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Bridge Builder - Balsa Wood and 3D printed plastic

This contest is open to students enrolled in any public or private high school or junior high school in South Dakota or adjacent states. No more than two students may share one entry.

One or two students will design and fabricate a model or a type of bridge structure. The bridge will be tested, per the rules and restrictions listed below, to determine the maximum amount of load (pounds) it is able to withstand.

Participants can refer to the following website, http://stephenjressler.com/wpbd/  (link at bottom of page), for guidance on configuration of the elements of their bridge.

Rules

  1. A bridge model must adhere to the restrictions listed below. Failure to meet all material, dimensional, and fabrication-related restrictions will result in the disqualification of the entry. A disqualified entry may be modified at the competition to meet the restrictions, if approved by a judge.

  2. An incrementally increasing load will be placed on the model bridge until the bridge is unable to resist any additional load (lbs.). This load will be recorded. The bridge must be able to resist a minimum load of 25 lbs. when supported and loaded as shown in the accompanying figures.

  3. The value of the maximum resisted load (lbs.) will be divided by the mass (oz.) of the bridge structure to determine the structural efficiency of the model bridge.

  4. Prizes will be awarded for the top three bridges in structural efficiency in two divisions:  balsa wood and 3D printed plastic.

Geometric Design Restrictions:

  1. The bridge must be a truss-type structure. A truss is a lattice of straight members connected only at their ends. Locations where the ends of the members come together are referred to as a joint.

  2. Refer to the accompanying figures for a visual explanation of the dimensional constraints. The details of a bridge model lattice system are left to the imagination of each contestant.

  3. The length of the bridge structure must be 17 inches.

  4. The maximum outer width (side-to-side) must not exceed 4.25 inches.

  5. The maximum depth (bottom to top) must not exceed 4.5 inches.

  6. The top of the bridge must not be more than 4 inches above the top of the loading jig support.

  7. The bottom of the bridge must not be more than 0.5 inches below the top of the loading jig support.

  8. The top of the loading platform may not be more than 1 inch above the top of the loading jig support.

  9. The test load consists of a single load placed at the middle of the bridge span. The load is applied by a 2-inch by 2-inch square loading block.

  10. A loading platform must be provided at the mid-span of the bridge. The platform must extend side-to-side the full inside width of the bridge. The length of the platform must not be less than 2 inches, and no more than 6 inches. The space above the loading platform must be completely unobstructed to allow for the insertion and removal of the loading block.

  11. A block, 2.5 inches wide by 2 inches tall by 2 inches in length must be able to pass through the inside of the truss model from end to end. This block is to represent a vehicle moving across, or through, the bridge structure.

Construction Restrictions: Balsa Wood

  1. The bridge must be fabricated using Balsa wood sticks. The cross-sectional dimensions of any individual stick may not exceed ¼ inch by ¼ inch. The length of any individual stick may not exceed 5 inches.

  2. Sticks can be joined using any type of glue.

  3. Sticks can be joined, or connected, only at their ends. No stick can be continuous through a joint. No stick can attach to the middle of another stick.  Gusset plates and pegs may be used to connect the sticks.  The gusset plate thickness may not exceed 1/16 inch and neither the length nor width can exceed ¾ inch.

  4. Lamination, or gluing members together in parallel, is only allowed for the surface of the loading platform.

  5. Sticks cannot be coated, painted, or stained with any material that, in the judges’ determination, will add to the structure’s ability to resist an applied load.

Construction Restrictions: 3D printed Plastic

  1. The bridge must be printed in whole or part by a 3D printing process utilizing plastic.  The cross-sectional dimensions of any individual truss structural member may not exceed ¼ inch by ¼ inch. The length of any individual 3D printed truss section may not exceed 5 inches.  PLA is the suggested plastic to use for 3D printing.

  2. 3D printed parts can be joined using any type of glue or gusset plates and pins can be used to connect printed truss sections.  The gusset plate thickness may not exceed 1/16 inch and neither the length nor width can exceed ¾ inch. 

  3. Lamination, or gluing members together in parallel, is only allowed for the surface of the loading platform.

  4. 3D printed parts cannot be coated, painted, or stained with any material that, in the judges’ determination, will add to the structure’s ability to resist an applied load.

Contacts for restriction clarifications:

Balsa Wood Bridge:   Zachary.gutzmer@sdstate.edu
3D Printed Bridge:     Suzette.burckhard@sdstate.edu

Prizes for Balsa Wood

1st Place: $60
2nd Place: $40
3rd Place: $20

Prizes for 3D Printed Plastic

1st Place: $60
2nd Place: $40
3rd Place: $20