Seismic Performance Study Of Special-shaped Column-beam Joints With Partial Longitudinal Reinforcements Grout-filled Sleeve Splicing

Fabricated special-shaped column frame is a green and economical structural form suitable for low and medium-rise civil buildings.Under horizontal earthquakes,the beam-column joints are the weakest and most critical part of the frame structure,and its bearing and deformation capacity is always the most concerned aspect of structural experts and scholars.This article takes the rural green residential project as a prototype,including assembled monolithic and a new type of fully prefabricated assembly dry joint design.The partial longitudinal reinforcements of the prefabricated special-shaped columns are spliced by grout-filled sleeve,which solves the problem of poor pouring quality caused by the thinner-shaped column limbs,which improves the economics and convenience of production.In order to study the seismic performance of fabricated special-shaped column frame joints,three internal frame joints(cast-in-place 1-shaped column,assembled monolithic1-shaped column,assembled monolithic L-shaped column)and two T-shaped column external frame joints(assembled monolithic and fully prefabricated assembled),quasi-static loading test on the beam end.The analysis results found that: 1)Shear failure occurred at the joints of the frame with 1-shaped column,and both the L-shaped and T-shaped column frame joints suffered bending failure at the beam end.The stiffness of the joints of the same section column frame is similar to the degradation of the joints.Partial grout-filled sleeve splicing of the longitudinal reinforcements of the precast column is effective,and the bearing capacity of the prefabricated special-shaped column frame joints is equivalent to cast-in-place;2)The descending section of the skeleton curve is gentle,showing strong deformation ability.The ductility coefficient is 1.2 times that of the same-section column cast-in-place and fully prefabricated assembly nodes.The seismic performance is better than the cast-in-place node;3)Fully prefabricated T-column frame joint beam hinges have weak plastic deformation capacity,large angular slip caused by bending failure,serious hysteresis curve pinch,and poor seismic energy dissipation;4)Compared with the 1-shaped section,the L-shaped and T-shaped column limbs increase the joint height,which significantly increases the joint’s shear capacity,but its bending capacity is reduced.By discussing four contact models of Coulomb Friction,Spring Elements,Surface-based Cohesive Behavior and Cohesive-Coulomb Friction,Abaqus was used to establish a nonlinear analysis model of materials and contact,and numerical calculations were performed for beam-column joint seismic tests.Comparing the failure characteristics,load-displacement curves and secant stiffness curves of beam-column joints,the numerical calculations are basically consistent with the test results,which can effectively reflect the bearing and deformation characteristics of each joint and verify the correctness of the simplified method of the analysis model.The axial compression ratio parameter analysis was performed on the fully prefabricated T-shaped column side frame joint.The initial stiffness of the prefabricated node increased with the increase of the axial compression ratio,and the axial compression ratio was too large or too small.The ductility decreased,but the bearing capacity of the beam end was affected by it.It is not large,and the design axial pressure ratio is best controlled between 0.2 to 0.5.According to the bending failure phenomenon of the fixed end of the beam,the optimal design analysis is performed from two angles of material strengthening and structural reinforcement: 1)Adding steel fiber to the concrete at the fixed-end beam can increase the bearing capacity of the beam end,and increased the joint ductility is most effective;2)The vertical stirrups at the fixed-end beam are reinforced to enhance the restraining effect of the ferrule to improve the compressive performance of concrete,the bearing and deformation capacity of the prefabricated joints have been strengthened to a certain extent;3)Additional reinforcement on the cross section of the fixed-end beam strengthens the connection of the joints,and the bending bearing capacity increases significantly with the increase of the diameter of the reinforcement,but the diameter of the reinforcement is excessive or the cross section of the beam is too long,and the deformation capacity of the plastic hinge is weakened.