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Bridge Shaken, Not Stirred, in Mega Sim

Friday, August 22, 2014

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A gigantic bridge model has survived a tremendous amount of seismic shaking—the equivalent of a magnitude 6.9 earthquake—without collapsing.

Researchers said the modela 70-foot-long, 52-ton concrete bridgesurvived 10 simulated earthquakes during the first round of experiments at the University of Nevada, Reno.

The test took place at the university's new 24,500-square-foot Earthquake Engineering Lab, the latest addition to its Large-Scale Structures Laboratory.

“This can’t be done anywhere else in the nation, and perhaps the world,” said Ian Buckle, director of the lab and professor of civil engineering.

Watch the lab at work putting the 70-foot-long concrete bridge through a series of simulated earthquakes.

The entire facility makes up the U.S.'s biggest, most versatile seismic/earthquake engineering facility for large-scale structures, according to the National Institute of Standards and Technology (NIST).

Zipper Shearing

In the bridge test, three 14-by-14-foot, 50-ton capacity hydraulically driven shake tables were used to move the huge structure.

“It was a complete success,” said John Stanton, civil and environmental engineering professor and researcher from the University of Washington.

Stanton collaborated with Professor David Sanders of the University of Nevada, Reno.

“The bridge performed very well,” Sanders said. “There was a lot of movement, about 12 percent deflection—which is tremendous—and it’s still standing."

“You could hear the rebar inside the columns shearing, like a zipper opening. Just as it was designed to do.”

Rubber Band Effect

The bridge support system, which  took only about a month to build, is a new engineering design developed with the goal of saving lives, reducing on-site construction time, and minimizing earthquake damage.

University of Nevada, Reno / Mike Wolterbeck

“Sure we broke it, but we exposed it to extreme, off-the-scale conditions," Professor John Stanton said of the experiment.

The bridge was designed and pre-cast at the University of Washington, Seattle. The team included an important pre-tensioning feature in the columns, which Stanton compared to a toy set of wooden building blocks with a hole through each one.

"Stack them on top of one another, put a rubber band through the central hole, stretch it tight and anchor it at each end," he said. "The rubber band keeps the blocks squeezed together.

"Now stand the assembly of blocks up on its end, and you have a pre-tensioned column. If the bottom of the column is attached to a foundation block, you can push the top sideways, as would an earthquake, but the rubber band just snaps the column back upright when you let go," Stanton explained.

Since real bridge columns don't have rubber bands, very high-strength steel cables can be used to achieve the same effect, Stanton said. The cables, as well as some conventional rebar, are installed during the pre-fabrication process to help reduce site operations.

'We Broke It'

The bridge, done at 25 percent of full-scale, was then built on top of the shake tables and tested in a series of earthquakes that culminated in the large ground motions similar to the deadly magnitude 6.9 earthquake in Kobe, Japan, in 1995.

University of Washington, Seattle / NEES photo

The bridge's design accomplishes pre-tensioning with very high-strength steel cables.

Stanton commented, “Sure we broke it, but we exposed it to extreme, off-the-scale conditions. The important thing is it’s still standing, with the columns coming to rest right where they started, meaning it could save lives and property. I’m quite happy. “

Unique Facility

The earthquake simulation facility is managed as a national shared-use Network for Earthquake Engineering Simulation equipment site created and funded by the National Science Foundation.

A grand opening was recently held for the $19 million lab expansion. The facility was funded with $12.2 million from NIST, funds from the Department of Energy, and funds from the university and donors.

“Our facility is unique worldwide and, combined with the excellence of our faculty and students, will allow us to make even greater contributions to the seismic safety of our state, the nation and the world,” said Manos Maragakis, dean of the College of Engineering.

“We will test new designs and materials that will improve our homes, hospitals, offices and highway systems. Remarkable research is carried on here.

“Getting to this point has taken a lot of hard work. It’s both a culmination and a beginning, ushering in a new era.”

   

Tagged categories: Bridges; Colleges and Universities; Concrete; Construction; Laboratory testing; Research; Roads/Highways

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