This award aims to understand and characterize, at a fundamental level, the influence of reserve capacity on the seismic performance of low-ductility steel concentrically-braced frames up to the point of collapse. Although low-ductility steel braced frames have brittle brace elements and connections, they can achieve system ductility if their gravity framing and gusset plate connections act partially-restrained after braces fracture. These partially-restrained connections form a "reserve" moment frame system that can prevent sidesway collapse even when the primary lateral force resisting system is significantly damaged. Design provisions for steel structures in low and moderate seismic regions implicitly rely on reserve capacity for collapse prevention, even though the nature of this reserve capacity is not well-understood and can vary widely. Thus, there is an essential need for clarity and consistency in considering reserve capacity for seismic design in moderate seismic regions. Foundational understanding of reserve capacity will provide broad national benefit by establishing an economical and reliable framework for design of new buildings in low and moderate seismic regions and for evaluation of existing buildings in all seismic regions of the United States. These significant contributions will be accomplished through integration of large-scale testing, design studies, computational simulations, and reliability-based performance assessments. The research team from the University of Illinois at Urbana-Champaign and Tufts University will use the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) facilities at Lehigh University. Collaboration with complementary research being conducted at Ecole Polytechnique Montreal will provide valuable synergistic opportunities and enhance the research impact. Data from this project will be archived and made available to the public through the NEES Project Warehouse/data repository (www.nees.org).
The philosophy and application of system reserve capacity developed out of this research will open new possibilities for designing and assessing structures in all seismic regions, with special importance for moderate seismic regions, renovation in high seismic regions, and the design of special structures. Engineers will have simple yet effective tools for rationally designing and assessing low-ductility structures using reserve capacity to prevent seismic collapse. This philosophy of reserve capacity, which prioritizes cost reduction over achieving optimum levels of ductility, can also significantly impact design in developing countries where the seismic details that have become standards in the United States are not affordable or achievable with available technology. While this work focuses on steel structures, the scope of reserve capacity is much broader and more general. Once understood in the context of steel, reserve capacity may also find uses in other materials and systems both in the United States and abroad. This award is part of the National Earthquake Hazards Reduction Program (NEHRP).
