Why build a wooden bridge?
1) To take math and science out of the textbook and into a project involving design, planning, and construction. It fits into our new curriculum for British Columbia – Applied Skills and Technology.
2) Because the process is instructive and fun, and it exemplifies the difficulties of putting theory into practice.
Math and science?
Now I’m worried. What kind of math and science?
In principle, you can build a bridge without math and science. But if you want to build one that can carry a maximum load, then you need to understand the material properties of spaghetti, the theory of beams, and the physics of cancelling forces (statics).
Design and construction ideas:
1) Triangles are a construction engineer’s best friend, i.e. there are no bending moments in triangular elements.
2) Taller is better
3) Don’t forget about the 3rd dimension. A good design in the x-y plane, may be a terrible one in the z-direction.
4) Recall: tension members do not need to be fabricated as trusses. Their strength depends only on cross- sectional area.
5) Plan the total bridge design. Estimate the weight of each of the components, so that you will not exceed the weight limit.
6) Make a full-size pattern of your bridge. Build the bridge on this pattern. This will ensure that all components will assemble properly.
7) If a number of strands of spaghetti are to be used together as a
single member, do not glue their entire lengths. “Spot” glue them at intervals of about 1”. This will provide adequate strength without adding excessive weight.
8) For economy of time, joints should be “overlaid” not “butted”. Butt joints require careful sizing. Overlaid joints do not. Excess material may be cut off after assembly.