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Instructions for Building Your Bridge

Getting Started (MSWord document)

A. Bridge Contest Summary:
Teams will construct balsa wood bridges to be load tested on the day of the event.

Four awards will be given (1st, 2nd, 3rd, and 4th Place) in each category to the team with the highest score determined from the Bridge Efficiency. Bridge Efficiency is a ratio of how much load the bridge can handle to the mass of the bridge.

Efficiency of your bridge will be determined using the following formula:

E = Efficiency = (LOAD IN kg) (1000 grams) =


The load will be measured in kilograms, while the mass of the bridge will be measured in grams.

Example: If your bridge weighed 22 grams and supported 42 kilograms of weight for 30 seconds during the test, you would calculate efficiency as follows:

E = Efficiency = (LOAD IN kg) (1000 grams) = (42)(1000) = 1909

(MASS OF BRIDGE IN grams) (22)  

One additional award will be given in each category for Bridge Aesthetics.

B. Dimensional Parameters for Bridges:
* Test Block (50mm x 50mm) must be able to pass through bridge.
* Judges will provide blocks to use on day of event.
* Bridges must have a deck structure to support the test platform (provided).
* Bridges shall be loaded only on the bottom of the truss (deck and lower chord).
* Bridge decks must be accessible to test platforms.
* See Diagrams 1 and 2 for a schematic of the testing platforms.

The bridge must be built within these dimensions (See Dimensional Envelope):

  Bridge Roadbed Optional
Length 250 to 300mm 200 to 300mm Less than 180mm 50mm
Width 50 to 75mm 50 to 75mm 50 to 75mm 50mm
Height Less than 100mm Less than 50mm Less than 20mm** 7mm

* Testing Platform will be provided and should be integrated into your bridge.
** Included in the overall height of the bridge

It is imperative that bridges are built to the dimensional envelope shown within these rules. Bridges not meeting the geometric requirements will be disqualified.

* Bridges may undergo repairs to meet the dimensional specifications. Only the respective team members shall be allowed to make alterations to the structure.

Blueprints or plans of the bridge will be very helpful prior to final construction of the bridge.


C.Wooden Test Platform:
A 50mm square wooden board will be used during testing to apply stress to the bed of the bridge. Please allow space in your design so that the testing crew can place this in the center of your bridge. Teams can use a 50mm cardboard square to mimic this board.

For Category I and II bridges, the load will be applied to this board from below. The hook, illustrated in Diagram 1, must be able to pass below the bed where the load cell will be connected.

For Category III teams, the applied stress will be applied to the board by a dowel rod from above. Again, make sure the dowel can be centered on the bridge deck from above. See Diagram 2.

Diagram 1

Diagram 2

D. Construction Requirements & Techniques:

  • Only the provided materials can be used in the construction of the bridge.
  • All bridges must contain a truss design element (vertical triagnles).
  • Splitting of members (wood pieces) is not allowed.
  • Wood pieces may be bonded together with glue only at joints. If two or more strips of wood are placed parallel to each other, they must be at least the thickness of this page apart from each other.
  • No laminating of members (wood pieces) is allowed for Category I or Category II.
  • Laminating is allowed for Category III teams only.
  • The term “Laminating” for purposes of this competition is defined as bonding (gluing) together multiple pieces of wood, parallel to one another to create a larger composite truss member.
  • See sketch below for allowed types of connections.


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