Influence Of Grouting Defects On Seismic Performance Of Precast Concrete Beam Column Joints

Prefabricated building is a new type of building,which is made in advance in the factory and transported to the construction site.In recent years,the state vigorously promotes prefabricated buildings.In 2016,the State Council issued relevant documents to focus on prefabricated buildings such as prefabricated concrete structure,steel structure and wood structure,and increase the proportion of prefabricated buildings.Prefabricated concrete frame structure is an important part of prefabricated building.The structure and construction of concrete beam column joint is the decisive factor of prefabricated concrete frame structure.The main connection form of prefabricated concrete beam column joint is grouting sleeve connection.Grouting sleeve often leads to grouting defects due to construction errors and improper project management.Grouting defects will affect the mechanical properties of joints,and China is an earthquake prone area,Therefore,this paper studies the seismic behavior of precast concrete beam column joints with grouting defects under cyclic loading.On the basis of understanding the current situation of grouting sleeve connection and the stress mechanism of prefabricated concrete frame joints,the existing unidirectional tensile tests with grouting defects are introduced,and then the modeling accuracy is verified by simulation in ABAQUS under two working conditions.Then the finite element model of prefabricated concrete beam column joints is established to study the influence of grouting defects on the seismic performance of joints under nine different working conditions,Finally,based on the finite element results and theory,the existing formulas are modified,and the shear capacity calculation formula considering grouting defects is derived and verified.The first chapter introduces the development status of prefabricated building and grouting sleeve connection in China.On this basis,it is necessary to study the prefabricated concrete beam column joints with grouting defects.The second chapter introduces the origin,classification,action mechanism,construction process,material specification requirements,grouting defect types and causes,connection requirements,current concrete frame joint calculation theory and calculation formula at home and abroad.In the third chapter,the existing uniaxial tensile tests are introduced and the finite element simulation is carried out to verify the accuracy of the modeling.In Chapter 4,the influence of grouting defects on seismic performance of beam column joints is studied,including hysteretic curve,skeleton curve,stiffness degradation curve,ductility and energy dissipation capacity.Then,the parameters of the joint defect size,axial compression ratio and reinforcement ratio are analyzed to study the influence of these parameters on the bearing capacity and stiffness of the joint.Finally,on the basis of the finite element results and the existing theories,the formula of shear capacity of the joint considering grouting defects is derived and verified.The main conclusions of this paper are as follows:（1）grouting defects can cause bond slip of the joint under cyclic load,the area of the joint hysteretic curve becomes smaller and smaller with the increase of defects,and the influence of horizontal defects on the hysteretic curve is greater than that of vertical defects.（2）The peak bearing capacity of the joints decreases by 4.1% to 24.6% and the ultimate bearing capacity decreases by 1.1% to 14.4%when the vertical 2D defect increases to the vertical 5D defect;The peak bearing capacity of the joint decreases by 2% to 28.8%,and the ultimate bearing capacity decreases by 1.4%to 21.2% when the defect of 5mm increases to 20 mm.（3）When the vertical defect increases to 5D,the initial stiffness of the joint is only 62% of that of the non defect joint,and when the horizontal defect increases to 20 mm,the initial stiffness of the joint is only 56% of that of the non defect joint.（4）The ductility of joints decreases from 3.2 to 2.6 with the increase of vertical defects,from 3.2 to 2.37 with the increase of horizontal defects,and the energy dissipation capacity decreases with the increase of defects.（5）When the axial compression ratio increases from 0.3 to 0.5,the peak bearing capacity of vertical defective joints decreases by 0.6% and 2.5%,the ultimate bearing capacity decreases by 3.7% and 7.1%,the peak bearing capacity of horizontal defective joints decreases by 1.2% and 2.7%,and the ultimate bearing capacity decreases by 5.5% and 8.7%.（6）When the reinforcement ratio of beam end increases from 1.4% to 2.1%,the peak bearing capacity and ultimate bearing capacity increase by 9.7% and 17% and 3.4% and 9.9% respectively;The peak bearing capacity and ultimate bearing capacity of the joints with horizontal defects increase by 8.5%and 15.3% and 3.6% and 13.1% respectively.（7）The finite element simulation results show that the influence of horizontal defects on the seismic performance of joints is greater than that of vertical defects,and horizontal grouting defects should be avoided in practical engineering.