Though it took more than 10 years to complete and ran US$5 billion over budget, engineering experts warn that the eastern span of the Bay Bridge in San Francisco could be highly susceptible to corrosion.
Speaking before the California state Senate Transportation and Housing Committee, a panel of six engineers said a definite proportion of the bridge’s rods and bolts suffered from an excessive susceptibility to corrosion, and that some of the span’s tendons had already become corroded.
The panel warned that some 2,000 rods and bolts “cannot be considered immune” from failure throughout the life of the bridge, while also censuring state infrastructure agency Caltrans for leaving the high-strength steel tendons used for the skyway section of the bridge exposed to water for months on end, causing them to corrode.
The engineers further point out that the main cable for the bridge could also be at risk of corrosion, particularly those sections which are less protected, and recommended a “full cable dehumidification as a future enhancement” in order to safeguard the integrity of the structure.
According to the panel, while these defects “may not compromise the bridge’s safety at the moment,” they could eventually lead to a major increase in the scope and cost of maintenance and repair work for the structure.
The testimony serves to further tarnish the reputation of the Bay Bridge’s recently completed, controversy-fraught eastern span, particularly given that it was intended to replace the pre-existing cantilevered structure on safety grounds due to the vulnerability of the latter to earthquake damage.
The Bay Bridge is actually a complex of bridge structures spanning San Francisco Bay, serving to provide a direct road connection between San Francisco and Oakland along Interstate 80.
The bridge is comprised of two sections of approximately equal length – an older western section consisting of a double suspension bridge running from the San Francisco CBD to Yerba Buena Island in the middle of the bay, and a more recent eastern section running from the island to Oakland.
The original eastern section incurred severe damage during the 1989 Loma Prieta earthquake, eventually prompting its replacement with a self-anchored suspension bridge attached to a pair of viaducts. According to Guinness World Records, the resulting structure is currently the world’s widest bridge, accommodating a total of 10 general purpose vehicle lanes.
Construction of the bridge was fraught with controversy, however, taking more than a decade long period – from 2002 to 2013, to complete, as well as costing approximately US $6.5 billion, or $5 billion more than originally expected.
Despite the exorbitant cost and building time for the eastern span, the panel chaired by Georgia Tech engineering Professor Reginald DesRoches found that quality control during the construction process had been severely wanting.
“Based on our discussions with the project team on various issues, the implementation of the construction quality assurance has been deficient in some critical areas,” said the panel.
According to the engineers, these shortcomings may have arisen as a result of “an underlying problem of inspection vigilance of the field staff.”
Chairman of the transportation committee, State Senator Mark DeSaulnier, said the panel report served as a “public indictment of Caltrans,” particularly given how much the project has cost California already.
“We know it came 10 years late. We know it cost $5 billion more than expected,” said DeSaulnier. “How much more will we incur in maintenance costs?”
Caltrans director Malcolm Dougherty defended the agency’s work, however, by pointing out that the findings of the panel were consistent with his organisation’s own assessment, concluding “that the bridge is safe.”
Dougherty said, however, that the Caltrans could continue to engage in discussions with the engineers with respect to quality control in relation to the bridge.
“We want to make sure to follow up with them so we can add those to our lessons learned,” he said.