Study On Seismic Behavior And Design Method Of Reinforced Concrete Frame With Buckling-Restrained Braces

Reinforced concrete frames(RC frames)is one of the common structural system in China,which have flexibility in application,good economic benefit.However,it was always found that RC frames deformed seriously or collapsed under earthquake due to limited lateral stiffness.Besides,many existed RC frames don’t have sufficient capacity to resist earthquake,due to lower seismic fortification level,change of use function and degradation of structural durability,resulting in unexpected potential in serious damage or even collapsing when suffered from earthquake.These deficient buildings imposed great threat on life safety and economy loss.Consequently,whatever new constructed or existing buildings,it is essential to improve the performance of buildings to meet the requirements of present seismic code.As a new structural system,buckling-restrained braced frames(BRBFs)could dissipate large amount of input energy with buckling-restrained braces and maintain the stability of main frame structure,therefore it was gradually applied in practical engineering.Moreover,using buckling-restrained braces(BRBs)in RC frames has great advantage in improving the lateral stiffness,bearing capacity as well as global seismic performance.It can also significantly reduce the damage on the main frame by dissipating energy through plastic deformation.BRB could achieve yielding capacity in compression and tension,avoiding the buckling problem in compression of ordinary brace.However,researches on buckling-restrained braced frame concentrates on the steel frame,rare study on RC frame with BRBs especially the study on the eccentrically braced RC frames was conducted,and it lacked a practical design method for the seismic design of buckling-restrained braced frames.In this paper,the seismic performance of reinforced concrete frames with buckling-restrained braces and the seismic design method were studied,and the main research object and the primary conclusions are summarized as following:(1)In terms of the influence of buckling-restrained brace on the reinforced concrete frames,prestressed steel strips was used to improve the deformation capacity and ductility,then the buckling-restrained braces were used to improve the seismic performance.Totally five 1/2 scaled specimens with different layout of brace were tested by means of pseudo-static test,during the test,the damage development of different members and the failure mode were observed.In addition,the seismic index such as hysteresis behavior,bearing capacity,lateral stiffness,energy-dissipation capacity and ductility were analyzed.Based on the experimental results,it was proved that the prestressed steel strips could improve the ductility of the framing components and beam-to-column joints and the buckling-restrained braces could significantly improve the seismic performance of bare RC frame.(2)Numerical simulation using Abaqus and Opensees was performed to furthermore study the seismic performance.By the coMParison between experimental results and calculated results,the accuracy of the finite element model was validated and based on the validated model,parametric study was conducted to get better understanding of the influence of different parameters such as axial compression ratio,length of link beam and stiffness ratio on the seismic performance of the structures.The simulations showed that the layout of brace had great influence on the global behavior while the axial compression ratio had little effect on the structural behavior when less than 0.6.(3)With the analysis on the mechanism of buckling-restrained braced frame,it was found that the yield displacement was determined by the yielding stress of members but not the stiffness.With the theoretical analysis of damping performance,influence of stiffness ratio and the target displacement on the effective equivalent damping ratio was studied.(4)On the basis of existing seismic design method and the theoretical analysis of buckling-restrained braced frame,the direct displacement-based seismic design method of buckling-restrained braced frame was proposed using the performance target and shear ratio between braces and structure,and then the proposed design method was verified.