2006-08-12 17:47:56 · 5 answers · asked by chacha4u2 1 in Cars & Transportation ➔ Safety
The columns are driven several feet below the sea floor or lake bed into bedrock when the bridge is constructed.
2006-08-12 18:18:54 · answer #1 · answered by crazytrain_23_78 4 · 0⤊ 0⤋
Bridges aren't standing on the water unless they're pontoon bridges or wooden bridges for pedestrians.
Pontoon bridges are basically floating metal, wooden or plastic boxes that are laid alongside each other then attached together - the military use them as a quick method to construct a bridge across a river.
Traditional bridge building comes in many forms such as arches, cantilevers, suspension, slabs, trestles etc. All but the most basic have piers or legs which either support the bridge from underneath or are used to hang cables so as to suspend the bridge from above.
The piers are often in the water below the bridge. In some cases they can be constructed in the water itself, there are types of concrete that set underwater so it's possible to build things out of stone, brick etc underwater. This would be OK for a small bridge but larger bridges are made out of concrete.
In these instances a caisson is used, this is a watertight, hollow structure a bit like a tin can without any ends on. The caisson is either constructed on the river bed or is lowered onto the river bed by crane. The base of the caisson is secured to bedrock or is set into the mud of the river bed. Once in place the water is pumped out and the bridge piers can be constructed in the same way as they would be on dry land - by pouring concrete and fixing pre-formed concrete blocks into place.
Once the pier is constructed the caisson is removed and the river flows as normal (apart from the fact it now has a concrete pier in it).
This is a simplified answer, there are different types of caisson used in different situations and in some cases the caisson itself forms part of the bridge structure. More info about caissons here... http://en.wikipedia.org/wiki/Caisson_(engineering) and http://www.encyclopedia.com/html/c1/caisson.asp
2006-08-13 01:42:04 · answer #2 · answered by Trevor 7 · 1⤊ 0⤋
I'm not sure I understand your question, but they are supported by steel (mabye titanium) beams that go hundreds of miles deep into the ocean floor.
2006-08-13 00:53:54 · answer #3 · answered by r0b0tj0n3z 2 · 0⤊ 1⤋
how are they, they are fine ,concrete to the bed rock steel reinforced caisson columns,
2006-08-13 01:57:59 · answer #4 · answered by Mechanical 6 · 0⤊ 0⤋
by pols
2006-08-13 00:58:57 · answer #5 · answered by Orangie 3 · 0⤊ 1⤋