Tacoma Narrows Bridges
47.266388888889 - 122.54972222222Koordinaten: 47 ° 15 ' 59 " N, 122 ° 32 ' 59 " W
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Tacoma Narrows ( Puget Sound)
The Tacoma Narrows Bridge (English Tacoma Narrows Bridge ) is a suspension bridge in the U.S. state of Washington.
Location
She leads the highway-like -developed state road 16 Tacoma Tacoma over the Narrows, a side arm of Puget Sound, according to Gig Harbor and so opens the connected only in the southwest to the mainland Kitsap Peninsula with the main town Bremerton from the southeast. The bridge consists of two parallel structures, each of which receives the movement of a direction of travel. Prior to the commissioning of the second bridge in July 2007 flowed all traffic over the building completed in 1950.
The bridge 1940
Description
The first Tacoma Narrows Bridge was built in 1938-1940 also at the same place as the suspension bridge. It is famous for its spectacular collapse after only four months of operation.
Designed by Leon S. Moisseiff bridge at that time had only two lanes and each a narrow walkway, but had a main aperture of 853 m at the time of its completion, the third largest wingspan of all suspension bridges in the world ( after the Golden Gate Bridge and the George Washington Bridge ).
Her two pylons standing in 37 m deep water made when building the biggest problems. They had with caissons to 68 m depth and 54 m for the one for the other pylon be established - at that time one of the deepest foundations at all. The pylon foundation swallowed up 40 % of the total budget of the bridge.
Moisseiff, who had founded by Joseph Melan Deflektionstheorie first applied to suspension bridges and then further developed, provided for a very low and sleek design of the roadway support than steel - plate girder. This development should have initiated Fritz Leonhardt planning the Rodenkirchener bridge in Cologne, she was in the U.S. but also in the trend made possible by the Deflektionstheorie ever lighter bridges. Prior to suspension bridges were always carried out with much higher and stiffer trusses. The new concept was before construction started on the Rodenkirchener bridge among others been taken over and continued by Othmar Ammann City for the Bronx - Whitestone Bridge in New York, which was also Moisseiff had cooperated. Moisseiff went to narrow this path and light bridges in the Tacoma Narrows bridge even further. His design, however, did not offer any reason to doubt. He looked at wind speeds of 96 km / h in front of lateral deflection of the bridge deck of 2.8 m, which would hardly have been noticeable in the span of 853 m. At 161 km / h, the deck would be evaded by 6.1 m. These values presented everyone happy, but they were based on the calculation of static wind loads, aerodynamic effects were not known in the former structure calculations.
Bethlehem Steel created in a short time the longitudinally little rigid pylons. Even John A. Roebling 's Sons, who had just significantly improved their air spinning method at the Golden Gate Bridge again, needed not long strong for the production of the 44 cm extension cable. Bethlehem Steel mounted the bridge decks made of solid web girders in just 6 weeks. Thus, the construction time of only 19 months was a record for the entire bridge - and the bridge had cost less than 6.6 million U.S. dollars.
Even before the completion had pointed out the movements of the bridge workers. The client had instructed Frederick Burt Farquharson of the University of Washington with studies which, although causing a model of the bridge vibrations, but this could not explain.
The bridge was opened on 1 July 1940.
Soon after, she received because of her up-and Abschwingens the nickname " Galloping Gertie " and was a magnet for tourists. Some motorists came especially to the " roller coaster ". Others prefer took a detour through Olympia in the south west in purchase, the bridge was supposed to save. End of July 1940, a camera on the roof of the toll cottage has been installed, registered the waves in the bridge deck up to an amplitude of 60 cm at 25 oscillations per minute. However, the bridge at different wind strengths showed a completely different behavior.
Comparison of the first suspension bridges with full wall brackets
The table shows that the Tacoma Narrows Bridge was significantly longer than the other two bridges, but it had the shallowest and narrowest track support and therefore also lies with two indices for slimming at the top.
These slimming led to a very low stiffness and a very low weight. Together with an aerodynamically unfavorable shape of the carrier made the bridge very sensitive to wind. Even the slightest wind formed behind the wearer a Karman vortex street, the vortex became detached with approximately one natural frequency of the bridge so that the bridge fell into resonance. However, these oscillations then theoretically described, but still hardly known for their impact on road carriers were not the cause of its collapse.
Collapse of the bridge in 1940
On November 7, 1940 came from the south-west, across the bridge, strong winds on. This placed the bridge in a different vibration mode and now led from torsional vibrations. It was a self-excited vibration, which does not require excitation of a certain frequency. The is a twisting road carrier could so by changing its position in the wind continues to refer to this energy to enhance the vibration, completely independent of the frequency of a Karman vortex street that already by a factor of five over the road vibration would have been lying. After three quarters of an hour tore at a wind speed of 67 km / h ( wind force 8 ) the ropes and the road crashed with an abandoned car and a dog in the Tacoma Narrows. The event was filmed by engineers at the University of Washington, who already observed the bridge due to the vibrations long time systematically. As a result of these investigations, the facilities of the platform girder was provided with deflectors made of steel sheet already for the following days.
People were not used in the disaster killed since the bridge was already closed some time before the collapse of public transport. That in the film on the collapse to seeing the car on the bridge was one of dealing with the monitoring of bridge expert who, as also to see the bridge leaves seemingly unimpressed shortly after two other people.
After the collapse
It puzzled at first about the causes, since the aerodynamic effects on bridges were not yet understood at the time. It took many years, many wind tunnel tests and calculations, to the dynamic effects of wind on bridge structures and the impact of aeroelastischem flutter were reasonably understood.
The immediate impact was that Ammann's slim Bronx - Whitestone Bridge was subsequently reinforced in calming the (toll payable ) motorists with trusses, although they had significantly better ratios than the Tacoma Narrows Bridge. As a backlash to the slim floor beams preferable Deflektionstheorie was completed in 1950 construction of the new Tacoma Narrows Bridge, and especially David B. Steinman's Mackinac Bridge Opened in 1957, with high and already visually solid acting trusses provided. Othmar Ammann also used in the Throgs Neck Bridge (1961 ) high and stiff truss; at the Verrazano -Narrows Bridge ( 1964) it became not the problem because of the two-story construction.
The remains of the crashed road are still in place under water; they have been declared a National Monument in 1992. The owner of the toppled into the water with the Cocker Spaniel cars was compensated by the state bridge management. He received $ 450 for the car as well as further $ 364.40 for the content of the car including the dog. The Tacoma Narrows Bridge has been rebuilt with new pylons on the foundations of the old bridge and conventional trusses. Ten years after the collapse of the new bridge on October 14, 1950, reopened.
The construction with trusses should last a long time worldwide. Although it would have been possible to use properly designed solid wall or hollow box girders, even with large suspension bridges, the Severn Bridge in England was completed in 1966 as the first major suspension bridge box girder.
The film of the collapse is often used as illustrative material for the aerodynamic and vibration control operations. It is the only known film of a suspension bridge collapse. As a culturally and historically significant film document was this film, which is present in many other edits, so for the contemporary American newsreels, taken in 1998 in the National Film Registry of the United States.
The most significant result of the disaster was that since in addition to the statics and the dynamics is taken into account in the design of bridges. In addition, a model of the bridge is tested in a wind tunnel before the construction of larger bridges.