The Wooden Bridge

Our second project is to constuct a bridge. Here are the requirements and restrictions:

1. The bridge is to be built from hardwood dowels (1/4” in diameter) and carpenters wood glue only.

2. The bridge shall be freestanding and must span two level surfaces that are one meter apart.

3. The support for the bridge shall be from the top of the level surfaces. The edges of the level surfaces can’t be used in any way for support.

4. The bridge must include a deck to provide a suitable road surface at least 5cm
wide across the full span of the bridge. Three conditions must be met:
a) the surface of the deck must be made out of cardboard, a block of wood (5 cm x 5cm x 10 cm) representing a car must be able to move along
the length of the deck unobstructed from end to end, the deck of the bridge must not be more than 5 cm above or below the ends of the bridge at any point along its length.

5. You must incorporate a "loading platform" consisting of a U-bolt secured to a piece of plywood (0.7 cm x 5 cm x 10 cm) in your design. This platform is to be attached at the center of the bridge such that the bottom of the U-bolt is no more than 5 cm from the top of the bridge decking. All loads will be suspended from this U-bolt, and there must be a clear space directly below it to allow loads to be hung. Otherwise, we won’t be able to perform a load test and your design will be disqualified. Loads will be attached using an S-hook, and a 1 cm diameter metal rod extension. If during loading, the bridge twists in such a way as to cause the bridge to touch the rod at any point other than the U-bolt, thus lending additional support, the bridge will be disqualified.

6. The maximum vertical depth of the bridge, from the highest point in its structure to the lowest cannot exceed 50 cm.

7. The maximum weight of the bridge including the loading platform must not exceed 0.75 kilograms.

8. The load test will start with 20 pounds. Therefore, one of the design criteria is the minimum weight the bridge must withstand.

9. The material cost of the bridge can’t exceed $8. (48”´1/4” hardwood dowels are about $.50 at Hardware Stores)

At first we looked at many designs for bridges and decided which one would be the easiest to build, would be the most durable under pressure, and still be very cheap to build. The most tedious part of the project was cutting the pieces to fit perfectly into the angles. After that we glued everything together and waited.





We chose a design but modified it a bit to fit into the height restrictions. Here is our final product.