Behaviour and design of spatial triple-truss-confined BRBs with a longitudinal shuttle shape

Abstract

For several decades, innovative studies on the external restraining system of the buckling-restrained brace (BRB) have focused on the design and application of BRBs. This paper presents a Spatial Triple-Truss-Confined BRB (STC-BRB) with a longitudinal shuttle-shape and investigates its buckling behaviour, static strength and seismic design. The STC-BRB could significantly improves the material utilization and particularly enhance the architectural aesthetics when it is used as an exposed design externally. The overall elastic buckling performance, load resistance and hysteretic responses of the STC-BRB are investigated numerically by adopting a finite element model (FEM) validated by previously conducted test results of a truss-confined BRB (TC-BRB). A design method regarding the lower limit of the restraining ratios of the STC-BRBs is recommended. First the overall elastic buckling performance of the STC-BRB is comprehensively investigated by using a beam element FEM, leading to an explicit expression for the overall elastic buckling load of the STC-BRB, which is further adopted to define a restraining ratio of the STC-BRB design. Consequently the load resistance of STC-BRBs under monotonic axial compression is numerically analyzed. Accordingly a lower limit of the restraining ratio of the STC-BRBs is recommended for monotonic axial load resistance design, such that the core reaches the fully sectional yield, along with a plasticity strain amplitude of 2% without a global instability of the STC-BRBs. Finally, the hysteretic responses of STC-BRBs subjected to axially compressive-tensile cyclic loads are studied numerically, and the corresponding lower limit of the restraining ratio of STC-BRBs is proposed in the design as an energy-dissipating device. The two lower limits of the restraining ratios of the STC-BRBs obtained in this study form fundamentals for the preliminary static and seismic design of STC-BRBs.