NEESR-CR: Enabling Performance-Based Seismic Design of Multi-Story Cold-Formed Steel Structures

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This award is an outcome of the National Science Foundation (NSF) 09-524 program solicitation "George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) Research (NEESR)" competition and includes Johns Hopkins University (JHU) (lead institution) and Bucknell University (subaward). This project will utilize the NEES equipment site at the University at Buffalo (UB), State University of New York. The goal of this research is to generate the knowledge needed to increase the seismic safety of buildings that use lightweight cold-formed steel (CFS) for the primary beams and columns, and enable engineers to account for complete building performance in predicting the response of these buildings to earthquakes. The U.S. academic research team is strengthened by collaboration with Canadian supported researchers at McGill University, and by the engagement and support of industry facilitated by the American Iron and Steel Institute (AISI) and Bentley Systems.Lightweight CFS framing is a unique and effective building solution for low and mid-rise structures, but one in which much remains to be understood for the system to achieve its full efficiency and for modern performance-based seismic design methods to be fully enabled. This project builds on single-story shear wall research to address multi-story, CFS lateral force resisting systems. Component-level experimentation at JHU, combined with full scale building experiments at the UB NEES facility, will lead to improved understanding and provide validation and verification for computational models that will be developed. The computational models will include high fidelity models for exploring and expanding on the experimental efforts, and high efficiency reduced order models appropriate for utilization in nonlinear time history analysis and incremental dynamic analysis of CFS buildings.Throughout this research, the structure will be treated as a complete system, and the floor (diaphragm) and wall will not be idealized as simple collectors for the shear wall, but as systems themselves contributing to the seismic resistance of the building. In particular, the UB NEES shake table facility will be utilized to test a multi-story, CFS framed building with (a) only the lateral system in-place, (b) the lateral and gravity system fully in place, and (c) structural and nonstructural systems in place. This series of tests will enable identification of these separate systems and their interactions, and provide validation modeling for the simulation tools. A key advancement for inelastic time history analysis of CFS buildings, necessary for modern performance-based seismic design of CFS members, is the development of a high efficiency beam element that incorporates the strength and stiffness reductions inherent in local and distortional buckling of thin-walled CFS cross-sections. This project will develop a new frame element coupled with finite strip cross-section analysis for implementation in OpenSees. This new element lays the foundation for other thin-walled structures to be utilized in seismic design, e.g., structural plastics, aluminum, ultra-high strength steel, all of which must include cross-section deformation due to their inherently thin-walled nature.Intellectual Merit: The research plan addresses the most pressing shortcomings of seismic design of CFS structures: multi-story shear walls cannot be effectively modeled, and knowledge of their interactions with the complete structural system is incomplete. Broader Impacts: Research activities will be used to expand ongoing outreach with the research practicum program at Baltimore Polytechnical High School and will involve students from JHU and Bucknell. The research will be utilized to improve undergraduate education, including courses at JHU and Bucknell, and to develop instructional shake table models appropriate for repetitively framed structures. The PIs will actively disseminate findings to the research and practicing engineering community. Specifically, the PI works extensively with AISI and its committees, as well as the Cold-Formed Steel Engineers Institute, which has significant outreach to the practice.Data from this project will be archived and made available to the public through the NEES data repository. This award is part of the National Earthquake Hazards Reduction Program (NEHRP).