Research On Seismic Performance Of Parcially Post-tensioned Precast Concrete Frame Jiont

Since reform and opening up,China has vigorously promoted urbanization,and the construction industry has come to a new stage.Under the new development situation,the industrial structure system,represented by precast concrete structure,is consistent with the strategic goal of energy conservation and sustainable development.It can be used as the mainstream of the modern architecture of construction industry.Among all kinds of precast structural systems,the precast concrete frame structure is the most easily modular,standardized and stereotyped,and has wide application scope.The performance of beam column joints is the key factor affecting the seismic performance of the whole frame structure,especially for the precast concrete frame structure.At present,the connection forms of precast beam column joints are mainly divided into two types: "wet" and "dry".The "wet" connection node has good integrity and strong energy dissipation capacity,but the installation efficiency is poor and the cost is high."Dry" connection is mainly in the form of prestressed connection,with high installation efficiency and strong resilient ability,but the ductility and energy dissipation capacity are weak.In addition,the conventional prestressed precast joints are mostly assembled by using prestressed steel strands to penetrate the whole precast beam,thus,the perforation work is large and it is inconvenient for construction.In this paper,a new type of partially post-tensioned prestressed concrete frame joint is proposed.Using the connection mode of "dry and wet combination",it is a new structure with high efficiency,strong resilient ability of “dry” node and good integrity,strong energy dissipation capacity of "wet" node.In this paper,the experimental research and finite element analysis of the new type of precast joint are carried out,and its fabrication process and seismic performance are preliminarily explored,and the basis for further optimization of the jiont structure is provided.The main contents are as follows:1)based on a seven-storey frame structure,a cast-in-place contrast jiont and four partially post-tensioned prestressed joints with different types of prestressed reinforcing bars,bonding modes and grouting materials as test parameters,are designed and built.2)low-speed cyclic loading tests of five test components are carried out,and the seismic performance of the test component is preliminarily analyzed through the observation of the test phenomenon and the failure state of each joint component.At the same time,the parameters such as hysteresis curve,skeleton curve,yielding load,stiffness degradation and energy dissipation value are obtained by collecting the load,displacement,stress and strain datas of the test components in the process of low-speed cyclic loading test.The seismic performance of the joint is analysed from three aspects,which are strength,deformation and energy.3)Using the finite element analysis platform OPENSEES,the experimental components are simulated under low-speed cyclic load,and the accuracy of the model is verified by comparison with the test results.On this basis,the precast component is parameterized and the influence of different factors on the seismic performance of the joint is explored,which provides the basis for further optimization of the node form.Research shows:1)Compared with the cast-in-place joints,the partially post-tensioned prestressed concrete frame joints have higher lateral stiffness and bearing capacity,smaller residual deformation,stronger self resilient ability,and better energy dissipation capacity under large deformation.2)The bonding strength of the longitudinal reinforcement in superimposed concrete,the performance and the bonding mode of the prestressed reinforcing bars have important influences on the seismic performance of the partially post-tensioned prestressed frame joints.3)The finite element analysis program OPENSEES can properly simulate the reaction of beam-column joints under low-speed cyclic load.Through parametric analysis,it can be found that increasing the number of the longitudinal reinforcing bars in superimposed concrete,the bonding strength and the initial stress of prestressed reinforcing bars can effectively improve the energy dissipation capacity and ductility of the partially post-tensioned prestressed frame joints.