2018 International Bridge Building Contest Rules
These rules have been developed by the International Bridge Building
Committee for the Forty-First International Bridge Building
to be held on Saturday, April 21 in Chicago, Illinois, USA.
If you have a question that is not answered by our
FAQ, please direct it to George Krupa at
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: firstname.lastname@example.org. Students may
participate in person, by proxy or by mail entry.
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
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.
The official basswood may be notched, cut, sanded or laminated in any
manner but must still be identifiable as the original official
No other materials may be used. The bridge may not be stained,
painted or coated in any fashion with any foreign substance.
The bridge mass shall be no greater than 25.00 grams.
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 150. mm above the support surfaces, and have a width
(W) no greater than 80. mm.
The bridge must be constructed to provide a horizontal support for the
loading plate and at each of the two possible loading positions (see
3c). The bridge structure must allow the loading rod (see
3c) to be mounted from below.
The bridge must be constructed to allow a 48 mm diameter,
400. mm long pipe (1.5 inch schedule 40 PVC pipe) to be passed
horizontally across the bridge with the pipe's lower surface on the
loading plane (P) between 80. and 100. mm above the base
of the bridge. This pipe must touch both loading locations
simultaneously (see 3c).
The bridge structure may not project below the support surfaces (see
Competition loading will stop at 50. kg, loading will continue
until bridge failure (see 4d).
The load will be applied by means of a 40. mm square plate (see
Figure 2) with a thickness (t) of at least 6 mm but less
than 13 mm. A 9.53 mm (3/8 inch) diameter eyebolt is
attached from below to the center of the plate. The plate will be
horizontal and will be mounted with its edges parallel to the
longitudinal axis of the bridge. Masses will be supported on a
vertical loading rod suspended from the eyebolt. The minimum initial
load will be 2. kg.
The load will be applied with the center of the plate at one of two (2)
possible locations on the longitudinal axis of the bridge: 30. mm
to the left and 60. mm to the right of the center of the bridge
span (see Figure 1). The two loading locations must lie in the same
horizontal plane. This loading plane must lie a distance (P)
between 80. mm and 100. mm above the base of the
On the day of the competition, the judges will decide which one of the
two loading locations will be used; ir will be the same for all
On the day of the contest, contestants will center their bridge on the
loading surfaces. They will have previously located the loading plate
and 3/8 inch eye bolt to the selected loading position with the
edges of the plate parallel to the longitudinal axis of the bridge.
The load will be applied from below, as described in section
Competition loading will stop at 50. kg. However,
loading will continue until bridge failure (see 4d).
Bridge failure is defined as the inability of the bridge to carry
additional load, or a load deflection of 25.4 mm under the loading
location, whichever occurs first.
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
All construction and material requirements will be checked prior to
testing and may be checked after testing. Bridges failing to meet
these requirements will be disqualified. Bridges disqualified prior
to the start of the contest may be tested as exhibition bridges at the
discretion of the builder and the contest directors.
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. If the
disqualified bridge can accommodate loading, it may still be tested as
an exhibition bridge as stated above.
Decisions of the judges are final; these rules may be revised as
experience shows the need. (Please check our web site,
after February 5, 2018, to learn whether any changes have been made.)
Last update: November 15, 2017
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For further information, contact: Prof. Carlo Segre -
Illinois Institute of Technology
© International Bridge Building Committee, 2017