2019 International Bridge Building Specifications
These rules have been developed by the International Bridge Building
Committee for the Forty-Second International Bridge Building Challenge
to be held on April 06, 2019 in Baltimore, Maryland, USA. If you have
a question about these specifications that is not answered by our
please direct it to Chief Judge Ruth Akers, at
In order to receive official wood and participate in the challenge, a
High School student must have placed first or second in a Regional Contest
ant be reported, by the Regional Coordinator, to Mr. Michael Dodd-O, by
e-mail at firstname.lastname@example.org. 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
challenge for individual high school students, not teams.
The object of this challenge 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 challenge 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 shall rest on two support surfaces separated in elevation
(E) by 10. mm and horizontally by a gap (S) of
300. mm (see Figure 1).
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 upper support surface, and no wider
(W) than 80. mm at the loading surface.
The bridge must be constructed to provide a horizontal support for the
load (see 3b) at each of the three possible loading locations.
Any portion of the structure above the loading plane must allow
clearance for the plate and the loading rod above as well as for the
rod projecting below the loading plate (see Figure 2).
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 30. and 50. mm above the
upper support surface. This pipe must touch all three loading
No part of the bridge may extend below the upper support surface
within the span (see Figure 1).
Competition loading will stop at 50. kg, loading will continue
until bridge failure (see 4d)
The load will be applied from above by means of a 40.0 mm square
plate with a thickness (t) of at least 6 mm but less than
13 mm. A 9.53 mm (3/8 inch) diameter rod is attached from above to
the center of the plate and projects below the surface of the loading
plate (see Figure 2). During loading, the edges of the plate will be
parallel to the longitudinal axis of the bridge.
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 and 30. mm to either side of the center of the bridge
span (see Figure 1).
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
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 the edges of the plate parallel to
the longitudinal axis of the bridge.
The load will be applied from above, as described in section 3. 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. mm under the
loading location, whichever occurs first. If a bridge has leg(s)
which fail, the bridge will have failed regardless of deflection.
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 7, 2019, to learn whether any changes have been made.
Last update: September 21, 2018
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For further information, contact: Prof. Carlo Segre -
Illinois Institute of Technology
© International Bridge Building Committee, 2017