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What is a Cable-Stayed Bridge?
A cable-stayed bridge is a bridge design which uses large steel cables suspended from high towers or pylons to support the bridge decking. The cable-stayed bridge design is typically used on bridges that span great distances. Some of the longest bridges in the world are built using the cable-stayed bridge design.
One of the greatest difficulties in building a long bridge is the wind. The constant battle between the bridge and the wind can cause the bridge to sway drastically. In an effort to eliminate the effects of the wind on the cable-stayed bridge design, the bridge's roadway is made up of open grid iron panels. These open panels act much like screen doors in the bridge's decking and allow wind to pass right through without placing any interference on the bridge. The result is a cable-stayed bridge that does not sway in the wind.
The use of open grid panels works so well that most cable-stayed bridge design are able to remain open and safe for use in all but the most severe windy situations. In the event of an unusually strong wind or storm, the bridges will typically close to traffic. Upon the reduction of the wind speed or the dissolution of the storm, the bridge will re-open. This action has been adopted due to vehicles being blown off of the huge bridge's roadway.
The large cables traveling the length of a cable-stayed bridge are not single cables. These large cables are actually composed of thousands of small cables wrapped around each other to form a single large cable. The multi-weaved cable is actually many times stronger than a single strand cable of the same dimensions. The large cables hold up all of the smaller cables which are attached to the decking of the bridge. The cables all work together in order to create a strong and safe bridge which can support heavy traffic volumes for a very long time.
Most of the largest cable-stayed bridges in the world are toll bridges. This is due in part to the tremendous cost in building the large structures as well as the convenience in having a bridge which connects two points of land otherwise unconnected by any other means. Prior to the completion of many cable-stayed bridge projects, the only way for a person to travel across the path of the bridge was by boat. This made the route nearly unusable for every day travel.
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Discussion Comments
@clintflint - I just want to point out that cable-stayed bridges and suspension bridges are not the same thing, even though they look a little bit similar. I don't understand all the physics involved, but apparently they work in completely different ways.
A suspension bridge is one like the Golden Gate Bridge, where you have a cable running horizontally and vertical cables attached to it.
A cable stayed bridge is one like the Skybridge in Canada, which have rays of cables coming out from a tower and attaching along the length of the bridge.
Galloping Gertie was a suspension bridge, although the problems with it were applicable to cable stayed bridge structures as well.
@MrsPramm - I have walked across several of the famous cable stayed bridges in my life and I was always kind of amazed by how little they did move, even when the wind was blowing quite hard and they were loaded with traffic.
I think, possibly, they might have swayed a little bit, but that could have been my imagination! Honestly, the cables don't really seem to act like wires, they seem far too solid.
There are some amazing videos online of one of the first long suspension bridges to be built. Unfortunately, they didn't realize that the wind could create that kind of problem (I believe that it's called resonance) where it builds up the swaying motion of the bridge over time until the bridge is far too dangerous to use.
The one in the videos was nicknamed "Galloping Gerta" and it's really amazing how much it moves, even while cars were still trying to cross over it.
It did break in the end, but at least they managed to learn a lesson and all the cable stayed bridges since then have owed something to that first design.
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