Research On The Force Transfer Mechanism Of PC Beam-column Joints Under Earthquake Action

Compared with the cast-in-situ concrete structure,the Precast Concrete(PC)structure has many characteristics of diversification of design,modern function,manufacturing factory,construction assembly and time optimization.During the "13th Five-Year Plan" period,China focuses on the development of green building and intelligent building,and the main point is put on the modernization of the construction industry,adjust the structure of the construction industry vigorously,use the various policies and measures to comprehensively promote the assembly structure and promote the transformation and upgrading of the construction industry.For PC frame,that is usually assembled at the beam-column joints,if the node is damaged under the action of the earthquake,it can directly affect the structural force path,and even lead the structure collapse.In this paper,the stress mechanism of PC frame beam-column joints is studied in this paper.The main results follows:(1)The quasi-static tests of four full-foot PC frame beam-column joints and one cast-in-situ joint are designed and completed.In order to study the seismic performance of the joints,the crack development process and the failure mode of each specimen are described.In order to study the stress mechanism of the joints,the strains of longitudinal reinforcement in different loading periods are measured.It is found that the stacking surface of the PC frame beam is not cracked,and the horizontal cracks appear on the column stack of the beam and column joints.(2)In order to study the seismic performance of PC frame beam-column joints,the hysteresis curves of beam-column joints are analyzed,and the seismic performance indexes such as skeleton curve,seismic energy dissipation displacement ductility coefficient and stiffness degradation are obtained.With the increase of the axial force ratio,the seismic energy consumption capacity of the PC frame joint and the ductility are reduced.Under the same conditions,the greater the axial force ratio and the faster the stiffness degradation.Compared with the cast-in-situ concrete joint J-5,the ductility coefficients of J-1,J-2,J-3 and J-4 are improved by 60.8%,55.9%,50.52%and 41.98%respectively,indicating that the ductility of PC structure beam and column joint has better performance.(3)In order to study the stress mechanism of the beam-column joints of the PC frame,the balance of the horizontal shear force of the truss mechanism is obtained by the balance analysis of the different period of the bond degradation.Which is the dominant role in the action of transferring shear between the truss mechanism and the diagonal strut mechanism.By measuring the strain of the stirrup legs in the different direction,the tension of the hoop limb is obtained from the constitutive relation,and the confinement mechanism is judged in the role played.At the same time,the following conclusions are obtained:???2,the shear is mainly transferred by the truss mechanism;??? 4,the shear transferred by the truss mechanism is reduced significantly,and the majority of the shear is transferred by the diagonal strut mechanism;and 2<??<4,the truss mechanism or the diagonal mechanism to play a major role to be based on different circumstances.The tension Pa of the stirrups in the direction of the longitudinal reinforcement of the beam is always larger than the tensile force Pc of the stirrups perpendicular to the longitudinal reinforcement of the beam.