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Nevada Lab: Quake-resistant Bridge Design Tests Well

  • Associated Press

A portion of a new offramp, center right, for Highway 99, stands completed and adjacent to the entrance for northbound traffic into the tunnel being constructed in Seattle. The offramp has a new type of column that flexes when the ground shakes in an earthquake, then snaps back to its original position.

Scientists at a Nevada earthquake lab Wednesday tested new bridge designs with connectors they say are innovative and created to better withstand violent temblors and speed reconstruction efforts after major quake damage.

University of Nevada, Reno engineers performed the experiments on a giant “shake table” to simulate violent motions of an earthquake to rattle a 100-ton (91-metric ton), 70 foot (21-meter) bridge model to determine how well it would hold up.

The tests, conducted a day after a big quake struck Mexico, shook large concrete columns and beams back and forth for about 30 seconds at a time, displacing some nearly a foot before returning largely to their original spot.

Graduate students measured and marked indications of tiny fractures but no major structural damage was observed in the initial review of the experiments.

Saiid Saiidi, a world-renowned professor of civil and environmental engineering at the University of Nevada, Reno, Sept. 20, 2017, after conducting a series of tests on a giant shake table intended to simulate violent earthquake activity at the school's lab.
Saiid Saiidi, a world-renowned professor of civil and environmental engineering at the University of Nevada, Reno, Sept. 20, 2017, after conducting a series of tests on a giant shake table intended to simulate violent earthquake activity at the school's lab.

“The bridge has done better than we expected,” said Saiid Saiidi, a professor of civil and environmental engineering who served as the project leader. He’s done related research for more than 30 years.

Bridges are already designed not to collapse in earthquakes but often are unsafe for travel after big quakes. He said the designs that were tested employed special types of connectors to link prefabricated bridge parts, including ultra-high performance concrete.

“Earthquakes by themselves don’t kill people, it’s the structures,” Saiidi said.

The elements have been tested on their own but never before combined in a bridge model subjected to realistic earthquake motions, like the 1994 Northridge, California quake. Wednesday’s test inside the University of Nevada’s Earthquake Engineering Laboratory simulated activity of a quake as large as magnitude 7.5.

Graduate students at the University of Nevada, Reno's College of Engineering inspect a bridge model for damage after tests on a giant shake table intended to simulate violent earthquake activity at the school's new Earthquake Engineering Building in Reno, Nevada.
Graduate students at the University of Nevada, Reno's College of Engineering inspect a bridge model for damage after tests on a giant shake table intended to simulate violent earthquake activity at the school's new Earthquake Engineering Building in Reno, Nevada.

Some design work by the engineers has been incorporated into a highway off-ramp under construction in Seattle. It’s the first bridge in the world that uses flexible columns and reinforcement bars made out of a metal alloy with titanium that bends and then springs back into shape when quakes hit.

Among other things, the innovative connectors allow for prefabricated concrete and other materials to be attached to an existing bridge foundation so as to speed repair and reconstruction.

Part of the research centers on a so-called “pipe pin” connection developed by the California Department of Transportation’s bridge designers for use in connecting certain beam interfaces in bridge construction.

The pin consists of a steel pipe that is anchored in the column and extended into a steel can embedded in the beam. A gap between the steel pipe and the can enables the extended segment to freely rotate inside the steel can and prevents bending of the protruded segment inside the can.

The University of Nevada’s Earthquake Engineering Lab is the largest of its kind in the United States.

The latest project is funded by the California Department of Transportation, which currently is developing plans for 10 pilot projects based on the developing bridge connector technology.

“This study today is going to allow them to make observations of those designs,” Saiidi said.

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