Bridges supporting the Orange Crush interchange, the fifth busiest in California, contain faulty welds that could fail in a Northridge-sized earthquake, and Caltrans is prepared to spend about $4 million to fix the problem, transportation officials say.
Problem welds--discovered by engineers during a statewide review of 1,100 bridges that began in 1996--will be replaced beginning in December, disrupting traffic for the average 189,000 commuters who drive each day through the crossroads of the Santa Ana, Orange and Garden Grove freeways.
The bridges, just three years old, are sturdy enough to handle everyday traffic. Caltrans engineers and outside experts stress that even with a few bad welds, the bridges would not collapse in a moderate-sized earthquake.
"I would not be afraid to drive through [the interchange] during an earthquake," said James Roberts, Caltrans chief bridge engineer. "You might have some damage, but you wouldn't have a collapse."
Tests earlier this year revealed that one in eight welds tested broke at pressures well below the design strength for resisting forces equal to a 6.5-magnitude earthquake. The Northridge quake was a 6.7-magnitude temblor.
The presence of faulty welds raises a number of questions, including why the state approved the welds in 1995, why the problems were not corrected when detected in 1997, why relatively new welds were so thin and brittle, who is responsible for making repairs, and how widespread the problem is.
"We don't have enough evidence to determine the adequacy of the structures the way they are now," said Phil Warriner, a retired Caltrans bridge engineer who is still part of the agency committee that has been investigating problem welds. "We're trying to determine how large of a problem it is, and what it would take to fix it."
One contractor involved in the Orange Crush project said Caltrans inspectors and engineers have known for years that there might be problems.
"They saw everything that we were doing," said Richard Guerrerio, former president of SGS U.S. Testing Corp., a Bay Area company that took industrial X-rays of many of the welds on the interchange. "This isn't anything new."
Caltrans learned that some bridges throughout the state might have faulty welds during construction four years ago of a San Diego interchange where Interstates 8 and 805 meet. That job was halted, and Caltrans demanded that the contractor fix the flimsy welds; it reportedly cost $5 million to strip away the concrete and replace the bad welds.
The repairs were made, but several contractors are still haggling with Caltrans over who should pay for the fixes.
Welds are used to fuse together steel reinforcing bars to form hoops, like a giant Slinky, wrapped within the concrete bridge columns. During an earthquake, the hoops are supposed to trap broken chunks of concrete within the bridge column and maintain the support needed to hold up the structure until the columns can be repaired.
"The weld is very critical to the performance of the column," said Frieder Seible, chairman of the department of structural engineering at UC San Diego and an outside Caltrans consultant. "It's just as critical as the horizontal reinforcement. We've got to make sure the welds are not the weak link."
Shaken by the extent of bad welds uncovered in San Diego, Caltrans vowed to make sure the same problem didn't exist elsewhere in new bridges or those retrofitted to withstand an earthquake. State engineers began scrutinizing 1,100 bridges built with the same type of weld used in the San Diego interchange.
During the statewide review of those bridges, engineers identified 299 that needed closer scrutiny. Eventually, Caltrans pinpointed several interchanges that needed still more attention because the welds in question were in critical support zones. Engineers couldn't be sure those welds were adequate, so they ordered some samples removed so they could be tested in labs.
Caltrans says it has ordered about $4.5 million in repairs made to bridges with bad welds, not including the Orange Crush. Among them were some faulty welds found in an onramp to the relatively new Century Freeway at Douglas Street, just south of Los Angeles International Airport. That problem was fixed in July.
Sometimes engineers found welds that didn't require repair. They include two bridges on the Foothill Freeway in La Canada-Flintridge, the intersection of the Foothill and Glendale freeways near Burbank, and the interchange at Interstate 5 and California Route 52 in San Diego.
Still under scrutiny, and of greatest concern, are the Orange Crush, 4.3 miles from the El Modeno/Peralta Hills fault, and the Golden State/Antelope Valley freeway interchange near Santa Clarita, where 45 welds will be tested over the next 18 months and an assessment made of what to replace, said Jim Drago, Caltrans state spokesman.