Core behavior and low-cycle fatigue estimation of the Perforated Core Buckling-Restrained Brace

The Perforated Core Buckling-Restrained Brace (PCBRB) is an all-steel BRB whose core has been split into two lateral bands connected by stabilizing bridges. The core, with a constant cross-section perimeter, can slide along the restrainer so that it can be inspected or replaced by simply removing a centering pin. We analyzed the behavior of two different Perforated Core (PC) geometries which we tested to failure with different load protocols of several maximum deformation amplitudes. The main difference between both geometries was the radius of the lateral band connections. The experimental results show how a low radius, despite offering a higher constant cross-section yielding length, leads to a lower dissipation capacity and to a closer distance between stabilizing bridges. The results also show a gradual drift of the internal and the external lateral band segments into permanent negative and positive elongations, respectively, which increases the minimum gap required between the core and the restrainer. We also analyzed the in-plane and the out-of-plane wavelength of the high-mode buckling of the PC and validated two wavelength prediction equations that would prevent the uncontrolled second-order deformations and the buckling failure of the PC. Finally, based on experimental data, we propose two low-cycle fatigue relationships for the PCBRB that would be valid for elastoplastic devices with uniform uniaxial strain distribution, such as BRBs and TADAS devices.