Seismic bridge retrofitting: And you didn’t even know it!

Tuesday, February 3, 2009

Winter is barely halfway over, but here at WSDOT we’re quickly transitioning into construction season. If you’re familiar with WSDOT projects, you know what that means: you’ll see the signature orange of our traffic cones, construction barrels, and safety vests as crews get to work improving our state highways.

What you might not know is that our construction activities aren’t limited solely to large, visible projects. Some of our projects are barely noticeable to freeway drivers, and you may not have realized that we’ve been working under your feet (er, car) all along. In fact, if you’ve traveled on I-5 from Seattle to Everett lately, you’ve driven right over one of our active construction sites. Since October 2008, crews have been working to retrofit 19 bridges (overpasses and underpasses) on I-5 between Tukwila and Lynnwood, and are currently working in both Tukwila and Mountlake Terrace.

In plain English, seismic retrofitting means improving a bridge to protect it against future earthquakes. Although these bridges are all structurally safe for everyday traffic, simple upgrades can go a long way towards keeping the bridge intact and motorists safe in the event of a large earthquake.

So how has this work progressed without you noticing all those orange barrels and construction equipment? The trick is that construction occurs beneath the surface of the roadway, focusing on bridge columns, crossbeams and girders.



Improvements to an individual bridge typically include one or more of the following:
  1. Column jacketing – installing a metal jacket around the bridge column. If a concrete column were to crack during an earthquake, the metal jacket would hold the pieces together, preventing the column from crumbling.
  2. Bolster retrofitting – extending the crossbeam to prevent girders from slipping off sideways during an earthquake. Girders support the roadway, so it’s important to keep girders intact.
  3. Girder stops – installing concrete blocks on either side of the girder to stop the girder from sliding or tipping over.



In addition to the 19 bridges that are slated for improvement as part of the I-5 project, there are more than 900 bridges across the state that will be improved as part of the Seismic Retrofit Program. For more information, take a look at the project Web site or the statewide Seismic Retrofit page.

Editor's note: post written by Aurora Jones.

3 comments:

Phil said...

How do you inspect for faults in a concrete column after it has been jacketed?

Aurora Jones said...

Phil,

Once a column has been jacketed, it is no longer possible to inspect the original column. Future inspections look at the condition of the steel jacket itself. However, since the jacket is designed to protect and support the column, there should be no change in the condition of the column itself (unless there is a sizeable earthquake).

Also, I'd like to correct my description of bolster retrofitting. Our Bridge Office informed me that the point of bolster retrofitting is to strengthen the crossbeam to ensure that all the columns work together as a unit, providing a higher level of protection against potential earthquakes.

The Geezer said...

Hey, better to jack a column, than jack the contents of my wallet, as is WSDOT's usual habit.

The Geezer

 

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