What do you think?

[orezok]

Someone sent me this. The photo is a channel-bridge over the River Elbe and joins the former East and West Germany.

Question:
Did that bridge have to be designed to withstand the additional weight of ship and barge traffic, or just the weight of the water?

Answer:
It 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.

I disagree, but what do you think?

 

[beenthere]

Designed for the weight of the water.

 

[smstonypoint]

My apologies in advance.


The weight of the water.

Sincerely,
Archimedes

 

[Mace Canute]

I agree that it only needs to be designed to withstand the weight of the water.

It's not like a tub of water where the water has no where to go. In a canal, it flows out both ends of the overpass. I think there might be a very very slight and insignificant increase in weight IF the boat was going fast enough to push a bow wave ahead of it when it entered the overpass but those boats seem to be moving at a sedate pace and not generating a bow wave.

 

[orezok]

I ran this one by my structural engineer, and it his opinion that since the canal has a maximum water height design, usually controlled by some sort of spillway, the structure only needs to be designed to hold the weight of the water in the canal at it's maximum level. Technically the boats do add load when the water level is low because the weight of the displaced water still exists, but it never exceeds the high water level design as the weight of the water displaced by the boats is overflowed.

 

[beenthere]

And the water runs out both ends, so it doesn't "raise" or spill over the sides. Only raises slightly as Mace Canute mentioned.
So the answer is still "for the weight of the water".