Adoption of new structural systems is hampered by the lack of a comprehensive method to evaluate their seismic performance. This report introduces a seismic performance evaluation procedure and demonstrates its application for the suspended zipper braced frame. The performance evaluation procedure includes laboratory and computer simulations. The laboratory simulations may be necessary in cases where behavior of a structural system or its components is inadequately understood and therefore cannot be modeled confidently for computer simulation. By integrating the laboratory specimen behavior and computer models, the complete system performance can be simulated.
The suspended zipper braced frame configuration is similar to the inverted-V braced frame except that a vertical structural element, the zipper column, is added at the beam mid-span points from the second to the top story of the frame. In the event of severe earthquake shaking, the lower-story braces will buckle and create unbalanced vertical forces at mid span of the beams. The zipper columns will mobilize the beams and the braces above the story where buckling occurs, to resist the unbalanced vertical forces. Such action will force the entire system to be engaged to resist the earthquake loads, hence preventing concentration of inelastic action in one story.
Seismic performance evaluation of the suspended zipper braced frame is conducted in two phases. Hybrid and analytical models of the suspended zipper braced frame are developed and validated in the first phase. These models are based on new analysis and simulation tools developed within NSF’s George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES). A probabilistic seismic performance evaluation method is developed and used in the second phase to evaluate the seismic risk of the suspended zipper braced frame. This method is based on the Pacific Earthquake Engineering Research Center (PEER) probabilistic seismic performance-based evaluation framework. The seismic risk evaluation is limited to risk of repair cost in the present study, and does not include other performance measures that might be important, including downtime and collapse. The results of performance evaluation conducted using validated hybrid and analytical structural models provide information that can be used to demonstrate the relative merits of the suspended zipper braced frame structural system compared with conventionally braced frame systems.
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