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by making good and careful caculations and looking to see what materials you will exactly need. Also they will be making test models.

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Like what most people say. They use the design process, until the bridge finally can hold and do it's function.

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by making careful  calculations and looking to see which materials are sturdy enough ...

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by making

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i think that they would run test models of bridges with different materials and see witch bridge is the sturdiest and witch bridge would be the best suite for the city. I also think they would learn these kinda things in school and it wouldn't be to difficult for them to figure out what to do and how to do it

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Alexia , I believe bridge designers know what materials to use because they test different things multiple times to make sure its steady and will work and cooperate on the real model. And if not proven to work they will the come up with another way to solve there structure.  

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Alexia , I believe bridge designers know what materials to use because they test different things multiple times to make sure its steady and will work and cooperate on the real model. And if not proven to work they will the come up with another way to solve there structure.  

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Trial and error

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They first use a blueprint to calculate their measurements and list where it goes. once that is done they start to build a design with sturdy materials and study the location as if it was windy they would make it that it is not affected by wind

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I suppose Bridge designers know how heavy the bridge will be and then that will depend on what material they would use becasue the stronger theh base the more stable the whole bridge will be but they would also have to find a strong and cheap material since they are going to be using massive amounts of that material

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by making careful calculations and seeing which materials are sturdy and how previous bridges functions/functioned

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I believe that they make model bridges/ buildings before they build the real thing. They could also make measurements and solve equations to find the strength/ balance.

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They might make smaller models with the same kind of materials to determine what will hold the bridge up. This way, if the bridge designs don't work and the materials fail to support the structure, it won't matter because it's not the real bridge.

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i believe that the builder will mainly have to make it sturdy so that means that they are going to put alot of triangles to where that theye are to where they stand and also triangles are the strongest matirials to use.

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I think that they probably studied things like that in school, and that they would test things like that before they built the bridge.

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I suppose that designers know which materials and designs will give a bridge the strength it needs by the research of how other bridges have been built and what the materials have been used to help the bridges be sturdy.
They also would know by the different shapes,angles, and the measurements of the design.

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Question 1
How do you suppose bridge designers know which materials and designs will give a bridge the strength it needs?