Experimental Research On Seismic Behavior Of A New Type Ring Beam Connection Of RC Frame Beams Constructed On Existing Columns

In order to reduce the construction difficulty and reduce the damage of the new beam to the old column,this paper proposes a new type of ring beam joint for the new beam connection of the old reinforced concrete column.The low-cycle repetition was analyzed by a comparison test of a new beam new beam test piece connected by a new ring beam type node,an old column new beam test piece connected by a planting bar and a whole cast beam test piece.The effectiveness of the new ring beam joints under load and its force transmission mechanism were tested.The seismic capacity,failure mode,hysteretic behavior,stiffness variation,ductility change and energy dissipation performance of each specimen joint were tested.The effect of different anchoring methods of longitudinal reinforcement on the seismic performance of the joint.The test results show that:(1)the connection form of the new ring beam joint is effective,and the force mechanism is preliminarily obtained: the interface rib effectively transmits the beam end shear force,and the shear failure between the new and old concrete does not appear at the beam end.The circumferential longitudinal reinforcement effectively transmits the tensile force of the beam end,and the plastic reinforcement is formed at the end of the beam after the longitudinal reinforcement is yielded,and the beam undergoes ductile failure.(2)The ultimate bearing capacity of the beam end of the new ring-beam type joints is significantly improved compared with the planting joints and cast-in-place joints,which are increased by 41.4% and 36.3% respectively,indicating that the new ring-beam joints have good carrying capacity;The beam end ductility coefficient of the ring beam joint is slightly smaller than that of the plant joint connection node and the cast-in-place node,but it is still greater than 3,which can meet the needs of engineering applications.(3)From the point of view of energy consumption,the new ring beam type node has the strongest energy consumption compared with the whole pouring node and the planting joint node in the pre-loading stage or the loading stage;from the analysis of the equivalent viscous damping coefficient It can be seen that the equivalent viscous damping coefficients of the test pieces are not much different.With the increase of displacement loading,the stiffness of the three test pieces decreases overall.In most cases,the average stiffness of the new ring beam joint is the largest,the casting node is the second,and the planting node has the lowest stiffness;(4)in the case of ensuring that other influencing factors remain the same,only the connection of the nodes is different.Under the action of reciprocating load,the new ring beam type node has high bearing capacity,rigidity and energy consumption capacity.It can be proved that the connection mode of the new ring beam type node is reliable and can provide reference for related reinforcement engineering.