Why aren't bridges made from plastic?

Question

why can't they i just need one reason i thought they could be better as they would be less corrosive then steel and stuff?

much appreciated

Answer 1

Not strong enough,plastic bridges only good for toy plastic cars.

Answer 2

because it can snap much faster than wood

Answer 3

As the name suggests it is "Plastic" and for load bearing structures very high Elasticity is necessary.

Steel and Reinforced concrete are highly "Elastic".

That is also a reason of  high Tensile strength of Steel and RCC and low Ten Str of plastic.

Answer 4

For a start it doesn't have the Tensile strength of steel.

Answer 5

Each material has its own advantages and disadvantages which makes its applications.

Bridges, as one of the most complex structures made by humans , has too many parameters and conditions in its design and construction . the most important factors are:

1- structural efficiency (mass of load to mass of bridge)

2- efficient life (operational period)

3- Cost efficiency (operation income to investment)

3- Visual effect (how beautiful they are)

4- unexpected force resistance (forces come from eathquake or explosions)

and ...

You can see that among all this factors, a designer must consider too many parameters other than corrosion resistance.

In general, it is not impossible to use plastics as main structure material of a bridge , but considering re-inforcements , moldings and ... in my opinion, it is not financially acceptable.  

Answer 6

Peanut.......it cannot bear the weight of a lorry even as it is less than. But it could be possible as if the scientist mixed a new percentage of foreign mixture to make iut more harder

Answer 7

There is no engineering reason why a properly designed and specified  plastic bridge could not be built.  The probable disadvantage would be expense. Different plastic materials each have disadvantages including  UV degradation from the sun and susceptibility to fire.