West Seattle High-Rise Bridge creeps toward potential collapse

Cracking Down

West Seattle High-Rise Bridge creeps toward potential collapse

The West Seattle High-Rise Bridge under construction around 1983 (Courtesy Seattle Municipal Archives)

The West Seattle High-Rise Bridge, an important commuter route for the Seattle, Washington, area, has been closed since March 23, 2020, because inspectors discovered new cracks in its structure. While inspectors first noted cracks in the bridge in 2013, the damage seemed to be relatively stable, but conditions deteriorated enough in the early part of this year that Seattle mayor Jenny Durkan closed the bridge while the city studied its options. The earliest that the bridge could reopen appears to be 2022.

A new report covered in The Seattle Times describes how partial failures in the bridge could trigger a total collapse, and the report outlined a zone that would need to be evacuated if the condition of the bridge deteriorated to a dangerous level.

According to The Seattle Times, the cracks stem from creep in the bridge’s concrete, a process by which the material shrinks over time. Potential solutions involve bolstering the bridge’s post-tensioned steel system to help the structure bear the stresses caused by creep, but the extent of the repairs would depend on whether or not the city decides to try to keep the bridge around for the long-term.

KING-TV, a Seattle NBC affiliate, quoted Mayor Durkan as saying, “We’re going to do everything we can to see if that bridge can be fixed, and if so, how quickly we can fix it…At the same time, we’re going to be working on how we can replace the bridge if we need to do that.”

The West Seattle High-Rise Bridge only opened in 1984, and its life span was expected to be much longer than the 35 years it had been in operation before being closed. The Seattle Times reported that a variety of factors may to be blame for the bridge’s failure, including an added traffic lane, earthquakes, and the original design. The bridge’s 590-foot main span is unusually long for a pre-stressed concrete bridge, and designers may have underestimated the amount of creep over the bridge’s lifetime.

The American Society of Civil Engineers has claimed that the United States is underspending on infrastructure, and infrastructure investment has been an off-and-on topic of national political conversations since the start of the Trump presidency.