U.S. 95 bridge studied for seismic risk

Thursday, March 15, 2001 | 11:19 a.m.

University of Nevada scientists will test the risk that an earthquake could knock down a 32-year-old section of U.S. 95, state officials said.

The stretch of expressway, a concrete bridge, lies between Las Vegas Boulevard and the eastern edge of the Spaghetti Bowl, where Interstate 15 and U.S. 95 intersect. About 190,000 vehicles a day stream across that section.

The oldest section of the route is at the top of the state's priority list for earthquake evaluation, according to Bill Crawford, chief bridge engineer for the Nevada Transportation Department.

The three-year study will cost $450,000. Portions west and east of the stretch already meet stricter earthquake standards in place since the 1980s, he said.

While the Las Vegas Valley has a lower risk for a major temblor of 6.0 magnitude or above than Northern Nevada, the downtown portion of U.S. 95 has heavy daily traffic and the replacement costs would rival the $300 million spent to replace similar spans damaged in the San Francisco earthquake, Crawford said.

"For that reason, it is the most important structure in the state to study," he said.

Scientists from the University of Nevada, Reno, and UNLV will evaluate the seismic risk, Crawford said.

"We have a major challenge at hand," Salid Saiidi, the project's principal investigator from UNR, said.

"The bridge was built in 1968-69 based on standards that satisfied the seismic codes at the time," he said. "But much has been learned about the inadequacies of those codes, and catastrophic failure could happen even in a moderate earthquake."

Scientists have learned a great deal about earthquakes from major temblors in California in 1989 and the 1990s, Crawford said.

Saiidi is working with Ahmad Itani, associate professor of civil engineering at UNR and Samaan Ladkany, UNLV civil engineering professor.

The research team will build a computer model of the oldest section of U.S. 95. Information for the model will come from a shake table at the university's Center for Civil Engineering Earthquake Research in Reno, which simulates earthquakes on critical parts of the bridge.

Three graduate students will assist the professors in their studies, Saiidi said.

The Nevada Transportation Department gave the bulk of the $450,000, which included a $97,000 match from the university's Applied Research Initiative program.