The Bridge That Fell After Only 4 Months | Answers With Joe

good morning everybody today let's talk about something sexy infrastructure sorry i got to be careful don't want to get this video demonetized so if you've been paying any attention to the screaming hairdos on tv you might have heard about the infrastructure investment and jobs act which was signed into law this last november 2021. it was contentious because well everything is these days but it was specifically contentious because it's a huge spending bill it was budgeted at a trillion dollars that's trillion with a t and an r and an i and an l but the argument for it is that it would create jobs and send billions of dollars to state and local governments to upgrade things like airports roads transit systems water systems and so on with 26.5 billion dollars of an earmark specifically for bridges the department of transportation actually has a program for this it's called the bridge replacement rehabilitation preservation protection and construction program or the excuse me this is the largest dedicated bridge investment since the interstate highway system was first built and it'll help prepare around fifteen thousand highway bridges but it's a lot of money and it's been a challenge to get some people behind it so at the beginning of this year president biden did some traveling around and was going to some places giving speeches to promote it one of those places was pittsburgh pennsylvania because there's a lot of bridges in that area that need repair so he went there on january 28th to give a speech about how important it is to upgrade bridges but he had to cancel his speech because a bridge collapsed it's a 477 foot bridge called the fern hollow bridge that was built in 1973 and had been listed in poor condition by the national bridge registry since 2011. there were actually five cars on the bridge when it went down and 10 people were injured but thankfully nobody was killed and it really could have been a lot worse the bridge carries 14 000 cars a day and the fact is there are thousands of bridges just like it all around the country some of them several decades old and just barely hanging on but at least they got several decades of good use unlike the tacoma narrows bridge which despite being a modern marvel when it was first built barely lasted four months it's become one of the most spectacular bridge disasters of all time a disaster that taught us a lot of lessons that would then go on to save a lot more bridges [Music] if you've never been to seattle you should go it's a lovely town and one of the reasons why it's so lovely is puget sound puget sound is a complex system of channels embayments estuaries and islands where the pacific ocean flowed in and just kind of went all crazy in there it's the home of seattle but also tacoma everett and olympia all separated by maze of peninsulas and inlets so it's not the easiest place to get around people wanting to travel from say tacoma to the kitsap peninsula would have to travel far south west and then back north to get where they wanted to go and sure there are ferries that can transport people and are often used at the sound but they can be slow and you have to follow their schedules and if there's one thing that we americans love it's being able to hit the open road and not being on somebody else's schedule so what do we do to guarantee these god-given rights from our founding fathers well in the case of the city of tacoma you build a bridge but before you can build a bridge you need the money to build the bridge which is not always easy to come by so the washington state legislature created the washington state toll bridge authority in 1937 and gave five thousand dollars about ninety seven thousand dollars a day to commission a study for a bridge over the narrows an engineer named clark eldridge was hired and he proposed a suspension bridge design which was still a fairly new idea at the time but had been working well in other places and they were hoping that tolls would be enough to pay for the bridge but the study showed that no it wouldn't be nearly enough so they turned to the federal public works administration this was the program set up by fdr to help create jobs during the depression and they asked the pwa for 11 million dollars which would be about 220 million dollars in today's money and many buttholes puckered they needed to get the cost down so they brought in a guy named leon moisieff he was a bridge engineer from new york he was actually a consultant for the golden gate bridge and he had some ideas so early plans for the bridge included a set of 7.6 meter deep girders that should go underneath the bridge making it more stiff and less movable so he suggested using a shallower 2.4 meter deep support which means a slimmer bridge but also a cheaper bridge and like most things in life the pwa chose the cheaper design so the pwa approved six million dollars for the bridge and bridge tolls were gonna make up another two million dollars bringing it to a grand total of eight million all of that worked out got approved and construction began on the tacoma narrows bridge in september 1938. it took 19 months to complete and actually came in under budget at 6.4 million dollars and they had a main span of 853 meters which at the time was the world's third longest suspension bridge pretty cool and it wasn't really expected to carry a whole lot of vehicular traffic so it's designed with just two lanes and only 12 meters wide so this was really narrow uh considering how long the bridge was and those 2.4 meter deep girders made the roadway extremely shallow as well so the bridge opened on july 1st 1940 and around 10 000 people showed up for the dedication and opening ceremony tolls started at 55 cents and were reduced to 50 cents two months later after the bonds were refinanced at the opening officials praised the bridge as an essential economic and military portal to the olympic peninsula and at the time it was considered a triumph of man's ingenuity and perseverance over nature everyone marveled wrote historian murray morgan at the gossamer grace of a structure so long long story short everybody fell in love with this graceful slim wonder of engineering but uh the the honeymoon period lasted a very short amount of time because before the bridge was even finished construction they began to notice a little it's problem little problem yeah it turns out when the wind blew which is the thing that happens um it started to kind of wave a little bit which is not what you want in a bridge yeah workers gave it the nickname galloping gertie and they actually took to sucking on lemons to combat seasickness they were actually getting sick working on this thing and because people be crazy when this thing opened and it was galloping they still drove across it it was like a carnival ride for people in fact they would wait until the wind was just right and then pull their cars in to ride the bridge it was like a thing they did it's hard to believe this but people actually thought this bridge was safe to the point that a local bank put up a billboard right next to the bridge saying that their bank was as strong and sturdy as this bridge was still the engineers were concerned about all the motion and several ideas were proposed to help the bridge move less these included adding cables to the girders they were attached to a 50 ton concrete blocks on the shore but they broke after they were added they tried adding cable stays these would connect the main cables to the bridge deck in a mid-span but they didn't stop the bridge from moving less and they tried adding hydraulic buffers between the deck's floor system and the towers but this system was damaged when the bridge was sandblasted before being painted eventually the washington told bridge authority hired engineering professor frederick bert farkharson from the university of washington to create tests of the bridge in a wind tunnel so the professor and his students built a 1 to 200 scale model of the bridge in a 120 scale model of the section of the deck they concluded their studies on november 2nd and offered two solutions to fix the issue one was create holes in the lateral girders along the deck so that air could flow through them and help reduce the lift forces and two was adding fairings or deflector veins along the deck to give it a more aerodynamic shape the first option was rejected because these were changes that couldn't be undone so the second option was chosen and they didn't get that up because by the time they were going to put that up there was no bridge anymore the tacoma narrows bridge collapsed on november 7th 1940 at 11 a.m with cable snapping and concrete crashing into the water below its collapse would eventually enter the nickname the pearl harbor of engineering a tacoma reporter named leonard codesworth happened to be driving across the bridge with his dog tubby on the day that the bridge collapsed he said quote just as i drove past the towers the bridge began to sway violently from side to side before i realized that 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 he could hear the concrete cracking all around him and he tried to get to his dog but he got thrown against the curb again i mean you have to kind of imagine how difficult this was he was literally being thrown around like he was on concrete ocean waves or something like that so he crawled as far as he could it was 457 meters to the towers his hands were bleeding he was bruised swollen his knees were raw somebody else who just happened to be there was professor farquarson and he tried to run out and help the dog but tubby was scared and bitten so he finally gave up and had to get out to save himself coatsworth could only stand and watch from the side at the toll plaza as the bridge finally fell apart and went into the cavern below his car and his beloved dog along with it thankfully outside of tubby there were no deaths so why did this bridge collapse well two reasons one high winds and a design that was not created for high winds like i said before suspension bridges were still pretty new at the time most of the bridges up to that point were built on concrete or stone and uh wind wasn't really much of a factor for them but with the tacoma narrows bridge there were winds of over 70 kilometers per hour on the day that it collapsed and what happened is its center torsionally vibrated about 36 cycles per minute across nine different segments and as that vibration increased the motion changed from a rising and falling to a two wave twisting motion so while the center part remained pretty steady the other two halves twisted in opposite directions and something called aero-elastic flutter is what eventually caused the bridge to finally collapse so most bridges have trusses that let the wind pass through but with this bridge the wind was forced to move above and below it this caused what they call flow separation when this happens and there's an object present it can lead to a carbon vortex street situation in the case of this situation the winds would hit the top part of the bridge pushing it one way while winds would hit the bottom part pushing it the other way this is what caused the twisting motion and increased vibrations that eventually led to it collapsing so one way to make sure that this wouldn't happen again would be to place gaps in the middle of the bridge to allow the air to kind of flow in and around the structure also having trusses that would allow wind to pass through would be helpful designers can also install diagonal braces made from steel to help make the structure stiffer when it experiences a high wind load in this case the cross braces squeeze together and help prevent the bridge from flopping over today engineers and designers test model bridges and wind tunnels long before they ever get to construction to prevent something like this from happening of course winds affect all other kinds of structures too not just bridges like skyscrapers for example the higher up we go the more we have to account for wind forces so engineers use computational fluid dynamic analysis and wind tunnel testing to identify the pressure loads and then designed to counteract those forces they also have to design for resonance much like a plucked string on a musical instrument buildings have resonance frequencies that they tend to be naturally inclined to vibrate at and if wind passing around it creates vortices that happen to be resonating at that exact resonant frequency they can create huge forces just like what happened on the tacoma narrows bridge so designers use things like rough surfaces or irregular shapes to help break up the wind energy and create smaller fragments instead of those massive wind vortices smaller fragments lead to smaller vortices which lead to a more stable structure so in the end the tacoma narrows bridge was rebuilt it was reopened in 1950 and you can still drive across that one today and this time the workers named it sturdy gertie because it was galloping no more by the way can everything just be named by construction workers from now on so yeah suspension bridges were still new at the time but the lessons learned from this collapse have ensured that nothing like it would ever happen again so all we have now is this crazy footage of this bridge made of steel and concrete flapping and swaying around like it's made out of rubber it's amazing footage like i've always been fascinated with this newsroom footage i remember seeing it as a kid and was just like how and it was only when i researched this video that i realized that there was a dog in that car so r.i.p tubby [Music] this video is sponsored by hellofresh i'm not even going to try for a clever segue hey do you like eating do you like putting food in your mouth crushing it with 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Channel: Joe Scott

Views: 337,538

Keywords: answers with joe, joe scott

Id: n9Tyk0G096k

Length: 14min 43sec (883 seconds)

Published: Mon Apr 04 2022