Question about toothpick bridge?

Question

Im building a truss bridge out of toothpick for science class. It has to be able to hold a lot of weight. Is it better if the bridge is as light as possible or as heavy as possible?

Answer 1

Too light and the bridge won't have enough structure if your only using toothpicks and glue therefore it will not bear a lot of weight. On the other hand if the bridge is too heavy it won't be able to carry it's own weight a any dead load would break the bridge. My advice would be not to add any unnecessary trusses so you can keep the weight down but not too light and still have a lot of support.

Answer 2

Well, based on your words "...able to hold a lot of weight...", I would say that is has to be as strong as possible.



But how, you say...



Look how triangles are used. Triangles can not be bent or "squashed" like squares can.

http://en.wikipedia.org/wiki/File:Parts_of_a_truss_bridge.svg



Here's a few things to help.



1 - Round toothpicks are stronger than the square/flat ones.



2 - Put two or three toothpicks together for a stronger stringer. Three round toothpicks glued side-by-side in a triangle like this pretty strong:

O

O O



However, do not let any joints be at the same place. Have the toothpicks overlap, then cut them to end at the same place. You can make a long stringer that way.



When I helped my son do his, we had to use only one box and it held something like 20 or 30 pounds. (long ago)



Good luck...

Answer 3

You probably have a toothpick limit.

Build stiff trusses for the compressive members and make triangles. Design for the test load.

Overlap for strength.