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N0KFQ > TODAY 07.11.16 15:03l 59 Lines 2616 Bytes #999 (0) @ WW
BID : 12547_N0KFQ
Read: GUEST
Subj: Today in History - Nov 7
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Sent: 161107/1252Z 12547@N0KFQ.#SWMO.MO.USA.NA BPQ6.0.13
1940
Tacoma Narrows Bridge collapses
The Tacoma Narrows Bridge collapses due to high winds on this day
in 1940. Fortunately, only a dog was killed.
The Tacoma Narrows Bridge was built in Washington during the
1930s and opened to traffic on July 1, 1940. It spanned the Puget
Sound from Gig Harbor to Tacoma, which is 40 miles south of
Seattle. The channel is about a mile wide where the bridge
crossed the sound. Sleek and slender, it was the third longest
suspension bridge in the world at the time, covering 5,959 feet.
Leon Moisseiff designed the bridge to be the most flexible ever
constructed. Engineers of the time believed that the design, even
though it exceeded ratios of length, depth and width that had
previously been standard, was completely safe. Following the
collapse, it was revealed that the engineers had not properly
considered the aerodynamic forces that were in play at the
location during a period of strong winds. At the time of
construction, such forces were not commonly taken into
consideration by engineers and designers.
On November 7, high winds buffeted the area and the bridge swayed
considerably. The first failure came at about 11 a.m., when
concrete dropped from the road surface. Just minutes later, a
600-foot section of the bridge broke free. By this time, the
bridge was being tossed back and forth wildly. At one time, the
elevation of the sidewalk on one side of the bridge was 28 feet
above that of the sidewalk on the other side. Even though the
bridge towers were made of strong structural carbon steel, the
bridge proved no match for the violent movement, and collapsed.
Subsequent investigations and testing revealed that the bridge
was vulnerable to vibrations generated by wind. When the bridge
experienced strong winds from a certain direction, the frequency
oscillations built up to such an extent that collapse was
inevitable.
A replacement bridge opened on October 14, 1950, after more than
two years of construction. It is the fifth longest suspension
bridge in the United States, 40 feet longer than the original.
Construction of the new bridge took into account the lessons
learned in the collapse of the Tacoma Narrows Bridge, as did that
of all subsequent suspension bridges.
Today, the remains of the bridge are still at the bottom of Puget
Sound, where they form one of the largest man-made reefs in the
world. The spot was placed on the National Register of Historic
Places in order to protect it against salvagers.
73 - K.O., n0kfq
N0KFQ @ N0KFQ.#SWMO.MO.USA.NA
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E-Mail : kohiggs@gmail.com
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