Seismic Bebavior And Application Study On Local Post-Tensioned Pecast Concrete Beam-to-Column Connections

In recent years,with the promotion of precast buildings,the development of precast structures has flourished in China.Precast concrete frames with the advantages of high prefabrication rate and high production and construction efficiency are an important structural form suitable for the construction industrialization.At present,cast-in-place concrete is mainly used to connect the prefabricated components in China,which causes poor quality and low construction efficiency.Supported by the National “Thirteenth Five-Year” key R & D Plan(No.2011BAJ10B03),in order to further improve the assembly efficiency of prefabricated concrete frames,In this paper,a new dry-wet mixed local post-tensioned precast concrete beam-column connection was proposed,which could be widely used in multi-storey and high-rise buildings in seismic zones.The seismic performance and influencing factors of the new connection,design method and construction technology of the frame using connections were deeply studied.The main work and achievements are as follows:1.The forms of existing beam-column connections of prefabricated concrete frames in the world were reviewed.A new dry-wet combined precast concrete beam--column connection with local post-tensioned tendons was developed,resulting in realization of bay-by-bay and top-and-below stereoscopic construction.2.Four precast and one monolithic full-scale specimens were tested under reversal cyclic loading to evaluate the earthquake resistance and relevant details that may affect the structural performance,including the type of post-tensioned(PT)arc tendon,bonding condition of PT tendons and composite beam top longitudinal reinforcements,and type of grouting materials in the longitudinal reinforcement duct.The results show that the proposed connection fails in a flexural mode at beam ends,which satisfies the design principle of strong-column and weak-beam.The experimental strength is consistent with the theoretical value,and has a sufficient margin.Compared with the monolithic connection,it shows better deformation capacity,comparable ductility and lower energy dissipation due to the steel bar slippage.3.After optimizing some details of the connection,four full-scale precast specimens were tested under reversal cyclic loading to further evaluate the seismic performance and relevant deta1 ils,such as the type of grouting materials,the connection form of composite beam top longitudinal reinforcements,the value of prestressed tension and the form of stirrups in the plastic hinge zone near the beam end.The results show that the performance of the specimen with high-strength steel bars is similar to that of the cast-in-place specimen,and the optimal scheme of the new connection is a combination of high-strength steel bars,local unbonded,grouting connection and open stirrups.4.The nonlinear analysis modes of beam-column aseembly were systematically reviewed and summarized.A fiber model was built using the Open SEES software,and calibrated by test results.Parametric analysises were carried out on the type of PT tendons,the magnitude of tension and the bonding conditions.5.The new connection is emulative,and its design process can be carried out in accordance with the current design and construction codes.The design flow of the precast frame structure was proposed,and on the basis of the previous experiment and theoretical results,several design issues were further discussed,including the design of beam and column members,the shear design of the joint core,the design of corbels and dapped-end beams and related detail requirements.The calculation methods or design recomendations were given.6.There is no mature experience for reference in its key construction technology,due to its novel details.Some key construction methods were proposed,such as arc steel bar processing,location of corrugated ducks,prestress tensioning and gap connecting.On the basis of the process test and the application of the pilot project,the key construction technology and control standards in the fabrication and installation stage were systematically summarized.It also shows that the key construction technology and control standards can meet the requirements of practical application.