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Gold Line bridge is in need of repair

The Chinatown span has shed bits of concrete for 18 months. MTA sees no risk to trains, and a net shields pedestrians.

February 19, 2007|Jean Guccione | Times Staff Writer

For 18 months, small chunks of concrete have been falling from the Metro Gold Line's elevated station in Chinatown and crashing onto the sidewalk several yards below.

No one has been hit by the debris, but transit officials acknowledge the potential danger to pedestrians near the station.

Black webbing has been hung under the Gold Line bridge from Union Station to Chinatown to catch falling rubble (it's also provided a nesting place for pigeons). Workers routinely survey the $21-million bridge for signs of new damage. Two more cracks have recently been detected.

Transit officials don't know what went wrong or how to fix it. But they insist the 14-mile light-rail line linking downtown Los Angeles and Pasadena is safe to ride.

After months of finger-pointing between the Metropolitan Transportation Authority and the Pasadena Gold Line Construction Authority over who was responsible for repairing the bridge, the MTA has agreed to make the necessary repairs.

The joint venture that designed and built the bridge was dissolved after completing its portion of the work six years ago. Neither the Gold Line Construction Authority, which built the commuter rail line, nor the MTA, which has operated the line since July 2003, wanted to take the lead in fixing it. Each said the other was responsible.

No one is sure when the work will begin.

"Until we know what the cause is, we can't really come up with a fix," said Rick Thorpe, the MTA's chief capital management officer.

Whatever the cause, transit officials estimate the repairs could cost as little as $50,000, a small fraction of the railway's $450-million price tag.

Los Angeles County Supervisor Gloria Molina, who's also chairwoman of the MTA, warned transit officials in October that the falling concrete presented "a grave danger to the public."

The transit agency, also known as Metro, has hired an engineer to evaluate the bridge's design and offer a second opinion. A report is expected soon.

Today, passersby can look up at the tracks from the sidewalk at Alameda and College streets, near the ticket machines, and see pieces of fallen concrete in the netting.

A quarter-mile bridge runs from Union Station to a point several yards past the Chinatown station, where the tracks then run at street level most of the way to Pasadena.

From a technical standpoint, the problem lies in the "shear key," the place where two giant slabs of concrete loosely interlock to absorb lateral movement during an earthquake. The keys are expected to crumble in a temblor -- but not from everyday use.

"The cracking that we are getting is beyond what you would normally anticipate," Thorpe said.

The concrete bridge was designed by HNTB Corp. of Santa Ana and built by Modern Continental Co., the Massachusetts-based company that was the contractor for Boston's Big Dig highway tunnel. (A motorist was killed in that tunnel last year when her car was crushed by falling concrete ceiling panels.)

Another joint venture, Kiewit/Washington of Santa Fe Springs, laid the track and built the station on top of the bridge.

On Aug. 23, 2005, two years after the Gold Line opened, transit workers noticed fallen concrete, after spotting a child holding chunks of it in her hands, according to internal MTA documents obtained by The Times.

The concrete had fallen more than 16 feet from the bridge, shattering on the sidewalk below.

The MTA temporarily rerouted Gold Line trains onto a single track, causing minor service disruptions to as many as 18,000 passengers on an average workday.

Both tracks were reopened the next day, when an initial report by HNTB concluded, "It is acceptable from a structural loading standpoint to operate trains."

The report also recommended that more concrete be removed to examine the workmanship underneath. That has not been done.

"It wasn't built the way it was designed," said Mike Kraman, vice president of HNTB.

A visual inspection at that time revealed that Modern Continental deviated from the plan, building the affected shear key 6 inches short of its 18-inch design. The significance of that is unknown: "We don't know if that 6 inches is the total reason for the cracking or if there is some other reason," Thorpe said.

All of the shear keys are short, Kraman said.

In addition, he said, the placement of the steel reinforcing bars appears to have deviated from the bridge design.

Modern Continental officials did not return calls seeking comment.

Cracking also may have occurred because the trains, as they snake along the S-shaped bridge, might exert more lateral force than the track was designed to hold, Thorpe said.

Some transit officials have expressed concern that the movement could cause a dangerous kink in the track. But Thorpe said the rails are inspected daily and repaired as needed.

Since the HNTB report was issued, transit officials have put up webbing under another portion of the bridge to prevent falling concrete from hitting the ground, Thorpe said. They are also monitoring a crack in a third shear key.

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