How are they able to build bridges across water?
I have always been intrigued with engineering. How are they able to build bridges across canyons, mountains and water?
Ex: Golden Gate Bridge
Looking at Point A to Point B it is really massive and how is the structure able to stay?
Would love to see a hub about this
Bridges are a piece of engineering which take months and sometimes years to build with many people being involved in the building process. Here's an overview:
Determine what type of bridge you need for the situation. The common types are arch, suspension, truss, cable and beam types. If you're crossing a short span, you probably only need to build a beam or a small truss bridge. If you're crossing a deep ravine, an arch bridge might be the best choice. A bridge to span an ocean bay requires a very expensive suspension bridge.
Identify an ideal place to build the bridge. A lot of legwork goes into determining the ideal site to build anything, and when you're talking about something as expensive as a bridge, engineers are even more careful. The engineering team will send out surveyors, people who use electronic measuring devices to make a map of the general area. From this map, they will make calculations and determine the length and placement of the bridge.
Design the bridge. The engineer will take into account the potential traffic load of the bridge and use steel design manuals, computer aided design programs to aid the bridge design process.
Once the design has been finalized and approved, the building can begin. This will involve excavation or filling the banks on either side, stabilizing the ground where the supports will be placed and, depending on what type of bridge is going to be built, pouring concrete.
Some bridges are built on site and some are put together in pieces small enough to take to the location and then assembled. Using the anchors points placed in the concrete, the steel is put together with huge cranes with nuts and bolts and welding.
Once the main structure is in place the surface can be put in place, this is normally built on steel cross members attached to the main supports. Concrete is then poured section by section until the surface is built. It is then a matter of either attaching rails if its a train bridge or adding a further surface like tarmac to make the final service to make a road.
You then get some important person to come open the bridge, ha-ha
There are probably as many different ways to build a bridge as there are bridges, and the design of the bridge and building technique often are designed based on the specifics of the situation.
Sometimes a river may be dammed temporarily for the construction. Other times construction may be done from a ship or barge. Piers may be sunk into the riverbed and the support structure and decking pre-built on shore and lifted into place using cranes mounted to the piers. Suspension bridges may be built by running cable over piers and hanging work in progress from the cables. The structure may actually be built as a cantilevered beam until it reaches the other side, often with both sides being built concurrently and meeting in the middle.
There are many factors to consider in addition to the current of the water. Is there seasonal variation in current? Freezing? Variations in water depth? Is there a lot of silt that can cause erosion? What is the composition and stability of the ground, whether underwater or not, where the piers mount? Expansion due to temperature change must be accounted for. The bridge must be able to withstand winds. It needs to provide drainage for rain water
Appreciate both Brian's and future's answers. Interesting question. However, I'd got to say (a little 'tongue-in-cheek') that if all else fails and you don't have access to either months or engineers ($) ??, there's always the old, old swing bridge. Of course, then you've got to go back, not forward, to find the necessary materials!
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