Steel in the News
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Posted by Tasha Weiss on September 27, 2011 at 10:09 AM.
Laboratory technician Chad Lyttle makes adjustments to sensor cables in final preparations for earthquake engineering tests at the University of Nevada, Reno’s Large-Scale Structures Lab. The first-ever tests on a bridge with truck traffic will help improve design regulations and standards and assure safer bridges during large earthquakes. Photo by Mike Wolterbeek, University of Nevada, Reno.
A team of engineers, including eight graduate students, at the University of Nevada, Reno are performing first-ever earthquake tests on a bridge with truck traffic to help frame changes to current codes and lead to safer bridges during strong earthquakes. Six full-size pickup trucks are placed on a 16-ft-high, 145-ft-long steel bridge as it moves vigorously atop four large 14-ft by 14-ft hydraulic shake tables in the university’s Large-Scale Structures Earthquake Engineering Laboratory.
“We took the bridge to its extreme, almost double what we planned at the outset,” Ian Buckle, professor of civil engineering and director of the large-scale structures lab, said. “Preliminarily we see that in low amplitude earthquakes the weight of the vehicles actually helps the seismic effects on the structure, while at higher amplitudes the trucks hinder considerably the bridges ability to withstand an earthquake.”
The 162-ton steel and concrete bridge, with 80 ft of curvature, fills the large high-bay lab from end-to-end. A three-minute video showing the largest motion applied to the bridge can be viewed by clicking on this link: http://bit.ly/qDW1Nq.
“Whether you saw the experiment in person or watch the video, remember that this is a 2/5 scale model, and the movement you see would be two and a half times greater on a full-scale bridge,” said Buckle, principal investigator of the research project. “It would be scary to be driving under those conditions.”
Buckle added that currently, bridges are not designed for the occurrence of heavy traffic and a large earthquake at the same time. “With increasing truck traffic and frequent congestion on city freeways, the likelihood of an earthquake occurring while a bridge is fully laden is now a possibility that should be considered in design. But there has been no agreement as to whether the presence of trucks helps or hurts the behavior of a bridge during an earthquake, and this experiment is intended to answer this question.”
The complete analysis will come after months of examining the many gigabytes of information gleaned from the 400 sensors placed on the bridge and trucks and the results of this work will be titled, “Seismic Effects on Multi-span Bridges with High Degrees of Horizontal Curvature”.
For more detailed information about the research project, visit the University of Nevada, Reno web site, here.