Why did the Galloping Gertie bridge fail?
The torsional motion began small and built upon its own self-induced energy. In other words, Galloping Gertie's twisting induced more twisting, then greater and greater twisting. This increased beyond the bridge structure's strength to resist. Failure resulted.
What caused the Golden Gate Bridge to collapse?
The pivotal event in the bridge's collapse, said the Board, was the change from vertical waves to the destructive twisting, torsional motion. This event was associated with the slippage of the cable band on the north cable at mid-span. Normally, the main cables are of equal length where the mid-span cable band attaches them to the deck.
What made the 1940 Gertie bridge so flexible?
In general, the 1940 Narrows Bridge had relatively little resistance to torsional (twisting) forces. That was because it had such a large depth-to-width ratio, 1 to 72. Gertie's long, narrow, and shallow stiffening girder made the structure extremely flexible.
Was the vortex shedding the cause of the bridge collapse?
It can be concluded therefore that the vortex shedding was not the cause of the bridge collapse. The event can be understood only while considering the coupled aerodynamic and structural system that requires rigorous mathematical analysis to reveal all the degrees of freedom of the particular structure and the set of design loads imposed.
See more
How did Galloping Gertie break?
Winds above 40 mph caused air-pressure changes and created vortices that swirled around the bridge, twisting, lifting and dropping it, which caused it to break apart.
Why did the Tacoma bridge collapse physics?
According to the two engineers, the failure of the bridge was related to a wind-driven amplification of the torsional oscillation that, unlike a resonance, increases monotonically with increasing wind speed.
Why the bridge has set in motion that led to its collapse?
A small amount twisting occurred in the bridge deck, because even steel is elastic and changes form under high stress. The twisting bridge deck caused the wind flow separation to increase. This formed a vortex, or swirling wind force, which further lifted and twisted the deck.
How long did the galloping gurdy bridge last before falling?
The first studies concluded on November 2, 1940—five days before the bridge collapse on November 7. He proposed two solutions: To drill holes in the lateral girders and along the deck so that the air flow could circulate through them (in this way reducing lift forces).
Why do soldiers not march past the bridge?
Solution : Army troops are not allowed to march in steps because it is quite likely that the natural frequency of the food steps may match with the natural frequency of the bridge and due to resonance the bridge may pick up large amplitude and Break.
Can a cat shake a bridge?
But a cat? No, that's pure myth.” The story of the company of soldiers bringing down a bridge by walking over it in step is based on an actual incident. The Angers Bridge, also called the Basse-Chaîne Bridge (shown below), was a suspension over the Maine River in Angers, France.
How would a bridge collapse?
The most common causes of bridge failure are structural and design deficiencies, corrosion, construction and supervision mistakes, accidental overload and impact, scour, and lack of maintenance or inspection (Biezma and Schanack, 2007).
Can a bridge collapse due to wind?
A physical phenomenon known as aeroelastic flutter caused the bridge to sway both vertically and horizontally for about an hour. At around 11:00 a.m. the Tacoma Narrows Bridge collapsed after the structure failed in the face of 40 mph winds.
What wave caused the Tacoma bridge to collapse?
The Tacoma Narrows Bridge collapsed primarily due to the aeroelastic flutter. In ordinary bridge design, the wind is allowed to pass through the structure by incorporating trusses. In contrast, in the case of the Tacoma Narrows Bridge, it was forced to move above and below the structure, leading to flow separation.
Was the dog saved on Galloping Gertie?
"Tubby" the dog fell into fame when Galloping Gertie collapsed on November 7, 1940. As the only victim of that great disaster, Tubby has earned a special place in the hearts of many. His death symbolizes the drama of that terrible day. All that is known about the unfortunate pooch is here.
What was the worst bridge collapse in history?
Ponte das BarcasPonte das Barcas History's deadliest bridge collapse occurred during the Peninsular War as the forces of Napoleon attacked the Portuguese city of Porto.
Did the dog survive Galloping Gertie?
Today I found out the only victim of the Tacoma Narrows, “Galloping Gertie”, bridge collapse was a three legged dog. The three legged dog in question was a black Cocker Spaniel left in the back seat of the lone car abandoned on the galloping bridge.
What happens when a bridge twists?
Any amount of twist in the bridge created vortices, or areas of low pressure, in locations that actually amplify the twisting motion. As the bridge returned to its natural state, its momentum twisted it in the other direction where the wind could catch it and continue the twisting.
When did the Tacoma narrows bridge open?
In July 1940 , the Tacoma Narrows bridge opened to traffic between Tacoma, Washington and the Kitsap Peninsula.
Why does a paper strap vibrate in the wind?
It’s a completely separate mechanism than resonance from vortex shedding, because the periodic forces are self induced from the naturally unstable aerodynamic shape of the bridge.
What is a suspension bridge?
A suspension bridge is essentially just a deck, two towers, two main cables, and connector rods which suspend the deck, hence the name. The primary advantage of suspension bridges is that they can so efficiently span long distances with only two towers, reducing the amount of material required, and more importantly, the cost.
Why do periodic forces add up to large oscillations over time?
With resonance, small periodic driving forces, like pushing someone in a swing, can add up to large oscillations over time because the energy is stored. In the case of wind-induced motion, the periodic driving force comes from an effect called vortex shedding.
How did Galloping Gertie's twisting affect the bridge structure?
In other words, Galloping Gertie's twisting induced more twisting, then greater and greater twisting. This increased beyond the bridge structure strength to resist.
Why did the wind separate on Galloping Gertie's deck?
A small amount twisting occurred in the bridge deck, because even steel is elastic and changes form under high stress. The twisting bridge deck caused the wind flow separation to increase.
Why did the Gertie bridge go into torsional flutter?
Because of Gertie's design, and relatively weak resistance to torsional forces, from the vortex shedding instability the bridge went right into "torsional flutter.". Now the bridge was beyond its natural ability to "damp out" the motion. Once the twisting movements began, they controlled the vortex forces.
Why was the narrows bridge so flexible?
Here is a summary of the key points in the explanation. In general, the 1940 Narrows Bridge had relatively little resistance to torsional (twisting) forces. That was because it had such a large depth-to-width ratio, 1 to 72. Gertie's long, narrow, and shallow stiffening girder made the structure extremely flexible.
How did the bridge deck work?
The bridge deck's twisting motion began to control the wind vortex so the two were synchronized. The structure's twisting movements became self-generating. In other words, the forces acting on the bridge were no longer caused by wind. The bridge deck's own motion produced the forces.
How much did it cost to build the Golden Gate Bridge?
Engineer Leon Moisseiff — who consulted on the Golden Gate Bridge in San Francisco — countered with a novel and aesthetically pleasing design that replaced the trusses with 8-foot-high plate girders, lowering the construction costs to $8 million but providing much less resistance to bending and twisting.
Why was the Brooklyn Bridge designed?
John Roebling consciously designed the 1883 Brooklyn Bridge so that it would be stable against the stresses of wind. In the early 20th century, however, says David P. Billington, Roebling's “historical perspective seemed to have been replaced by a visual preference unrelated to structural engineering.
What year was the Tacoma Narrows Bridge collapse?
Castle Films also received distribution rights for 8 mm home video. In 1998 , The Tacoma Narrows Bridge Collapse was selected for preservation in the United States National Film Registry by the Library of Congress as being culturally, historically, or aesthetically significant.
What was the first hypothesis of failure of the Tacoma Narrows Bridge?
The first hypothesis of failure of the Tacoma Narrows Bridge was resonance (due to the Kármán vortex street). This is because it was thought that the Kármán vortex street frequency (the so-called Strouhal frequency) was the same as the torsional natural vibration frequency. This was found to be incorrect.
What was the first bridge in the Tacoma area?
The original Tacoma Narrows Bridge was the first to be built with girders of carbon steel anchored in concrete blocks; preceding designs typically had open lattice beam trusses underneath the roadbed. This bridge was the first of its type to employ plate girders (pairs of deep I-beams) to support the roadbed. With the earlier designs, any wind would simply pass through the truss, but in the new design the wind would be diverted above and below the structure. Shortly after construction finished at the end of June (opened to traffic on July 1, 1940), it was discovered that the bridge would sway and buckle dangerously in relatively mild windy conditions that are common for the area, and worse during severe winds. This vibration was transverse, one-half of the central span rising while the other lowered. Drivers would see cars approaching from the other direction rise and fall, riding the violent energy wave through the bridge. However, at that time the mass of the bridge was considered to be sufficient to keep it structurally sound.
How long is the Tacoma narrows bridge?
The Tacoma Narrows Bridge, with a main span of 2,800 feet (850 m), was the third-longest suspension bridge in the world at that time, following the George Washington Bridge between New Jersey and New York City, and the Golden Gate Bridge, connecting San Francisco with Marin County to its north.
How much did the PWA approve for the Tacoma Narrows Bridge?
Moisseiff's design won out, inasmuch as the other proposal was considered to be too expensive. On June 23, 1938, the PWA approved nearly $6 million (equivalent to $110.3 million today) for the Tacoma Narrows Bridge.
How tall is the Bronx Whitestone Bridge?
The Bronx Whitestone Bridge, which is of similar design to the 1940 Tacoma Narrows Bridge, was reinforced shortly after the collapse. Fourteen-foot-high ( 4.3 m) steel trusses were installed on both sides of the deck in 1943 to weigh down and stiffen the bridge in an effort to reduce oscillation.
When was the Tacoma narrows bridge opened?
Efforts to replace the bridge were delayed by the United States' entry into World War II, but in 1950 , a new Tacoma Narrows Bridge opened in the same location, using the original bridge's tower pedestals and cable anchorages. The portion of the bridge that fell into the water now serves as an artificial reef .
