Reducing Damage Concentration with a Strongback System: SEMM Seminar with Dual Presentations

Seminar: Structural Engineering, Mechanics and Materials: Civil and Environmental Engineering | November 27 | 12-1 p.m. | 502 Davis Hall

 Barbara Simpson, Department of Civil & Environmental Engineering, UC Berkeley

 Civil and Environmental Engineering (CEE)

Multi-story braced frames exhibit large variations in inelastic demand over the building height and tend to concentrate damage in a few weak stories during an earthquake. This presentation will present the numerical and experimental results of a “strongback” system, a modification of the conventional braced frame that utilizes a vertical steel truss or “spine” to delay or prevent weak-story behavior. A cyclic test was performed on a nearly full-scale two story strongback retrofit design. The design was composed of two halves: an “inelastic” truss utilizing a buckling-restrained brace (BRB) to dissipate energy and an “elastic” truss designed to engage both stories to mitigate weak-story behavior. The strongback specimen was effective in impeding the formation of a weak-story mechanism and in mobilizing the reserve strength of other structural components, even after rupture of the BRB core. Test results established that the strongback can be a viable method of mitigating weak-story behavior, and subsequent numerical studies have shown that the strongback may also yield better performance than conventional braced frames. Ongoing numerical efforts have focused developing a reasonable design methodology to effectively utilize the strongback’s potential for increased seismic performance.