reduce the bearing capacity,stiffness,ductility and energy dissipation capacity of the specimens.The peak loads of ZP10,ZP20 and ZP30 are only 94%,90%and 84%of those of the specimens without defects,respectively.The energy dissipation capacity of 30%grouting defect specimens is significantly lower than that of other specimens,which indicates that the weakening of grouting defect on the energy dissipation capacity of specimens is not linear.The influence of connection defects can’t be judged only by tensile test.The tensile properties of semi grouted sleeve connection with 30%connection defects are basically the same as that of reinforcement and the connection specimens without defects,but the application to the connection of assembled integral columns will greatly weaken the seismic capacity of components.(3)ABAQUS finite element software is used to carry out numerical analysis of assembled column specimens,and the results are compared with the test results in terms of failure mode,hysteretic curve and skeleton curve.The results show that the tensile damage and PEEQ of the assembled columns are more in the upper region of the sleeve,and the steel bars in this region reach the yield strength earlier.The simulated bearing capacity is close to the test bearing capacity,and the trend of the skeleton curve is basically the same.The results of the finite element simulation are consistent with the test,which verifies the rationality of the model and the feasibility of the finite element analysis method.The research results of this paper can be used for reference to further evaluate and improve the performance of sleeve grouting connection.