EARTHQUAKE / LIFELINES OF L.A. : THE BRIDGES : Street Bridges Likely to Need Seismic Work : Good news is reinforced spans survived the temblor. Not-so-good news is that 25% of city’s and 33% of county’s bridges will require retrofitting, officials say.

They cross rivers and roads, linking neighborhoods and connecting homes with workplaces.

Although they do not get the attention of eight-lane freeways or towering interchanges, the 2,300 bridges crisscrossing the region are as vital to traffic flow and mobility as gasoline.

So since the Northridge quake, traffic engineers with the city and county of Los Angeles have been surveying bridges from San Pedro to Santa Clarita to see how they fared, especially those that have been reinforced in recent years to meet new earthquake safety standards.

The result? The good news is that the reinforced bridges survived the quake. And the vast majority of unreinforced older bridges that were deemed most at risk did not suffer serious damage, perhaps because of their locations at least 20 miles from the epicenter.

The not-so-good news, officials say, is that as many as a quarter of the city’s bridges and a third of the county’s will need some seismic strengthening to ensure that they can withstand a quake that might hit them with the same intensity of the Northridge temblor. The retrofitting is expected to cost more than $250 million and take years to complete.

“Our bridges held up pretty well,” said Robert Barsam, a supervising structural engineer for the county Department of Public Works. The department, he said, reported $1.6 million in damage to bridges and serious problems with only four of 1,500 spans countywide.

“The city has been pretty lucky in terms of bridges,” said Clark Robins, a division engineer for the city of Los Angeles. Of 800 bridges, only two were damaged so severely that they were closed, he said. Overall, there was $2 million in damage to 62 spans, Robins said.

Despite the performance of the bridges during the Northridge quake, engineers acknowledge the potential for serious damage in a future one--especially if it is centered closer to Downtown Los Angeles. That possibility alone, they say, creates a sense of urgency to complete the renovation of hundreds of bridges that, if severely damaged or lost, could cripple transportation throughout the county.

“I think the county bridges are safe and that they can withstand a large magnitude earthquake,” said Barsam. By his reckoning, up to 95% of the bridges--because of their strength, size, distance from faults and other factors--would not incur any major damage.

“However, since the epicenters are very unpredictable, I think it warrants us looking at all the bridges as though they were going to be at the epicenter,” he said. “And (we should) retrofit those that are vulnerable to collapse.”

Moreover, the recent quake reminded city and county officials of the need to accelerate earthquake safety programs.

In the city of Los Angeles, that means pushing forward with a nearly $400-million seismic safety program that voters approved as a bond issue after the 1989 Loma Prieta quake in Northern California. The retrofitting program for bridges and buildings got a slow start but was given a burst of urgency last year when city lawmakers--hoping to spur the local economy--called for advancing the timetable of repairs.

Since 1990, $12.9 million has been spent retrofitting city bridges. Now, officials say, $20 million in contracts are to be awarded by April. The entire $97-million program to repair 187 bridges is expected to be completed by 1996.

Among the highest priority bridges in the coming year, Robins said, are those spanning the Los Angeles River. In all, 44 of the 46 bridges will be reinforced at a cost of at least $20 million, he said.

One reason for their high priority is age. “Most of them were built in the ‘20s . . . (when) there was not much in the way of steel reinforcing,” Robins said.

In addition, the bridges over the river are taller and longer than many others in the city and more vulnerable to ground vibrations, he said.

The final reason has to do with how important the spans would be after a quake.

“They are our transportation links across the river and are important for rescue work, evacuations and police and fire emergencies,” Robins said. “So it is important that they be maintained in service. . . . If some were down it would tie up traffic in a major way.”

For the county, ensuring the safety of bridges is a larger task, both in terms of numbers and the area to be covered.

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Up to 540 bridges under county jurisdiction, from remote unincorporated areas to mid- size cities, will be carefully analyzed, Barsam said. About 216 could require “serious work” to ensure their safety in an earthquake, he said, while the remainder may require less extensive repairs.

He said the county has identified 19 bridges that are high priority for repairs--six have been retrofitted, four are being bid on, and the remainder will go to contract before May.

Within the next two years, he said, the county is looking at another 216 bridges to be reinforced through a federal highway bridge replacement and rehabilitation program. The preliminary cost estimate for that program is at least $150 million.

The remaining 200-plus bridges will be strengthened, as funds are available, in three to five years.

Many of the high-priority bridges are in the Long Beach area, including the Long Beach Freeway overpass of the Los Angeles River, Barsam said. In that $2.1-million project, workers will strengthen the bridge by, among other things, retrofitting its columns.

Another high-priority area will be the Antelope Valley, he added.

And like Los Angeles, the county also will focus on bridges that span the Los Angeles, Rio Hondo and San Gabriel rivers.

Although the bridges are slated for strengthening, Barsam said, he believes many have proven their durability by surviving quakes.

So as they ready for the worst, city and county bridge engineers voice confidence that the most vulnerable bridges have been--or will soon be--strengthened.

“I have been around here 30 years now and I have been through Sylmar and Whittier and now Northridge. And we did well in all of those,” Robins said. “So based on that, I feel pretty comfortable about the city’s bridges.

“That doesn’t mean the retrofit program is any less urgent than it would be if we had more damage. . . . We have probably been lucky that we have not had an epicenter near our major bridges Downtown.”

Local Bridge Damage

Of the 2,300 bridges owned by Los Angeles County and the City of Los Angeles, several suffered major damage. The worst damage to county bridges occurred in or near Santa Clarita, while in the Los Angeles, the two bridges in the San Fernando Valley were damaged enough to be closed.

COUNTY

* Damage to columns and abutments on Sierra Highway bridge over railroad tracks, $500,000.

* Damage to abutments on McBean Parkway, also over the Santa Clara River, $400,000.

* Buckled girders and other damage along The Old Road over Santa Clara River, $350,000.

* Damage to approaches to The Old Road bridge above Southern Pacific railroad, $150,000.

CITY

* A 70-foot pedestrian span over Wilbur Avenue at Collins Street in Tarzana suffered some $100,000 in damage to its columns.

* Approach roads on both ends of a six-lane highway that takes Nordoff Street over the Southern Pacific rail line in Northridge incurred some $500,000 in damage.

Sources: Los Angeles County and City of Los Angeles