A deep dive on the final stages of repair to the West Seattle Bridge

Aug 30, 2022, 8:20 AM | Updated: 8:29 am


(KIRO 7)

(KIRO 7)

Load testing is one of the final steps to perform before the West Seattle Bridge can reopen to traffic. We’ve talked about it a little bit before, but it’s time for a deep dive.

It’s one thing to say engineers are going to put dump trucks full of rocks at key points on the bridge to test its strength. I wanted to hear from an actual engineer on the subject.

Residents celebrate West Seattle Bridge reopening, but still much to do

Greg Banks is the top engineer for this repair project. I met with him on the West Seattle Bridge during my tour inside the box girders Thursday. Banks said there will be static and dynamic testing, with those trucks being stationary and moving.

“We have six different load cases, and we’re positioning them at various locations,” he said. “Up to twelve trucks will be on the bridge at a time, but each of those trucks will weigh 80,000 pounds.  They’re strategically placed to create worst-case stress conditions.”

So what will Banks be looking for in these tests? He will be watching all the sensors which have been embedded in the bridge to make sure the numbers he sees are what he expects. Banks will be looking for an expansion of the concrete cracks under the load, and he’s looking for movement in the fractions of millimeters. That’s how small and precise this testing is.

What if the numbers don’t line up?

“If it doesn’t, then we go and look at the analytical prediction to make sure we didn’t mess something up with data input,” Banks said. “We’re going to make sure a sensor hasn’t popped or anything like that and is giving us faulty readings. We are going to ground-truth it first before we think it’s not behaving as expected.”

Heather Marx is the project director for the Seattle Department of Transportation. She expects this load testing to go as planned. Her confidence comes from the last two and a half years of the repair work, and the bridge has been responding as expected.

“When it was cold and we had a huge weight of snow on the bridge, it behaved as we expected it to,” she said.  “During the heat dome, the bridge behaved as we expected it to.  We have no expectation that any of those tests are going to come back anything other than exactly as anticipated.”

But if they do, Marx will not hesitate in delaying the reopening, which is now scheduled for September 18.

“We need to make sure,” she said.  “We are not going to open a bridge that isn’t safe for ordinary travel.”

You might find it interesting that live traffic doesn’t add that much weight to the bridge. Most of the weight stresses come from the weight of the bridge itself. Only about 20% of the weight comes from the vehicles using it.

Check out more of Chris’ Chokepoints.


left lane camping...

Chris Sullivan

Left lane camping rule doesn’t apply to express toll lanes

It's been eight years since the 405 Express Toll Lanes opened, and there continues to be confusion over whether the left lane camping rule applies.

5 days ago

Gorst road rage...

Chris Sullivan

Felony traffic crimes continue to skyrocket in King County

Washington state is coming off back-to-back record years for fatal crashes, and the aggressive and risky behavior behind the wheel isn't letting up.

7 days ago

I-5 construction...

Chris Sullivan

Construction has returned to I-5 through JBLM

Just when you thought it was safe to get on Interstate 5 south of Tacoma, the construction workers, heavy machinery and lane closures are back.

12 days ago

(Photo from Chris Sullivan)...

Chris Sullivan

I-405 shuts down again this weekend

Interstate 405 will be a no-go all weekend between Coal Creek Parkway in Factoria and Sunset Boulevard in Renton.

18 days ago

de-fishing hylebos creek...

Chris Sullivan

Thousands of fish removed from the Hylebos Creek

Just out of sight, thousands of small animals and fish were removed from Hyelbos Creek in Fife to restore nearly 200 acres of habitat.

26 days ago

Photo from Chris Sullivan...

Chris Sullivan

A reminder: Get your trailer out of the left lane

We're rolling into the final holiday weekend of the summer, and we know you're already hooking up your trailer to get ready.

28 days ago

Sponsored Articles

Swedish Cyberknife...

September is Prostate Cancer Awareness Month

September is a busy month on the sports calendar and also holds a very special designation: Prostate Cancer Awareness Month.

Ziply Fiber...

Dan Miller

The truth about Gigs, Gs and other internet marketing jargon

If you’re confused by internet technologies and marketing jargon, you’re not alone. Here's how you can make an informed decision.

Education families...

Education that meets the needs of students, families

Washington Virtual Academies (WAVA) is a program of Omak School District that is a full-time online public school for students in grades K-12.

Emergency preparedness...

Emergency planning for the worst-case scenario

What would you do if you woke up in the middle of the night and heard an intruder in your kitchen? West Coast Armory North can help.

Innovative Education...

The Power of an Innovative Education

Parents and students in Washington state have the power to reimagine the K-12 educational experience through Insight School of Washington.

Medicare fraud...

If you’re on Medicare, you can help stop fraud!

Fraud costs Medicare an estimated $60 billion each year and ultimately raises the cost of health care for everyone.

A deep dive on the final stages of repair to the West Seattle Bridge