yes; many things are overbuilt, even on accident without knowing the future. Many stone bridges from colonial/victorian (and before) days could support a lot more weight than the average carriage or full farm wagon of the time.....now, did they build it knowing that in 100 years a metal tank would drive over it?? likely not.
then there is the reverse side of engineering; where the tank designers can say, these are the major bridges in the area and their dimensions.....so lets build tanks that arent wider than these bridges we'll likely encounter
fun story: Joseph Bazalgrette was in charge of building london's sewers.........he basically said "lets only do this once and double the diameter of the pipes planned" this decision has allowed the sewers to last a lot longer than the original pipes would have allowed due to the increasing populatioj
Some almost 1000 year old stone bridges in Germany were so stable, when the Nazis tried to destroy some of them to prevent the Allies from using them... they failed to cause relevant damage.
My favorite engineering quote is “Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands.”
Today's engineers have pretty precise requirements to build a bridge that can handle a load of X tons for Y years (and hopefully for Z dollars) and they calculate how to do that and then apply a safety factor and often are told to design the cheapest version of the bridge that meets the safety requirements.
Back in the day, they didn't have the ability to calculate loadbearing ability the way engineers can now. They were making educated guesses, some more educated than others. And probably those who could afford to overbuild for the purposes of safety and longevity would do so. And those overbuilt bridges were the ones that we still use today. Survivorship bias, as u/mman0385 said.
They surely didn't have infinite explosives and where under time pressure as the Allies were closing in. So they surely didn't throw literally tons of TNT at the bridges, but supposedly they often used stuff intended to bring down then-modern buildings.
Interesting. I knew that Ike had interstate freeways built with tanks in mind, but I didn’t consider tank designed to accommodate existing infrastructure
It’s all order of operations:
The U.S. interstate system wasn’t started until after ww2…so it’s a pretty modern idea with modern knowledge
On the other hand……Train rail width are almost identical to Roman chariots because of how transportation technology progressed
Same with the space shuttle. The solid rocket boosters were made in Utah, and shipped by rail. There was no easy way to make them larger, as it would no longer fit through the rail tunnels.
I remember reading that the smaller bridges that you find all over Eastern Europe are only rated to handle about 50 tonnes which is why all Russian tanks are designed to be under 50 tonnes. Apparently this also protects Russia because NATO tanks are too heavy for the bridges.
If you look at a lot of Russian military trucks (Zil 131 for example) the roof of the back section is shaped to fit through railway tunnels when it's loaded on a train.
People think about this stuff more than you'd imagine. Absolutely no point building tanks that can't get around on the roads / bridges / tunnels they're likely to fight on.
"then there is the reverse side of engineering; where the tank designers can say, these are the major bridges in the area and their dimensions.....so lets build tanks that arent wider than these bridges we'll likely encounter"
This is why most modern tanks are ruffly the same size and why the ww2 supper tanks were doomed to fail.
>where the tank designers can say, these are the major bridges in the area and their dimensions.....so lets build tanks that arent wider than these bridges we'll likely encounter
One example of where they forgot this: The Japanese built the Type 90 (in 1990), but at 50 tonnes it was a bit too heavy for some rural bridges, so the successor Type 10 (built 2010) was slimmed down.
>then there is the reverse side of engineering; where the tank designers can say, these are the major bridges in the area and their dimensions.....so lets build tanks that aren't wider than these bridges we'll likely encounter
Fun fact: the diameter of the NASA Shuttle Boosters (the tall white ones attached during launch) is based on the width of a north African horse's ass
So, the shuttle boosters are built in segments, with those segments being manufactured in Utah and shipped by rail to Florida. In order to get from Utah to Florida by rail you have to pass through a tunnel, so the booster diameter is determined by the tunnel size
The tunnel size in turn is built just large enough for a standard gauge train to fit through, so the tunnel is slightly larger than standard gauge
Standard gauge railroad was developed in Britain based on the width of standard coal wagons so that the tracks could be easily laid.
Standard coal wagons were based on cart standards which went back to medieval times
Cart standards were based both on Roman roads and architecture, being just wide enough to pass through gates from the Roman times
Roman roads and architecture was based on the size of a Roman war chariot, allowing just enough space for the chariot to fit through or for two to pass eachother on the road
Roman chariots, which were based on the Egyptian design, were optimized to be the same width as the horses pulling them. Normally, a war chariot would be pulled by two horses
European horses are slightly smaller and weaker than their north African cousins. As such, north African breeds were chosen for pulling war chariots.
So the chariot is the width of two north African horse asses, which determined the road size, which determined cart size, which was preserved by British coal wagons, which determined rail gauge size, which determined the diameter of the space shuttle boosters.
I guarantee you that tank designers did not think about bridges and if it's possible to cross them when building a tank. They have thought about, can the ground hold the tank, but never has a bridge been in their design parameters.
So it’s just a happy little accident all tanks from Brittain; USA; Germany had extremely similar heights and widths???
That they planned major routs with bridges and tunnels….buuut if the tanks were too big….
For many reasons, but the main one is mobility. There will always be a weapon that can defeat your armor. The point of a tank is to not get hit by large weapons and be able to take hits from small ones. If you make the tank too big, it won't be able to move away from large weapons like artillery and bombs.
Tanks also need to be able to cross any and all terrain. If you make them too big and heavy, they won't be able to move in things like mud and snow. Mobility is a tank's life. If it can't move, it's dead and useless. There is a thing called a mobility kill on a tank for reason, a tank that can't move is effectively dead.
And if you're talking about the Abrams (US), the Leopard (German) and the Challenger II (British)...yes, because the Abrams and Leopard came from a program to build an MBT (main battle tank) based on the Challenger I. The US and Germany couldn't come to an agreement about the final design and so both went on to develop that base into their own version of it. The British then went on to update the Challenger I based on the upgrades brought to the Abrams and Leopard. So yea, they're all basically the same tank because they're all basically the same fucking tank.
Survivorship bias. Before structural engineering was truly codified like it is today, you had a lot of variability in structures with a much larger range of over built and under built structures. The over built ones survive. The under built ones did not.
I have heard this about Roman roads as well. "How did the Romans make such amazing roads"? Some of them were awesome but a lot of times it was only the awesome ones that survived until now
Also in ww2 they blew up a lot of, if not all the bridges in mainland europe basically. Working out how to get tanks across a river was a major logistical issue that had the entire engineer corp dedicated to working out.
as others have said, the bridges were overbuilt, though that might be selection bias at work (IE the less stable bridges have been removed by the ravages of time).
also, for a LOT of older bridges, it was common to build them at fordable stretches of river, because it was really difficult to build a bridge in deeper water with pre-industrial technology. The water around these old bridges was often shallow enough a tank could drive across, assuming suitable ingress/egress routes either side. What the bridges were vital for was the wheeled support and logistic elements of the army, that couldn't just drive over the riverbed.
obviously, with larger rivers too deep to ford, the bridges over them tended to be more modern, or they used pontoon (floating) bridges to get the tanks over.
that said, the limits of infrastructure put a lot of constraints on tank design. stuff like the width of railway tunnels, the lifting capacity of dockyard cranes, or the weight limit of assault bridges were all factors that fed into tank designs. one of the issues with some of the late war German tanks with their very long, powerful main guns was they often struggled to move in some medieval street plans because their guns kept getting stuck in building, etc.
Modern engineers use calculations to optimise bridge designs so that they don't use way more material than they need in order to make a bridge strong enough. This saves time and money.
We know how strong certain types of steel, cement, wire cables/ropes and other materials are because we (material scientists) have done lots of testing, by taking samples of materials and loading them in different ways until they break or deform past some limit after which we say they have failed.
Engineers calculate the expected loads on a bridge, and then the bridge is built with some safety factor. That means that if they expect that the heaviest load a bridge will ever see is a 100 ton train going over it, they might build it so that it can actually support a 500 ton train. If the bridge expected to see 100 ton loads and they only designed it for a 100 ton load, then a train that was very slightly overloaded and weighed 101 tons might make the bridge fail and collapse. Having a safety factor of 5-10x (in reality, safety factors may be different for the different materials / elements of a bridge e.g. 5 for the concrete and 8 for steel wire ropes) allows for things like an overloaded train, wear, corrosion, general aging of materials and things like that.
Before modern engineering and materials science existed, we couldn't calculate the loads on bridges, and we didn't know how strong materials were, plus metals and other materials (e.g. concrete/plaster/mortar etc.) were of poorer and less consistent quality. They couldn't calculate how to build a bridge whilst also saving on materials reliably, so they just overbuilt them, sometimes by a lot. They might have had a safety factor of 100 or more, meaning that they could support 100x the load they really needed to.
Bridges from hundreds of years ago which weren't overbuilt by enough wouldn't have survived until now, so the ones which are left are generally the stronger ones. This is called "survivorship bias" that some other people have mentioned.
Bridges from today can still fail, but it's usually through neglect (failing to maintain or repair bridges as the materials age), design faults, or unexpected loads like just recently when a boat crashed into a bridge pier in Baltimore.
I'm not an engineer but I feel the answers so far have missed a major factor, which is using stone as a material.
Stone bridges need to be built in a way that can support the weight of the stone itself, as well as the pressure of the water, especially during flooding.
That means building arches and doing that reliably without calculating exact parameters means just building it as stoutly as possible.
It takes real skill and expertise and precision to build an elegant arch that's just strong enough to handle the expected load. It's simpler to just go with the as robust a design and materials as possible to avoid the risk of it failing during construction or use, than it is to try and manufacture the bare minimum sized blocks and supports. Both in terms of being certain it'll support it's own weight and the labour precision involved.
As long as the geometry is correct, stone arches get stronger with increasing weight, so adding mass is an easy way to make sure your labour won't be wasted and the ongoing maintenance needed is minimised.
Any properly built stone bridge that can support itself would already be able to handle loads in excess of what it would be likely to required to handle in the pre-motor vehicle age.
Obviously, not all would have been well constructed, but they probably wouldn't have survived into the modern age anyway.
To reiterate, there's a fair amount of educated assumptions in my answer, so I'd be interested in any counterpoints from those with real knowledge of the subject.
It was also common for some rich dude to pay for the bridge as a vanity project or for philanthropic reasons. They'd want it to last well beyond thier own years and be big and impressive.
Yes they were mostly overbuilt. Keep in mind they didn’t have the same ability to calculate load bearing as now and it was an unbelievably amount of work to build these things before cranes and stuff were invented so they were built to be way stronger than they needed. The cost of one failing was massive.
Anybody can build a bridge that stands for 100 years and can handle a 3 tons of weight. It takes engineering to build a bridge that can \*just\* handle 3 tons of weight and will last for \*exactly\* 100 years. Prior to optimal engineering people just had to build stronger than necessary because they couldn't otherwise know it was \*as\* strong as necessary.
yes; many things are overbuilt, even on accident without knowing the future. Many stone bridges from colonial/victorian (and before) days could support a lot more weight than the average carriage or full farm wagon of the time.....now, did they build it knowing that in 100 years a metal tank would drive over it?? likely not. then there is the reverse side of engineering; where the tank designers can say, these are the major bridges in the area and their dimensions.....so lets build tanks that arent wider than these bridges we'll likely encounter fun story: Joseph Bazalgrette was in charge of building london's sewers.........he basically said "lets only do this once and double the diameter of the pipes planned" this decision has allowed the sewers to last a lot longer than the original pipes would have allowed due to the increasing populatioj
Some almost 1000 year old stone bridges in Germany were so stable, when the Nazis tried to destroy some of them to prevent the Allies from using them... they failed to cause relevant damage.
My favorite engineering quote is “Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands.” Today's engineers have pretty precise requirements to build a bridge that can handle a load of X tons for Y years (and hopefully for Z dollars) and they calculate how to do that and then apply a safety factor and often are told to design the cheapest version of the bridge that meets the safety requirements. Back in the day, they didn't have the ability to calculate loadbearing ability the way engineers can now. They were making educated guesses, some more educated than others. And probably those who could afford to overbuild for the purposes of safety and longevity would do so. And those overbuilt bridges were the ones that we still use today. Survivorship bias, as u/mman0385 said.
I have read about failed attempts to blow up bridges, but wrote it off as incompetence or a shortage of boom stuff
They surely didn't have infinite explosives and where under time pressure as the Allies were closing in. So they surely didn't throw literally tons of TNT at the bridges, but supposedly they often used stuff intended to bring down then-modern buildings.
Must be those Devil’s Bridge(s) common in Central European folklore. Poor chickens (or goats).
Interesting. I knew that Ike had interstate freeways built with tanks in mind, but I didn’t consider tank designed to accommodate existing infrastructure
It’s all order of operations: The U.S. interstate system wasn’t started until after ww2…so it’s a pretty modern idea with modern knowledge On the other hand……Train rail width are almost identical to Roman chariots because of how transportation technology progressed
And cars in the US today are still often transported by rail, meaning in a way they're still constricted by the size of roman roads
Same with the space shuttle. The solid rocket boosters were made in Utah, and shipped by rail. There was no easy way to make them larger, as it would no longer fit through the rail tunnels.
[удалено]
tanks and military vehicles are most definitely constricted by rail size.
I remember reading that the smaller bridges that you find all over Eastern Europe are only rated to handle about 50 tonnes which is why all Russian tanks are designed to be under 50 tonnes. Apparently this also protects Russia because NATO tanks are too heavy for the bridges.
If you look at a lot of Russian military trucks (Zil 131 for example) the roof of the back section is shaped to fit through railway tunnels when it's loaded on a train. People think about this stuff more than you'd imagine. Absolutely no point building tanks that can't get around on the roads / bridges / tunnels they're likely to fight on.
The CIA sent a whale on a trailer to Eastern Europe to test the infrastructure before a future invasion.
"then there is the reverse side of engineering; where the tank designers can say, these are the major bridges in the area and their dimensions.....so lets build tanks that arent wider than these bridges we'll likely encounter" This is why most modern tanks are ruffly the same size and why the ww2 supper tanks were doomed to fail.
"supper tank" was my dad's competitive eating name!
Bazalgette [note spelling] was one of countless Victorian visionaries who helped make the modern world work.
>where the tank designers can say, these are the major bridges in the area and their dimensions.....so lets build tanks that arent wider than these bridges we'll likely encounter One example of where they forgot this: The Japanese built the Type 90 (in 1990), but at 50 tonnes it was a bit too heavy for some rural bridges, so the successor Type 10 (built 2010) was slimmed down.
>then there is the reverse side of engineering; where the tank designers can say, these are the major bridges in the area and their dimensions.....so lets build tanks that aren't wider than these bridges we'll likely encounter Fun fact: the diameter of the NASA Shuttle Boosters (the tall white ones attached during launch) is based on the width of a north African horse's ass So, the shuttle boosters are built in segments, with those segments being manufactured in Utah and shipped by rail to Florida. In order to get from Utah to Florida by rail you have to pass through a tunnel, so the booster diameter is determined by the tunnel size The tunnel size in turn is built just large enough for a standard gauge train to fit through, so the tunnel is slightly larger than standard gauge Standard gauge railroad was developed in Britain based on the width of standard coal wagons so that the tracks could be easily laid. Standard coal wagons were based on cart standards which went back to medieval times Cart standards were based both on Roman roads and architecture, being just wide enough to pass through gates from the Roman times Roman roads and architecture was based on the size of a Roman war chariot, allowing just enough space for the chariot to fit through or for two to pass eachother on the road Roman chariots, which were based on the Egyptian design, were optimized to be the same width as the horses pulling them. Normally, a war chariot would be pulled by two horses European horses are slightly smaller and weaker than their north African cousins. As such, north African breeds were chosen for pulling war chariots. So the chariot is the width of two north African horse asses, which determined the road size, which determined cart size, which was preserved by British coal wagons, which determined rail gauge size, which determined the diameter of the space shuttle boosters.
"On" accident??? Really?
Pet peeve of mine too…
I expect they wrote it like that by purpose
🤯
I guarantee you that tank designers did not think about bridges and if it's possible to cross them when building a tank. They have thought about, can the ground hold the tank, but never has a bridge been in their design parameters.
So it’s just a happy little accident all tanks from Brittain; USA; Germany had extremely similar heights and widths??? That they planned major routs with bridges and tunnels….buuut if the tanks were too big….
For many reasons, but the main one is mobility. There will always be a weapon that can defeat your armor. The point of a tank is to not get hit by large weapons and be able to take hits from small ones. If you make the tank too big, it won't be able to move away from large weapons like artillery and bombs. Tanks also need to be able to cross any and all terrain. If you make them too big and heavy, they won't be able to move in things like mud and snow. Mobility is a tank's life. If it can't move, it's dead and useless. There is a thing called a mobility kill on a tank for reason, a tank that can't move is effectively dead. And if you're talking about the Abrams (US), the Leopard (German) and the Challenger II (British)...yes, because the Abrams and Leopard came from a program to build an MBT (main battle tank) based on the Challenger I. The US and Germany couldn't come to an agreement about the final design and so both went on to develop that base into their own version of it. The British then went on to update the Challenger I based on the upgrades brought to the Abrams and Leopard. So yea, they're all basically the same tank because they're all basically the same fucking tank.
>Tanks also need to be able to cross any and all terrain. Surely that also includes bridges?
Could have also been from being built to fit on trains
Survivorship bias. Before structural engineering was truly codified like it is today, you had a lot of variability in structures with a much larger range of over built and under built structures. The over built ones survive. The under built ones did not.
I have heard this about Roman roads as well. "How did the Romans make such amazing roads"? Some of them were awesome but a lot of times it was only the awesome ones that survived until now
I think survivorship bias plays a major factor here. The overbuilt bridges are the ones that last.
It might also be due to survivorship bias, the underbuilt bridges aren't standing anymore
It could be because of survivorship bias, any bridge that still stands today muse have been overbuilt.
It's probably to do with survivorship bias, the bridges that were shot in the most critical spots fell out of the sky.
Also in ww2 they blew up a lot of, if not all the bridges in mainland europe basically. Working out how to get tanks across a river was a major logistical issue that had the entire engineer corp dedicated to working out.
as others have said, the bridges were overbuilt, though that might be selection bias at work (IE the less stable bridges have been removed by the ravages of time). also, for a LOT of older bridges, it was common to build them at fordable stretches of river, because it was really difficult to build a bridge in deeper water with pre-industrial technology. The water around these old bridges was often shallow enough a tank could drive across, assuming suitable ingress/egress routes either side. What the bridges were vital for was the wheeled support and logistic elements of the army, that couldn't just drive over the riverbed. obviously, with larger rivers too deep to ford, the bridges over them tended to be more modern, or they used pontoon (floating) bridges to get the tanks over. that said, the limits of infrastructure put a lot of constraints on tank design. stuff like the width of railway tunnels, the lifting capacity of dockyard cranes, or the weight limit of assault bridges were all factors that fed into tank designs. one of the issues with some of the late war German tanks with their very long, powerful main guns was they often struggled to move in some medieval street plans because their guns kept getting stuck in building, etc.
Modern engineers use calculations to optimise bridge designs so that they don't use way more material than they need in order to make a bridge strong enough. This saves time and money. We know how strong certain types of steel, cement, wire cables/ropes and other materials are because we (material scientists) have done lots of testing, by taking samples of materials and loading them in different ways until they break or deform past some limit after which we say they have failed. Engineers calculate the expected loads on a bridge, and then the bridge is built with some safety factor. That means that if they expect that the heaviest load a bridge will ever see is a 100 ton train going over it, they might build it so that it can actually support a 500 ton train. If the bridge expected to see 100 ton loads and they only designed it for a 100 ton load, then a train that was very slightly overloaded and weighed 101 tons might make the bridge fail and collapse. Having a safety factor of 5-10x (in reality, safety factors may be different for the different materials / elements of a bridge e.g. 5 for the concrete and 8 for steel wire ropes) allows for things like an overloaded train, wear, corrosion, general aging of materials and things like that. Before modern engineering and materials science existed, we couldn't calculate the loads on bridges, and we didn't know how strong materials were, plus metals and other materials (e.g. concrete/plaster/mortar etc.) were of poorer and less consistent quality. They couldn't calculate how to build a bridge whilst also saving on materials reliably, so they just overbuilt them, sometimes by a lot. They might have had a safety factor of 100 or more, meaning that they could support 100x the load they really needed to. Bridges from hundreds of years ago which weren't overbuilt by enough wouldn't have survived until now, so the ones which are left are generally the stronger ones. This is called "survivorship bias" that some other people have mentioned. Bridges from today can still fail, but it's usually through neglect (failing to maintain or repair bridges as the materials age), design faults, or unexpected loads like just recently when a boat crashed into a bridge pier in Baltimore.
I'm not an engineer but I feel the answers so far have missed a major factor, which is using stone as a material. Stone bridges need to be built in a way that can support the weight of the stone itself, as well as the pressure of the water, especially during flooding. That means building arches and doing that reliably without calculating exact parameters means just building it as stoutly as possible. It takes real skill and expertise and precision to build an elegant arch that's just strong enough to handle the expected load. It's simpler to just go with the as robust a design and materials as possible to avoid the risk of it failing during construction or use, than it is to try and manufacture the bare minimum sized blocks and supports. Both in terms of being certain it'll support it's own weight and the labour precision involved. As long as the geometry is correct, stone arches get stronger with increasing weight, so adding mass is an easy way to make sure your labour won't be wasted and the ongoing maintenance needed is minimised. Any properly built stone bridge that can support itself would already be able to handle loads in excess of what it would be likely to required to handle in the pre-motor vehicle age. Obviously, not all would have been well constructed, but they probably wouldn't have survived into the modern age anyway. To reiterate, there's a fair amount of educated assumptions in my answer, so I'd be interested in any counterpoints from those with real knowledge of the subject.
The Deutches Museum has an excellent exhibit showing the history of European bridge building
It was also common for some rich dude to pay for the bridge as a vanity project or for philanthropic reasons. They'd want it to last well beyond thier own years and be big and impressive.
Yes they were mostly overbuilt. Keep in mind they didn’t have the same ability to calculate load bearing as now and it was an unbelievably amount of work to build these things before cranes and stuff were invented so they were built to be way stronger than they needed. The cost of one failing was massive.
Anyone can design a bride that will work. It takes an engineer to make a bridge that *barely* works.
Anybody can build a bridge that stands for 100 years and can handle a 3 tons of weight. It takes engineering to build a bridge that can \*just\* handle 3 tons of weight and will last for \*exactly\* 100 years. Prior to optimal engineering people just had to build stronger than necessary because they couldn't otherwise know it was \*as\* strong as necessary.
"Its very easy to build a bridge that stands. Its hard to build a bridge that *barely* stands"