Research On Shear Resistance Of Pre-Compressed Fabricated Concrete Frame Joints

With the development of building industrialization,precast concrete structure has become one of the important forms of building structure.In the prefabricated concrete frame structure,the beam-column members carry out the load-bearing and transfer of force through the core area of the node,which shows the importance of the node in the prefabricated concrete structure.Therefore,based on the existing precast concrete frame structure,this paper proposes a new type of pre-compressed assembled concrete beam-column joint.The beams and columns of this node are connected by unbonded prestressed steel strands,and the unbonded prestressed steel strands are set in the center of the beam;The joints are only provided with shear steel bars and energy-dissipating steel bars penetrating the contact surface of the beam-column on the upper side of the beam,so that the joint is designed as asymmetrical;The joint beam adopts superimposed components,which are divided into two parts: prefabricated and cast-in-place.The cast-in-place beam and the floor are poured at the same time.The connection method of the beam-column joints not only meets better construction efficiency,but also can improve the problem of insufficient energy consumption performance of pre-compressed assembled concrete joints.And the beam end is equipped with shear reinforcement,which can provide sufficient bearing capacity of the beam-column interface for the node.Based on the research at home and abroad,three pre-compressed assembly concrete beam-column joint specimens were made in this paper.Change the reinforcement ratio of the shear steel bars in the three joint specimens,and study the influence of the shear steel bars on the seismic performance of the pre-compressed fabricated concrete beam-column joints through low-cycle reciprocating load tests and finite element analysis.The main conclusions are as follows:（1）Judging from the failure modes of the three specimens,there are obvious "plastic hinge" failures on the beams,and only a few cracks in the core area of the node,indicating that this node conforms to the seismic concept of "strong joints and weak members,strong columns and weak beams".（2）By comparing the prefabricated test pieces JD1,JD2,JD3,it is found that the bearing capacity of the test piece is related to the reinforcement ratio of the shear reinforcement.With the increase of the reinforcement ratio of the shear reinforcement,the yield,The ultimate load is also correspondingly increased.（3）Due to the asymmetrical design of the nodes,the energy-dissipating steel bars and the shear-resistant steel bars are only arranged on the upper part of the beam,and the hysteresis curves of the three specimens are all asymmetrical.The ability of the node to bear the positive effect is much greater than the negative effect,and the node has a better load-bearing efficiency.（4）The influence of comprehensive shear reinforcement on the seismic performance of joints,such as energy dissipation capacity,bearing capacity,ductility and self-replacement capacity,is recommended to be 0.3%-0.5% for the reinforcement ratio of shear reinforcement in actual projects.（5）Through the finite element simulation,the parameterized analysis of the joints,it is found that increasing the concrete strength level of the joints,the ultimate bearing capacity of the joints will also increase;the axial compression ratio has an impact on the seismic performance of the joints,but the impact is small.（6）Aiming at the asymmetrical design of the joint,it is found that the shear bearing capacity of the joint beam-column contact surface is mainly provided by the friction action of concrete and the pin action of the shear steel bars,so that the shear bearing capacity formula suitable for this joint is given,and Be verified.