WSDOT Admits 520 Bridge Problems Result Of Design Flaw

Feb 27, 2013

Washington Secretary of Transportation Paula Hammond said Tuesday that cracks in the pontoons for the state Route 520 floating bridge project were largely the result of a flawed design by the state.

The pontoons are the floating part of the 520 bridge across Lake Washington, the longest floating bridge in the world. They’re huge concrete structures that support the roadway; the larger pontoons are about the length of a football field and weigh the same as 23 Boeing 747 jetliners.

Last year, cracks were discovered in the pontoons for the new bridge, which prompted then Governor Chris Gregoire to convene an expert panel to review the situation. The panel released their findings on Tuesday.

The panel found two reasons for the cracks: the contractor didn’t follow the state’s engineering guidelines as it was building the pontoons, and the state had a faulty design. 

WSDOT never ran models that tested the pontoon design.


Specifically, the cracks occurred when the steel bands were used to compress the concrete pontoons, a process called post-tensioning. Originally, those bands were inserted through the lengths of the pontoons.

In an ironic twist, the fix involves using the same technique but in a different direction. WSDOT said it would insert the steel bands across the width of the pontoons and compress the concrete, which should eliminate the major cracks.


Washington Secretary of Transportation Paula Hammond said her department did not follow standards of good practice. She said WSDOT never ran models that tested the pontoon design.

“Engineering is all about analyzing and testing, and checking, whether it’s a pontoon or bridge or highway off ramp. And so I think a step was missed,”she said.

Hammond said she didn’t know why that step was missed, but she said she requested an internal review and heads might roll. “What are the accountabilities for those employees?” she said.

The development comes at a time when there will be a change in leadership at WSDOT.
Last week, Governor Inslee announced a new transportation secretary, effective next month.

Hammond said the pontoon problems have been frustrating for her. “I know I’ve taken a very strident approach to lessons learned, what exactly happened, how do we go after making sure this never happens again. And as I leave, if that’s what I can leave the agency, an awareness of what we did wrong and how we can improve ourselves for the future, then I would say that at least that’s a positive note,” she said.

Hammond said the contractor, Kiewet-General Joint Venture, will work to fix the pontoons. The state has about $200 million in its contingency fund to cover the costs. WSDOT will have to negotiate with the contractor to determine which party pays for the repairs of the different cracks, because both WSDOT and Kiewet-General are responsible for the problem.

The work means that the floating section of the bridge will probably open in the fall of 2015, Hammond said. The contract for the floating bridge calls for the project to be open by July 2015, although officials had publicly said they hoped it would be open by the end of 2014.

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