Research Of The Seismic Performance Of High-strength Concrete Beam-column Joints Reinforced With High Strength Mixed Reinforcement

High strength concrete structure is suitable for super high-rise buildings,and has many advantages,such as high strength,good corrosion resistance,etc.However,with the increase of concrete grade,its ductile deformation ability gradually weakened,which will have a very large impact on the energy consumption effect of high strength concrete structure.The seismic performance of the beam-column joint may be obviously affected because it is in the complex bearing area.Carbon fiber reinforced composite bars(CFRP)can improve the ductility of highstrength reinforced concrete members,and the residual deformation of concrete joints can be reduced and the post-yield stiffness can be increased by using the linear elastic characteristics of CFRP.Therefore,the mixed reinforcement of CFRP bars and high strength steel bars of high strength concrete structure can maintain good ductility while having high strength,save structural materials,and achieve the effect of energy saving and emission reduction.High performance fiber reinforced cement-based material(ECC)is set in the plastic hinge area of the beam end to increase the energy dissipation capacity of the joint by increasing the deformation ability of the beam end.This paper studies the seismic performance of CFRP bars and high-strength reinforced high-strength concrete beam-column joints,and analyzes: different strength of concrete beams,reinforcement ratio,the presence of CFRP tendons and axial compression ratio on the seismic performance of beam-column joints,it is concluded that the deformation of beam bearing capacity,joint capacity,eventually damage state,hybrid reinforced high strength reinforced high strength concrete beam-column joints,shear bearing capacity and ductility coefficient of energy consumption and stiffness degradation curve change rule,The finite element analysis and simulation of the beam-column joints are carried out in Open Sees.The main research conclusions are as follows:1.All the beam-column joints have "X" shaped cracks at the beams,resulting in bending failure,and the joint damage is relatively light;The seismic performance of the beam-column joints equipped with CFRP bars is better than that without CFRP bars under the same working condition.ECC can improve the plastic hinge Angle,shear deformation and ductility of joints,and also help to slow down the formation of "X" cracks,so that the cracks in the plastic hinge area are thin and dense.Low axial compression ratio can significantly increase the ductility coefficient of high-strength beam-column joints.Low stirrup ratio in the core area can improve the post-yield stiffness curvature and shear deformation capacity of beam-column joints.Using low strength concrete C30 in the high strength concrete beam can improve the ductility coefficient of joints.The higher axial compression ratio and the higher joint stirrup ratio are more beneficial to the high elastic modulus effect of the high strength rebar,and improve the utilization rate of CFRP bars.2.The shear bearing capacity of CFRP bars and high-strength reinforced high-strength concrete beam-column joints is checked by using the calculation formula of the code calculation,the simplified tension-compression bar calculation model and the general calculation model after considering the revision of CFRP bars.The results obtained by checking are all more appropriate.The average value of safety reserve coefficient of the calculation model of shear capacity provided by the code is the highest,and the calculation result of this formula is the most safe and reliable.The prediction results using the simplified tension-compression bar model are the most stable.3.The software Open Sees is used to conduct simulation analysis on the beam-column nodes under reciprocating displacement loading.The results show that: the cross joint method and the Pinching4 shear parameter modeling method are used to model and analyze the joints,and the results are in good agreement;The influence of different shear parameters on the shape and size of hysteretic curves was discussed by using finite element model.The energy dissipation capacity of high-strength concrete beam-column joints decreases with the increase of reinforcement ratio of CFRP bars,and increases with the increase of reinforcement area and yield strength.The bearing capacity of the beam joints using low strength concrete decreases faster than that of the high strength concrete beam-column joints.