2020 International Bridge Building Contest Rules
These rules have been developed by the International Bridge Building
Committee for the Forty-Third International Bridge Building
to be held on Saturday, May 9 in Chicago, Illinois, USA.
If you have a question that is not answered by our
FAQ, please direct it to George Krupa at
firstname.lastname@example.org. For questions on
any contest topic EXCEPT the rules, please contact Prof. Carlo
Segre at email@example.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: 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 80. mm above the support surface, and no wider
(W) than 80. mm at the loading surface. The bridge
structure may project a maximum of (B) of 20. mm below
the support surfaces (see Figure 1).
The bridge must be constructed to provide a horizontal support for the
load at each of the three possible loading locations (see 3c).
Any portion of the structure above the loading plane must provide
clearance for the loading plate and for the eyebolt which extends
below the plate (see 3b).
The bridge must be constructed to allow a 48 mm diameter,
300. 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 0. and 20. mm above the
support surface. This pipe must touch all three loading
On the day of the competition, the judges will decide which one of the
three loading locations will be used; it will be the same for all
bridges. 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 two 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 three
(3) possible loading locations on the longitudinal axis of the bridge:
The center, 40. mm to the right of center and 60. mm to the
left of center. The 3 loading locations must lie in the same
horizontal loading plane (P) between 0. and 20. mm above the
support surface (see Figure 1).
On the day of the competition, the bridge will be centered on the
The loading plate will be lowered from above on the bridge at the
selected loading location with two edges of the plate parallel to
the longitudinal axis of the bridge.
The load will be applied from below, as described in section 3 above. Competition loading will stop at
50. kg. However, loading will continue until bridge failure
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.
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. 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
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.
Decisions of the judges are final; these rules may be revised as
experience shows the need. Please check our web site,
after January 30, 2020, to learn whether any changes have been made.
Last update: September 2, 2019
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For further information, contact: Prof. Carlo Segre -
Illinois Institute of Technology
© International Bridge Building Committee, 2017