NEESR-CR: Multi-Scale, Mechanistic Fracture Prediction and Optimal Panel Zone Participation in Steel Moment Frame Buildings

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This award is an outcome of the NSF 09-524 program solicitation "George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) Research (NEESR)" competition and includes Texas A&M University in College Station, Texas (lead institution), The University of Texas in Austin, Texas (subaward), Lafayette College in Easton, Pennsylvania (subaward), and Texas A&M University in Galveston, Texas (subaward). This project will utilize the NEES equipment site at the University of Minnesota.Steel moment frames are widely used for seismic-resistant building construction throughout the United States and in many other parts of the world. Although steel moment frames were studied extensively following the 1994 Northridge, California, earthquake, one critical technical issue remains unsolved: the role of the panel zone in steel moment frame joints (beam to column connections). Recent U.S. building codes have significantly increased the required strength of panel zones in steel moment frames. To satisfy these requirements, column sizes must be increased or doubler plates must be welded to the column, resulting in increased cost, sometimes substantially so. However, there is significant experimental evidence that moment frame joints with weak panel zones show highly ductile performance, and consistently achieve large interstory drift angles under cyclic loading without strength degradation. There is also analytical evidence suggesting excellent overall seismic performance can be achieved by moment frames with weak panel zones. This strongly suggests that current building codes have adopted an incorrect approach to panel zone design, needlessly increasing the cost of construction while potentially degrading seismic performance. The overall goal of this research is to resolve the question: how much panel zone participation should be permitted in evaluating the inelastic seismic response of a steel moment frame? Despite a number of past studies on this issue, there are sharply conflicting views of how panel zones should be treated in design, both within the research community as well as within the building regulatory community. At the crux of the disagreements are concerns regarding fracture induced by panel zone yielding. There appears to be broad agreement that panel zone yielding is a highly ductile process. However, there is broad disagreement on the role that panel zone yielding plays in joint fracture. To address these concerns will require the fundamental capability to predict fracture at joints with weak panel zones subject to seismic loading. Thus, the intellectual merit and a key objective of this research is to advance the state of the art in predicting cyclic rupture within critical ductile components of steel building structures, and to apply this knowledge to the problem of the panel zone in steel moment frames. To meet these goals, this research project will integrate (1) fundamental studies on cyclic rupture of steel components combined with high resolution finite element simulations of beam-column joints,(2) advanced frame simulation studies, (3) large-scale experimental studies conducted at the NEES equipment at the University of Minnesota, and (4) parametric computational studies on joint performance. With respect to broader impacts, the knowledge gained from this research is expected to impact design practice and building codes for seismic-resistant steel moment frames. The project team will conduct a professional development program for high school science and mathematics teachers to create and deliver web-based instructional materials to bring concepts of earthquake engineering-related problems into the classroom. Data from this project will be archived and made available to the public through the NEES data repository.