Effects of ductility on residual deformations of bilinear systems and seismic design of buckling-restrained braced frames

This study systematically investigates the effects of ductility ( μ ) on residual deformations ( u r ) for bilinear systems with different values of post-yield stiffness ratio (PYSR). First, constant-ductility analyses were conducted on single-degree-of-freedom (SDOF) bilinear systems, considering fundamental periods ( T ) ranging from 0.1 s to 3.0 s, μ from 4 to 12, and PYSR from −0.02 to 0.10. The SDOF analysis results reveal a counterintuitive phenomenon: increasing μ reduces u r , but only when the PYSR is large. Conversely, this trend reverses when the PYSR is small or negative. Then, the underlying mechanisms driving this behavior are discussed and explained. To further validate these findings at the structural level, two sets of six-story steel buckling-restrained braced frames (BRBFs) with PYSR of 0.05 and 0.01, respectively, were designed and numerically analyzed. All frames were designed to achieve the same peak interstory drift (PID) of 1.5 % for a fair comparison. Buckling-restrained braces (BRBs) were modeled using both the simplified bilinear model and refined Giuffre-Menegotto-Pinto (GMP) model that additionally incorporates smooth elastic–plastic transition, isotropic hardening, and tension-compression asymmetry. The results show that for BRBFs with PYSR = 0.05, the largest μ results in the lowest residual interstory drift (RID), regardless of whether they were modeled with the bilinear or the GMP model. Finally, to avoid the potential fracture of BRBs and mitigate increased internal force in the system under maximum considered earthquakes (MCE), a friction fuse mechanism is conceptionally recommended and its efficiency is numerically verified. • The effects of prescribed ductility target depend on the post-yield stiffness ratio. • Yielding behavior helps to reduce residual deformation if the system has a large post-yield stiffness ratio. • BRBFs designed with a large ductility target have smaller residual deformations at the design basis earthquakes.