Wednesday, September 7, 2016

A lot has changed since the late 1930s, including bridge standards

By Marqise Allen

The Coal Creek Bridge near Kendall will get some
much-needed updating over the next month.
Old bridges can be really cool, but, well, they’re also old. And in many cases, they need to be updated. Our crews in Whatcom County will be doing just that on the Coal Creek Bridge west of Kendall and another unnamed bridge east of the Maple Falls area along State Route 542/Mount Baker Highway starting Thursday, Sept. 8. Both wooden bridges were built in the early part of last century and need to be strengthened and brought up to current codes. The first phase of work will require three separate hour-long single lane closures between 7 a.m. and 4 p.m. Tuesday through Friday for a couple weeks. The second phase will begin immediately after the first phase and require a continuous single lane closure from 7 a.m. to 4 p.m. daily Tuesday through Friday. The project is expected to be complete by early October.

These bridges have several inches of asphalt on top of both decks – too much for the bridges’ design by today’s standards. So there’s two ways to go about fixing that. You can take asphalt off to lighten the load on the decks, or you can beef up the bridges. We opted to go with Plan B. Removing asphalt from the bridge isn’t more cumbersome for us, but it certainly would be for drivers. We’d have to completely close both bridges for an extended period of time. However, making the bridges stronger only requires single-lane closures, which means people can make one last trek to Artist Point before it shuts down for the winter.

So how do you make a bridge stronger?
This bridge near Maple Falls may not have a name,
but it’s going to get some attention as it needs to
be brought up to modern bridge standards.
Before I answer that question, here’s an abridged version (get it?) of how a bridge works. The surface that you drive on when crossing a bridge sits on a deck. It’s basically like the floor of the bridge. The deck sits on top of wooden planks, called stringers, that run lengthwise on top of the bridge supports. Still with me? Those stringers sit on top of other wooden planks, called caps, that run horizontal across the width of the bridge. The caps sit on top of the piers, which are the posts that hold up the bridge. Got it?

To strengthen these bridges, we’ll raise each bridge about an inch, replace some caps, and add some stringers to make the bridge stronger. Think about it this way. You may have seen a kitchen that has had a refrigerator or oven sit in the same spot for a while, and the floor starts to sink a little. To fix that and help the floor hold that weight, you’ll go under the house and add new floor joists. This bridge maintenance work is essentially the same thing.

And as always with any of the work we do that requires us to reduce lanes of traffic, thank you for your patience. We’ll do the best we can to finish the work and reopen both lanes as soon as possible.