How to Fix West Seattle Bridge?

Tue June 30, 2020 - West Edition #14
SDOT



The Seattle Department of Transportation recently conducted a study to figure out how to best repair the West Seattle Bridge.

New analysis indicates that repairing the West Seattle High-Rise Bridge may be possible, but the department still do not know how long any repairs would last or whether useful repairs allowing us to reopen the bridge, even partially, for the time it would take to plan, design and construct a replacement would be feasible.

The West Seattle High-Rise Bridge is a complex structure that uses a post-tensioned segmental box girder system to span between four sets of columns. In simple terms, there are two structural systems that work together:

  • The concrete structure, which is visible to the naked eye
  • An internal steel structural system, called a "post-tensioning system," contained within the concrete

Over the past few months, SDOT has conducting more than 100 scientific tests to analyze the structural stability of the West Seattle High-Rise Bridge. The tests completed so far have not found indications of problems with the post-tensioning system, comprising the steel strands running through the structure like a skeleton. Problems with this system would mean repairs would be much less likely to succeed.

It is continuing to analyze how long repairs would take, how much they would cost, whether or not repairs would allow traffic to return to previous levels and how long and in what capacity the bridge could remain open after potential repairs were completed.

It is continuing to analyze how long repairs would take, how much they would cost, whether or not repairs would allow traffic to return to previous levels and how long and in what capacity the bridge could remain open after potential repairs were completed so that we can tell whether or not fixing the bridge is a worthwhile investment.

SDOT has also installed an intelligent monitoring system to track movement and growth of cracks in the bridge. While cracks in the bridge have slowed, they have not stopped growing entirely and we are continuing to plan for every possibility.

SDOT is keeping all options open and are still moving forward with their search for a team to design a replacement for the bridge in case repairs are not a feasible option. Meanwhile, we have begun assembling our construction equipment to stabilize the bridge, which will be a necessary step in every possible scenario.

The full analysis of the structural stability of the bridge should be complete in early July.