Seismic Behavior Of Concrete Column Base Joints With Post Pouring Area Connected By Grouting Sleeve

Grouting sleeve connection is a common connection method for vertical members of prefabricated concrete structures.However,due to the grouting sleeve is built into the column before assembly,the traditional prefabricated members have some problems,such as invisible grouting construction process and poor controllability of grouting quality,which directly affect the installation quality and mechanical performance of prefabricated concrete structures.In order to realize the visual grouting process and controllable grouting quality of grouting sleeve connection joint,a column base joint with post pouring area connected by grouting sleeve is proposed in this paper.In order to explore the seismic performance of column base joint with post pouring area connected by grouting sleeve,this paper designs and makes one cast-in-situ,one traditional grouting sleeves connection and six new grouting sleeve connection column base joints specimens,and carries out the research by combining the natural vibration characteristic test,low cycle reciprocating load test under axial compression and ABAQUS finite element numerical simulation.It provides key technical support for the engineering application and performance-based design of concrete column base joints with post pouring area connected by grouting sleeve.The main research results of this paper are as follows:（1）The similarities and differences between cast-in-situ,traditional grouting sleeve connection and new grouting sleeve connection column base joints are clarified.The results show that the integrity of the new grouting sleeves connection column base joint is basically equivalent to that of the cast-in-situ specimen,and the natural vibration frequencies of each step of the traditional sleeve connection specimen are basically lower than that of the cast-in-situ and new column base joint specimens.The plastic hinge and column body cracking height of the two fabricated column base joints move up by about one grouting sleeve height compared with the cast-in-situ specimen.It is appropriate to extend the stirrup densification area appropriately.The stiffness degradation law of the three column base joints is the same,and the ductility coefficient is more than 3.0.The energy dissipation capacity of the characteristic points of the new grouting sleeve connection specimen is significantly better than that of the cast-insitu and traditional sleeve connection specimens.The cracking displacement angle and ultimate displacement angle of the three column base joints are greater than the limit value of the code respectively,meeting the seismic fortification requirements.（2）The influence of axial compression ratio on the seismic performance of concrete column base joint with post pouring area connected by grouting sleeve is proved.The results show that the grouting sleeves of each column base joint specimen are intact under different axial compression ratio.With the increase of axial compression ratio,the cracking height of column increases.The cracking,yield and ultimate load of column base joints increase with the increase of axial compression ratio,the ductility coefficient decreases and the stiffness degradation process shortens with the increase of axial compression ratio.With the increase of axial compression ratio,the cracking displacement angle becomes larger and the ultimate displacement angle becomes smaller,and the minimum values are 1/479 and 1/35 respectively,which are greater than the limit value of the code,meeting the seismic design requirements of "no damage in small earthquake and no collapse in large earthquake".（3）The size effect of column base joint with post pouring area connected by grouting sleeves is proved.The results show that the failure modes of column base joints with different section sizes and post pouring materials are bending failure,the plastic hinges move up to the top of the grouting sleeves,the grouting sleeves are intact,and the internal reinforcement is not pulled out.With the increase of the column section size,the lateral bearing capacity of the specimen is greatly improved,but the hysteretic curve is more pinched.After replacing concrete with high-strength cement-based grouting material in the post pouring area,the yield load and peak load increase by 9.97% and 6.31% respectively.The relative nominal flexural strength and energy dissipation coefficient decrease with the increase of column section size and post pouring material strength,showing an obvious size effect.The ultimate displacement angle of column base joints under different section sizes and post pouring materials is greater than 1/50,which meets the seismic design requirements of "no collapse in a large earthquake".（4）The refined finite element analysis method of column base joint with post pouring area connected by grouting sleeve is established and verified.Based on the experimental study of low cycle reciprocating load,the refined finite element calculation and analysis of column base joints are carried out in this paper.The lateral bearing capacity,damage nephogram and stress nephogram are compared with the test results.The strength degradation and stiffness degradation process of the simulated loading process are consistent with the test results.The average peak load error between the simulated value and the test value is 6.26%.The simulation results are in good agreement with the test results,which verifies the effectiveness of the finite element model.The established model has high accuracy and reliability.It verifies and provides a reliable simulation method,and provides key technical support for the expansion analysis of column base joints with post pouring area connected by grouting sleeve.（5）A two-parameter damage model of concrete concrete column base joint with post pouring area connected by grouting sleeve is established.In order to realize the performancebased design,seismic damage performance evaluation and characterization of assembled column base joints or structures with post pouring area,a two-stage two parameter damage model is established based on Park-Ang classical damage model by introducing the proportion correction coefficient of displacement term and energy term and taking yield as the boundary.The model can not only characterize the damage and deterioration process of column base joints,but also has clear physical significance and good universality.Based on the test,the corresponding relationship between the damage degree of column base joints,the interlayer displacement angle and the damage index are clarified.The discrimination criteria are divided according to five performance levels: normal use,basically normal use,temporary use,use after repair and close to serious damage.The seismic damage performance evaluation and quantitative characterization are realized,which has both theoretical and practical value.The innovation of this paper is discussed as follows:（1）The effects of axial compression ratio,section size and post pouring material on the seismic performance of concrete column base joints with post pouring area connected by grouting sleeve are proved,and the failure mechanism is revealed.（2）The Park-Ang two parameter damage evaluation model of concrete column base joint with post pouring area connected by grouting sleeve is modified and established.