SEATTLE — Nine new pontoons float in Lake Washington and crews have started topping them with the superstructure, all part of the plan to completely rebuild the world’s longest floating bridge, part of State Route 520 that connects Seattle to points east.
Pontoon W received its concrete superstructure at the east end of the lake to support the new SR 520 floating bridge deck. The five columns on the pontoon are approximately 55 ft tall and 4 ft in diameter. Raising them above the pontoons—the current bridge doesn’t have this elevation, instead placing the bridge deck onto the pontoons—not only erases the worry of waves whipping across the roadway, which currently happens in high-wind events, but also provides ample maintenance space for crews.
The Pontoon W columns will mark the transition from the floating section to the land-based supports in Medina for the new $586.6 million six-lane bridge and highway that is scheduled to open in July 2015.
But getting Pontoon W to where it is now didn’t come without challenges. The pontoon was one of six built in Aberdeen—part of a $367 million project—that required repairs in May after the pontoons were formed because of end-wall cracking and interior spalling or chipping.
The pontoons were repaired during the summer and the construction process was amended to secure a 75-year design life for the new bridge. At the same time, a panel of experts convened to review the repairs and make recommendations for future pontoon cycles.
John Reilly, chair and representative of the panel, says the condition of the pontoons now on the lake have greatly improved from what they were when first observed in Aberdeen. The cracks were repaired with epoxy grout or crystalline sealant.
“We are moving ahead with major work on Lake Washington because there is no question that when complete these pontoons will support the world’s longest floating bridge for 75 years or more,” says Julie Meredith, SR 520 program directors, in a statement. “With each new column that goes up on Lake Washington, drivers can see measurable progress toward replacing the vulnerable SR 520 floating bridge.”
But there are still a few questions surrounding the pontoons from the first cycle of production. WSDOT is still analyzing potential effects of the omission of a 90-degree bend in rebar that was designed to minimize cracking. This bend wasn’t made and WSDOT and Kiewit/General/Mason, along with marine construction experts from Ben C. Gerwick Inc. are devising repair options, if further repairs are needed.
In all, 21 of the 360-ft-long longitudinal pontoons will form the majority of the floating structure. Currently, nine pontoons are floating on the lake, with five from the first cycle in Aberdeen and four smaller pontoons from a casting facility in Tacoma.
Moving forward, expect to see continued construction on the east- and west-end bridge piers, the setting of anchors for the new pontoons and pontoons outfitted to receive the precast deck panels. All hopefully crack free.
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