University Of Nevada, Reno, Engineers Simulate Large Quake On Curved Bridge

Six full-size pickup trucks took a wild ride on a 16-foot-high steel bridge when it shook violently in a series of never-before-conducted experiments to investigate the seismic behavior of a curved bridge with vehicles in place. The 145-foot-long, 162-ton steel and concrete bridge was built atop four large, 14-foot by 14-foot, hydraulic shake tables in the University of Nevada, Reno'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 trucks bounced and swayed as the four-span bridge's concrete columns deflected more than 14 inches in each direction, the steel girders twisted and the floor of the lab shook from the energy applied to the bridge. The bridge, with 80 feet of curvature, filled the cavernous high-bay lab on the University of Nevada, Reno campus from end-to-end.

A 3-minute video featuring the largest motion applied to the bridge can be viewed by clicking on this link http://imedia.unr.edu/media_relations/VNR_shake_trucks_2b.mp4.

"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," Buckle, principal investigator of the research project, said. "It would be scary to be driving under those conditions."

"Currently, bridges are not designed for the occurrence of heavy traffic and a large earthquake at the same time," he said. "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 answer will come after months of examining the many gigabytes of information gleaned from the 400 sensors placed on the bridge and trucks. The results of this work, titled "Seismic Effects on Multi-span Bridges with High Degrees of Horizontal Curvature," will be used to frame changes to current codes and lead to safer bridges during strong earthquakes.