Was Rejected as a Crank Idea 500 Years Ago

[a1call]

Engineers put Leonardo da Vinci's bridge design to the test.

[ewmayer]

Ugh, a Google-amp link. Here is a Gizmodo one -- the Sultan didn't reject Leonardo as a crank, but the design was so radical, and Leonardo offered no physical prototypes, that it's understandable they passed on it, especially as the area is highly earthquake-prone. The MIT team mentions this aspect, but IMO they downplay it:

As the story goes, in 1502 A.D. the Sultan Bayezid II wanted to build a bridge to connect the city of Istanbul to its neighbor, Galata. One of the proposed designs came from Leonardo da Vinci, who had already made a name for himself in the arts and sciences at the time. In a letter he sent to the sultan, accompanied by a notebook full of sketches, da Vinci described a bridge that would span the proposed distance using a single, flattened arch design, supported by bases on either shore. Bridges at the time were typically made using a series of semicircular arches, and to span the distance between the two cities would have required at least 10 evenly spaced piers in between to support the entire structure. Da Vinci’s design, which would have easily allowed sailboats to pass beneath it, was radically different (and centuries ahead of its time), which is probably why the sultan decided not to take the risk. Half a millennium later, researchers were curious if it would have succeeded.

The original notes and illustrations describing the bridge didn’t specify what materials would be used to build it, or how it would actually be constructed. But the MIT researchers concluded that the only material that would have provided adequate strength was stone, and based on the building techniques commonly employed around the same time da Vinci came up with this design, the bridge would have probably been engineered to rely on gravity to hold all of its pieces together.

To test their assumptions, the team at MIT created a 1:500-scale replica, measuring about 32 inches long, that would be assembled from 126 blocks of varying shapes and sizes, created by a 3D printer. The real bridge, had it actually been built, would have required thousands of precisely chiseled stone blocks for its assembly, but the approach MIT took for the replica still allowed them to properly test the feasibility of its design.

Not only did the bridge work, remaining strong and stable without the use of any mortars or fasteners, but the team at MIT also realized that da Vinci had even engineered a way to minimize unwanted lateral movements in the structure, which would have quickly led to its collapse. The footings on either side of the arched bridge featured designs that splayed outwards to add a considerable amount of stability. The bridge would have even survived most earthquakes, which were common at the time in that area, as the MIT researchers discovered by putting their replica on two movable platforms. It wasn’t indestructible, but it would have been an ancient architectural marvel.

Note the careful wording: "The bridge would have even survived most earthquakes" -- so it might have survived for what, 20, 50, 100 years? The reliance - even by Leonardo - on purely compressional-load structures points up another key advantage of a more conservative multiarch structure in a highly-earthquake-prone context: Had Leonardo's bridge been built, when the Big One inevitably came sometime in the following century, it would have suffered catastrophic collapse of the single huge span. A multi-arch bridge might have one or a few subspans collapse, but it would have been straightforward to rebuild those, as the remaining piers and spans would have been usable for moving material and workers to the destroyed areas.

So it's still a triumph of design, but there are perfectly good reasons it was rejected for the intended purpose. Sorry if that offends the uncritical-Leonardo-hagiography industry.

[a1call]

The 4 proceeding bridges that were made starting in the 19th century would not have fared any better in an earthquake, since they were made of wood.
None is standing now. It is arguable if Leonardo's bridge would have survived with future reinforcement and maintenance.


https://en.m.wikipedia.org/wiki/Galata_Bridge

"it has been [the Sultan's] intention to erect a bridge from Galata (Pera) to Stambul… across the Golden Horn (‘Haliç’), but this has not been done because there were no experts available. I, your subject, have determined how to build the bridge. It will be a masonry bridge as high as a building, and even tall ships will be able to sail under It."

https://en.m.wikipedia.org/wiki/Vebj..._Vinci_Project

[a1call]

Well, had a day to think about the concept and here is my 2 cents.
While I think the bridge would be highly stable after being assembled, having it assembled across a large body of water would not be an easy task. The bridge was intended to be held together by the force of gravity, so it would probably have to be Supported in whole before completion. But then again I am no architect.
A similar structure is probably the Montreal Olympic stadium which I believe is equipped with giant hydraulic pumps at the base to keep it together.
So base soil shift over time must also have been addressed somehow.

[kriesel]

Originally Posted by ewmayer

it might have survived for what, 20, 50, 100 years?

Little of all we value here, sees the dawn of its hundredth year.
Single or multiarch, after it fell, they wouldn't have far to go for most of the materials to rebuild, and properly selected and used, stone has a very long service life. (Limestone not so much, with acid rain. But even that can manage more than a century.)
I wonder how the amount of stone for the various designs compare to river depth, and how failure might affect the prospects of local flooding. Having a bridge turn into even a rather leaky dam or weir could be bad for the local residents, especially if adding peril atop an earthquake event and possibly resulting fires and other structure collapses.

[kriesel]

Originally Posted by a1call

While I think the bridge would be highly stable after being assembled, having it assembled across a large body of water would not be an easy task. The bridge was intended to be held together by the force of gravity, so it would probably have to be Supported in whole before completion
...
So base soil shift over time must also have been addressed somehow.

From what I've read the whole span has to be supported by wood scaffolding until the keystone is in place. Rather like building a wood bridge that can support the stone bridge. The advantage is the wood does not have to last long, and river navigation can be temporarily interrupted.
I think to have reasonable service life for the stone bridge, its footings would have to go clear down to bedrock, and key into that rock. Even so, rock distorts over time. I've been in the Homestake mine (in Lead, South Dakota), which was around 140 years old, and the mine car rail tracks and tunnel floors had obvious considerable lateral slope. They were originally cut and installed level.
Correcting for end support drift would be a major construction effort, involving reinstalling the entire wood scaffolding and removing it again afterward.

[xilman]

Originally Posted by kriesel

From what I've read the whole span has to be supported by wood scaffolding until the keystone is in place. Rather like building a wood bridge that can support the stone bridge. The advantage is the wood does not have to last long, and river navigation can be temporarily interrupted.
I think to have reasonable service life for the stone bridge, its footings would have to go clear down to bedrock, and key into that rock. Even so, rock distorts over time. I've been in the Homestake mine (in Lead, South Dakota), which was around 140 years old, and the mine car rail tracks and tunnel floors had obvious considerable lateral slope. They were originally cut and installed level.
Correcting for end support drift would be a major construction effort, involving reinstalling the entire wood scaffolding and removing it again afterward.

There are Roman viaducts which are still usable 2000 years later.

I remember reading about one in Spain which was used by heavy trucks transporting something like a power station generator because the 20th century alternatives were not strong enough to carry the weight. )One day, perhaps, I'll be able either to provide documentary evidence or to reveal that it's an urban legend.

[Till]

One Roman bridge in Spain which has a very strong construction is
https://en.wikipedia.org/wiki/Roman_...f_C%C3%B3rdoba.
I like it a lot.


But of course there are many more, see
https://en.wikipedia.org/wiki/List_of_Roman_bridges

[kriesel]

Originally Posted by xilman

There are Roman viaducts which are still usable 2000 years later.

Exactly. They built things to last. It's easier to do when you control a large part of the known world, have slaves and conquered peoples to contribute to the cause, and plan for the VERY long term, compared to usual human endeavor. Still pretty ephemeral compared to geological time scale.

Then there's the story about why the Space Shuttle solid rocket boosters were the diameter they were. It relates to the size of rail tunnels, which were designed around standard rail spacing and feasible rail car size, which was traceable back to the spacing of ruts in roads created by Roman war horses and what they towed. So indirectly, it was decided by the widths of large horses.

[a1call]

So Leonardo was not as ancient as the Romans and presumably the knowledge might have been lost by then. But there must have been concrete at his time. Why bother with precise cut stone as the only possibility?
Re Roman bridges lasting long, unlike the modern cement, their formula strengthened underwater:

The strength and longevity of Roman marine concrete is understood to benefit from a reaction of seawater with a mixture of volcanic ash and quicklime to create a rare crystal called tobermorite, which may resist fracturing. As seawater percolated within the tiny cracks in the Roman concrete, it reacted with phillipsite naturally found in the volcanic rock and created aluminous tobermorite crystals. The result is a candidate for "the most durable building material in human history". In contrast, modern concrete exposed to saltwater deteriorates within decades.[8][9][10]

https://en.m.wikipedia.org/wiki/Roman_concrete

Which raises the question, why not use their formula in modern bridge construction instead?

[Uncwilly]

Originally Posted by kriesel

It relates to the size of rail tunnels, which were designed around standard rail spacing and feasible rail car size, which was traceable back to the spacing of ruts in roads created by Roman war horses and what they towed. So indirectly, it was decided by the widths of large horses.

Why then are there so many differing gauges in the same areas? Not all carriages were of the same width.
https://en.wikipedia.org/wiki/Track_gauge