Bay Bridge Corrosion Threatens Supporting Cables

Bay Bridge San Francisco (Frank Schulenburg / Flickr / CC / Cropped)
Frank Schulenburg / Flickr / CC / Cropped

The lead designer of the Bay Bridge is warning that the cables holding up the eastern span are vulnerable because of water leaking into the twin steel boxes anchoring them.

On July 9, the San Francisco Chronicle reports, Marwan Nader of T.Y. International told a Caltrans-convened peer review panel that a real danger from corrosion exists in the steel boxes, which are 90 feet wide, about 120 feet long and 25 feet deep. Caltrans acknowledged at the meeting that water leaked into the boxes because of design problems with the guardrail system.

Nader reportedly went so far as to say that the danger from the corroded anchorages presented a greater danger to the bridge than the corroded 25-foot-long cable rods that have snapped from exposure to water. He was relatively unconcerned about the flooding of the sleeves that hold over 400 high-strength steel rods at the tower’s foundation.

He said “as the official engineer of record” on the eastern span part of the bridge, he was “more concerned about the water inside the east anchorage than the tower anchor rods.” In 2013, thirty-two steel rods failed on the bridge’s seismic-stabilizer structures from being soaked in rainwater, triggering work by Caltrans that cost $45 million.

Nader added that the dehumidifiers for each anchorage were ineffective if water leaked into the east anchorages, he added.

The cable holding up the bridge is comprised 137 strands of steel that are covered with steel to protect them, but the anchorages on either side of the eastern end are exposed.

Russell Kane, a Texas-based corrosion expert, told the Chronicle: “In a suspension bridge, the cable is what holds the whole thing up. The issue here is corrosion damage–any kind of pitting or loss of steel weakens those strands. The bridge wouldn’t stay up if enough metal is lost from those cables. Anything that reduces the load carrying of those cables decreases the durability of the design, reduces safety factors and reduces the service life.”


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