We weren’t even going to have a bridge update this month. Although the Sellwood won the design process award last month, we’re all mostly in a holding pattern waiting for the design to finish and the construction to start. Then, suddenly, the clouds parted and NEW INFORMATION was revealed… and you won’t believe this one.
Here’s the current plan for construction: The new bridge will be built along the south side of the existing bridge while traffic continues on the old bridge. When the first half is complete, traffic will shift there while the old bridge is removed and the north side of the new bridge is built. When that’s complete, the two sides will be seamed together and we’ll have a spiffy new bridge. As you might imagine, there are some drawbacks to this plan. It takes nearly as long to build a bridge in two halves as it does to build two complete bridges, plus there is extra structure needed to build this way. This all translates to time and money, requiring about 4-5 years to build and leaving a current $20million shortfall for the current estimated construction cost.
The proposed new option, called the “Shoo Fly” technique, is completely different. Temporary foundations and columns would be built to the north side of the existing bridge, and the crews can actually MOVE THE OLD BRIDGE OVER to rest on the temporary structures! Traffic can proceed on the old bridge while the new bridge is built, and when the new bridge is complete the old bridge can finally be removed. This process would save millions in materials cost, and could shorten construction time by up to a year. There are drawbacks, not the least of which is that much of the old bridge is not structurally sound enough to move. However, it seems to be a strong option to save time, money, and effort. This isn’t a new and unproven technique, either. It’s been used on bridges in Oregon and throughout the country, and a fascinating video is available of the technique in use in Elkton, Oregon.
As always, the best place for the latest Bridge info isn’t our newsletter (much as we might like to think) but the Multnomah County website dedicated to the Sellwood Bridge project at sellwoodbridge.org. If you go there you’ll find archived updates that describe the entire planning of the bridge to date, and the 3/11 posting describes the entire Shoo Fly concept in complete detail.