9/4/2009
A group of researchers, led by Professor Jerry Hajjar of the Department of Civil and Environmental Engineering and colleagues from Stanford University, the Tokyo Institute of Technology, Hokkaido University, and E-Defense in Japan, have successfully tested a new structural system that will make steel-framed buildings more resilient in earthquakes.
Written by
A group of researchers, led by Professor Jerry Hajjar of the Department of Civil and Environmental Engineering and colleagues from Stanford University, the Tokyo Institute of Technology, Hokkaido University, and E-Defense in Japan, have successfully tested a new structural system that will make steel-framed buildings more resilient in earthquakes.
The "controlled rocking" system enables buildings to sway during earthquakes and return to their original positions without sustaining irreversible damage.
"In moderate to large earthquakes, structures sustain significant damage throughout the core structural framing systems," Hajjar explained. "While they are designed not to collapse, many structures are permanently damaged after such an event, such that they may need to be condemned, even if they were designed to satisfy the building code.
Developing new systems that focus the damage into structural ‘fuses' that may be replaced after the earthquake, and that self-center the structure to ensure plumbness, provides both safer and more sustainable options for building design in seismic zones. The most recent testing completed at the shake-table facility in Japan has validated the effectiveness of this structural system when subjected to earthquakes.”
The technology, which just completed testing at Japan's Hyogo Earthquake Engineering Research Center (E-Defense), is the culmination of more than a decade of ideas and developing technologies. Three major components make up the seismic lateral resisting system—a stiff steel-braced frame that remains virtually elastic, but is not tied down to the foundation and thus allowed to rock; vertical post-tensioning strands that anchor the top of each frame down to the foundation and bring the frame back to plumb; and replaceable structural fuses that absorb seismic energy as the frames rock, fabricated from steel plates with water-cut diamond-shaped slits.
In an earthquake event, the flexible steel "fuse" takes the brunt of the force, keeping the frame and constituent tendons from shouldering the entire load. The fuses are easily replaceable when they blow—similar to an electrical fuse. Following a quake, the building can be refitted with fresh fuses for the next tectonic event.
The first phase of the project included experiments at Stanford University of various fuse configurations to develop and optimize the fuse shape and characteristics. Phase two featured quasi-static testing of a half-scale three-story model of the complete structural system at the University of Illinois' Multi-Axial Full-Scale Subassemblage Testing and Simulation Facility (MUST-SIM) located within Newmark Civil Engineering Laboratory. The facility is part of the National Science Foundation's George E. Brown Jr. Network for Earthquake Engineering Simulation.
In summer 2009, the research continued with a two-thirds scale dynamic testing of the structural system on the E-Defense shake table in Miki, Japan. For testing, the team constructed a two-thirds-size model of a standard three-story office building, representative of a building with a footprint 120 by 180 feet, and a mass comparable to a full-size building. Even at a magnitude-seven earthquake, the only damage recorded in the frame was in the replaceable fuses.
Perhaps the most promising aspect of the system is that it can be retrofitted to existing buildings using readily available materials. In addition to saving countless lives, this technology could greatly soften the economic and environmental costs earthquakes exact on societies. Even directly after a violent quake, buildings remain habitable, keeping humanitarian disasters at bay.
Project investigators include principal investigator G. G. Deierlein, and professors S. Billington and H. Krawinkler from Stanford University. Collaborators in Japan include professors T. Takeuchi and K. Kasai, Tokyo Institute of Technology; M. Midorikawa, Hokkaido University; and T. Hikino, Hyogo Earthquake Engineering Research Center.
Funding is being provided by the National Science Foundation, the American Institute of Steel Construction, Stanford University, the University of Illinois at Urbana-Champaign, and the Hyogo Earthquake Engineering Research Center. In-kind funding has been provided by Tefft Bridge and Iron, M.C. Detailers, Infra-Metals, Prestressed Engineering Corporation, Wagner Machine Company, Japan Iron and Steel Federation, and Nippon Steel Engineering Corporation
________________
If you have any questions about the College of Engineering, or other story ideas, contact Rick Kubetz, Engineering Communications Office, 217/244-7716, writer/editor.