Monday, November 25, 2019

1939 Deer Isle-Sedgwick Bridge

(Bridge Hunter; Historic Bridges; HAER; BridgemeisterSatellite)

I was aware that the Tacoma Narrows Bridge was designed with a thin deck made of steel girders instead of a deep truss so that it would look "streamlined." I was not aware that this was a fad that other engineers adopted until recently. In fact, steamlining was a general fad in the 1930s. Four months after the Tacoma Narrows opened, engineers learned that fad was wrong because the bridge was torn apart by torsional waves. This bridge was David Steinman's streamlining mistake because he designed it with a lightweight deck. He learned it was unstable during construction so he added cable and floor stays to (almost) stabilize the bridge. (The Bronx-Whitestone Bridge was another "streamlined" bridge that had problems with wind. The designer, Othmar Ammann, added stiffening  trusses to the deck to stabilize it.)

Photo from ME,5-SEDG.V,1--5 from me0300

The popularity of Eggemoggin Reach as a yachting area called for a 200' wide channel at midspan with a minimum 85' underclearance, placing the roadway at 98.7* above mean water level. At the same time, the depth required for foundations at this location called for minimizing the length of the approach spans. This height problem was solved by employing steep 6-1/2 percent approach grades and a fairly short 400' vertical curve at the center of the main span. In this manner, the needed height was attained and the approach viaducts were kept to a minimum length. [HAER-data]
To meet the requirement of opening before the Summer tourist season, they had to work during the Winter. To minimize the hardships of working in the Winter weather, they pushed prefabrication techniques past what had been used before. In addition to assembling prefabricated modules for the deck and tower, they also built the cofferdams from prefabricated sections. And they used the prestressed twisted-strand cables that they developed for earlier bridges such as the 1931 Waldo-Hancock Bridge. [HAER-data]

Before the bridge was finished, unexpected wind-induced motion in the relatively lightweight deck indicated the need for greater stability. Diagonal stays running from the main cables to the stiffening girders on both towers were added to stabilize the bridge. [HAER-data]
Two years after the Tacoma disaster, Stienman's reinforcements got their test on Dec 2, 1942. "That day a severe storm ripped down the Maine coast, smashing into the bridge with winds of up to 80 miles per hour. The bridge oscillated in 12-foot waves that snapped a quarter of the cable stays, cracked the expansion joints, caused the suspension cables to slip through the cable ties, and generally wrought havoc on every part of the bridge. The damage was extensive, but when the gale blew itself out, the bridge was still standing.

"The storm left Steinman more convinced than ever that he was on the right track. What the bridge needed, he decided, was more of the same. Steinman added another, far more extensive set of cable stays, and he didn’t stop there. By 1944 there were vertical stays between the tops of the towers and the roadway, transverse stays that crossed over the roadway, and zigzag stays from the roadway to the main cable and back, crisscrossing the secondary cables the whole length of the span. The bridge became an enormous cat’s cradle of metal rope, as if it were woven by the hands of a giant." [InventionAndTech, p5]

"More recently, in 1993 the bridge received additional protection from wind. A special system of fairings that direct wind over and below the girders were attached to the outside of the girders." [Historic Bridges] These fairings were evidently the result of wind-tunnel testing done by the Federal Highway Administration. [ScienceDirectResearchGate, but I didn't request full-text]

This photo shows some gaps in the faring on the side of the deck. That makes it easy to understand what was added in 1993. If you look very closely, you can see diagonal cables as well as the usual vertical suspender cables. I think those diagonal cables are the cable stays that were added to help save the design. I'm still trying to figure out what the "floor stays" were.
When David Steinman heard that the Tacoma bridge was experiencing wind driven problems, he wrote to the authority and offered to provide a solution to their problem. But his offer to help was turned down. Four months later, when the bridge tore itself apart, he let people know that he offered to solve the problem, but he was refused. But given the need for additional solutions to stabilize this bridge and the more extreme length-to-dept ratio of the Tacoma bridge, some engineers think that no amount of additional cables could have saved the Tacoma. [InventionAndTech]

The caption on this construction photo implies that some of the prefabricated pieces were quite large.
PenobscotBayPress, Penobscot Bay Press file photo
The Mainland side tower being raised on finished piers and base in summer of 1938.

Unlike the Waldo-Hancock Bridge, MDOT successfully completed rehabilitation of this bridge in 2008. The narrow deck, 20' curb to curb, was replaced 9' at a time in sections of 200' so that traffic could use both lanes for most of the crossing. [cianbro]
MDOT via ChildsEng
The pier work consisted of removing deteriorated concrete and using stay in-place forms made of steel for pouring the new concrete. Leaving the steel forms in place will help protect the piers from ice. [ChildsEng]

Additional work was planned between July-Dec, 2013. [CastinePatriot] But that work spilled over into February, 2014. [WeeklyPacket]

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