[HN Gopher] Engineers put Leonardo da Vinci's bridge design to t...
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Engineers put Leonardo da Vinci's bridge design to the test (2019)
Author : hidden-spyder
Score : 58 points
Date : 2021-08-21 08:18 UTC (14 hours ago)
(HTM) web link (techxplore.com)
(TXT) w3m dump (techxplore.com)
| blaaee wrote:
| They created one in Norway with that design I think?
|
| https://no.wikipedia.org/wiki/Da_Vinci-broen
| blunte wrote:
| You can take one fast look at the design and see where the
| biggest problem is going to be: the lateral (spreading) forces
| against the ends of the bridge will require some clever anchor or
| ground lock of sorts, otherwise the ends will just shove apart
| and the middle will collapse.
|
| Notice in the modern model, they have the ends not only anchored,
| but actually blocked within boundaries that prevent spreading.
|
| Other bridges have used a similar design, but they had much more
| of a vertical component. Then the forces at the ground were more
| perpendicular to the earth plane, so gravity and mass of the
| stones (and friction of the stones against the earth) could
| better prevent separation.
| sfteus wrote:
| To be fair, even modern arch style bridges have the same
| concerns. For example, overhead arch bridges get around it by
| using ties between the ends running underneath the actual
| bridge itself to prevent the ends from separating. The Hernando
| de Soto bridge used this type of design and was recently closed
| for a few months because one of the ties had started to fail.
| Galanwe wrote:
| I'm a bit shocked that in 2021, students rely on physically
| building the bridge and simulating earthquakes with moving
| platforms. This feels like dummy engineering.
|
| I would have expected a mechanical engineer to actually be able
| to prove or disprove the feasibility through math, and create a
| CAD model on which to apply forces simulating earthquakes,
| heatwaves, etc.
| [deleted]
| IfOnlyYouKnew wrote:
| In a biology course, less than ten years ago, we cut out the
| graphs we sketched and weighed them, to calculate area-under-
| curve.
| R0b0t1 wrote:
| Why spend a lot of money making an error prone program when you
| can have reality simulate it for you?
|
| This is a problem I had at my last job, actually. We'd spend a
| lot of time on simulation that was kind of accurate but still
| need to do a fair bit of rapid prototyping to make up for
| simulation deficiencies afterwards.
|
| For simple stuff like a prototype jig to hold equipment mockups
| can be faster to make out of rough cut materials instead of
| spending 2 weeks making everything fit in a CAD program.
| fuzzfactor wrote:
| >create a CAD model
|
| I would think that could commonly be done without any
| university.
|
| Making the actual physical model could be considered a better
| use of MIT resources while they are there.
| rini17 wrote:
| On contrary, I am actually delighted to see the hands-on
| approach. Pure math is vulnerable to missed
| preconditions/unknown unknowns, with potentially catastrophic
| ramifications when it's carelessly applied to real building.
| You must know in advance what you're going to prove.
| Galanwe wrote:
| > Pure math is vulnerable to missed preconditions/unknown
| unknowns, with potentially catastrophic ramifications
|
| Interestingly I see the opposite. I expect the replica to be
| full of dangerous approximations: scaled weight of the stones
| not realistic, friction of the material not taken into
| consideration, earthquake ground vibrations not properly
| emulated by just shaking plates, etc
| klyrs wrote:
| I take issue with the term "pure math" here. Engineering
| simulation is strictly the realm of applied math, a dark
| art of floating point calculations, finite element
| analysis, idealized material properties, etc. Pure math
| demands much more rigor, and gets exact answers, but the
| methods available cannot handle the complexity of a bridge
| in this lifetime.
| unearth3d wrote:
| Like London's Millennium Bridge
| https://arstechnica.com/science/2018/10/new-study-sheds-
| more...
|
| I agree, engineering is art + science, impossible to iron
| everything out theoretically.
| jaclaz wrote:
| Only as anecdata, many years ago, circa 2000, I was marginally
| involved in a project for the re-building of Stari Most (the
| bridge at Mostar):
|
| https://en.wikipedia.org/wiki/Stari_Most
|
| the initial team of "modern" structural engineers were
| convinced - after mathematical analysis and computers
| simulations - that the bridge could not possibly be re-built
| exactly as it was.
|
| Then we contacted to verify the calculations an "old"
| structural engineer that believed that if something has been
| built and resisted (before the bombing) some 400 years, it can
| be built and is resistant enough.
|
| It came out that due to some limitations of the software used
| at the time, and to some approximations in the design of the
| computer model, the resistance (and influence) of the lead
| fixed steel pins (that were - for the time of building - a
| technical marvel) was greatly underestimated, as well as the
| effect of the steel strips.
|
| See here for some details on how the bridge was built:
|
| https://www.litosonline.com/en/article/old-bridge-mostar-rec...
| cseleborg wrote:
| We're all speculating here, of course, but I would expect it to
| be rather difficult to simulate both the static properties of
| the finished bridged and the dynamics of putting it together,
| which is obviously an important part of the process (see the
| keystone anecdote).
| wiredfool wrote:
| They probably did both. You end up remembering physical lab
| stuff differently than problem sets.
|
| I still remember some of the shake table stuff I did 30 years
| back.
| icegreentea2 wrote:
| They did do both. From the linked abstract:
|
| > Both of these factors are tested through analytical means
| and a 3D physical model supported by moveable abutments
|
| http://congress.cimne.com/formandforce2019/admin/files/filea.
| ..
| ColinWright wrote:
| It's the "Unknown Unknowns" that bite you. Via simulations and
| calculations you can be fairly sure that everything you've
| thought of will be fine, but there may be things you haven't
| thought of, and they may prove fatal to the design.
|
| In a later comment you say:
|
| > _" I expect the replica to be full of dangerous
| approximations: scaled weight of the stones not realistic,
| friction of the material not taken into consideration,
| earthquake ground vibrations not properly emulated by just
| shaking plates, etc"_
|
| How do you know that your model accurately represents the
| earthquake ground vibrations? How do you know that your model
| accurately represents the friction? Compressibility and
| friability of the materials? The scaled weight of the stones?
|
| How many times have you written a large and complex program,
| only to find that there are real world cases you haven't
| considered?
|
| I'm sure they did the computer modelling, but personally, I'm
| happy to see people building real-world versions to verify
| their (software and mathematical) models.
| Galanwe wrote:
| > Via simulations and calculations you can be fairly sure
| that everything you've thought of will be fine, but there may
| be things you haven't thought of, and they may prove fatal to
| the design.
|
| I don't deny that, the theorical approach will surely not be
| 100% accurate. Still, I expect that I would give me thousands
| of time more confidence than a 3D printed replica.
|
| > How do you know that your model accurately represents the
| earthquake ground vibrations?
|
| Because I expect the earthquake simulations in architecture
| CAD software to be made by physicists that spent time
| carefully modeling the realistic and complex set of forces
| that a structure would feel during an earthquake.
|
| > How do you know that your model accurately represents the
| friction?
|
| Again, because architecture CAD software are specifically
| crafted for that purpose, and can theorically simulate the
| friction and adherence of various materials much more
| realistically than a mockup 3D printed replica.
| spenczar5 wrote:
| You say that architecture CAD programs simulate things
| better than physical models with a lot of confidence, but I
| am not sure why.
|
| One way to think of this is that the physical world is a
| vastly superior computer. We cannot make a fluid simulation
| that runs as precisely as _an actual river_ , for example.
| Tribological models have to make tons of approximations
| since friction is insanely complicated - but the physical
| universe manages to calculate the real friction effect
| basically instantly!
| sollewitt wrote:
| Arches are tricky. The undergraduate way to model arch bridges
| is as three hinged structures - free to rotate at both ends and
| with a virtual "pin" in the middle, in order to make the math
| tractable. That's the kind of approximation that goes into
| mathematical models.
| chrisseaton wrote:
| "Beware of bugs in the above [bridge]; I have only proved it
| correct, not tried it." is some wisdom to go by.
| IfOnlyYouKnew wrote:
| It not only works, but is among the most beautiful structures
| I've seen. Someone should really build that.
|
| It also once again makes me consider the idea that da Vinci was a
| time travelling physicist having the time of his life.
| perihelions wrote:
| I wonder if it would have survived into the modern era, like many
| [0] of the compression-arch Roman bridges have. I imagine
| engineering history could have gone very differently, with such a
| crazy artifact standing as a proof-of-concept, inciting even
| bolder ideas. (What's the da Vinci version of steampunk called?)
|
| [0] https://en.wikipedia.org/wiki/List_of_Roman_bridges
|
| Apparently there's a lot of other attempts (beside OP's) to build
| scaled versions of this bridge. (The article mentions a steel
| footpath bridge in Norway). Here's one I think is particularly
| interesting: a reasonably faithful replica at the 100-meter
| scale, built of pykrete [1] (sawdust-reinforced water-ice
| composite).
|
| https://www.cursor.tue.nl/en/news/2015/april/tue-team-to-bui...
|
| https://www.youtube.com/c/BridgeInIce/videos
|
| [1] https://en.wikipedia.org/wiki/Pykrete
|
| I can't find a good post-mortem article, but it looks like it
| collapsed during construction and was abandoned. (?)
| sandworm101 wrote:
| >> I wonder if it would have survived into the modern era
|
| No. The roman bridges, the ones still up, lasted so long
| because they were ridiculously overbuilt. The romans lacked a
| full understanding and so made everything far stronger than we
| now know is necessary. Even with a millennia of weathering and
| erosion they still have more than enough strength to remain
| standing. Da Vinci's bridge design is more efficient and uses
| less material. It spreads a similar load on a lesser amount of
| material. If using the same materials as the romans (stone) it
| would not last the centuries because it would have less reserve
| strength to lose to weathering.
| CapitalistCartr wrote:
| "What's the da Vinci version of steampunk called?"
|
| Clockpunk.
| stan_rogers wrote:
| Not even that, really. He predates the pendulum by just about
| a century (and I mean Galileo's discovery of its regularity,
| not Huygens' employment of it). Sure, there was verge-and-
| foliot in limited number in cathedrals and monasteries, but
| _common_ clockwork - Nuremberg eggs and that sort of thing -
| came along shortly after Leonardo went away. Sundials and
| water clocks were the order of the day in Leonardo 's time.
| Jach wrote:
| > inciting even bolder ideas
|
| Even if it would have lasted, which I doubt, I also doubt it
| would have successfully inspired much, and certainly not any
| time before real engineering came about as a consequence of
| understanding physics and thus having a theory guiding and
| supporting work, rather than a cookbook of rules. (Like, the
| surviving ancient marvels notwithstanding, you can really only
| go so far in structures without an understanding of beam
| theory, stresses, even the square-cube law which wasn't
| articulated until Galileo.) When the architects and builders of
| the past (I think it's a stretch to call them engineers) veered
| too far from established practice, things tended to frequently
| collapse. A Roman example:
| https://en.wikipedia.org/wiki/Insula_(building)
| shadilay wrote:
| The headline made me think it was a different bridge of
| Leonardo's. https://www.researchgate.net/figure/A-design-for-a-
| temporary...
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