The Italians are getting ready to bridge the Straight of Messina (between Sicily and the mainland)-this will be the longest span of a suspension bridge in the world. What I wouldlike to know-if one abandoned steel, and instead used high-tech materials like carbon-fiber beams/cables, and titanium, how long COULD you make the main span of a suspension bridge? What is the main problem-the weight or the wind loading? I guess on such a long span, the wind could be a real issue.
I need to know this, because my company is preparing a bid on the upcoming “Bering Straights Bridge/Tunnel” Project (to be announced. We want to be sure that our bid is accepted…all you dopers had better start buting up land in an around the Alaskan side-it’s going to be somemighty valuable real estate!
I don’t know the answer, but I wonder what the maximum length is given:
a) Commercialy viable materials (high stength steel mostly)
b) Commercially available materials (kevlar? carbon fiber?)
c) Theoretical but probable materials (nanotube fibers)
d) Way out there materails (scrith, adamantium)
I’m think a bridge made of kevlar or whatever may be possible, but may be so expensive it would be cheaper to buy everyone a boat. (or institute a C-5 based ferry service)
Brian
It seems suspension bridges are falling out of favor and instead they are building those which have many cables direct from the towers to the roadway and the roadway is under compression. (I hate not knowing the right words).
Weight for weight I believe nylon has much greater bearing capacity than steel. OTOH nylon is very elastic so it may not be such a good idea unless you want the bridge to be bouncing about.
Here is a simple little cite explaining the possible spans of many types of bridge construction.
For a suspension bridge, made of conventional steel, the estimate for the maximum span is approximately 4750m. For other materials, if you have the tested tensile strengh, I’m sure you can guesstimate the maximum span using the same math.
Sailor, Cable-Stay bridges is what you were describing, I believe.
Sailor, Cable-Stay bridges is what you were describing, I believe.
I’d question your business model. Exactly how many people want to go from Eastern Siberia to Alaska?
Isn’t the main limit on suspension bridges cost? At some point it becomes cheaper to dig a tunnel.
The proposed Italy-Sicily bridge will have a 3300m (2 mile) main span, with towers 370m (1230 ft) high. The Humber Bridge in England has a 1410m main span and 155m towers. Based on the same proportions, a 10 mile span would need towers over a mile high; I don’t know exactly how it would scale up for a Bering crossing, but you’re talking an incredibly high structure.
That said, I believe a Japan-Korea bridge has been considered: see http://www.iijnet.or.jp/IHCC/outl.html
http://edition.cnn.com/2002/WORLD/europe/06/06/italy.bridge/
http://www.humberbridge.co.uk/techspec.htm
A helluva lots of people want to. Shipping goods between North America and Asia over land would save countless billions of dollars a year.
That said, a bridge over the Bearing Strait is, I think, not quite yet within the realm of possibility. In addition to creating such a huge bridge, there’s the problem of billion-ton chunks of ice sloshing around.
Cable stay bridges are more popular than suspension bridges because they’re easier to build. You need fewer bents (the bit that goes to the ground that’s not at the end) - most cable stay only need one as opposed to the two required for suspension bridges. Plus, suspension bridges require something real solid to anchor into at each bridge end. Ever been on the Golden Gate of the Brooklyn Bridge? At each end the cables are anchored into solid bedrock. You don’t have that available at many sites where you might want to have a bridge.
That said, a lot of cable stay bridges have had excessive deflection problems so they’re being re-evaluated.
On topic, the curve a suspension bridge forms is called a catenary. It’s the shape a materal makes as it sags under it’s own weight. That’s what dictates the length of spans; the weight of the materials rather than the traffic load. The depth of the catenary also dictates the heights of the bents. So, theoretically, with high tech lightweight materials, spans could be much longer.
But, deflections would probably be the limiting factor. With such a long span, you’d undoutably get excessive deflections. Everyone has seen that famous footage of the Tacoma Narrows Bridge shaking itself apart. That was a very long, very narrow (only two lanes!) span. So the deck of your proposed bridge would have to be very stiff yet not brittle and there probably aren’t materials invented that are suitable yet.
Cite, please?
It is my understanding that ocean transport is the cheapest method of moving goods/materials. This is especially true if shipping goods/materials with a low value/weight ratio.
Secondly, neither Siberia nor Alaska are major commerce hubs. One would also have to consider the cost of building roads and/or rail to your bridge.