A Unique Bridge

[MountainDon]

Thanks to John (redoverfarm), again. John seems to have a "thing" about bridges; and I'm glad. This is cool.



He sent me some notes along with the photo...

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.

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

Viewing this I thought of Escher.....     ...this is hard to fathom...

[desdawg]

I wonder how many gallons it holds at 8# per gallon? Looks like tricky business. Are you going to build your own bridge John?

[Sassy]

That is quite remarkable!

[MountainDon]

I was intrigued by this, so did a little research. There is a lock at both ends.

It connects two canals to each other.

http://www.dw-world.de/dw/article/0,,990878,00.html

http://cncfnbamilwaukee.newsvine.com/_news/2007/12/20/1177307-awesome-magdeburg-water-bridge-in-germany

[peternap]

Don't  Cross  The  Streams

[John_C]

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]

Viewing this I thought of Escher.....     ...this is hard to fathom...

Ummm, not exactly.  That would be the case if the canal was filled to the top and the water displaced by the ships flowed over the banks.  That does not appear to be the case here.  The premise is easily proven with a pail of water, some largish pieces of wood and a suitable scale.  If the pail is filled 3/4 full and you float a piece of wood in it the weight will increase until the water flows over the rim & out of the pail.

One interesting engineering quirk would be the absence of point loadings.  Wherever the ships were the water would evenly distribute the weight,  unlike our manufactured home on a bridge that was posted a day or so ago.

[MountainDon]

Since there is a lock at both ends the water level is under control of the canal operators. Wouldn't the premise of requiring to build only for the water weight hold true IF we assume that once the ship is in the elevated section of the waterway the lock/canal operators maintain the water level at the predetermined "neutral" point?? 

[glenn kangiser]

...or if it was designed to carry water to the top edge but never reached that point.

[MountainDon]

I believe the operators make adjustments to maintain the water level to some predetermined "safe passage" point. That way the level in each lock would be brought up to that level whenever the need to open a gate to allow a ship passage. The level in the lock must be matched closely to the level in the transport section before the gates can be opened. If the water in the lock is too low the pressure on the high side will keep the gates in the closed position. And vice versa, the gates could be forced open.

[MountainDon]

Ships are not plopped into the canal waterway from the air. From one low end the ship enters the lock. The water level would be raised (water pumped into the lock from the lower level) to the level of the water in the water bridge canal. The gates open. The ship passes into the water bridge canal. As the ship moves from lock to canal water flows from canal to lock and the water level stays the same in both canal and lock. However the volume of water in the canal is less as it was displaced by the ship. The ship moves on. A ship going in the other direction moves into that lock and the gates close. The water level in the lock is lowered. Etc.

[John_C]

In that case the design load would be for the highest anticipated level of the highest canal. 

You've made me recollect the place I've locked through years ago on sailboats.  Welland canal, Dismal Swamp Canal, Cape Kennedy and a few others.  Lots of different parameters. 

Looking at this picture again make me wonder if the level of the canals at each might be the same as that of the waterway under this bridge and the locks at each end are there to raise the vessels in order to clear the center canal.  An aquatic overpass so to speak.

Good thing they didn't have the engineers and construction talent from THE BIG DIG on this project.

[MountainDon]

Most canals ans locks go from a higher level to a lower level. The smaller ones I remember from back home use gravity flow with the water always flowing from the high end to the lower. This canal bridge is simply an elevated waterway. I believe you're right in thinking the water level is the same a either end, or at least within a few feet of the same elevation. It traverses a distance between two non directly connected canals. The canal bridge is similar to a pedestrian bridge across a busy roadway.

Ya' gotta wonder how much of the expenditure went to the symbolic joining of east to west Germany. 

Cool engineering though.

[John_C]

You got me reminiscing the canals & locks I've negotiated in my sailboat days. Lots of these were built for different reasons.  The Dismal Swap Canal in NC & Virginia is the oldest operating canal & lock in the U.S.  It was proposed by George Washington as a means to drain the Dismal Swamp and create a more efficient alternative to the overland traffic of the day.  Dug by hand, mostly with slave labor, it has a colorful history.

"At about the time the canal opened, the Dismal Swamp Hotel was built astride the state line on the west bank. It was a popular spot for lover's trysts as well as duels; the winner was rarely arrested as the dead man, as well as the crime, were in another state. As the state line split the main salon, the hotel was quite popular with gamblers who would simply move the game to the opposite side of the room with the arrival of the sheriff from the other jurisdiction."  wikipedia

My recollection is the almost black water,  due to the abundance of decaying organic matter.  Rain over the swamp sometimes raised the water level enough that the locks at South Mills had difficulty dealing with the ht. difference.  This is a small waterway by todays standards and locking through in a small boat presented few difficulties. If you weren't in a hurry you could, with favorable winds, sail some stretches. Traveling silently you would encounter deer, bear & turkeys in or adjacent to the canal. It was one of many place I would not have enjoyed before the invention of mosquito repellent.  As with some other canal I was familiar with, contemporary environmental standard would preclude their construction today.