Fact Check: A Bomb Resistant, Floating Coronado Bridge?

Fact Check: A Bomb Resistant, Floating Coronado Bridge?

File photo

Coronado Bay Bridge

 

Image: falseStatement: The center span of the Coronado Bay Bridge was designed to float in the event of a bombing, according to local urban legend.

Determination: False

Analysis: When we asked readers to pinpoint local urban legends, this decades old storyline surfaced: The center section of the Coronado Bay Bridge is designed to float. That way, if the bridge were bombed, the Navy could easily push the largest pieces of the bridge aside and still exit the bay.

Caltrans, which oversees the bridge’s maintenance, has consistently denied the tale. It “was not designed with that in mind,” spokesman Steven Saville told Coronado Lifestyle for a story about the bridge’s 40th anniversary last year. “It would float like a stone.”

Structural engineering experts agree with Caltrans. Though the 1,880-foot-long center section of the bridge is hollow, the circumstances that would allow it to fall 200 feet and somehow still float are beyond improbable.

The Coronado Bay Bridge, which opened Aug. 3, 1969, is mainly constructed out of steel and reinforced concrete, with a center span built like a hollow box. Designers wanted to cut costs and give the bridge a sleek look by concealing its network of supports. The chamber is so expansive that maintenance workers can walk from end to end.

Had the center section been built solid, the steel and concrete mass would sink if it fell into the water. But since the section is hollow, it could theoretically float, said Robert Dowell, a structural engineering professor at San Diego State University who’s familiar with the bridge. At our request, he calculated whether the span could float. As long as the hollowed box was plugged airtight to prevent leaking, he said, it would.

But that’s in theory. It doesn’t account for one decisive factor — the urban legend’s imaginary bomb.

The legend assumes the bombing would neatly break off the almost half-mile center span and cause it to fall about 200 feet without damage, still preserving a somewhat airtight chamber crucial to its buoyancy.

The bridge’s principal architect, Robert Mosher, who now lives in La Jolla, called the urban legend “absolute nonsense” since the center span is firmly connected to each side of the bridge. The separation wouldn’t be precise, he said, and any crack or hole created in the process would cause the section to flood and sink like a wounded ship.

“There’s no way that it could physically happen,” he said.

Dowell also expressed similar doubts. He imagined the section falling into the bay, floating for a short time and then sinking as a result of flooding, either from damage or opened access tunnels.

We’ve called the urban legend false for two reasons. First, the center section wasn’t designed to float in water. Builders thought the model was cheaper and looked better. And second, the bomb storyline doesn’t fit what structural experts predict would ultimately happen — the center span would sink.

One final note worth adding to this story refers to its beginning. Caltrans says the urban legend grew after pieces of the center span were shipped to the bay on barges during its construction. From the shore, it may have appeared the pieces were themselves floating on water.

Mosher said harbor tours picked up on the rumor and continued telling the tale to thousands of tourists. Now 90 years old and retired, he hopes to finally put this urban legend to rest.

For more on this series about local urban legends, check out our stories about a mysterious blob, secret underground caverns, a graveyard turned park and a rumored village of miniature houses atop Mt. Soledad.

You can also find a longer list of urban legends we’re researching here. If you want to add a local fable to our queue, simply send an email to factcheck@voiceofsandiego.org.

Please contact Keegan Kyle directly at keegan.kyle@voiceofsandiego.org or 619.550.5668 and follow him on Twitter: twitter.com/keegankyle.

 

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Keegan Kyle

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1 comments
Frances O'Neill Zimmerman
Frances O'Neill Zimmerman

I have a smart and skeptical friend who would rather take a water taxi to Coronado than drive across that bridge, and now I know why.