The replacement of the Sellwood Bridge is about to reach a major milestone. Over a 12-hour period next month, the old bridge deck will be slid about 60 feet north onto some temporary supports in the river.
The roadway on either end will then be reattached, so drivers can still use the old bridge. Then, workers can start in earnest to build the new bridge. Commuters will drive alongside the new one as it takes shape. The completion date is in 2016.
Standing under the 77-year-old bridge, it’s a little worrisome to think that the entire deck — which is essentially an 1,100-foot long, green steel box — it is going to be shoved sideways and then stay in use for another three years.
But Mike Pullen of Multnomah County says there’s no need to worry.
“The engineers tell us that the detour bridge will actually be in better shape than the bridge that’s there now,” Pullen says. “The weakest part of the existing Sellwood Bridge will not be used in the detour bridge. And that’s the concrete part of the bridge that’s on the westside over land.”
One of the main reasons Multnomah County is rebuilding the bridge is because of a slow moving, ancient landslide on the westside, which has pushed the bridge’s concrete and buckled it.
Pullen said there are other problems too, “Its original design was just too light weight of a design. It is not really a bridge that can handle modern traffic.”
That’s because, unlike many of the older bridges in Portland, the Sellwood was not built to carry streetcars — or, by extension, the large buses and trucks in use nowadays. In fact, any vehicle over 10 tons has been banned since 2004.
Barring an ice storm or high winds, the bridge move has been scheduled for Jan. 19. It’s quite the engineering feat. A series of computer-controlled jacks will slowly push the whole structure along a series of teflon-coated rails. And just to make things a little more complicated, one end of the bridge will be moved twice as far as the other end, Pullen says.
“It also has to move all at the same time, so the jacks that are at the far west will be moving twice as far as the east,” he says. “And the biggest risk in this project is not dropping the bridge, which a lot of people have said, ‘Aren’t you afraid of dropping it?’ Well, it’s supported on its whole trip across by this rail system. The real risk is that you could twist it, or bend it.”
After the move, Pullen says the old concrete piers that kept the old bridge supported will be cut into pieces with a water-saw and taken away. The remaining foundations under mud, will stay in the river. Then, new supports for the new bridge will be built and large steel arches put in place to support the new deck.
“The new Sellwood Bridge is going to be more than twice as wide as the existing bridge at its narrowest point,” Pullen says. “And there’ll be some points such as at the west end where it flares out. It’ll have four traffic lanes at the west end because we want to have the extra lanes to push traffic through that intersection at peak times.”
Pullen says for bikes and pedestrians there’ll be a 12-foot sidewalk on either side of the bridge, and a shoulder on the road that’ll serve as another bike lane and an area for breakdowns. “The faster bicyclists, the commuters will be using that because they won’t have to be dodging any pedestrians.”
Few doubt the need for a new bridge. In fact, the steel girders that link the big, green deck to the crumbling concrete roadway were actually recycled from an old bridge that crossed the Willamette River at Burnside in 1894. There’s a dip in the structure where those girders are, apparent even to the naked eye.
Just how much the new bridge is going to cost is a moving target. It’s somewhere between $270 million and $330 million - depending on everything from how much it costs to stabilize the landslide, to steel prices.
The money is coming from the Multnomah County vehicle registration fee, the state, the feds and the city of Portland.
Clackamas County voters decided not to contribute.
Weather permitting, the bridge closes Jan. 17 for about a week as the old deck is moved.