AISC Research: Development of a Design Methodology for Steel Strongback Braced Frames [N2]

Conventional steel braced frames have a tendency to concentrate damage in one or a few stories during large earthquakes, indicative of ""weak"" story behavior. Recently, there have been a number of studies involving the ""strongback"" system -- a modification of the conventional braced frame that utilizes a vertical steel truss to delay or prevent weak stories. The remainder of the braced frame is then designed and detailed to yield, thereby controlling the system's energy dissipation under seismic excitation. A recent experimental test and past numerical studies have shown that the strongback system can be successful at mitigating weak story behavior. However, the behavior of this system has not been systematically assessed or evaluated. Nor is there a coherent and robust design methodology for strongback system. The objective of this research was to develop a generalizable and practical design method for the strongback system using the linear design methods traditionally used in current building codes. The behavior of several strongback archetype designs were compared to conventional braced frames in OpenSEES. The reliability of these design methods were evaluated using the minimum acceptable design criteria from FEMA P695. These nonlinear analysis methods validated the ability of the strongback designs to achieve the basic seismic performance objectives for standard code-approved seismic-force-resisting systems while successfully mitigating a weak story response.

Intended Audience: Engineers
Track: Design & Analysis

View content