Experimental and numerical studies of hysteretic response of triple-truss-confined buckling-restrained braces

A new type of BRBs, namely a triple-truss-confined BRB (TTC-BRB) is proposed, and its hysteretic response is investigated experimentally and numerically in this paper. The TTC-BRB is formed through introducing an additional structural system of rigid trusses to the outside of a common BRB to effectively increase its external restraining flexural stiffness and its overall load-carrying capacity, especially when it is utilized as a long-span and a heavily axially loaded brace. The TTC-BRB may be adopted innovatively as diagonal braces in mega-frame structures of high-rise buildings and in long-span spatial structures. A total number of two TTC-BRB specimens have been designed and the hysteretic responses of the two TTC-BRB specimens are experimentally investigated under a combination of standard and fatigue loading protocols. The obtained experimental results indicate that both the TTC-BRB specimens have excellent hysteretic responses as well as being able to attain stable and ample hysteretic curves under cyclic loads, with both cumulative ductility and total accumulated cycles of loading, being well above the requirements specified respectively in the AISC seismic provisions and the Chinese code GB50010 for seismic design of buildings. The experimental results obtained are compared with those obtained by numerical analysis from a simplified FE model consisting of BEAM188 element, indicating that the FE model provides good correlations with the experimental results. Moreover, relevant failure mechanism and design suggestions of the TTC-BRB specimens are discussed and provided based upon the FE results. At last, as a mega brace, the influence of its self-weight, length and imperfection are investigated numerically to reveal the performance of the TTC-BRBs under cyclic loads.