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Northwest Voices

Seattle Times letters to the editor

May 27, 2013 at 7:54 AM

Interstate 5 bridge collapse

Deception Pass bridge could be next

Detoured traffic creeps slowly heading south along the Burlington Blvd. bridge at the scene of Thurday's I-5 bridge collapse at the Skagit River near Mt. Vernon. (Ken Lambert / The Seattle Times)

Detoured traffic creeps slowly heading south along the Burlington Blvd. bridge at the scene of Thurday’s I-5 bridge collapse at the Skagit River near Mt. Vernon. (Ken Lambert / The Seattle Times)

The Interstate 5 Skagit River bridge collapse is a wake-up call. Next could be Washington Highway 20 bridge at Deception Pass, constructed 78 years ago when designs were made using slide rules and charts.The weight and frequency of traffic and the uneven expansion joints are concerning. Heavy trucks, including extended trailer dumps, frequently cross the bridge. Many expansion joints protrude from the road surface and noticeably jar every wheel crossing them. Merely annoying to drivers and passengers, the jolts progressively damage the bridge. Each jar causes a downward, hammer-like impulse (like a sound wave) that propagates through the steel structure.

Where stresses are highest (around rivet holes), the repetitive “banging” induces in the steel crystallization, embrittlement (exacerbated by salt air) and ultimately “cyclic fatigue failure.” Rivets can then pull through the holes and the entire structure can “unzip” resulting in sudden collapse.

Should you cross the Deception Pass bridge, pay attention to the jarring, particularly very near the center of the span. Should the bridge go down, the only practical way to get a vehicle on and off Whidbey Island will be by ferry at the south end. Unlike the I-5 Skagit River bridge, there are no alternate routes.

Tom Churchill, LaConner

Comments | Topics: collapse, I-5, infrastructure

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