This is a Design and Technology project which I complete with my new class every year. Pupils are challenged with investigating the different types of bridge and some of their features. In groups they design and make their own bridge. I've done it with Year 4 (3rd Grade) pupils using art straws or rolled up paper tubes and they loved it. With older children we use wood or any other products they might end up suggesting. This can be great fun and I always find the pupils absolutely love building and testing their bridges.
Hope you find it useful.