[Grade Groups do apply] 3:00 PM Sunday, November 20 Centennial Building, Fair Park Balsa Wood Bridge Building Competition (Back to Competitions) (Printable Version)

The Challenge: Build a freestanding bridge from balsa wood that meets the following guidelines:

1. The bridge shall allow a 10-cm cube to slide underneath it at center span without touching.
2. The bridge shall allow a 40-cm wide by 2.0-cm high board to slide underneath without touching
3. The bridge must be “free standing.”
4. The bridge shall provide an approximately level surface (horizontal plane), from end to end, above the 10-cm level across which a small wooden “car” may be pushed from end to end. The roadway must be continuous and complete from one end of the bridge to the other. The roadway must also be continuous and complete from side to side.
5. The roadway holding the “test car” must be longer than 40 cm.
6. The bridge design shall allow the standard test frame to be placed on the roadway surface at the center of the span with the load rods extending beyond the sides of the bridge. All bridges must use the test frame. It is not optional. A picture of the test frame is provided in the printed rulebook.
7. Laminating will be allowed, however, be aware that glue has considerable mass.
8. Any size balsa wood and Elmer’s white glue are the only building materials that can be used.
9. The balsa wood may be notched and interlocked as a mechanical fastener. “Interlocking” and Elmer’s white glue are the only fasteners allowed.
10. The total mass of the bridge shall not exceed 70 grams for Grades 6-8; 50 grams for Grades 9-12.

1. Contestants must arrive at least 30 minutes in advance of the event to have their bridges evaluated by the judges.
2. The bridge will be weighed and tested with the 10-cm cube and the 40-cm flat piece of wood. Any bridge not passing these tests will be disqualified.
3. The bridge will be placed upon a testing stand, which will consist of two flat, level surfaces, which will be level with respect to each other and separated by 35 cm.
4. The standard test “car” shall be moved from one side of the bridge to the other. If it does not pass this test, the bridge will be disqualified.
5. The standard test frame shall be placed on the road surface at the center of the span. The iron rod will be attached and the rest of the testing apparatus will be hung beneath the bridge. If the test frame cannot be placed at center span the bridge will be disqualified.
6. The weights shall be added to the bucket in five-pound increments until the bridge breaks or until the fifty pound limit is reached.
7. The bridge holding fifty pounds plus the weight of the apparatus and having the lowest mass wins the competition. If no bridge holds fifty pounds, the bridge supporting the greatest weight will be declared the winner. In the case of a tie with the greatest weight held, the bridge that has the lowest mass wins.
8. If a bridge breaks, the last weight it held will be recorded as the weight supported by the bridge. The weight that broke the bridge will not be the recorded weight