SEATTLE — Construction sites can prove impressive based on scale alone. When building the world’s largest, biggest, tallest or ‘est’ of anything, the sheer size of the project has the power to impress. It isn’t often, though, that a project can impress based on both scale and nuance.
The world’s longest floating bridge build, a Washington State Dept of Transportation project on Lake Washington in Seattle, does just that. A recent tour of the site with members of WSDOT and Kiewit for a future Engineering News-Record article allowed me to take in the scale of the site—more on that in a bit—but also the singular notion of a floating concrete structure.
And nothing quite makes the point of the bridge as descending into a floating pontoon and dropping below water level in the watertight chamber.
With the new bridge-deck roadway elevated above the floating pontoons to make maintenance a much easier effort than on the current bridge, the tour easily navigated both on the bridge deck of a structure set to open in spring 2016 and then below the bridge deck on the concrete pontoons. A trip into Pontoon W, though, added a new dimension.
Dropping below the top of the pontoon, down a ladder, into the hollow structure, you experience the quietness of the surroundings and are met with the fact that this concrete has one simple, yet all-important job: to float. Built watertight with multiple cells that lock down for safety redundancy, these main pontoons that make up the spine of the new bridge are each 11,000 tons and stretch 28 ft tall by 75 ft wide by 360 ft long. Climbing inside of one gives the nuance of the project, without losing the impressiveness of the size.
Climbing into another portion of Pontoon W, the pontoon’s anchor gallery, offers another glimpse to the relation between the concrete and the water. It is here the steel anchor cables leave the pontoon and enter the water on their way down to an anchor at the lake’s bottom. As water laps the entry point, the system that tightens and holds the anchors again shows how this bridge structure differs from so many others.
Inside the dark pontoon or the anchor gallery, as you play on the balance of the waterline while standing on concrete, you have nuance. Back on top of the pontoons or the bridge deck, you’re met with size, as crews construct a 7,710-ft-long floating bridge on a lake.
Come July, the floating portions will all swing into their final place, keeping the bridge well on track for what could be an April 2016 opening to traffic, replacing what is already the world’s longest floating bridge with one 132 ft longer.
Impressive in scale. Impressive in nuance.
Tim Newcomb is Engineering News-Record’s Pacific Northwest contributor. He also writes for Popular Mechanics, Sports Illustrated and more. You can follow him on Twitter at @tdnewcomb or visit his website here.