Nevada quake lab tests new bridge design after Mexico quake
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Scientists at a Nevada earthquake lab tested new bridge designs last Wednesday. The designs have connectors they say are innovative. The designs were 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." They attempted to simulate violent motions of an earthquake to rattle a 100-ton, 70 foot bridge model. They wanted to see how well it would hold up.
The tests were conducted a day after a big quake struck Mexico. That quake shook large concrete columns and beams back and forth for about 30 seconds at a time. It displaced 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.
"The bridge has done better than we expected," said Saiid Saiidi. He is a professor of civil and environmental engineering. He 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 they are often unsafe for travel after big quakes. He said the designs that were tested used special types of connectors to link pre-made bridge parts. This included 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 they were never tested 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.
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. They are made out of a metal alloy with titanium that bends and then springs back into shape when quakes hit.
The innovative connectors allow for prefabricated concrete and other materials to be attached to an existing bridge foundation. This should speed repair and reconstruction.
Part of the research centers on a so-called "pipe pin" connection. It was developed by the California Department of Transportation's bridge designer. They intend to use it for connecting certain beam interfaces in bridge construction.
The pin consists of a steel pipe. It is anchored in the column. It is 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. This 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.