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Engineering masterpiece

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T

Tinster

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The Germans have constructed a bridge that carries one
river over top of another river- including huge ships
up in the air. Awesome photo:

https://www.funonthenet.in/content/view/223/31/

To those who appreciate engineering projects, here's a puzzle
for you armchair engineers and physicists.
How can sush a slim bridge be designed to withstand the
tremendous weight of the water, ships and barge traffic?


(answer below)I'm a boater so I know the answer.



Answer:
The bridge structure only needs to be designed to withstand
the weight of the water!

Why? A ship always displaces an amount of water that weighs
the same as the ship, Regardless of how heavily a ship may be
loaded. As weight increases, either draft or width must also be
increased. But the loading remains concstant at 62# per
cubic foot of water.

d
 
That's a lotta weight!
 
Anthony-

It really is quite amazing if you think about it.
Your brain tells you a bunch of 140,000 pound canal ships
would bust down the bridge for sure. But in reality,
the boats add no more weight than the water bridge empty of ships and containing only water.

I had to play around with a 1'X1'X1' cube of steel before I finally grasped the concept of H2O displacement and floating.

d.
 
Must be interesting topography in the area to so that you can have the water level at two largely different heights. Other than that, the water must be going up hill somewhere.
 
Bridge looks cool. Wouldn't it have been a lot easier to install a 4-way stoplight and some cross walks though?
 
While it is true that a ship will displace a volume of water equal to it's weight, it is not true that the stress on the bridge is the same with or without the vessel.

The bridge is in essence a contained vessel, so as the ship moves over it, the water it displaces must go somewhere. Some of the water is pushed ahead of the hull resulting in a bow wave raising the water level there, the rest passes the sides, and because the water is restricted to the channels side it will rise then fall with the passing.

To minimize the effect, the canal traffic speed is at best just enough to provide steerage.

Also, did you know that a ship can draw more water then it's weight? True, a ship passing through shallow water will draw more water then a ship on the open sea. The cause of this phenomenon is the Bernoulli effect created by the accelerated movement of the water between the hull and sea floor. The same principle as an airfoil only reversed.
 
<span style="font-weight: bold"> </span> <span style="color: #FF0000"> </span> <span style="font-family: 'Arial Black'"> </span> I'm impressed!
 
I don't believe that the engineers only had to calculate in the weight of the water. According to this Wikipedia description of the bridge, there are LOCKS on both ends of the bridge. That would mean that the water has nowhere to go, and therefore the weight of the ships has to be considered. Of course, if they calculate the weight with the bridge being FULL of water, then the weight of the ships is of no consequence. Either way, as the ships enter the bridge section, the water level will rise due to the ships displacement, and the weight on the bridge will increase.
 
No, Martx5, not so. As the shipe enters the bridge through an open gate, it dispaces water out of the gate.
The gate isn't a one-way valve that allows ships in but not water out!
 
I'm trying to picture a water bridge with gates closed at both ends.

Plop the ship in from up above (!).

How much weight is the bridge holding?

T.
 
If they really wanted to impress me, they would have made it a drawbridge. :devilgrin:
 
70herald said:
Must be interesting topography in the area to so that you can have the water level at two largely different heights. Other than that, the water must be going up hill somewhere.
Click to expand...

Ah according to the Wikipedea article it has three locks now it makes sense.
 
tr6oldtimer, as long as the water in the channel is not confined/contained as in a swimming pool any "rise" in the the water level would be localized and momentary at best, if they somehow managed to drop a large number of boats in the channel simultainiously the result would be a sudden and dramatic water level rise until the effected volume takes its natural course of evacuation/dissipation/escape. :savewave:
 
kennypinkerton said:
If they really wanted to impress me, they would have made it a drawbridge. :devilgrin:
Click to expand...

:lol: Now that would have been impressive!
 
70herald said:
70herald said:
Must be interesting topography in the area to so that you can have the water level at two largely different heights. Other than that, the water must be going up hill somewhere.
Click to expand...

Ah according to the Wikipedea article it has three locks now it makes sense.
Click to expand...

I was going to post that M.C. Escher print that makes the water appear to run uphill, but it's copyrighted.
 
anthony7777 said:
tr6oldtimer, as long as the water in the channel is not confined/contained as in a swimming pool any "rise" in the the water level would be localized and momentary at best, if they somehow managed to drop a large number of boats in the channel simultainiously the result would be a sudden and dramatic water level rise until the effected volume takes its natural course of evacuation/dissipation/escape. :savewave:
Click to expand...

You are correct that the rise in water level is localized, local to the immediate location of the vessel. As the boat moves through the water the water must move around the boat. This can only happen by the water speeding up to go around and under the vessel, or rise up, as in a wake away from the boat. Both things happen. So where the moving boat is at any one point in time there will be more weight on that part of the structure then where the boat is not, all due to the vertical movement of the water displaced.

The engineers had to consider this in their design as well as the fact that as the boat moves over the canal bridge the load changes follow it. To minimize the effect, the speed and size of vessels passing are strictly controlled.

An easy way to visualize what I am talking about is to look at what happens when you put your finger in a stream of water. Where the water first contacts your finger it swells up (bow wake), and along side the swell continues. Eventually every thing down stream settles back to equalibrium, but where your finger was, the water was deeper.
 
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