Is it possible to build bridges and other structures out of composite materials. (like plastic?
Yes. It just isn’t done. Carbon Fiber is stronger than steel and, if memory serves, at least as strong as titanium. It is also many times lighter and swells less in heat. If cars were made out of carbon fiber, they would be much safer because the carbon fiber frame would be molded in one piece rather than multiple pieces connected so there would be no weak points. Why bridges and other things that require immense amounts of strength don’t use it, I don’t know.
Composites such as Carbon fiber are generally only beneficial in high performance applications such as aerospace and racing, where we want the parts to have a high specific strength. In general, if weight isn’t such an issue, there’s not much point in using composites. This is because while money/weight savings can be realised over more conventional materials, composites have a number of issues and require very careful attention during their design. E.g. Steel is strong in all directions, its cheap, plentiful, versatile, easy to join, large parts can be made easily, it’s resistant to fairly high temperatures and moisture, not to mention having good impact resistance. With bridges weight isn’t such an issue as we can just use efficient designs and structures. On the issue of cars, making the shells out of carbon fibre in one piece would be very difficult and no doubt expensive, there would be issues joining the parts together, and they would have poor performance in a crash – composites
