Seismic Performance Of High Strength Concrete Frame Joints With Centrally Reinforced Column

With the development of civil engineering structures in the direction of long span and high height,the traditional reinforced concrete frame structure design often causes the phenomenon of "large-sized beams and stout columns",which not only occupies the use space,increases the dead weight of the structures,but also causes serious waste of resources.In recent years,the high strength concrete frame structure with centrally reinforced column has attracted extensive attention.Among them,the most simple form of centrally reinforced columns is to add longitudinal reinforcement in the middle section of the traditional frame column and form a centrally reinforced column with composite stirrups,so as to further improve the bearing capacity of high-strength concrete column and reduce the section size.However,at present,the failure mechanism,mechanical properties and seismic design methods of such high-strength concrete frame joints with centrally reinforced column need to be solved.Based on this,the main research work and results of this paper are as follows:Based on the low reversed cyclic loading tests of five high-strength concrete core-column frame joints with centrally reinforced column and a traditional high-strength concrete frame joint,the failure characteristics,stiffness and strength degradation,hysteretic energy dissipation and other mechanical properties were discussed.The results show that shear failure occurs in the core region of all specimens.Moreover,the axial compression ratio,longitudinal reinforcement ratio and stirrup ratio of centrally reinforced column all have influence on seismic performance of frame joints.The frame joints with centrally reinforced column can help to slow down the strength degradation after the peak strength of the traditional high strength concrete frame joints and improve the ductility more significantly.Based on modified compression field theory(MCFT)and Attaalla model,the theoretical models of shear strength of high-strength concrete frame joints with centrally reinforced column were established respectively.The shear capacities of the test specimens were analyzed by Matlab programming,and the calculation results of the two shear analysis models were compared with the test results.The results show that the theoretical calculation values of MCFT model and Attaalla model are in good agreement with the experimental comparison results.The results show that MCFT model and Attaalla model can be used to predict the shear bearing capacities of high-strength concrete frame joints with centrally reinforced column.The finite element analysis software is also used to simulate the frame joints with centrally reinforced column.Although the pinching phenomenon of load-displacement hysteresis curve of each test specimen is more serious than that of the test,the load-displacement skeleton curve is in good agreement with the test.Based on the finite element parameter analysis,the effects of axial compression ratio,longitudinal reinforcement ratio,stirrup ratio and area of centrally reinforced column on the shear performance of the joints are discussed in detail.The results show that when the design axial compression ratio is changed from 0.1 to 0.8,the load-displacement hysteresis curves of each model have little difference.With the increase of the axial compression ratio,the shear capacity of the joints is improved to a certain extent,and the lifting effect is gradually weakened.The existence of the centrally reinforced column can improve the seismic performance of the joints.The greater the reinforcement ratio and stirrup ratio of the central longitudinal reinforcement,the slower the strength and stiffness decrease,and the greater the ultimate displacement at failure.However,the enhancement of ultimate shear capacity of joints is not significant.The variation of the area of centrally reinforced column has little effect on the bearing capacity and deformation capacity of the joints.The research results of this paper are of great scientific significance for exploring the failure mechanism of high-strength concrete frame joints with centrally reinforced column and improving the seismic design and calculation method of the joints,and can provide a reference for further promoting the engineering application of high strength concrete frame system with centrally reinforced column.