Improving energy dissipation capacity of naturally buckling braces under low-cycle fatigue loads

Naturally Buckling Braces (NBBs) utilize a built-up dual material steel section given a parallel offset (i.e., eccentricity) from the normal working points of a conventional brace. NBB sections consists of a low-yield-point steel (LYS) channel and a high-strength steel (HSS) channel connected in parallel through steel battens. This new brace configuration provides a combined axial-flexural behavior that improves the buckling performance and post-yielding stiffness of braced framed structures. In this paper, on the basis of test results on a full-scale NBB specimen, a detailed computational study is performed with the aid of the finite element software ABAQUS. The specimen is subjected to a low-cycle fatigue protocol with increasing amplitudes and repeated inelastic loading cycles at the event of local buckling. The parametric study aims to evaluate partial strengthening methods for NBB sections that aim to delay local buckling initiation and local buckling growth. It was found that the energy dissipation capacity of NBBs can be enhanced up to 40% at a story drift ratio (SDR) of 2.0% by using transverse rib stiffeners at the central part of the LYS channel, while the use of thicker channel battens can provide further restrain to local buckling growth up to a 3.0% SDR.