Harvard Model Bridge Testing! Trusses and Beams
Learning by Doing!
When I was teaching Structures II at Harvard's GSD, we decided to do a bridge competition where the students design and build bridges with limited materials to span approx 10ft (3m).
We gave three prizes (all of equal value):
1) Best looking bridge as voted by the whole class (before testing took place).
2) The bridge that could carry the heaviest load.
3) The bridge that could carry the heaviest load per self-weight of bridge itself.
Each team loaded their own bridge until failure. They also had a related report assignment which was in two parts:
1) Before testing: Why this design, how they expected it would fail, and under how much load.
2) After testing: How their bridge actually failed, how and why (if) that was different to what they expected, and what they would do differently to improve it.
Thanks to Andrew Gipe for pushing the concept, to the TAs Andrew Gipe, Alex Karadjian, Dimitris Venizelos, and Wen Wen. Also to the GSD Fab Lab Burton LeGeyt and Rachel Vroman and to Juhun Lee for video editing. Most of all thank you to the students for an awesome set of work!
You can find the full video of the tests without commentary here: vimeo.com/128034912
I'm Paul Kassabian. I'm a structural engineer and a Principal at SGH in Boston, MA. I taught graduate students at MIT for nine years and currently teach on/off at Harvard's Graduate School of Design (GSD). These are videos based on my structural design projects and years of teaching structures to students.
This would be super interesting to see students try at the first class and again at the last class to see their progress :)
that would be very fun and interesting, "pure" gut feeling at the start and then see what happens after you added the knowledge to it. love the idea
We had this type of excercise in programming class in college. "write a program that finds all prime numbers between 0 and let's say 100.000 as fast as possible". 3 times a year you made this excercise. Everytime you find something to improve in your code or algorythm.
Zach cared about production, that's when Mr. Kasperski left...
Maam I have to say, your Dad had it rite. Zach was wrong, now just imagine. A 1/4 of a million Dollars to replace what he' F[EXPLICIT]ed up for you. You'r name, name your family...
Dear Mr. Paul Kassabian, I had the privilege of being part of this class, which to me, has been one of the most rewarding experiences provided by GSD. I express my gratitude for your efforts in creating such an engaging and productive learning process. Thank you.
interesting, what do you do now?
congrats on being in harvard
Lol nerd
Must kinda suck to know the most rewarding part of your experience there resulted in a quick free to view youtube video showing that you can do at home for about $100 with extremely simple explanations.
@@jonathansturgisjs ???
I don't know what I love more... how excited the students get or how excited the teacher gets. This is how education should be done!!
Classes like these are life changing. It changes your perspective about learning mechanics. I wish i had u as a teacher sir😢
An educator who makes learning interesting AND fun. Well done, sir.
Many thanks!
@@PaulKassabian : You're very welcome. I wish I had teachers like you when I was in school, which was about 100 years ago. 😂
@@PaulKassabian nice reuse of the Ottawa University materials science lab final exam project ... you missed having them do a full failure analysis on the end result as well ... back when I did this at Ottawa University in 1987 the report was 1000 pages long and the bridge I built carried 573lbs of weight before a miniature knot in the wood gave way ... more was learned from that project by everyone INCLUDING the professor that he kept at it until 92 or 3 ... . Balsa and string at 5lbs total bridge weight ... pre tensioned for 500lbs ..
@@PaulKassabian I wonder if you would entertain having anyone that has watched these, and has not had formal engineering to submit a design for one of your student teams to build? Simply put, the team should choose a bridge out of a “pot,” and make it according to the spec given. I would do this AFTER this competition, and as a bonus point to their score if they choose well.
@@PaulKassabian hi, Sir. I would just like you to know how much I admire your giggles when the bridges are about to collapse. Proves that you're emotionally invested in your craft. To my memory, my best tutors has always been those who truthfully enjoy the subject they're teaching. I'm sure many of your students will remember you and your lessons for the rest of their lives. Hope this comment reaches you; thanks for the video!
KZhead amazes me how it shows me things I never knew I was interested in. A phenomenal teacher and I imagine every student is proud to have studied under you.
They use the data of the other users that watch similar videos for recommendations. And this is my most favorite thing on the internet.
Same shit! Im from chile psicopedagogo ajajaj and look im here
low learning curve tbh yes this is a project that is fun but clearly if you are of the mind of "what will fail" then you can almost make the teachers run out of weight
Paul my father was a bridge engineer and worked his whole life building and maintaining structures. Your passion, enthusiasm and attention to detail reminds me very much of him. Wonderful teaching and great to see some engineering passion. Thank you.
That’s very kind of you to share that…thank you…
I love how he's just as excited as I am watching the video, yet he was already for it. That's real passion right there.
I remember doing this in high school in my architectural engineering and design class. My little balsa wood bridge held 176lbs before giving out! Great fun and an awesome learning experience!
One of my very treasured memories in school as well. Loved the bridge design project.
I could stand on it xD
yeah ... highschool kids did better than people at HARVARD...
@@agnidas5816Kids bridge could've had a shorter span
I am an undergrad Structural student. Your students are so lucky. I wish I could have you as a teacher
Very kind - thanks!
It would be amazing to start a class with a two week build like this, then finish it with another two week build to let the students demonstrate what they’ve learned.
I participated in one of these exercises back in college (35 years ago). Our span was to be roughly 18”. Material efficiency was the goal, so I made mine very light. The weight being used were bricks. Knowing the size the brick, my design used the first brick as a structural element. We ran out of bricks and the bridge never broke. A fun memory. Nice video. 👍🏻
@gerald_featureworx @GERALD_Featureworx
The problem with weights on top is that balance becomes a factor. The weight should be in a basket that is hanging from the center point of the bridge deck.
Yes, it's amazing that the one to carry the most weight was the only one that wasn't subjected to twisting forces. Some of the others may have done much better if a portion of the weight had been suspended below in buckets as it was on bridge 13.
The first one would have done even better if the loading had been vertical. Some bridges received loading that was much more vertical than others. Suspended weight would have been a more accurate test of relative load bearing.
I thought designing with that fact in mind was part of the point.
@@tristanmoller9498 , such a situation is not possible in reality.
@@Tohellem there are plenty of twisting forces that a bridge encounters, from having more weight on one side of the deck to wind pushing on sections above or below the deck.
there is NO substitute for hands-on application and learning. Engineering colleges are failing miserably at this of late. This is a perfect example of how learning should be done. Hands-on application, with a little trial and error. Let them test their ideas, take notes, and try again. Couple this with classroom learning and you have a winning combination. So much wasted opportunity in engineering colleges to really give students a truly great education with little extra effort.
Thanks! It really made a difference with, as you noted, the coupling with classroom learning...it's like concrete plus reinforcement...better together!
A lot of colleges participate in student steel bridge competition and concrete canoe. kzhead.info/sun/lbOlpJmro4iYdaM/bejne.html
This is the kind of professor that you would want to learn from, Good job Mr K! we enjoy your videos so much, more!!
Thanks! 😃
I participated in the Alumni competition at the University of Houston model span contest. These were small balsa wood packages that you could only use what was in the package. Walter, very innovative transmission tower designer caused them to have to rewrite the rules. The new rule was: You can only use glue on the joints. Walter had sliced the wood into fine sheets and glued it back together. He created plywood with no weak ends and the dried glue was stronger than wood. Other things he did to walk away with the win: They could not prevent his best of all. He baked the model in the oven on low heat to dry the wood/glue. Everyone found out that kiln dried wood is much stronger than air dried wood. He sanded the shape to eliminate any excess weight. You have to consider shear in your wood design.
That was amazing to watch as a spectator, I can only imagine the problem solving and learning plus team building that took place to get to the test of all 13 bridges. Thank you for taking the time to record this and let all of us participate.
You're welcome!
This. Great student project, but tripple the value for recording and uploading, with commentary.
Soo cool seeing how past and present bridges get planned, tested, and refined! 😊❤
Now that reminds me of the college I went to between 1973-1976. It was ALL hands on. 2 years of forestry, we were in the bush just as much as in the class, learning by doing. 1 year of welding and fabricating, skills I've used my entire working life. Keep doing it this way, we need people who THINK instead of parroting the party line they are being indoctrinated with. Those young people are having a blast, putting what they learned into actual use.
Just an outside admirer here. I have to say, professor Kassabian reminds me so much of my physics professor. Someone who truly cares about the subject, his students and their overall engagement with the material and makes it all fun at the same time. Well done! Even though I am a graphic designer, I am always interested in all engineering subjects. And I f I had someone like YOU back in the day, I really think I would have become an engineer just because of the way you teach. Well done sire! Well done.
Old school teaching is way way more fun and a richer learning experience than digital world. Great to see it up to date again!
This is not old school, look at all the materials being used for such project
@@1NightInParisOfficial string or cable and wood... Whats new on that?
We did something similar in my civil eng class 35yrs ago, with a fixed amount of balsa wood for each team to span a 400mm gap. Fascinating to see the much more elaborate designs in the video.
Paul, you are a fabulous educator! So good to see the enthusiasm and interest of the students. They are clearly getting a very special education.
🎓✨ Mr. Paul Cassabian, I want to express my sincere appreciation for the incredible learning experience you provided through this class. It was truly a privilege to be a part of it. Your dedication and effort in creating an engaging and productive learning process are commendable. Thank you for enriching our knowledge and inspiring us to reach new heights. Grateful for this opportunity! 🙏🏼🌟📚
This is so cool! Teachers that love what they do makes everything better and fun 💗 I can’t wait to see how far these students go in the future
It’s not a matter of knowledge, but a matter of experiences. But if you look only at knowledge, you will find a lot of better university than Harvard, even in USA. To know who they are, just watch where the big ingeneering compagnies get their new recrutes.
I was IT teacher for 6yrs and had students do their own projects with a common goal. It was just amazing to see and feel the enthusiasm by everyone, except one that wasn’t really into IT.
I’ve never watched anything remotely similar to this but I’m pretty happy it got recommend! Enjoyed watching it and I really love how enthusiastic you are about your craft and students!! You are awesome much respect!!
The Poly Bridge 4 graphics look insane. And the replay comes with a custom commentary so you know what to improve.
I love this! In highschool my absolute favorite class was drafting, all T squares and velum. We did a bridge every year and if you got to around 850 e factor you were doing pretty good. They were small and the best ones were relatively simple and light. He lets and my partner do a suspension bridge, nothing like this though. We pulled from the bottom and had a share built into the bridge that accepted the tray pulling down and put weights on the tray.
Outstanding.....your observation of the intrigue and engagement of everyone in the class, and all cheering for success....as good as it gets
I wouldn't fail this, I got my degree from Poly Bridge
Yeah same I think I peaked at like #36 in the world in poly bridge 2. Most of my bridges were not bridges though
I remember doing something similar to this in my Highschool physics class. We had to span a 1-foot distance between two desks using only plastic straws to make the bridge. I remember making a crisscross arched bridge that held up very well, it was a fun time trying to think of a bridge that would work.
I'm interested in a chart of how each bridge did on the three criteria: beauty, weight held, material efficiency.
Should add number of pieces too. System reliability is a very important component
These are engineers, not architects, function over form, how it should be. xP
@@acyweiThat’s when I was the most annoyed when he was talking about looks, all I care about is functionality. It’s not art, it’s a structure designed to hold heavy loads while being as cheep as possible.
I would recommend AGAINST putting non-functional judging into something that's strictly an engineering discipline. Do you know why STEM isn't a buzzword anymore? They diluted it to "STEAM" by adding "Arts" to it. Then later on they killed it with "STREAM" by adding "Reading." This is also the difference between Japanese and American automotive engineering. Americans usually start with aesthetics first and the shoehorn the engineering into it, while most Japanese manufacturers over-engineer the mechanics first, and then add the aesthetics later.
@@matthewxavier8067 Some bridges have stood for centuries, or even millennia. Over that time, many of those bridges have become tied to the cultural identity of the city or nation they were built in. Obviously, function and safety are more important to their purpose in transportation rather than as an artpiece, but form has value too. Think of how many people will cross it, or see it from a distance during the time it is in use. Do you want them to feel it is a necessary eyesore, or should they feel appreciation, awe, respect, etc.?
I'm from Seville but have lived in the UK for more than a decade. I thought it looked like el puente del Alamillo, but I never imagined you were going to mention it. It made my day. 😊 Who would want to learn with a professor like you!? ❤
i did a 1/10th scale version of this in highschool once and it was probably the most enjoyable thing i ever did in all my school years
As a high school educator we have made spaghetti bridges. I have used timber before also. Spaghetti is generally used due to financial and or time constraints. The students are amazed that spaghetti can hold so much weight. It’s a great project, regardless of material, though I would want senior students, like those studying architecture to be using materials closer to those which bridges are made of. It’s interesting to discuss with students shock loading, UDL..etc. great video. Would be interesting to know what constraints you gave the students.
Harvard doesn't think much about the financial constraints. I'm in agreement that spaghetti is a good tool for younger folk. I remember a summer camp activity at the local community college that used glue and index cards to make a bridge. Lots of corrugation :)
One sheet of paper and one foot of tape is an interesting constraint for most projects.
Why not use popsicle sticks? A wonky bridge I made couple years ago held 400lbs+ while weighing 350g or so, it was one of the most memorable and impressive things we did at school
Sounds like a pointless thing to teach 🙄
KZhead watchers suddenly clicking a lot more bridge related content than normal and the algorithm recognizes the uptick and recommends videos accordingly.
Bro, I thought it was just me
I cant believe that I've watched all of your videos and I barely recognized that additively manufactured part that you have at the background! What a masterpiece!
My high school physics teacher had us do a similar project. We each got the same materials and how to build a bridge spanning 12 in. That was very educational and Unforgettable experience and made the study of Science and physics so much more interesting!
Me getting this video in my feed after the Baltimore bridge collapse!
I'm surprised at the low standard of design of these bridges considering the level of the students. I've done this in secondary schools with 16 year old and they have come up with some impressive designs. I am particularly surprised at the cable designs that were obviously in compression. What on earth were the students thinking!
They copied an existing design that was anchored and weighted differently. Every design in use, has a certain way of working, and if you don't utilize the design as it was intended, it may fail due to the difference.
Those cables are typically under tension, but they didn’t account for the movement of the anchor points (towers) which in real life often have cables on the other side of the tower holding it up.
About the saying, "learning from mistakes/failures' only applies to things like this. Another great day for learning
You got that right! Thanks!
This is absolutely amazing! I never even knew this was possible.
Glad you liked it!
We did this in 7th grade science class, except our building material was newspaper. I absolutely dominated. The trick was rolling the newspaper from corner to corner, as tightly as possible. Some of the other designs were smart, but they rolled the paper into floppy hollow tubes instead of tight rigid sticks, and thus didn't stand a chance. I would have loved the opportunity to extend my model bridge building domination to Harvard, and indeed, around the world, but alas I am a poor.
you are better off without harvard. Teach yourself programming.
@@agnidas5816or any of the trades.
4:38 I just caught the huge grin on my face as you’re talking about how the students are interested. This is a great looking class Well done sir!
So nice for them to actually be creative and do their own design. When I had this class in university we had to recreate a moving model of a bridge that actually collapsed and recreate the the conditions that led to its collapse. If your bridge didn’t collapse or collapsed the wrong way you failed the class, while the professor was asking questions about the forces involved and theories behind the collapse. Some people got some really weird bridge collapse cases that were very difficult to recreate.
He seems like the kind of teacher to literally be the one you have the best memory of.
This is absolutely amazing! This is what we need in college and high school to make things interesting for everyone. Awesome and congrats to being so awesome!
Two things i took away from this its interesting to see how the forces are applied to the bridge and how failures can happen more due to twisting also that the center point is the weakest on lots of the structures. Which leads me to more questions and thoughts...def love this sort of thing :)
I was having so much fun watching this video. I think this is definitely the best way of teaching, letting students do their research on one subject and verify their understanding through hands-on projects. I can see your students were having a lot of fun in this learning process. By the way, I realised many of the bridges actually failed by laterally torsional bucking. I think that's because the second moment of area in the lateral direction is not high enough, these bridges can be improved by designing the cross section in a closed shape (like circles & rectangles). Based on my engineering intuition (which might not be correct), I think the best failure mode should be failed by tension-compression in order to reach the designed bridge's maximum capability.
This is so much fun for students to learn this way. They learn from doing and from each other’s experiences. We did this when I taught a class on architectural materials and construction methods but with a reinforced concrete beam. When I was a student we used 1/8”x6” wood dowels which were skewers with a pointy end. I used wood glue and my bridge held over 300 lbs. others used epoxy which flexed so much they lost their spanning and popped out of place and never broke. Shape is key.
This is how teachers should be. Allowing the students to express their curosity in the field, outside of writing notes.
I want to see him play Poly bridge.
Why is Matt Walsh in the attendence ?
Thank you Sir for bringing the competitors’ hearts very close to many who associate with the discipline and shear fun.
Architecture grad here studying for licensing exams and your videos are so fun and educational. Thank you :)
I would love to see more of it and would also be great to understand the different forces on the different area and how they could be improved… I definitely studied the wrong subject back at the University 😂❤
This is great, I did the same thing using balsa wood paper and wood glue at university in England thirty years ago..
"wow! it all failed! that was amazing.." - the one thing you don't want your bridge engineer to say but you love it when you hear it :)
This is how learning should be for all professions, especially Engineering… but we spend a good chunk of our time solving theoretical stuffs
Really cool to see an advanced class take on this challenge. My secondary school did the challenge using 1cm diameter wood stretching over a 1m gap if i remember correctly. I had watched a documentary on bridges at the time and built a girder box bridge (with underside suspension as afterthought) which broke the school record - managed tohold one teacher and one student before breaking (we ran out of weights). Needless to say i still have a sense of pride over it 😅 Looks like that last one might have a similar design internally? Couldve been an engineer but find myself as a ux specialist today.
I love contests like this! I mean, they all took the same class, and yet came up with such different ideas (speaks well of their teacher, to. Like they GOT it, didn't just copy something. That first bridge? I've NEVER seen cables under a bridge like that! NOTE: I also noticed that it didn't actually break, just twisted off it's anchors.
Maybe becaus it would be difficult to build?
Amazing. I remember doing this as an assignment in my design and technology class in year 12, our teacher scored us on the weight our bridges held before failure against the weight of the bridge itself to determine the best build. It was a super fun assignment and this video really brought back my memories. Thank you for sharing this. 👍
You're welcome!
I remember doing this back in middle school workshop class, we did use mostly pencil size long wood to build the bridges. But instead of sand weight test we use a compactor pressure test where we put them in a wheel turning compactor to see how long they can take before breaking. Also if I remember, there was some before that if you're bridge was best there was, your bridge drawing would be saved for future ones to use.
The majority of the load on a bridge is due to self weight, it can be as high as 85% and more of the total load for cable-supported long-span bridges like those mimicked here. Therefore a more realistic loading would be for the majority of the load to be distributed over the full length of the bridge and a smaller concentrated load or better a distributed load applied over a portion of the bridge. With a concentrated load alone the beam still has a lot of work to do in flexure and the cables don't help as much.
Thanks Gregor and you're absolutely right on bridges of course. I know we titled it "model bridges" but it was essentially a beam contest and, most importantly, one where the students learned about beam/spanning behavior. They also knew all of them would be loaded until collapse and that could be done at our discretion/fun! Thanks again.
Excellent content as always Mr Paul..wish we had exposure to such practical structures classes here in kenya🇰🇪
I'm glad the videos are helpful!
What's stopping you?
This is how you learn hands on try fail try again . Seems as everyone was involved and talking about outcomes. Bravo.
I just love the good vibes and the enthusiasm that I see on your face and the students faces. Unfortunately, since I live in the Middle East I didn’t experience none of that.. I did a major in Highway and Bridge engineering for for years, and haven’t seen a teacher made such an effort nor were the students engaged in the classes..The atmospheres were simply toxic. I really like what you guys have. I wish I had the chance to experience it, this is making me sad but at the same time. I’m really happy for you guys.
Looks like a lot of fun! In terms of stability testing the last one cheated a lot with the buckets on the sides and with a lower center of gravity. The moment of rotation is favored by the adition of the buckets. I think this is what allowed it to fail structurally and not on stability. Some of the others might have resisted just as well.
I was going to say something similar. I'm surprise the teacher didn't notice this or point it out. Not that good a teacher IMO.
I was looking for this comment. I wonder how the other would've fared with the side buckets method.
All of the students could have thought of the idea and used buckets, but only one group did - so kudos to their creativity. It's weird that a number of comments and responses imagined the worst case, then magically convinced themselves it was true, and then felt the need to publicly state their thoughts.
@@23lkjdfjsdlfj Speaking of weird, it is weird of you to magically convinced yourself that the people you commented on don't realize that and then felt the need to publicly state this. Of course the students thought of this, if not when loading on their bridge, then at least when they saw the other students do this. But if you're testing a scale model of a bridge, you're trying to simulate the actual thing, so not a high center of gravity for the load as occurs when stacked. The professor could've pointed this out as well, or prohibited the last team from loading with a lower COG. Given the amount of discussion this probably has been talked about, so my guess is that the students agreed this was fine and were just curious about the result. Hence these comments and the wonder of how the other bridges would've fared with a lower COG.
That was really fun to watch, now what would be a lot of fun is to get as many of the students back together at some point like 10 years out of school and into their real world and have a similar competition that would be an excellent follow on video and honestly you should really do that I just think how much fun you guys would have for that weekend Well done, as a contractor, an electrician and someone who used to maintain 20 story building I wish all engineers spent two years in the field doing some work instead of coming out of school with no practical experience, I get that there are trade-offs its risk versus cost or whatever but when guys like me have to fix stuff that people build week sometimes really want to scream at that person who put this piece of equipment in her room and there’s no way to get it out without blowing a hole and getting a crane Well Done 👏👏👏👏
Really cool!! Very interesting and fun to watch! Makes ya wanna try your own designs. Thank you for sharing!
The model bridge testing project is what made me want to get into the engineering field. I would have loved your class.
Really fun class. I would have liked to see a standardized way of applying weights -- the bridge that did the best had weights hanging from the bottom, which stabilized the structure. Most of the bridges actually failed because the center of gravity of the bridge was raised high above the base, meaning any small misalignment in weight caused the bridge to flip.
Exactly
I am not a student or into building but I really enjoyed this video. Stumbled across it by accident.
"I am Vietnamese, and I wish my country offered such education. Thank you very much; I will continue to follow and learn a lot from you! I hope you produce many more videos like this!"
Back in 2002, I had this kind of experiment in structure class too. The first one used A4 papers and scotch tape to build a bridge, the second one used popsicle sticks with glue. I can remember it well because that class was so much fun. I wish I could go back to learn all these thing again. 😊
I like how the professor giggled like a child when the last one cracked and failed. What a wonder to maintain one 's curiosity.
I can definitely say I would have loved to have studied under paul, he's such a fun teacher. What a great class.
I did this at Ottawa U back in 87 ... the ORIGINAL first class of bridge busting ... got a nice b+ for the final report on the failure ... and had the leftover bridge for 5 years at home too ... (573lbs for a 5 lbs bridge made of Balsa and string)
@@kaboom-zf2bl Wow, that's some going!
@@TheLondonForever00 yeah and I wasnt first ... gt beat by 4 others ... the best took the weight of the teacher ... plus another 35 lbs ...
Congratulations to all. Amazing jobs. So much fun and creativity. So cool. 🎉🎉
I remember having a project like this when I was 10 years old. We had learned simple bridge types and had to build our own bridges following those models, using recycled materials. My team built an arch bridge with thin cardboard and popsicle sticks, which ended up supporting 3 dictionaries surprisingly. Unfortunately we lost the competition to a suspension bridge (which to be fair was more of a beam bridge with high pillars, as most of its strength was in its beam, made out of a large chunk of staircase ramp). Fun times...
We did something like this in Grade 5 with glue and toothpicks. Obviously not at the same span or weights but it was one of the most memorable projects of my school years. Glad to see this video!
Yes! Toothpicks and wood glue are great for this contest. It has to be a particular brand and type of toothpick for an even playing field. Span a 12” gap and of course the weight should be hanging underneath from a specific sized block of wood that is placed into/onto the bridge. Sand can be used to fill a bucket hanging underneath. I participated in this at my elementary school’s science fair in the 80’s.
Great contest ideas and prizes, Paul. ---For these courses it's far better to require a single, detailed model at the finish. I've seen too many Construction Technology / Structures courses overwhelm students to the point where the 'prize' is merely finishing the course and surviving it. They learn almost nothing as a result.
Good thoughts...and I agree!
I enjoyed this video! It reminded me of my own college experience at the Purdue University School of Engineering and Technology at Indianapolis. I was in a double degree program that awarded an Associate of Science in Civil Engineering Technology and a Bachelor of Science in Construction Technology. We took structural design classes in that program, part of which we took two classes at the same time, Strength of Materials and Materials testing. The second class acted as a lab for the first. As a semester project we were given four small pieces of lumber and were told to use them to make a beam we would test, then right a report on the test. It was expected the beams would fail when the load would push the beam past the maximum to bending moment it could handle. My group had the only beam that didn't fail due to bending, but it failed due to shear. Our beam was the only I-beam shape in the competition. One group made a beam that was larger in depth than all the rest, making it two pieces of lumber thick and tall. The other two groups made box beams. In theory, the I beam should have supported the most load before failing. The beam with the large depth supported the most load before failure, but it was pointed out that the depth would have been limited in actual practice. We were not permitted to cut the pieces of lumber, so the I-beam had on extra thick flange. Had we been able to cut that extra piece, we could have used it as stiffeners to help with that shear. That was a fun project and the most fun class I took in college.
Great stuff! I always say an idea is only ever as good as your ability to realize it. This video is also a great example of why precision in execution matters.
5:11 up until this moment, I thought your students were having a laugh and submitted a plank of wood.
These events are much more interesting for everyone involved when the teacher competes as well.
We did something similar at Napier (Engineering, Mechanical and Production) in the 70s. We each got a sheet of balsa wood, a tube of glue and a craft knife and we had to span a small gap. Individual effort rather than teams and they were judged simply on weight bearing. My triangular hollow section came second and the winner used a truss design. That was one of the most useful engineering learning experiences ever (along with the bending of the cut and brazed 10mm square bar). I sometimes wish younger engineers did more with balsa wood and less with Ansys because it taught a certain intuition about material efficiency!
I can tell you are great teacher, just by look at how your class learn and still have fun ❤
The loading is problematic. The dumbell extends past the side of the bridge causing a twisting force wouldn't be present in an actual bridge with actual traffic loads. Given the narrarator's negative comments in the introduction regarding how spaghetti and glue models used in other schools doesn't test real life structures, it's a little silly to then test these wooden models using a load that doesn't mimic real life bridges and traffic loads. P.S. little sticks of wood don't behave like the steel used in bridges either. I assume the purpose is to teach the principles and test the students' knowledge in a fun way rather than simulate actual bridges and loads so the negativity regarding other schools' approaches is a little disingenuous.
A load extending beyond the edge of a bridge does not exert any twisting force at all provided it is overlapping the same both sides. Its centre of gravity is… central. Also, actual traffic *does* exert a twisting force unless it is exactly equal on both sides of the bridge - an unlikely occurrence. Bridge design needs to allow for some twisting.
Also, wind.
I agree, but the contestant from what I could tell is also the one placing the weight on their bridge. Also the contestants knew in advance what was going to be used as a weighting system to test the weight of the bridge, and could have built their bridge appropriately for the test weights to be used.
But the twisting forces do exist. If you put a heavy load toward one side of the bridge you will get a twisting load anyway. All bridges have to be designed with twisting forces in mind.
The way the dumbbell is placed adds zero moment to the equation like you mention. It's got equal weight off both sides, so the moment cancels out leading to no bending of the truss. You always calculate moment on the center of mass of the object, and the cent of mass of the dumbbell is square in the middle of the bridge.
They should make an engineer verse architect competition! As a bridge engineer this was great fun to watch.
Thanks! I was never build a bridge but watched to the end with a lot of curiosity. I'd love to see more of that kind of the videos on YT💕
great practical teaching.. it was really fun watching how different solutions performed. thanks for posting
I was frightened for their toes! Speaking as someone who managed to drop a weight on their foot and smash a toe! Do you recall which bridges won the popular vote and efficiency prizes?
Yup...we had lots of checks at start and throughout to look after toes! I think it was Bridge #4 that won "best looking" and Bridge #13 (the last one) won the other two awards which was lovely to see!
Interesting! Judging from video alone, I would not have guessed that bridge number four would have been the winner for best looking. As it was beautiful, I thought others would have taken this award.
My toothpick bridge broke at 486 pounds. It still holds the school record to this day.
The fact that you still check back in to find that information out is very telling...
4 decades ago i was student in engineering. Beautiful to see the young generation in times of 3D virtuality, coding, CAD, fluid dynamics and A.I. doing some handcraftsmanship in construction. The physical experience engraves much derper in the learning process than just sitting front computer screens where smart 3rd party software is going the anslysis of steess loads. Tks for sharing
Excellent demonstration,stimulates the mind more that studying it of a textbook.
Your tests looked like a lot of fun, we did similar tests in my college days using a testing machine and balsa wood pieces. Each entrant got a kit with the same pieces of balsa and the same glue and had to build a model out of only those materials to fit a certain testing and loading arrangement. I'm sorry but the bridges at 7:40 and 9:29 should have been immediate fails. The students were recreating something that they had seen done without understanding how it worked and how to make their models work the same way. The towers were not participating in carrying loads, they were just additional mass and complication for no reason. This doesn't help to enhance MIT's reputation. I saw a similar thing done in a Mythbusters episode where they modeled a suspension bridge without understanding how a suspension bridge worked and how the cables needed to be anchored at the ends. I think your loading unfairly penalized some of the designs in that you had the center of gravity of load quite a bit higher than the "roadway" so this tested the torsional stiffness as much as anything.
Thanks, I was looking for someone pointing this out. The Towers can just pivot freely with no anchoring. I wonder why even the Prof. thinks it‘s a sound idea.
I hope he doesn't really believe what he says when he talks about the rigidity of the anchor for the 7:40 bridge
Thank you for sharing. Mr Kassabian. This brought me some wonderful memory where we also did similar (designing bridges using balsa wood) but at much smaller scale in high school.
Learned a lot just watching this. Amazing stuff and very entertaining
Cool to watch. I noticed something too. most of the first ones to feel twisted first. remember seeing somebody doing the test on a straight iBeam. It wasn't about just supporting loads going straight down. It also twisted in the middle before it failed. The ends were still untwisted on the banks