Parametric investigation of the assembled bolt-connected buckling-restrained brace and performance evaluation of its application into structural retrofit

In this paper, the hysteresis performance of an assembled bolt-connected buckling-restrained brace (AB-BRB) is experimentally discussed by a parametric study, and five changing factors are selected to analyze the corresponding influence in static behaviors. The deformation modes of core plates are compared, the critical points of hysteresis curves are analyzed, and six static indices for hysteresis responses are assessed. Afterwards, the seismic evaluations of AB-BRB applied into structural retrofit are conducted, based on an aged 3-span-3-story and 5-span-10-story reinforced concrete frame. The numerical model is established and verified for both local AB-BRB and integral frame structure, and the simulation details as well as selection strategies are suggested during the process. The nonlinear time history analyses, incremental dynamic analyses and seismic fragility analyses are all performed, and three dynamic indices, three limit states, three fractile probabilities, three comparing conditions and two intensity levels are well discussed for assessment, before and after retrofitting, respectively. In general, the influences of shell thickness are less than shell height, and a larger gap clearance may transfer the deformation pattern into end-wave modes. Less bolt number may affect the assembly operation and global buckling capacity, which proves the effectiveness of bolt design equation in a sense. Bolt number contributes greatly to the macro hysteresis trends, and less tightening bolts may weaken the retraining property, accompanied with the bolt-slippage occurrence under huge vertical thrusts transferred from core plates. The seismic indices for each ground motion are below limitations and are more uniform with less discreteness after retrofitting with AB-BRB. The structural capacity can be guaranteed safely, and the damage degree of the integrated system can be controlled with the application of AB-BRB, illustrating the apparent retrofitting superiority in performance enhancement and providing reference for the follow-up research of AB-BRB in the earthquake-prone areas.