PACIFIC NORTHWEST EDITION
A Supplement to:
®
June 12 2016 Vol. I • No. 5
“The Nation’s Best Read Construction Newspaper… Founded in 1957.” Your Pacific Northwest Connection – Patrick Kiel – 1-877-7CEGLTD – pkiel@cegltd.com
Galloping Gertie’s Failure Leads to Safer Bridges Today By Lori Tobias CEG CORRESPONDENT
In Tacoma, July 1, 1940 was a day of celebration as a crowd estimated to number 7,000 gathered for the opening of the Tacoma Narrows Bridge, a suspension bridge with a main span measuring 2,800 ft. (853 m) over the Puget Sound. It was the third largest in the world, coming in after San Francisco’s Golden Gate Bridge at 4,200 ft. (1,280 m), and New York City’s George Washington Bridge at 3,500 ft. (1,066.8 m). But four months later, Nov. 7 became a day that would live on in infamy, as the bridge, dubbed “Galloping Gertie” collapsed during a windstorm. “The bridge became famous as ‘the most dramatic failure in bridge engineering history,’” according to the Washington Department of Transportation’s website. “Now, it’s also “one of the world’s largest man-made reefs.” The sunken remains of Galloping Gertie were placed on the National Register of Historic Places in 1992 to protect her from salvagers.” The bridge may have been a dramatic failure, but it also has since significantly helped shape the way we build suspension bridges, making them safer for everyone. “The Tacoma Narrows Bridge collapsed due to aeroelastic flutter,” said Tim
Moore, senior structural engineer at WSDOT. “A suspension bridge has many major components. The bridge deck and stiffening superstructure has to resist its own mass and any transient loads. All of that mass is supported by some kind of cable system. The Tacoma Narrows Bridge was an example of trying to minimize the weight with a cross sectional shape. Prior WSDOT photo to the Tacoma Narrows, there were only a couple of examples where they didn’t use trusses. The original suspension bridges were all framed with deep open stiffening trusses. For the Tacoma Narrows Bridge, they elected to frame with plate girders — girders on the edge of the roadway. That configuration is torsionally less stiff than a stiffening truss would have been.” The second instability in the bridge was vortex shedding — the vertical rising of the bridge deck — which occurred on the Tacoma Narrows Bridge even in mild winds, earning its nickname of Galloping Gertie. It is normal for a suspension bridge to move in the wind, but the Narrows Bridge was “different.”
At left, the newest Tacoma Narrows Bridge opened to traffic in the early morning hours of July 16, 2007. (Shown below) Looking east towards Tacoma and Mt. Rainier during construction of the 1940 Tacoma Narrows Bridge. This photo shows cable spinning and the catwalks, which were used for construction access. WSDOT photo
see BRIDGE page 10
‘One Oregon’ Addresses Transportation Issues Across State The Governor’s Transportation Vision Panel delivered its final report, One Oregon, A Vision for Oregon’s Transportation System, to Gov. Kate Brown. The release of this report culminates a yearlong public effort to develop a series of recommendations addressing transportation issues across all
modes and all regions of the state. While regions of the state have their own distinct characteristics and priorities, the panel found common threads shared across all of Oregon. Three key priorities affecting Oregon’s transportation system were heard by the panel consistently across the state:
• Seismic preparedness — The impact of a Cascadia Subduction Zone event, and the vulnerabilities of the transportation system, is a major concern for communities across Oregon. • Congestion — Portland metro area congestion is having a major impact on the economic vitality of
all regions of Oregon. • Transit — Improved transit is a top priority for communities across the state, both to get people around locally and to connect communities across the region. “While the landscapes differ in our vast state, this report finds we have much in common in relation
to our transportation system,” said Transportation Vision Panel cochair Gregg Kantor. “We share in our desire to make this great state better, and we understand the importance of being one Oregon.” The 35 members of the panel include legislators, business ownsee PANEL page 8