Railroad Bridge Over Harbor Freeway Gets an Earthquake Test

Commuters whizzing by on one of Los Angeles’ busiest freeways this week had no idea what the engineers in hard hats were doing to the bridge above, and it was a good thing.

They were applying forces to the bridge on a par with the Big One.

The experiment, conducted above the Harbor Freeway in South-Central Los Angeles, was designed to assess how well railroad bridges can withstand earthquakes.

The test will be used by government officials to determine whether the 190 railroad bridges over state highways should undergo the same kind of retrofitting as freeway spans. Such a program could cost the railroads and the taxpayers millions of dollars.

Some scientists have suggested that railroad bridges have special features--such as the tracks that extend to land and half-inch steel plates that connect to the ground--that transfer seismic loads to the roadbed. They note that no railroad bridges collapsed in the Loma Prieta and Northridge earthquakes.

But Caltrans spokesman Jim Drago said the state transportation department is the “bureaucratic equivalent of Missourians. You have to show us.� Caltrans engineers monitoring the tests said there was no danger of the bridge, which moved six inches, collapsing onto the freeway during the experiment because it was still connected to an abutment.

Researchers used a hydraulic ram to “push� the 148-foot-long bridge, which was cut in half. The tracks and steel plate were severed from the adjoining land on one half while the other half was left intact.

“What they did is they pushed it to the breaking point,� Drago said. Caltrans is helping to fund the study.

The scientists completed the test late Wednesday. The disconnected end cracked first, said Manos Maragakis, professor and chairman of the Department of Civil Engineering at the University of Nevada at Reno.

But he said that more tests will be required in the laboratory and on other bridges before a conclusion can be reached.

The bridge was selected for the test because it was scheduled for demolition because of freeway widening.