Preliminary Design Method Of Buckling-restrained Braced RC Frames As Dual Systems

Buckling-restrained brace(BRB),which is one of the metallic yielding braces with buckling-restrained characeristics and stable energy-dissipation capacity,is widely used in new structures and seismic retrofit of existing structures.The buckling-restrained braced steel moment frame have been demonstrated as a dual system with high earthquake resistant capacity.However,there is few study about buckling-restrained braced RC frames dual systems,which lead to a lack of design theory and guidance when using BRBs in RC frames.Based on the accurate simulation of reinforce concrete component and BRBs,this paper studys the design procedures of BRB-RC frames using Chinese Code Method,American Code Method and performance based method.The main work and achievements are as follows:(1)The numerical simulation technology and method of buckling-restrained braced RC frames using Perform-3D is introduced,then verified through previous component tests.It is indicated that whether fiber model or plastic hinge model can all simulate the RC components accurately.The BRB element model in Perform-3D is applicable in simulating the hysteretic behavior of BRBs,including kinematic hardening,isotropic hardening,hysteretic curve shape,asymmetric tension and compression strength,asymmetric tension and compression stiffness after yielding,which is more accrute than elastic perfectly-plastic model.(2)The design theory of BRB-RC frames dual systems is introduced.Then a practical design method of BRB-RC frames through Chinese Code is proposed.The lateral stiffness ratio k of BRBs to RC frames is used to calculate the area of BRBs in each floor.The rational range of k factor is studied in this paper.By the time-history analysis,it can be found that the earthquake resistant capacity of structures will not always improve as lateral stiffness ratio k becomes larger.When k≤1.5,the peak story drift is sensitive to the k factor;When k≥1.5,the impact of k factor to the earthquake resistant capacity is small.lt indicate that the most rational range of k factor is k≤1.5.(3)According to the design theory in American design codes,a new method using Pushover and FEMA440 equivalent linearization method to calculate R factor is proposed.The accuracy of different methods to calculate target displacement is compared in this paper.Then the R factor of BRB-RC frames is calculated.The analysis indicate that FEMA440 equivalent linearization method is more accurate than displacement modification method of FEMA356 and the Capacity-Spectrum Method of ATC-40.The R factor calculated in this paper for BRB-RC frames less than 9 floors is 5.5.(4)Based on desirable deformation shape,equivalent elastic-plastic SDOF system and equivalent linearization method,a direct performance based seismic design approach is developed for BRB-RC frames dual systems in consider of the stiffness degration of RC frames.The results show that the BRB-RC frames designed following the proposed approach can successfully achieve the inter-story drifts limit.The yield mechanism and deformation demand is rational and acceptable.It has a higher accuracy to low-rise structures.