Experimental study of high-mode buckling behavior of flat steel core in a-restrained brace

Buckling -restrained braces (BRBs) featuring flat steel core plates can be susceptible to local bulging failures when the restrainer lacks the necessary stiffness and strength. These failures arise from outward forces generated by high -mode buckling waves within the steel core. However, the methods for evaluating these high -mode buckling waves and the associated outward forces have remained elusive. This study addresses this gap by conducting cyclic loading tests on five BRB specimens with all -steel restrainers. These tests allow for direct observation of high -mode buckling waves during loading. Among the specimens, three have core segment lengths of 300 mm, each with varying debonding layer thicknesses (0.6 mm, 2 mm, and 4 mm). The remaining two specimens have approximately 900 mm core segments with a 2 mm thick debonding layer. All five specimens displayed stable hysteretic responses until the steel core fractured. Load cells were used to directly measure the outward forces induced by the steel core plate during testing. Strain gauges attached to the steel core surface provided insights into the distribution of strain variations at the high -mode buckling waves. The results indicate that adopting the tangent modulus theorem is a suitable method for estimating high -mode buckling wavelengths. Furthermore, this study establishes relationships between the outward forces and gap dimensions, including their growth over time. This research proposes a method to estimate outward forces, accounting for bending moments developed at the crests of high -mode buckling waves and considering restrainer stiffness. This method can serve as a valuable tool for assessing the risk of local bulging failure in BRBs.