Nevada lab tests new bridge design after Mexico quake

RENO, Nev. — Scientists at a Nevada earthquake lab on Wednesday tested new bridge designs with connectors they say are innovative and created to 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 motions of an earthquake to rattle a 100-ton, 70 foot 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.

“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 quake. Wednesday’s test inside the University of Nevada’s Earthquake Engineering Laboratory simulated activity of a quake as large as magnitude 7.5.