© 2007 All Rights Reserved. Do not distribute or repurpose this work without written permission from the copyright holder(s).
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In early 1940, engineers and construction workers put the finishing touches on what was to be the the longest man-made span in the US, and the third-longest in the world: the Tacoma Narrows bridge. The half-mile-long structure linked Tacoma, Washington to Gig Harbor, and its completion inspired statements such as “a triumph of man’s ingenuity,” and all other manner of gratified exuberance. But as workers finalized the construction, a curious behavior became evident. Although the bridge had been designed to withstand winds up to 120 miles per hour, observers noted that even a mere breeze would occasionally cause wavelike ripples to travel up and down its length. Many workers had to chew on lemon wedges to suppress motion sickness.
Experiments with a scale model produced no clear solution to the unwanted movement. Though the gentle wave motion didn’t put the massive bridge in any structural distress, it was clear that motorists would find it disconcerting as cars ahead of them bobbed in and out of view. In spite of the complication, the bridge was opened to the public on 1 July 1940. It did not remain open for long.
The Tacoma Narrows bridge was originally designed by an engineer named Clark Eldridge, with some later revisions implemented by Leon Moisseiff, the renowned designer one of the designers of the Golden Gate in San Francisco. The final design departed from the tried-and-true conventions of suspension bridge-building in several ways, including the use of “I” beams rather than lattice-style deck supports. This modification, among others, preserved the structure’s strength, but at a decreased cost.
After opening, the new bridge shortly came to be known as “Galloping Gertie,” so named by white-knuckled motorists who braved the writhing bridge on windy days. Even in a light breeze, Gertie’s undulations were known to produce waves up to ten feet tall. Sometimes these occurrences were brief, and other times they lasted for hours at a time. Numerous travelers shunned the route altogether to avoid becoming seasick, whereas many thrill-seeking souls paid the 75-cent toll to traverse Gertie during her more spirited episodes.
Immediately after the problem was first observed, a number of engineering professors were hired to devise a method to reduce these movements. Tie-down cables and hydraulic buffers were employed with limited success. The matter wasn’t considered terribly urgent because the winds were causing longitudinal waves along Gertie’s center span—waves which traveled back and forth along the length—which did not put undue stress on the roadbed. The structure was not at risk, nor did it create unsafe driving conditions. It was largely a problem of motorists’ comfort. But on the morning of 7 November 1940, four months after the bridge was opened, something new happened. While enveloped in a steady 42 mile per hour wind, Gertie abandoned her usual rippling action in favor of a never-before-seen twisting motion which increased in intensity at an alarming rate.
As crowds gathered on either end to watch the structure thrash about, a college student named Winfield Brown paid the 10-cent pedestrian toll and ventured onto the bridge on foot:
“After walking to the tower on the other side and back, I decided to cross again. It was swaying quite a bit. About the time I got to the center, the wind seemed to start blowing harder, all of a sudden. I was thrown flat. A car came up about that time. The driver got out, walking and crawling on the other side. We didn’t have time for any conversation.””Time after time I was thrown completely over the railing. When I tried to get up, I was knocked flat again. Chunks of concrete were breaking up and rolling around. The knees were torn out of my pants, and my knees were cut and torn. I don’t know how long it took to get back. It seemed like a lifetime. During the worst parts, the bridge turned so far that I could see the Coast Guard boat in the water beneath.””As soon as I got off the bridge, I became sick. So, I went to the home of a cousin and laid down for a while. I’ve been on plenty of roller coasters, but the worst was nothing compared to this.”
Another man, a newsman named Leonard Coatsworth, became stranded on the bridge while driving across it:
“I drove on the bridge and started across. In the car with me was my daughter’s cocker spaniel, Tubby. The car was loaded with equipment from my beach home at Arletta. Just as I drove past the towers, the bridge began to sway violently from side to side. Before I realized it, the tilt became so violent that I lost control of the car. . . . I jammed on the brakes and got out, only to be thrown onto my face against the curb.””Around me I could hear concrete cracking. I started back to the car to get the dog, but was thrown before I could reach it. The car itself began to slide from side to side on the roadway. I decided the bridge was breaking up and my only hope was to get back to shore. On hands and knees most of the time, I crawled 500 yards or more to the towers . . . . My breath was coming in gasps; my knees were raw and bleeding, my hands bruised and swollen from gripping the concrete curb . . . . Toward the last, I risked rising to my feet and running a few yards at a time . . . . Safely back at the toll plaza, I saw the bridge in its final collapse and saw my car plunge into the Narrows.”
Unable to withstand the increasingly brutal torsional twisting, a number of Galloping Gertie’s suspender cables snapped, shifting the weight of the deck onto the remaining cables. Under the increased load and enormous strain, the cables broke one by one until there were too few to support the massive roadbed. After weathering over an hour of the punishment, a huge portion of Gertie’s steel-and-concrete center deck broke off and fell 195 feet, plunging into the Tacoma Narrows with a terrific crash. A column of dust rose into the sky, and sparks crackled from broken powerlines. Clark Eldridge, the bridge’s original designer, was present to witness the destruction:
“I was in my office about a mile away, when word came that the bridge was in trouble. At about 10 o’clock Mr. Walter Miles called from his office to come and look at the bridge, that it was about to go. The center span was swaying wildly, it being possible first to see the entire bottom side as it swung into a semi-vertical position and then the entire roadway.”I observed that all traffic had been stopped and that several people were coming off the bridge from the easterly side span. I walked to tower No. 5 and out onto the main span to about the quarter point observing conditions. The main span was rolling wildly. The deck was tipping from the horizontal to an angle approaching forty-five degrees. The entire main span appeared to be twisting about a neutral point at the center of the span in somewhat the manner of a corkscrew.””At tower No. 5, I met Professor Farquharson, who had his camera set up and was taking pictures. We remained there a few minutes and then decided to return to the east anchorage warning people who were approaching to get off of the span. At that time, it appeared that should the wind die down, the span would perhaps come to rest and I resolved that we would immediately proceed to install a system of cables from the piers to the roadway levelin the main span to prevent any recurrence….”
“I was then informed that a panel of laterals in the center of the span had dropped out and a section of concrete slab had fallen. I immediately went to the south side of the view plaza. The bridge was still rolling badly. I returned to the toll plaza and from there observed the first section of steel fall out of the center. From then on successive sections towards each tower rapidly fell out.”
Though no human life was lost when Gertie fell, Tubby the cocker spaniel did not survive.
Much of the catastrophic collapse was caught on motion picture film thanks to Barney Elliott, the owner of a local camera shop. Examination of the film, the bridge’s remains, and tests with scale models determined that resonance was responsible for Gertie’s demise. Due to the design decision to replace the lattice supports with “I” beams, the wind was unable to pass under the structure as readily as it it passed over it, causing a difference in pressure much like an airplane wing. Once there was sufficient sway to tilt the deck slightly, aerodynamics caused the roadbed to twist to the point that it sprang back, causing a repeating cycle of back-and-forth twisting. During this process, the steadily blowing wind added more and more energy to the vibrations.
The public was shocked that the beautiful state-of-the-art bridge—designed by one of the most respected bridge engineers in the world—could fail so spectacularly. The six million dollar structure had been approved by federal and state experts, and suspension bridges were not a new technology. Ultimately the bridge was not built from substandard materials, nor was it under-engineered; its designers merely overlooked the physical phenomenon of resonance. Though the suspension bridge had been designed to sway and to withstand some longitudinal waves, it had not been built to withstand the torsional punishment. Today, Galloping Gertie’s spectacular self-destruction stands as a cautionary tale, retold to countless students of civil and structural engineering.
The State of Washington collected on Gertie’s insurance—except for a small portion which had been unpaid due to fraud—and went on to build a replacement bridge ten years later. The harsh lesson of Galloping Gertie was not lost on the new designers, and the new span was built with resonance in mind. Its new design introduced openings for air to pass through, and scale models were thoroughly tested in a wind tunnel. “Sturdy Gertie” has stood since 1950, and will soon be joined by a sister bridge to accommodate increased traffic.
Much of the original Gertie’s wreckage still resides on the floor of the Tacoma Narrows today, forming one of the world’s largest artificial reefs. Though some of the steel was pilfered and reused for the war effort in the years following the collapse, what’s left of her remains are now protected as a historical site.
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DI! I hadn’t realised that the span was so long. I’ve only seen the famous footage of the break-up before which foreshortens the view and makes the far tower appear much closer. The MP4 download takes a while but shows fascinating shots of construction – and destruction.
Good article – thanks!
What gets me is all the joy riders that would get on her when she was swinging.
This is certainly interesting. I remember seeing a Modern Marvels episode (or something similar) about this on the History channel. The show included the video footage. The swaying and undulation of the bridge really was quite dramatic. I cannot imagine trying to walk across it when it was doing that, much less driving a car across it. Oh, and I will probably get yelled at but: First!
Aye, wruneblade, there are risks in claiming to be first!
Since the 18th century, there has been a catastrophic bridge failure about once every two generations. That’s the period when engineers have pushed the envelope a little too far. I seem to recall there was an early Victorian railroad bridge that collapsed killing many. The train traveled through iron boilerplate tubes riveted together.
A contemporary disastrous overreach was the de Havilland Comet, the world’s first jetliner. It had the nasty habit of bursting open like a Pillsbury can at altitude.
With NASTRAN and better wind-tunnel testing, bridge failures should be fewer and further between. From this page to God’s eyes.
Poor Tubby. : (
What the hell was Winfield Brown thinking when he crossed the bridge a second time? He would have definitely been up for a Darwin Award if he had died that day.
The Tay Bridge Disaster. It collapsed with a train on it during high winds in 1879.
I’ve never liked crossing the TNB ever since I saw the Gertie footage as a kid. Great article– loved all the eyewitness stories. But it’s funny how completely clinical the designer’s account is. He must have felt like a complete failure watching his work get ripped apart and fall into the Narrows, but his account is merely factual.
I had no idea that the remains had been made into a historic site. I would think that the civil authorities would want all the visible wreckage cleared away as soon as possible so as to not emphasize their failure to provide a safe bridge.
Then again, I didn’t know someone like Mr. Brown would have my middle name as his first – aside from my grandfather the only other person I’ve heard with that name anyplace in their title was the actor playing Capt. Tyrel in Star Trek 2.
DI Alan! I’ve known about the bridge and seen the footage for years, but you’ve breathed new life into the story. Kudos.
There was no resonance. If you watch the video closely, you can see squibs all along the length of the bridge. This was obviously done by the traitorcrats to get us into the war in Europe.
In all seriousness, I remember being taught this in my engineering classes many moons ago. It’s such a classic example of a fundamental property not being taken into account properly and bad things happening as a result.
He is an engineer what do you expect. I’m sure if there would have been loss of life he may have been more emotional. What surprised me was how calm everybody appeared in the footage. Walking slowly off the bridge, very calmly. Everybody had there back to it no looking back. They all seamed very unimpressed with the whole situation.
…well, it’s not as if Eldridge wanted his bridge to fail…and if people can’t walk a straight line across the bridge while it’s “swaying in the breeze”, that ought to be a good enough indication to get your tail to safer ground. Why Tubby didn’t jump over the seat and out the door when he had a chance…no one will ever know.
All objects have a natural frequency which when “excited” will/can create undo damage. Adding mass to an object will shift that frequency as well. In the case of Gertie, because the wind could not blow thru the spans, it had to go around…like the article says…and the bridge turned into something resembling an airplane wing. I’m sure as Eldridge stood there watching his dancing bridge, the one thing going thru his mind was something like…aw shit!
Drakvil said: “DI Alan! I’ve known about the bridge and seen the footage for years, but you’ve breathed new life into the story. “
I second that!
I live near the Narrows Bridge and cross it frequently. This can still be a scary proposition at times for someone who has a problem with heights! To correct the wind problem they added open grates on the bridge floor and it gets a little unnerving to look at when going across. They are now in the process of building (almost completed) a new bridge right next to the old one. When it’s finished each bridge will be one way because many people feel that the old bridge is too narrow for the traffic (no pun intended here). Personally, I’ve driven on pig-track wide bridges in rural Oklahoma and never found TNB to be a problem! Here are two good places to see info on the bridges.
Re: “Why Tubby didn’t jump over the seat and out the door when he had a chance…no one will ever know.”
Well, according to Wikipedia, there are two possibilities, illistrated in the quote from the Wiki page:
“Tubby, a cocker spaniel dog, was the only fatality of the Tacoma Narrows Bridge disaster. Leonard Coatsworth, a Tacoma News Tribune photographer, was driving with the dog over the bridge when it started to vibrate violently. Coatsworth was forced to flee his car, leaving Tubby behind. Two people attempted to rescue Tubby, but the dog was too terrified to leave the car and bit one of the rescuers. Tubby died when the bridge fell, and neither his body nor the car were ever recovered. Coatsworth had been driving Tubby back to his daughter, who owned the dog.
Coatsworth received US $364.40 in reimbursement for the contents of his car, including Tubby. In 1975, Coatsworth’s wife claimed that Tubby only had 3 legs and was paralyzed.”
Drakvil said: Then again, I didn’t know someone like Mr. Brown would have my middle name as his first – aside from my grandfather the only other person I’ve heard with that name anyplace in their title was the actor playing Capt. Tyrel in Star Trek 2.
Dave Winfield: National Baseball Hall of Fame
Winfield Scott: Longest serving U.S. Army general in American history (47 years!) and presidential candidate (lost to Franklin Pierce)
Winfield Scott Hancock: Civil War general and also a presidential candidate (lost to James Garfield)
Mason Winfield: author, “supernatural historian”
Google and Wikipedia are your friends ;)
As an engineer and future attorney – can someone enlighten me as to what this statement refers to:
What was the fraud? I don’t believe it had to do with the engineering design did it? Can you please fill me in?
IC, I assume it means a premium didn’t get paid because someone pocketed the money–fraud against the state, not against the insurance company. But I don’t know.
This is why I keep coming back to DI, great text, and it so takes me back, I watched a documentary about this event must be what, 20 years ago. Thanks…
Ironclaw said: “As an engineer and future attorney – can someone enlighten me as to what this statement refers to:”
maxwelton is correct… the agent working for Merchant’s Fire Assurance Company– with whom the state had a policy for $800,000– had been pocketing the insurance premiums all along. He was charged with grand larceny. The missing $800,000 represented about 20% of the bridge’s overall coverage.
Wasn’t there a similar effect when soldiers once marched across a bridge, leading to a collapse?
Dave Group said: “Wasn’t there a similar effect when soldiers once marched across a bridge, leading to a collapse?”
It was a myth. The Discovery Channel show “Myth Busters” tackled this and disproved it. They did another show about resonance effects on a bridge which “freaked out” the guys.
Radiatidon said: “It was a myth. The Discovery Channel show “Myth Busters” tackled this and disproved it. They did another show about resonance effects on a bridge which “freaked out” the guys.”
“Angers Bridge was a suspension bridge over the Maine River in Angers, France. The bridge is famous for having collapsed when 478 French soldiers marched across it in lockstep. Since the soldiers were marching together, they caused the bridge to vibrate and twist from side to side, dislodging an anchoring cable from its concrete mooring. Though a storm also raged during the collapse, engineering experts indicate the collapse was due to the soldiers instead of the storm.”
Mythbusters’ tests were at best inconclusive. They are f/x guys, not engineers, after all.
So, if you’re ever caught on a bridge rolling like this with torsional waves, crawl straight down the middle rather than trying to hold onto the railing.
San Francisco is misspelled in the third paragraph. Also, Leon Moisseiff was only a consultant on the Golden Gate Bridge, and not the “renowned designer of the Golden Gate Bridge” as stated above. Joseph Strauss of Levi Strauss & Co. was the main designer of the GG Bridge.
…and watching the movie of the Gertie right before she went into self-destruct mode, you would have never thought that steel and conrete could be “so flexible”.
As always, cost cutting measures end up costing more. As the saying goes, there’s never enough time (or money) to the job right the first time, but there’s always enough time (and money) to do it over.
I recall a fluid dynamics class where this incident was used to illustrate an effect called vortex shedding. Basically, any blunt obstacle in an airflow will cause little eddies or vortices to peel off the trailing edge. But some fundamental thingy causes the vorticies to alternate sides – first one spins off the top deck of the bridge, then one spins off the bottom of the deck in the opposite rotation. This imparts an oscillating torsional force to the bridge deck. When the frequency of this twisting matches the natural frequency of the bridge structure, london bridge comes falling down.
Mythbusters is a great show, but there has been more than 1 time I’ve watched it and thought, man, that is just about the most unscientific and incorrect way possible to do that. They’re still damn interesting, though.
errna said: “This is why I keep coming back to DI, great text, and it so takes me back, I watched a documentary about this event must be what, 20 years ago. Thanks…”
I couldn’t have said it better myself!! Good job Alan!! Keep it up!! :)
Re soldiers breaking step, etc. Even if pedestrians don’t deliberately walk in step on a bridge any small oscillation of appropriate frequency can cause them to walk in step which can, in turn, feed the oscillation. This happened on the Millenium Bridge, a footbridge across the Thames in London which was closed for a few months shortly after it was opened to allow dampers to be fitted.
This is pretty interesting. Did you know their is a bridge somewhere in china or Japan thats made up of 2 inch think superconcrete(or supersteel can’t remeber) but it was in the newspaper. Its pretty cool.
Secret Ninja said: “Mythbusters is a great show, but there has been more than 1 time I’ve watched it and thought, man, that is just about the most unscientific and incorrect way possible to do that. They’re still damn interesting, though.”
I’ve noticed the same thing. I watch the show religiously as its usually quite entertaining and they mostly appear to know their stuff. But I often think they are far too quick to pronounce “BUSTED”, just because their first test failed (Adam especially).
Back semi on topic, there was a film clip for an electronic song a long while ago (must be going back 10 years now), where it had a looping clip of the rotation and torsion of the tacoma bridge, all in time with the beat of the music, and as a climax was reached, the bridge broke. I can remember being fascinated at the time, how this could happen to such a large man made structure (in my immature, child-like view, I assumed mistakes like this would never happen), and read the story. Thanks for the revisit.. Damn Interesting, as always. Good work!
“After opening, the new bridge shortly came to be known as “Galloping Gertie,” so named by white-knuckled motorists who braved the writhing bridge on windy days. Even in a light breeze, Gertie’s undulations were known to produce waves up to ten feet tall. Sometimes these occurrences were brief, and other times they lasted for hours at a time.”
Ummm… you’re joking, right? Who in their right mind would drive across a bridge that has a wave that reaches up to TEN feet tall, much less any feeling of movement at all? I mean, maybe it was just the perspective of the time, but I can’t believe that the bridge, although supposedly safe, wasn’t immediately closed until they could figure out what was wrong. I just can’t understand how ten foot-tall bridge waves would be considered OK. Does the Golden Gate or any other large bridge noticeably move so much that the motorists can actually feel it?
Jaydawg53 – Having driven across the Golden Gate many times, I’d have to say the answer is a qualified yes. I say qualified because the effect isn’t anywhere near what is described in the article, and the effect is simply swaying with high wind – not quite the sinuous ‘wave’ motions described here. Frankly, I think anything with a ten-foot wave isn’t safe to drive, especially with the motorists around you appearing and disappearing due to the undulations of the road!!!
There is a traffic light on an overpass that sits right on top of a freeway near our house. When stopped at that light I can feel the whole structure bob up and down even when there are no cars moving on it. It’s either the wind and/or the cars passing underneath, I guess.
The last time I walked the GG bridge was in 2005 and it was very windy. I didn’t notice the structure sway at all.
Regarding the 10-foot wave: without more information, it is impossible to say whether this would be safe, barely perceptible, or worrisome. You would need to know more about the ratio of the wavelength to the amplitude and whether it is periodic. If two periodic, sinusoidal ten-foot waves are a mile apart, or if one ten-foot wave takes up the entire bridge, you may hardly notice the movement at all. If they are thirty feet apart, you would probably be thrown to the ground. One aperiodic ten-foot wave with a width of thirty feet may launch you into the air. Simply saying that the waves were ten feet high gives very little information at all.
Try this to get an idea of the difference: fill your bathtub halfway. Place a boat, rubber ducky, or other floatie near one end. Put your hand on the one side, then rather slowly move it about a foot toward the other side and stop. You will get one long wave. Let the tub return to normal. Do the same thing with the same speed, but repeat it. You will get several waves at a long wavelength. Let the tub return to normal. Move your hand faster, but not as far. You will get one wave with a greater height than the other one, but not as long. Finally, once the tub is normal once more, move your hand the way you did the last time, but repeat. You’ll get several waves of the same, higher amplitude but shorter wavelength. Throughout, compare how the boat/duck/thingy reacts. Imagine a tiny person standing on top of that and what it would feel like to them and you should start to get a feel for the information that is missing in just saying “a three-inch wave”.
As always, DI has just as much nifty info in the comments as the well-written feature. Thanks to all!
Once I started watching the footage, I realized I’d seen it before, but never knew the story. I’d always assumed it was shot during an earthquake or somesuch! Amazing that they didn’t close it down as soon as the problems became apparent.
It’s really unfair to say the engineers and researchers at the time should have been able to predict this based on the longitudinal wave problem. When they gave the bridge a clean bill of health after the initial waves, there was no reason to expect torsional waves would ever arise. It’s only when you consider the coupling between the aerodynamics of the system and the structure that problems arise. It was not some characteristic resonance in the structure itself that caused a problem but the interaction of different, complex phenomena. Most engineers don’t learn this in the introductory classes where the talk about Galloping Gertie because they don’t yet have the background to gain anything from a truly detailed discussion of the matter and then they never return to the matter in other classes. It actually contributed heavily to the creation of the field of aeroelasticity, “the science which studies the interaction among inertial, elastic, and aerodynamic forces,” (wiki) a field which has some frickin’ hard problems in it.
senorstu said: “I recall a fluid dynamics class where this incident was used to illustrate an effect called vortex shedding. Basically, any blunt obstacle in an airflow will cause little eddies or vortices to peel off the trailing edge.”
This is the reason that a flag waves in the wind – if you watch one carefully on a breezy (but not too windy) day you can clearly see a traveling wave move along the cloth. I think it looks cool.
Animation care of wiki:
Isn’t a 75 cent toll kind of steep for the 40’s? Kind of steep nowadays now that I think about it.
you would have never thought that steel and conrete could be “so flexible”.
Nor would one necessarily think that 2″ thick steel could be :
ripped apart like tinfoil.
DI is a great site (my new favourite), why haven’t I heard of it before now?
There were so many factors involved here it was a ‘perfect storm’ of engineering and environmental forces interacting to the detriment of the whole. One of the seemingly innocuous details is that the railings along the sidewalks did not allow the wind to pass through them, which in turn encouraged the formation of vortexes over the roadway. If I remember correctly this was not in the original design. The roadway itself was essentially a long slender glider wing that flew when the wind exceeded just a few knots. Once the wind velocity climbed sufficiently to lift the roadway the suspender cables no longer supported its weight and became slack, which then allowed the roadway to twist, -and a vortex was shed. Lift was lost and the roadway would drop. With the span of the bridge and the variability of the wind pressures against it, given enough time it would settle into a resonance of lift, twist, shed, and drop. Had the side railings allowed the wind to pass through, the vortexes may not have developed sufficiently to have had the effect that they did, and while it is likely that the bridge deck would still have had considerable movement, it is quite possible it might have survived the 40-knot wind that ultimately brought it down.
The new bridge is a pleasure to drive across. I’m hoping the Discovery Channel documented its construction. It’s one thing to see it going up over the course of a couple of years, but something else to see it all condensed down into an hour or so.
OMG!!!!!!!!!!! AHHH!!!!!!!!!!! WE’RE ALL GONNA DIIIIIEEEEEEEEEEEEEEEEEEEEEEE!!!!!!!!!!!!!!!!!! OMG OMFG OMG OMFG!!!!!!!!!!! HOLY SHET!!!!!!!!!!!!!!! AHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
“…a triumph of man’s ingenuity…”
Gotta love that phrase. Goes so well with so many other structures. Titanic, Gertie, Love Canal, that random hotel in North Korea……
I have also felt movement on the Lion’s Gate Bridge up here in Vancouver. I was stuck in traffic in the middle once, and I got quite motion sick. For someone who’s terrified of heights, it was definitely a white knuckle experience!!!
i would think modern engineers would have learnt a big lesson from this, but here in the uk we have had similar experiences check out Londons Millenium bridge; http://www2.eng.cam.ac.uk/~den/ICSV9_06.htm
Actually it’s called harmonic resonance. Because when it’s in harmony the resonance is amplified.
Great article and a very interesting event, but there is an error. It was aeroelastic flutter, not resonance that caused its motion and failure.
A short explanation:
A long explanation:
“…in the case of the Tacoma Narrows Bridge, there was no resonance. According to Farquharson, one of the main investigators of the cause of the bridge collapse, the wind was steady at 42 miles per hour and the frequency of the destructive mode was 12 cycles/minute. This was neither a natural frequency mode of the structure nor the frequency of blunt-body vortex shedding of the bridge at that wind speed (which was approximately 1 Hz). Thus it is improbable that the resonance with alternating vortices played an important role in the oscillations of the bridge.”
I have always been fascinated with Galloping Gertie. There was an engineer named Dexter Smith who knew the bridge would collapse even before it was opened.He tried to warn the lead designer,Leon Moiseiff, but Moiseiff paid no attention to Smith’s warnings. Smith later designed the replacement bridge, mindfull of Gerties failure. This TNB is sometimes called Sturdy Gertie. It is a wonderful bridge and has withstood many high winds.
A perfect storm of engineering and political issues. Eldridge, the local engineer, was replaced by Moisseiff, a New York engineer. Why? Because he’d written scholarly articles on his deflection theory and elastic theory. [Both are wrong.] He claimed that wind would only affect a suspension bridge side to side. Therefore he changed the original 25′ Warren truss design to 8′ I beam.
At least the failure caused engineers to rethink bridge design and consider aeroelastic effects and vortex shedding.
His estimate of $6mil appealed to the feds. The original design had an $11mil estimate.
If the Eldridge design had been chosen the bridge would still be standing.
Moisseiff worked on the Bronx Whitestone Bridge, designing 11′ solid I beams, which later had to be reinforced. He was chief engineer on the Manhattan Bridge, where he put the railway on the outside lanes, causing tbe bridge to lean 5′ on one side. He was consulted on the Golden Gate Bridge. His road decking had to be reinforced in 1954. He died in disgrace in 1943. Ironically an engineering award in his name is presented every year.
Gertie’s oscillations were eight longitudinally on tbe main span every minute.
Gertie’s remains were not pilfered; they were sold by the state and mostly melted down during WW2. Much of the 1943 Lower Liard River Bridge in British Columbia on the AlCan Highway was made from Gertie’s parts .
If anyone has not yet seen the video of this, it is well worth your time.