2023 International Bridge Building Contest Rules

These rules have been developed by the International Bridge Building Committee for the Forty-Fifth International Bridge Building Contest to be held on Saturday, April 29 in Chicago, Illinois, USA. If you have a question about the contest that is not answered by our FAQ, please direct it to Jamal Grainawi at Jamal.grainawi@wsp.com.

In order to receive official wood and participate in this contest, a High School student must have placed first or second in a Regional Contest and be reported, by the Regional Coordinator, to Prof. Carlo Segre by e-mail: segre@iit.edu. 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 the specifications. Model bridges are intended to be simplified versions of real-world bridges, which are designed to permit a load to travel across the entire bridge. In order to simplify the model bridge design process, the number of loading positions is 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. Materials
  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 official basswood may be notched, cut, sanded or laminated in any manner but must still be identifiable as the original official basswood.
  3. No other materials may be used. The bridge may not be stained, painted or coated in any fashion with any foreign substance.
2. Construction
  1. The bridge mass shall be no greater than 25.00 grams.
  2. The bridge (see Figure 1) must span a gap (S) of 300. mm, be no longer (L) than 400. mm, be no taller (H) than 180. mm above the support surface, and no wider (W) than 70. mm. It must have a horizontal loading plane that is a maximum height (P) of 80. mm above the support surfaces. The bridge structure may not project below the support surfaces.
  3. The bridge must be constructed to provide a horizontal support surface for the loading plate and rod at each of the three possible loading positions. These three positions, at the at the mid-span of the bridge and 60. mm to either side of the center, will be clearly and consecutively labeled "1, 2, 3" from either end of the bridge by the participant before check-in (see 3b). The bridge structure must allow the loading rod (see 3a) to be mounted from below.
  4. The bridge must have a minimum clearance (C1) of 60. mm in height above the support surfaces. This clearance extends a minimum length (C2) of 160. mm and be centered on the mid-span of the bridge. No part of the bridge structure may be built into this clearance area, and a 60. mm high by 160. mm wide block must pass cleanly under the bridge.
3. Loading
  1. The load will be applied downward, from below, by means of a 40. mm square plate (see Figure 2). The plate will be (t) of at least 6 mm but less than 13 mm and will have a 9.53 mm (3/8 inch) diameter threaded rod eyebolt attached from below at its center with a standard hex nut. The plate will be horizontal with two sides parallel to the longitudinal axis of the bridge.
  2. The three loading positions will be located on the horizontal loading plane (P). The center position (numbered "2") will be located at the center point of the bridge. The other two loading positions (numbered "1" and "3") will be located 60. mm toward either end of the bridge from the center.
  3. On the day of the competition, the judges will randomly decide which of the three numbered loading positions will be used; it will be the same for all bridges.
4. Testing
  1. On the day of the competition, contestants will center their bridge on the support surfaces with the threaded rod projecting from below at the designated loading position.
  2. The loading plate will be placed from above on the threaded rod with two sides parallel to the longitudinal axis of the bridge and secured with a hex nut.
  3. The load will be applied from below, with the contestant rotating the Vernier testing machine load wheel until bridge failure is sensed (see 4d). Competition loading will stop at 50. kg.
  4. Bridge failure is defined as the inability of the bridge to carry additional load as sensed by the Vernier testing machine.
  5. 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.

E = Load supported in grams (50,000g maximum) / Mass of bridge in grams

5. Qualification
  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 February 13, 2023, to learn whether any changes have been made.

Last update: January 19, 2023
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For further information, contact: Prof. Carlo Segre - segre@iit.edu, Illinois Institute of Technology
© International Bridge Building Committee, 2021