Study On Seismic Behavior And Effective Flange Width Of High Strength Reinforced Concrete Beam-column-slab Space Joints

The geographical location of our country leads to frequent earthquakes.Due to the ability of high-strength reinforced high-strength concrete frame structures to balance seismic resistance and economy,their application in engineering practice is becoming more and more widespread.However,the stress of frame joints is extremely complex.At present,research on the mechanical and seismic performance of space joints has not formed a system,and theoretical research on space joints with cast-in-place floors is even less.This article is based on the experimental research of high-strength reinforced high-strength concrete frame interior space joints conducted by the research group,combined with the experimental research of exterior space joints,and using the finite element analysis software ABAQUS to establish analysis models respectively.The mechanical characteristics and seismic performance of the interior space joints and exterior space joints under low cycle reciprocating loads are studied,and the problem of determining the effective flange width of the frame joint beam end under negative bending moment is also discussed,The main research content and achievements are as follows:(1)Through the experiment of high-strength reinforced high-strength concrete frames interior space joints,established a finite element analysis model,the relative errors between experimental data and simulation results were compared and analyzed,proving the correctness and rationality of the model.On the basis of this,variable parameter analysis was conducted on the interior space joints in the high-strength reinforced high-strength concrete,and the effects of concrete strength in the core area,floor reinforcement ratio,cast-in-place floor thickness,main beam height,and shear compression ratio on their seismic performance were studied.The failure forms of each specimen,plastic deformation of the concrete in the core area of the joint,stress distribution range of the steel skeleton,hysteresis characteristics,displacement ductility were analyzed.The seismic performance indicators such as energy consumption performance and stiffness degradation indicate that increasing the concrete strength in the core area of the joint and increasing the thickness of the cast-in-place floor slab will exacerbate the formation of plastic hinges at the end of the interior space joints,which has a significant impact on the ductility of the component;The reinforcement ratio of the floor slab has the most significant impact on the stress distribution of the slab reinforcement;Increasing the height of the main beam can improve the ultimate bearing capacity of the component.When the height difference between the main and secondary beams is too large,the rate of stiffness degradation is faster;Components with a shear compression ratio below 0.25 have better energy dissipation performance,which provides relevant data reference for seismic design of joints in space.(2)Referring to the finite element modeling method of the interior space joints,a finite element analysis model of high-strength reinforced high-strength concrete exterior space joints was established.On the basis of verifying the correctness and rationality of the model,the stress characteristics and relevant seismic performance indicators of spatial edge joint components were analyzed with the core area concrete strength,floor reinforcement ratio,cast-in-place floor thickness,main beam height,and shear compression ratio as research factors,the results show that increasing the strength of the concrete in the core area,increasing the reinforcement ratio of the floor slab,and the thickness of the cast-in-place floor slab can suppress the shear plastic deformation of the concrete in the core area,improve the ultimate bearing capacity of the component,but reduce the ductility of the component.Under the same loading displacement,the stiffness degradation rate of the component is also faster;When the height difference between the main and secondary beams is too large,the component will experience an increase in shear plastic deformation of the core concrete due to the rapid degradation of stiffness;Similar to the interior space joints,controlling the shear compression ratio of the exterior space joints at a medium to low level can ensure that the components have better energy dissipation.(3)Based on the results of finite element analysis,theoretical analysis was conducted on the interior space joints and exterior space joints of high-strength reinforced high-strength concrete frame.The effects of floor reinforcement ratio,cast-in-place floor thickness,and main beam height on the moment bearing capacity of the components were studied.Under the influence of various parameters,the recommended value formula for the effective flange width of the joint beam end under negative bending moment,and the correlation coefficients of the fitted formulas were all above 0.95,It can better reflect the reinforcement effect of the floor slab on the negative bending moment at the beam end,providing a reference for the engineering design of high-strength reinforced high-strength concrete space joints.