Professor Thomas O'Rourke's congressional testimony appears on C-SPAN. Photo courtesy of C-SPAN
A substantial portion of the nation's building stock is at risk from high-impact, low-recurrence earthquakes, Thomas D. O'Rourke, the Thomas R. Briggs Professor of Engineering at Cornell, told the basic research subcommittee of the House of Representatives Committee on Science last week. O'Rourke presented his testimony on lessons learned from the recent earthquakes in Turkey, Taiwan and Mexico City in a session held in the Rayburn House Office Building. His comments were drawn from his personal observations of the devastation wrought by the tremors in Turkey and Taiwan, which he visited shortly after the earthquakes on Aug. 17 and Sept. 21, respectively.
Shortly after returning from Washington, O'Rourke learned he had been elected a fellow of the American Association for the Advancement of Science for "international contributions to the field of earthquake engineering, especially for lifeline engineering in large urban centers."
O'Rourke told the subcommittee that two of the most pervasive images and lessons drawn from the earthquakes in both regions were the failure of thousands of non-ductile concrete buildings and the critical facilities, such as bridges, that were ruptured and made unserviceable because they were intersected by severe fault movements.
Non-ductile concrete buildings are those built of concrete structurally reinforced with too little steel -- especially hoop or spiral steel and steel at connections -- to strengthen the buildings against the swaying movement generated during an earthquake. As a consequence, these buildings are prone to catastrophic rupture and fracturing of the concrete, with lethal consequences for the occupants. Non-ductile concrete structures are a serious problem for the United States, O'Rourke told the committee. Not only is there a significant inventory of such buildings in California but also in places like Washington state, the New Madrid area (Missouri, Tennessee and Arkansas, adjacent to the Mississippi River), Charleston, S.C., and Boston. This, he testified, places a considerable number of buildings at risk from high-impact, low-recurrence earthquakes. And in high-impact, high-recurrence earthquake zones, he said, a considerable number of building are at risk of catastrophic collapse.
Critical U.S. lifelines, such as bridges, also are vulnerable, especially those outside California, O'Rourke said. As one example he cited the elevated reinforced concrete viaduct for Route 99 in downtown Seattle. "In the U.S., we have tended to forget about surface faulting, in part because it was missing from urbanized areas during the Loma Prieta, Whittier, Northridge and Kobe earthquakes," said O'Rourke. "Although significant surface faulting occurred in the 1979 Imperial Valley and 1992 Landers earthquakes, it was located principally in desert and agricultural areas. Turkey and Taiwan remind us that surface faulting can cause serious destruction and loss of life."
Indeed, said O'Rourke, the surface faulting in Turkey, and especially Taiwan, "was spectacular and frightening." He traveled to Turkey on Sept. 11 for the National Science Foundation (NSF) to evaluate the geotechnical and seismological aspects of the highly destructive earthquake that left thousands homeless. His goal was to observe and collect data on how well the water supply and gas distribution systems survived the earthquake. He also studied the effects of soil liquefaction on buildings supported by shallow foundations.
On Oct. 1, O'Rourke was again traveling to a devastated area, this time to Taiwan, as part of an earthquake investigation team organized by the Multi-Disciplinary Center for Earthquake Engineering Research, headquartered at the State University of New York at Buffalo. Cornell is one of the principal partnering institutions of the NSF-supported center. The team, hosted by the National Center for Research in Earthquake Engineering in Taiwan, visited the two main areas badly damaged by the tremor, Taichung and Nantou counties in the west-central part of the island.
In evaluating information and data from the earthquake-affected areas, O'Rourke was assisted by Cornell doctoral candidates Ilker Tutuncu, a graduate student from Turkey, and Jie-Ru Chen and Jung-Feng Chang, graduate students from Taiwan. For his congressional testimony, prepared in coordination with board members of the Earthquake Engineering Research Institute, O'Rourke was assisted by two doctoral candidates, graduate students A.J. McGinn and James Mason. The latter worked for the California Department of Transportation on the rehabilitation of the earthquake-damaged Oakland Bay Bridge before coming to Cornell to study for his doctorate.
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