What caused the Tacoma narrown 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.
Why was the Tacoma Narrows Bridge failed?
Why the Tacoma Narrows Bridge failed? The Tacoma Narrows Bridge collapsed primarily due to the aeroelastic flutter that was caused by high-speed winds that matched with the natural frequency of the structure. Click to see full answer. Keeping this in consideration, what was wrong with the Tacoma Narrows Bridge?
Why did the original Tacoma Narrows Bridge collapse?
The first Tacoma Narrows Bridge opened to traffic on July 1, 1940. Its main span collapsed into the Tacoma Narrows four months later on November 7, 1940, at 11:00 a.m. (Pacific time) as a result of aeroelastic flutter caused by a 42 mph (68 km/h) wind. The bridge collapse had lasting effects on science and engineering.
What intresting facts are there about Tacoma Narrows Bridge?
- The bridge earned the nickname "Galloping Gertie" for its unusual rolling, twisting behavior. ...
- Thrill-seekers often crossed the Tacoma Narrows just to experience the bridge’s unusual rolling, twisting behavior. ...
- In 1992, Gertie’s sunken remains were placed in the National Register of Historic Places to protect them from being stolen.
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Was the Tacoma Narrows Bridge a failure?
Tacoma Narrows Bridge, suspension bridge across the Narrows of Puget Sound, connecting the Olympic Peninsula with the mainland of Washington state, U.S. The original bridge, known colloquially as “Galloping Gertie,” was a landmark failure in engineering history.
Who was at fault for the Tacoma Narrows Bridge collapse?
The Board refused to blame any one person. The entire engineering profession was responsible, said the experts. They exonerated Leon Moisseiff.
What causes bridges to fail?
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).
What force caused the Dee River bridge disaster?
The most likely cause of the failure of the bridge was a torsional buckling instability to which the bridge girders were predisposed by the compressive loads introduced by the eccentric diagonal tie-rods on the girder.
When did the Tacoma narrows bridge open?
In July 1940 , the Tacoma Narrows bridge opened to traffic between Tacoma, Washington and the Kitsap Peninsula.
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.
How to stop a bridge from fluttering?
One way that modern bridges avoid flutter is to include a gap in the center of the deck so that the pressures on either side can equalize. I cut a slot in my model, and sure enough the vibrations almost completely stopped. Another option is just to make the bridge deck more aerodynamic to avoid creating vortices that push and pull on the structure. Of course, bridges aren’t the only civil structures affected by the wind. Take a look at the very first Practical Engineering video about Tuned Mass Dampers to learn about how wind-induced motion can be mitigated in skyscrapers. For a simpler example, take a look outside at just about any high voltage power line. You might notice small devices hanging near the insulators at each pole. These are stockbridge dampers that help suppress wind-induced vibration on long cables and signs. And of course, other types of engineers contend with flutter as well. I’ve heard that airplanes are designed for wind loads, but I can’t confirm it.
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.
What is a bridge?
A bridge is a quintessential civil structure. Humanity’s need to get from one place to another without getting wet is as old as history itself. And for so many years, there was one force with which bridge engineers had to contend: gravity. The fundamental question of bridge design was this: how can we hold up the structure itself and all the people and vehicles that may cross against the force of gravity pulling them downward. And secondary to that, how can we do it economically, for the least cost to the public, since most bridges are funded by the taxpayer. So over time, bridge designs evolved with our understanding of structural engineering and ability to produce better construction materials towards lighter and more efficient shapes, one of those shapes being the suspension bridge.
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.
Why did the Tacoma narrows bridge collapse?
The Tacoma Narrows Bridge collapsed primarily due to the aeroelastic flutter that was caused by high-speed winds that matched with the natural frequency of the structure.
Why was the narrows bridge built?
The 1940 Narrows Bridge was built "primarily as a military necessity" to link McChord Air Field south of Tacoma and the Puget Sound Navy Shipyard in Bremerton. This important fact is often is often overlooked today. But, it was well known to area residents and local newspapers in 1940.
What was the significance of the failure of the Tacoma Narrows Bridge?
The failure of the Tacoma Narrows Bridge effectively ended Moisseiff's career. More importantly, it abruptly ended an entire generation of bridge engineering theory and practice, and the trend in designing increasingly flexible, light, and slender suspension spans.
What caused the collapse of the Tacoma narrows bridge?
For over six decades, engineers have studied the collapse of the 1940 Tacoma Narrows Bridge. The experts disagree, at least on some aspects of the explanation. A definitive description that meets unanimous agreement has not been reached. The exact cause of the bridge's failure remains a mystery.
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.
How did the bridge control vortex forces?
Now the bridge was beyond its natural ability to "damp out" the motion. Once the twisting movements began , they controlled the vortex forces. The torsional motion began small and built upon its own self-induced energy.
What happens when a bridge is twisted?
When the bridge movement changed from vertical to torsional oscillation, the structure absorbed more wind energy. 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. Engineers call this "self-excited" motion.
Why is it important to know the exact cause of the 1940 bridge's collapse?
Why is it important to know the exact cause of the 1940 bridge's collapse? Engineers need to know how a new suspension bridge design will react to natural forces. The more complete their understanding, the better their problem solving, and thus, the stronger and safer their bridge. The fact that engineers still argue about the precise cause of the Galloping Gertie's collapse is testimony to the extraordinary complexity of natural phenomena. Today, the 1940 Tacoma Narrows Bridge's failure continues to advance the "scientific method."
What was the pivotal event in the collapse of the bridge?
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. When the band slipped, the north cable became separated into two segments of unequal length. The imbalance translated quickly to the thin, flexible plate girders, which twisted easily. Once the unbalanced motion began, progressive failure followed.
How long was the Tacoma narrows bridge?
The Tacoma Narrows Bridge was the third-longest suspension bridge in the United States at the time, with a length of 5939 feet including approaches. Its two supporting towers were 425 feet high. The towers were 2800 feet apart.
Why were suspension bridges used?
Suspension bridges were both more elegant and economical than railway bridges. The suspension design thus became favored for automobile traffic. Unfortunately, engineers did not fully understand the forces acting upon bridges. Neither did they understand the response of the suspension bridge design to these poorly understood forces.
How many halves does a torsional bridge have?
The torsional mode shape was such that the bridge was effectively divided into two halves. The two halves vibrated out-of-phase with one another. In other words, one half rotated clockwise, while the other rotated counter-clockwise. The two half spans then alternate polarities.
Why is the span of a bridge at an angle of attack?
Thus, the bridge is initially at an angle-of-attack with respect to the wind. Aerodynamic lift is generated because the pressure below the span is greater than the pressure above. This lift force effectively places a torque, or moment, on the bridge. The span then begins to twist clockwise as show in Figure 22.5. Specifically, the windward edge rotates upward while the leeward edge rotates downward.
Why does the span overshoot its initial rest position?
The reason is that there is little or no energy dissipation mechanism . Thus, the span overshoots its initial rest position. In fact, it overshoots to the extent that the wind now strikes the span from above as shown in Figure 22.6. The wind's lift force now effectively places a counter-clockwise moment on the span.
Why do suspension bridges have two half spans?
The two half spans then alternate polarities. One explanation of this is the "law of minimum energy.". A suspension bridge may either twist as a whole or divide into half spans with opposite rotations. Nature prefers the two half-span option since this requires less wind energy.
Who was the first to show that vortex shedding drove bridge oscillations?
Vortex Shedding. Theodore von Karman , a famous aeronautical engineer, was convinced that vortex shedding drove the bridge oscillations. A diagram of vortex shedding around a spherical body is shown in Figure 22.3. Von Karman showed that blunt bodies such as bridge decks could also shed periodic vortices in their wakes.
When was the Tacoma narrows bridge replaced?
Collapse of the Tacoma Narrows Bridge, Washington state, 1940. The failed 1940 Tacoma Narrows Bridge was replaced in 1950 by a new span stiffened with a web truss.
How did the Tacoma Bridge collapse?
Four months after the opening of the first Tacoma Narrows Bridge, on the morning of November 7, 1940, it suffered collapse in a wind of about 42 miles (67 km) per hour. The 2,800-foot (840-metre) main span, which had already exhibited a marked flexibility, went into a series of torsional oscillations whose amplitude steadily increased until the convolutions tore several suspenders loose, and the span broke up. An investigation disclosed that the section formed by the roadway and stiffening plate girders (rather than web trusses) did not absorb the turbulence of wind gusts. At the same time, the narrow two-lane roadway gave the span a high degree of flexibility. This combination made the bridge highly vulnerable to aerodynamic forces, insufficiently understood at the time. The failure, which took no lives because the bridge was closed to traffic in time, spurred aerodynamic research and led to important advances. The plate girder was abandoned in suspension bridge design.
How many lanes are there on the 1950 Tacoma Bridge?
To address growing congestion, a parallel bridge south of the original opened in 2007; the 1950 bridge now has four lanes of westbound traffic and the 2007 bridge four lanes of eastbound traffic. The 1950 Tacoma Narrows Bridge, Washington state, prior to the 2007 addition of a parallel bridge. The Editors of Encyclopaedia Britannica This article ...
What is the narrows bridge?
Tacoma Narrows Bridge, suspension bridge across the Narrows of Puget Sound, connecting the Olympic Peninsula with the mainland of Washington state, U.S. The original bridge, known colloquially as “Galloping Gertie,” was a landmark failure in engineering history. The modern Tacoma Narrows Bridge, Washington state.
When was the first narrows bridge built?
Spanning 840 metres (2,800 feet),... Four months after the opening of the first Tacoma Narrows Bridge, on the morning of November 7, 1940, it suffered collapse in a wind of about 42 miles (67 km) per hour.
What is the name of the bridge that connects the Olympic Peninsula to the mainland?
Tacoma Narrows Bridge, suspension bridge across the Narrows of Puget Sound, connecting the Olympic Peninsula with the mainland of Washington state, U.S. The original bridge, known colloquially as “Galloping Gertie,” was a landmark failure in engineering history.
When did the Tacoma narrows bridge collapse?
The Tacoma Narrows Bridge collapses due to high winds on November 7, 1940. The Tacoma Narrows Bridge was built in Washington during the 1930s and opened to traffic on July 1, 1940.
When was the Tacoma Bridge replaced?
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 ...
How high was the sidewalk on the bridge?
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.
How wide is the channel on the bridge?
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.
Why did the Tacoma narrows bridge collapse?
The PWA finally inferred that the Tacoma Narrows Bridge failed due to its extraordinary flexibility, lightness, and narrowness. These characteristics helped the wind force, which occurred on the failure day, to cause the torsional motions that led to the collapse of the bridge.
How tall is the Tacoma narrows bridge?
It was constructed in Washington, US, to connect the cities of Seattle and Tacoma. The main span of the bridge was 853 m, connected with two glazing towers of 128 m height. Despite the fact that, at that point, it was the third-longest suspension bridge in the world, the Tacoma Narrows Bridge was much flexible, smaller, ...
What is the width to depth ratio of the Tacoma narrows bridge?
Also, the Tacoma Narrows Bridge had a 1/340 span-to-depth ratio, and its 1/75 width-to-span ratio was much less than the Golden Gate Bridge. These special attributes, combined with its very low damping ratio, initiated enormous vertical motions during moderate to low wind conditions.
What caused the failure of the bridge?
These air vortices developed a wake zone, also known as Von Karman's zone. This wake zone strengthened the oscillatory motions , in the end causing the failure of the bridge.
How could the weight of a bridge have been increased?
By increasing the weight of the bridge, natural frequency of the bridge could have been increased. By improving the damping ratio of the bridge, oscillatory motions could have been absorbed and the movements could have been restricted. Use of dynamic damper could have restricted the motion of the bridge.
How can oscillation be reduced?
Also, researchers suggested after conducting multiple wind tunnel tests that oscillation motion can be reduced by installing deflector vanes or fairings. These measures could have reduced the lift and oscillation. But, the failure of the bridge occurred before these solutions could be introduced.
What would have happened if the open stiffening trusses had been used in the place of plate?
If the open stiffening trusses could have been used in the place of plate girders, the wind would have passed freely through the bridge and the collapse of the bridge could have been avoided.
Who was the engineer who worked on the narrows bridge?
A soft-spoken man with great energy, confidence, and determination, Andrew was a celebrity in engineering circles when he returned to Washington in March 1938. He immediately set to work on the Tacoma Narrows Bridge as chief consulting engineer. When "Galloping Gertie" failed in October 1940, some observers blamed Andrew. In fact, as an investigation soon revealed, he had fought hard against the cost-cutting design compromises that led to the bridge's collapse. The second Narrows span, designed to Andrew's standards and specifications, has withstood Northwest storms for over half a century.
What bridge collapsed in 1940?
Collapse of the 1940 Bridge GHPHSM, Bashford 2786
What bridge did Howard Clifford run on?
But, the wealth of fascinating experiences that have colored Howard Clifford's life are all surpassed by one—the run for his life on the collapsing Tacoma Narrows Bridge, "Galloping Gertie," in November 1940.
What was Andrew's transportation vision?
Among Andrew's unrealized transportation visions were a tunnel crossing of Puget Sound from Alki Point to Bainbridge Island, a floating bridge to Vashon Island from Fauntleroy, and a large suspension bridge over Colvos Passage.
Who was the photographer who photographed the narrows bridge?
From 1939 to mid-1940 Bashford worked for Thompson Photo Service, which the Washington State Toll Bridge Authority hired to document construction of the first Narrows Bridge. Bashford snapped over 400 photographs of the bridge's construction. He also did free-lance photography for Tacoma newspapers.
When did the Hood Canal Floating Bridge sink?
When the Hood Canal Floating Bridge partly sank in a 1979 storm, Andrew again became the mark of critics, although he had died ten years earlier. And, as before, the blame was unjust. Andrew had opposed the design compromises forced by budget limits, though whether these caused the bridge's failure is uncertain.
Who built the first two floating bridges in Washington State?
As chief consulting engineer for the Washington State Toll Bridge Authority for some 20 years, Andrew guided construction of the first two Lake Washington Floating Bridges, both Tacoma Narrows Bridges, and the Hood Canal Floating Bridge. His admirers called him "a genius.". His critics said he built "blow away bridges.".
