2015 International Bridge Building Specifications

In order to receive official wood and participate in the contest, a High School student must have placed first or second in a Regional Contest and be reported, by the Regional Coordinator, to Mark Wechter, by e-mail at mwechter@riverdale.k12.or.us. Two bridges from a single region must appear to be of different design. Students may participate in person, by proxy, or by mail entry.

This is a contest for individual high school students, not teams. The object of this contest is to see who can design, construct and test the most efficient bridge within these specifications. Model bridges are intended to be simplified versions of real-world bridges, which are designed to accept a load in any position and permit the load to travel across the entire bridge. In order to simplify the model bridge design process, the number of loading positions has been reduced, and to allow the contest to proceed in a reasonable amount of time, only one loading position is actually tested. These simplifications do not negate the requirement that the bridge must be designed to accept a load at any of the positions. Bridges determined by the judges to not meet this requirement will be disqualified and tested as unofficial bridges.

1. The bridge must be constructed only from the official 3/32 inch square cross-section basswood included in the kit and any commonly available adhesive.
2. The basswood may be notched, cut, sanded or laminated in any manner but must still be identifiable as the original wood.
3. No other materials may be used. The bridge may not be stained, painted or coated in any fashion with any foreign substance.

1. The bridge mass shall be no greater than 30.00 grams.
2. The bridge (see Figure 1) must span a gap (S) of 300. mm, be no longer (L) than 400. mm, have a maximum width (W) of 80. mm, be no taller (H) than 150. mm above the support surfaces.
3. No portion of the bridge may extend below the top of the support surfaces.
4. The two loading planes (P1 and P2) shall be horizontal and shall lie between 0. mm and 10. mm (P1) and 50. mm and 60. mm (P2) above the support surfaces.
5. The bridge must be constructed such that both loading planes are continuous with clearance provided for the loading rod to be attached to the plate and hang down vertically through the bridge below each loading point (see section 3 below) . No optimization for a specific plane or loading position will be permitted.

1. The load will be applied downward, from below, by means of a 40.0 mm square plate (see Figure 2) resting on the loading plane of the bridge. The plate will be no more than 10. mm thick and will have a 9.53 mm (3/8 inch) diameter eyebolt attached from below at its center. Force will be applied to the loading plate by means of an apparatus shown schematically in Figure 3.
2. The two edges of the loading plate will be parallel to the longitudinal axis of the bridge at the time of load application.
3. The load will be applied on the longitudinal axis of the bridge at one of six loading points: center and 50. mm on either side of the center of the 300.  mm span on each of the two loading planes.

1. On the day of the contest, a 6-sided die will be cast to determine which loading location is to be used. It will be the same for all bridges.
2. The bridge will be centered on the support surfaces.
3. The loading plate will be placed on the bridge at the specified loading location and the load will be applied from below, as described in section 3 above.
4. Competition loading will stop at 50. kg. However, loading will continue until bridge failure.
5. Bridge failure is defined as the inability of the bridge to carry additional load, or a load deflection of 25. mm under the loading location, whichever occurs first.
6. The bridge with the highest structural efficiency, E, will be declared the winner. Bridges failing above 50. kg will be considered to have held 50. kg for efficiency calculation.

1. All construction and material requirements will be checked prior to testing. Bridges failing to meet these requirements will be disqualified. If physically possible, disqualified bridges may be tested as exhibition bridges at the discretion of the builder and the contest directors.
2. If, during testing, a condition becomes apparent (i.e., use of ineligible materials, inability to support the loading plate, bridge optimized for a single loading point, etc.) which is a violation of the rules or prevents testing as described above in Section 4, that bridge shall be disqualified.
3. Decisions of the judges are final; these rules may be revised as experience shows the need. Please check our web site, http://bridgecontest.phys.iit.edu after January 15, 2015, to learn whether any changes have been made.

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Last update: December 11, 2014

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For further information, contact: Prof. Carlo Segre - segre@iit.edu, Illinois Institute of Technology

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