Ever seen a Water Bridge over a river?

Even after you see it, it is still hard to believe!

Water Bridge in Germany. What a feat! Six years, 500 million euros, 918 meters long.......now this is engineering! This is a channel-bridge over the River Elbe and joins the former East and West Germany, as part of the unification project. It is located in the city of Magdeburg, near Berlin. The photo was taken on the day of inauguration on 9th October, 2005.

The massive undertaking will connect Berlin inland harbour with the ports along the RHINE river. The huge tub to transport ships over the Elbe took 25,000 metric tons of steel and 68,000 cubic meters of concrete to build.

The water bridge will enable the barges to avoid a lengthy and sometime unreliable passage along the Elbe. Shipping can often come to a halt on the stretch if the river's water mark falls to unacceptably low level.

To those who appreciate engineering projects, here's a puzzle for you armchair engineersand physicists. 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.