Test Study On The Seismic Performance Of Joints In High-strength Concrete Frames With Centrally-reinforced Columns

High-strength concrete columns with central reinforcement(HCCCR)are columns made of high-strength concrete with additional longitudinal bars provided at the central parts of their cross sections combined with composite ties to form the cores,this type of columns significantly enhance the seismic resistant capability of ordinary reinforced concrete frames,it is also an economical and effective measure to reduce the phenomenon of “large column cross sections with little reinforcement” due to the restriction of axial compression ratio of columns in an ordinary concrete frame.Beam–column joint is one of the important structural elements for the seismic resistance of reinforced concrete structures with HCCCR,it is also the weak link of earthquake-resistance of the structures.When a beam-column joint is destroyed,it is hard to repair,resulting in great damage to a structure.So far there have been rare literatures in the research on HCCCR in reinforced concrete structures with columns with central reinforcement home and abroad,and few studies on the beam-column joints in reinforced concrete structures with HCCCR.Owing to this fact,pseudo-static tests were conducted on 6 specimens of beam-column joints in reinforced concrete structures with HCCCR.Their failure modes,hysteretic behavior,the lateral load carrying capacities,ductility factors and energy dissipation capacity were analyzed by measuring the load,displacements,stress distribution and the development of cracks,influences of axial load ratios,the ratios of stirrup in core area and core longitudinal reinforcement ratios.The major results of this dissertation are as follows.(1)Under repeated lateral loading,the desired shear failure modes in the core area of beam-column joint have been achieved;(2)When the core longitudinal reinforcement ratios are between 0 and 2.2%,shear capacity is improved with the increase of the core longitudinal reinforcement ratios,maximum growth rate is 24.5%.When the ratios of stirrup between 0 and 0.714%,shear capacity is improved with the increase of the ratios of stirrup,maximum growth rate is 7.2%.When the axial load ratios is 0.286 or 0.486,shear capacity is improved with a decrease of the ratios of stirrup,the rate is 7.4%.(3)When the core longitudinal reinforcement ratios are between 0 and 2.2%,the ratios of stirrup between 0 and 0.714%,the value of axial load ratios is 0.286 or 0.486,the increase of the ratios of stirrup and the core longitudinal reinforcement ratios,and the decrease of axial load ratios are beneficial to the displacement of joints from shear deformation.(4)Study on the displacement ductility coefficients and equivalent damping coefficients shows that when the core longitudinal reinforcement ratios are between 0 and 2.2%,the ratios of stirrup between 0 and 0.714%,the axial load ratios is 0.286 or 0.486,the joint with axial load ratios of 0.486,the core longitudinal reinforcement ratios 1.1%,and the ratios of stirrup 0.491% has the largest ductility and energy dissipation capacity,for its displacement ductility coefficients is 2.4,and the equivalent damping coefficients is 1.27.By comparing the joints with axial load ratio from 0.286 to 0.486,it has been found that axial compression ratio has little influence on the ductility and energy dissipation capacity of the joints.Test results indicate that the beam-column joint in reinforced concrete structures with HCCCR has good seismic performance.The research results can provide reference for the supplementation and perfection of seismic design codes.