S Curved Bridges

[IsaacStructural]

Just a general question. I haven't designed bridges before, so hopefully someone with experience in that regard can give their thoughts. I'm wondering why this bridge and others are curved in an S shape like the image linked below.

http://en.wikipedia.org/wiki/File:Donghai_Bridge.jpg

I have my own ideas of why this may be, but I'm interested to hear from others.

Thanks!

M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[rb1957]

underlying geology ?

 

[burningDiesel]

I would guess underlying geology and avoiding that the ships need to make a turn in their path under the bridge. Probably the underlying geology is more important in the way that the ships need sufficient dept.

 

[IsaacStructural]

I agree underlying geology is probably part, but I'm also thinking there may be a stability advantage vs. having the bridge run in one continuous, straight path.

M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[fcu45]

Or they couldn't put the start point to meet the destination point in one line.

In this case from Wikipedia info and plan view:

http://en.wikipedia.org/wiki/File:Donghai_Bridge_Map.png

And Google earth map it shows low water level acroos most of the bridge

http://wikimapia.org/#lat=30.7021144&lon=121.9525754&z=12&l=0&m=b&search=Donghai Bridge

So looks like they were following the natural shallow water contour + picking the best points for the ferries passage.

 

[dhengr]

The design engineer’s favorite letter always was “S.” And, he always claimed to like a big “S.” And, his fee was based on the number of linear meters of bridge length. So, once he had a design for a couple basic consecutive spans, he just took the total cost of his children’s college education to determine the number of span needed for the bridge. And finally, with the advent of CAD, he had sold his tee-square and all of his triangles, wouldn’t need them anymore. Nobody would buy his french curve, so he still had that in the back of his desk drawer.

 

[MiketheEngineer]

"S" curves keep you awakes - hopefully. They put curves in I-70 running across Kansas to just keep people awake!!

 

[macmet]

I heard before that it was to keep people awake, but I was never sure if that was indeed the case.

 

[IsaacStructural]

dhengr, excellent points all around!

The 'keeps you awake claim' seems a little odd to me just because I've certainly driven on very long stretches of very, very straight highway that were much longer than this bridge.

M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[concretemasonry]

On the long bridge on highway(13?) from Virginia Beach to the eastern shore, the tunnels and stopovers/rest areas are real safety item on a long bridge going over the water with no terrain or scenery. The stops provide a break and an opportunity to see some ships, carriers and an concessional sub plowing through the water under the water in the channel.

In the end, a bridge may be dictated by the geological and marine conditions and sometimes by aesthetic reasons (color, shape, preservation, clearance) to get it permitted especially with depth and clearances are the major criteria. Many major European bridges have extreme designs to adjust to the conditions that exist.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[JStephen]

From a quick google search: "To provide a safer driving route in the typhoons and high waves known to hit the region, Donghai Bridge is designed in an S-shape."

 

[macmet]

From a google search of another curved bridge,

"The Confederation Bridge was opened only 10 years ago and is a masterpiece of technology. With a length of 13km (!!!) it is among the longest bridges of the world. Interestingly, it is not completely straight, which according to the official website was done to ensure that drivers do not lose concentration when driving for more than 10 minutes on the narrow lane."

It would be interesting to hear if that is actually the case or just a story for the public

 

[JStephen]

Just looking at it, I would have assumed that they rotated the bridges to be perpendicular to the normal ship traffic, adjusted it for minimum cost, etc.

 

[chicopee]

Another thought is that it put more people to work.

 

[SAIL3]

I suspect it may have to do with wind vortex shedding and the continously varying stiffeness in the direction resisting the set-up of harmonic vibration......