January 21, 2013 6:53 AM

Moving the Sellwood Bridge: The most amazing engineering feat you probably missed

The Sellwood Bridge on Saturday provided daylong entertainment for a giddy crowd of hundreds of awestruck onlookers, as its 6.8 million-pound span moved — in what seemed miraculous to many — inches at a time onto new, temporary supports. The move came off flawlessly, capping months of intense planning and detailed preparations. Traveling about six feet per hour, the bridge’s 1,100-foot-long steel truss slid so slowly along specially built tracks that actual movement was nearly impossible to discern.

Not surprisingly, there are other things happening in our world besides the debate over gun control. One of those things was a truly amazing feat of engineering prowess that occurred here in Portland on Saturday. If you live outside Portland, you probably heard little if anything about it, so let me give you the short version: an 1100-ft. section of a bridge was lifted and moved to the north- in one piece. The bridge’s west end was moved 66 feet, and the east side 33 feet. Think about that for a second; I still am, and my inner History major still marvels at the feat.

If you live in Portland, you know what a decrepit, ready-to-drop-into-the-Willamette-River-at-any-moment relic the Sellwood Bridge is. Multnomah County has put off replacing the bridge for years, but the bridge’s condition could no longer be ignored. The Sellwood Bridge is the southernmost of Portland numerous bridges, connecting the west side of the Willamette River with SE Portland’s Sellwood neighborhood. Taking the bridge out of the equation means having to go almost 11 miles south down Highway 43 to Oregon City to cross the Willamette, and then about the same distance north to Sellwood. The option is neither direct nor convenient, and with the bridge having only two narrow lanes, it had long since outlived its usefulness.

The need to replace or repair the bridge has been evident for years. Workers have routinely wrapped the concrete railing with heavy plastic “bandages” to avoid chunks of concrete falling into the river.

On a federal bridge-safety scale of zero to 100, the Sellwood merited a miserable two. Its potential failure prompted Multnomah County officials three years ago to ban heavy trucks and TriMet buses from it.

Damage to the heavy concrete supports on the west end, caused by continuing movement of an ancient landslide on the slopes above, required repeated treatments of industrial glue to prevent collapse.

That explains the reason for what was a truly awe-inspiring feat on Saturday.

(Photos from The Oregonian)

About 35 yellow-vested crew members remained on the bridge throughout the move, operating the network of 50 hydraulic jacks that lifted and pushed the bridge to its new location and monitoring the condition of the truss.

They had previously calculated that four inches of bend along the length of the structure could be tolerated. Anything more might damage the steel.

The routine remained the same throughout the day: push the bridge a couple of inches at a time; stop to assess its progress; repeat….

The move was complicated by the fact that a new interchange at the west end must be considerably larger than the current one. To provide the extra space, the bridge had to move in a skewing motion like a windshield wiper, traveling 33 feet on the east end, but double that on the west.

I’ve watched the bridge being prepared for the move for months; one of my favorite bike routes passes the east end of the bridge, and even with my limited engineering knowledge it was clear that what was scheduled to happen on Saturday was a MAJOR undertaking.

Once the old span is secured in its new location, the temporary bridge will be re-opened for traffic on Thursday morning. The new bridge is built over where the old one’s footprint. The new Sellwood bridge is scheduled to be completed in 2015, when the old bridge would have turned 90. Nothing lasts forever and yes, it was time.

Lest you think the $307.5 million project was a tightly wound engineering tap-dance, there was also a certain making-it-up-as-we-go, improvised element to it. The move called for the bridge to be slid along specially-engineered beams. Engineers discovered the beams were the slipperiest and easiest to work with when coated with…wait for it…Dawn liquid dish detergent. I can hardly wait for the inevitable commercial.

I suppose we should be thankful it didn’t rain during the move; the suds probably would have complicated the move.

It seems that America can still do big things.

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This page contains a single entry by Jack Cluth published on January 21, 2013 6:53 AM.

Gun nut logic: The only way to prevent a police state is...wait for it..."MORE GUNS!!" was the previous entry in this blog.

Yet another reason I'm glad I'll never have to say "President Romney" is the next entry in this blog.

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