A low-cost system for enhanced seismic stability and mitigation of residual deformations in steel eccentrically braced frames

The response of stable yielding systems with enhanced ductility such as steel buckling-restrained braced frames (BRBFs) and eccentrically braced frames (EBFs) often exhibit a seismic response where their peak response is concentrated locally and results in large residual deformations. Gravity induced second-order P-Delta effects influence these response parameters and, in extreme cases, can compromise the global seismic stability of such systems. Furthermore, excessive residual deformations increase the required resources for post-earthquake repairs and elongate the recovery time for damaged structures. For EBFs, which rely on localized inelastic deformations in the yielding link, peak and residual link rotations are much larger than inter-story drift ratios. Recent experimental and numerical studies have shown that even with moderate residual inter-story drift ratios, severe residual link rotations could be expected, which could render the structure difficult to repair even for EBFs with replaceable yielding links. This paper presents the development of a low-cost dual system in EBFs, which is intended to enhance their seismic stability and mitigate their peak and residual deformations. After presenting the design concept, the proposed system is adopted for a prototype EBF designed with cast steel replaceable modular yielding links. The performance of the proposed system is evaluated through nonlinear time-history analyses under a suite of earthquake records. The results demonstrate that the proposed system is effective in increasing the seismic stability of EBFs, reducing both peak and residual deformations. Reduced link residual rotations will result in shorter repair and recovery time after major earthquakes and a more resilient and sustainable design for EBFs.