Expert: Steve Nelson - 11/3/2009

Question
1.Do you know much about bridge physics.
2.What would you say is the strongest bridge type: Suspension, arch, etc.
3.Would you say Beam bridges are the weakest type or, if not, what is.
4.Is there any equations I should know when modeling bridges.
5.What other advice could you give me on bridge type strength.

Answer
Bridges are just statics and strength of materials, but on a very large scale.  Strength is as much a matter of the design details as the type.  The advantage of suspension bridges is that they use less material, you'd have to build a massively heavy arch to match the strength of a suspension bridge.  Beam bridges tend to be weaker (again, if you make it out of enough material you can make them strong) because they only have vertical supports at various points.  

Are there equations you should know?  I don't have time to teach you a semester of statics and strength of materials, and this isn't the appropriate forum for it.  There are many equations, but basically the sum of torques and the sum of vertical forces are both zero on a bridge.  Using that, you can figure out maximum stresses and compare to material strengths.  If that made sense then use it, if it didn't then you need an entire course on the subject and not a few quick equations.