Replacement May Be Needed for Bay Bridge
The cost of retrofitting the San Francisco-Oakland Bay Bridge to protect it from earthquakes has risen so sharply that the state may be compelled instead to replace the bridge’s entire eastern span, state officials said Tuesday.
The cost of strengthening the landmark eight-mile, double-deck bridge is now estimated at $1.2 billion--far more than the $650 million earmarked in the Proposition 192 bond measure on the March ballot to retrofit all seven state toll bridges.
With the price tag for retrofitting the bridge approaching the cost of replacing it, officials say it would make more sense to tear down the eastern portion of the 60-year-old structure and build a four-mile span from Yerba Buena Island to the Oakland shoreline.
“The Bay Bridge is definitely the most difficult retrofitting job I have ever encountered,” said chief Caltrans engineer James Roberts. “There’s no textbook to go to. We’re essentially pioneering. Every time we turn around there’s something new to test.”
During the 1989 Loma Prieta earthquake--a 7.1 magnitude temblor centered 50 miles away--part of the eastern span’s upper deck crashed onto the lower deck, killing a woman and shutting the bridge for a month while emergency repairs were carried out.
In an embarrassment to Gov. Pete Wilson’s administration, the revelation of increased costs for the seismic retrofitting comes just six weeks before the public will vote on the $2-billion bond measure. The administration has backed the measure and said it would cover the cost of retrofitting major state bridges and highways.
Administration officials are planning to hold a news conference today in Sacramento to announce the revised cost estimates for the bridge and the possibility of building a new eastern span.
On Tuesday afternoon, Wilson received a 45-minute briefing on the retrofit program from his top transportation officials: Business, Transportation and Housing Secretary Dean Dunphy and Caltrans Director James W. van Loben Sels.
Afterward, Dunphy declined to discuss what he told the governor and would not answer questions about the retrofit program. “We’re going to be discussing that tomorrow,” he said.
Asked about the possibility of replacing the bridge’s eastern span, Dunphy said: “We will discuss that along with other issues involving the toll bridges.”
While the Golden Gate Bridge is the most glamorous of San Francisco’s monuments, the Bay Bridge is one of the world’s longest and tallest bridges and was once ranked as one of the nation’s seven modern structural wonders. When it was completed in 1936, the center anchorage that supports the western span was the tallest pier constructed and is larger than the Great Pyramid of Egypt.
The original rail line on its lower deck has long since been replaced by cars, and the structure is the most heavily traveled toll bridge in the state, carrying up to 250,000 vehicles a day.
The retrofit of the Bay Bridge is complicated by the presence of two major fault lines near opposite ends of the structure--the San Andreas fault to the west and the Hayward fault to the east.
According to state officials, earthquakes on the two faults would cause different kinds of ground movement, making it difficult to bolster the structure to withstand both types of potential quakes.
To solve the seismic problems of the Bay Bridge, engineers must improve on a design and building materials that are six decades old, Roberts said.
“The bridge encompasses about six different types of bridge designs,” he said. “It’s actually a series of bridges back to back. The root problem is that this bridge was designed 65 years ago and you could have [seismic] forces 10 times what it was originally designed for.”
Caltrans is conducting tests on the bridge, including sending a team underwater to cut one of the eastern span pilings loose and study what would happen to it during an earthquake.
“The foundations are the biggest problem,” Roberts said. “The most expensive part of all of this is below the water. On the East Bay side . . . it’s on Douglas fir timber pilings that are driven about 85 feet into bedrock.”
On the western side, engineers have found that the top layer of bedrock supporting the bridge is fractured, but that segment of the bridge could be tied down by anchoring it deeper into the bedrock.
Problems also abound above the waterline. Roberts said the structure has a riveted design that tends to work loose, the steel used is weaker than metal used today and most of the tresses on the eastern side need reinforcement to prevent buckling in a major quake.
Caltrans wants to make the west side of the bridge strong enough to withstand an 8.3 magnitude quake on the San Andreas fault and the eastern span strong enough to endure a 7.5 magnitude shaker on the Hayward fault.
“You have to analyze for both conditions,” Roberts said. “We’re analyzing for a shaking period of about 45 seconds.”
To determine the most cost-effective method of upgrading the bridge, Caltrans proposes to prepare a preliminary design for a new structure. A decision on whether to go forward would be made after the design is prepared.
The proposal to replace the eastern section would not alter the most recognized portion of the bridge, the western span that links San Francisco with Yerba Buena Island. That span can apparently undergo a cost-effective retrofit.
The soaring estimates on making the Bay Bridge seismically safe raise the question of where the state will find the money.
In negotiations over the wording of Proposition 192, Bay Area legislators, including Senate President Pro Tem Bill Lockyer (D-Hayward), succeeded in preventing the state from using bridge toll receipts to pay for the retrofit.
With the bond measure’s allocation of only $650 million for all the state’s toll bridges, any major reconstruction of the Bay Bridge will reopen debate over whether to finance work on the span with the bridge’s toll funds, or use gas tax money.
Motorists who drive across the Bay Bridge pay a $1 toll when traveling west. The $73-million cost of building the bridge during the Depression was paid off decades ago.
When the original Bay Bridge was built, it took 3 1/2 years, but two dozen men died during construction and more than 1,000 were injured. The new section would be built to the north of the existing bridge parallel so motorists could continue to use the old span during most of the construction.
Ellis reported from Sacramento and Paddock from San Francisco.