Experimental Evaluation and Design Procedure for All-Steel Tube-in-Tube Buckling Restrained Braces

This study presents an experimental investigation into the cyclic performance of a new tube-in-tube buckling restrained brace (BRB) configuration. In this study, reduced- and large-scale brace geometries are tested to quantify inelastic hysteretic response, understand core confinement parameters, and determine the influence of end connection constraints. A total of 11 reduced-scale brace specimens are cyclically tested, along with three large-scale braces representing two core geometries and two core constraint configurations. Results from the reduced- and large-scale brace testing suggest that the tube-in-tube BRB configurations are capable of achieving the required inelastic capacity for qualification in AISC 341-16 specifications. All scaled specimens survived cumulative inelastic demands that exceeded 240 times the yield displacement (with several surviving more than 400 times the yield displacement). Results indicate that tube-in-tube BRBs are capable of producing stable tension-compression hysteretic behavior during cyclic loading. Measured $\beta$ values for the large-scale Specimen G2 were lower than 1.06 for all deformation cycles at or below $9.2{\mathrm{\Delta }}_{\mathrm{by}}$, while measured $\beta$ values for the large-scale Specimen G3 were lower than 1.07 for all cycles at or below $3.6{\mathrm{\Delta }}_{\mathrm{by}}$. The peak $\beta$ value for Specimens G2 and G3 was 1.16 and occurred during the $15.3{\mathrm{\Delta }}_{\mathrm{by}}$ and $7.1{\mathrm{\Delta }}_{\mathrm{by}}$ cycles, respectively.