Volume 50, July 2013

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Parsons Brinckerhoff Designing New Span for Collapsed
I-5 Bridge

A new section of the Skagit River Bridge will be constructed adjacent to the temporary span. Once completed, the temporary span will be removed and the permanent structure will slide into place, causing minimal traffic disruption.

A month after the collapse of a section of the I-5 Skagit River Bridge, a construction team that includes Parsons Brinckerhoff as lead designer was selected to repair the bridge.

On the evening of May 23, a tractor-trailer carrying an oversized load struck the upper corner of the overhead steel frame of the 58-year-old bridge, a key link between Seattle, Washington, and Vancouver, British Columbia. The collision caused the collapse of a 49-meter (160-foot) section of the structure.

The Washington State Department of Transportation (WSDOT) on June 19 selected Spokane-based Max J. Kuney Company to construct a permanent USD $6.87 million replacement span for the bridge. Parsons Brinckerhoff will lead the project design on behalf of Kuney.

The Skagit River Bridge, part of a critical link along Interstate 5 between Seattle and Vancouver, had formerly accommodated about 70,000 vehicles per day. The loss of the bridge had an immediate impact on the local economy, causing detours with delays of at least a half-hour for motorists. A temporary replacement span opened to traffic on June 19 and will remain in place until the permanent replacement is complete.

Aggressive Schedule

The new span will replace a 49-meter (160-foot) section that collapsed into the Skagit River on May 23 after a tractor trailer carrying an oversize load accidentally struck the bridge's overhead steel frame.

Work on the replacement span will start this month, when crews begin installing temporary piles adjacent to the existing bridge on both the east and west sides. Once capped, the piles will support the weight of the new four-lane concrete span during its construction as well as a pair of skid beams that will be used to transition the temporary span to the new one.

While the new span is built, a floating barge will be prepared to receive the temporary span. Once construction is completed, crews will slide the temporary span and the new span along the skid beams and attach the new span. The temporary span will then be lowered to the barge for disassembly.

The work is to be completed on an aggressive schedule and with challenging restrictions. The permanent span can weigh no more than the original span and must maintain its predecessor's navigational clearance. The bridge must remain open throughout the summer to accommodate the heavy traffic on I-5, and all work must be completed by October 1.

"The switchover from the temporary span to the permanent replacement span is of utmost importance to the client," says Jared Smith, Parsons Brinckerhoff's Northwest Area Manager. "The artery is too heavily traveled to close for long without disrupting traffic and the local economy. The project team anticipates the switchover should occur in less than one day.

"Kuney and Parsons Brinckerhoff were able to combine their construction and design expertise, and deep local knowledge to present a cost-effective solution to replace the Skagit River Bridge on an incredibly tight deadline," says Smith.

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