EVENT:BALSAWOOD BRIDGE CONTEST
LEVEL:SENIOR HIGH SCHOOL
TYPE OF CONTEST:TEAM
COMPOSITION OF TEAM:2 STUDENTS PER TEAM
NUMBER OF TEAMS:3 TEAMS PER CENTER (Strength to weight winners)

OVERVIEW: To use math and science to implement engineering concepts in the design and construction of a model balsawood bridge from your own plans that will carry a maximum load while using as little wood as possible, and to develop neatness, craftsmanship and creativity.

MATERIALS: Ten 3 ft lengths of 1/4" x 1/4" square balsa wood (usually sufficient) and water soluble Elmer's white glue.

RULES FOR SIZE: Bridge Dimensions (see attached for Testing Apparatus Figures):

  1. Maximum length 40 cm
  2. Maximum width 10 cm
  3. Maximum height 21 cm
  4. Minimum clearance 10 cm
  5. Minimum span 25 cm

RULES FOR CONSTRUCTION:

  1. No lamination (lamination is defined as the gluing of two pieces of wood along their longitudinal length). See Attachment #1.
  2. Joints must be at or within 1/4" of the end surface of one of the members.
  3. Members joined at an angle must be at an angle of 30 degrees or more.
  4. Members may be carved, notched, or cut anywhere along their length.
  5. Pins and/or gussets are not allowed.
  6. No glue may extend 3 mm beyond any joint.
  7. No material (paint, varnish, glue, hairspray, etc.) may be applied to the bridge to strengthen the wood.
  8. Maximum weight of completed structure is 95 grams.
  9. Top of bridge must support a 12 cm x 12 cm plate which will bear the load for testing.
  10. Bridges must have supports at least 25 cm apart, and must measure 10 cm above a flat surface (an imaginary "river").

SPECIFICATION CHECK:

  1. Immediately upon submission for competition, the bridge receives a specifications check to determine whether it conforms to the mass, dimension, and construction rules (refer to attached test apparatus information).
  2. Bridge is weighed and its weight recorded.
JUDGING:

  1. Bridges are judged for neatness, craftsmanship, and creativity by a 3-person team selected by Host Center prior to testing.
  2. Bridge will be tested for load bearing capacity using the setup shown in Attachment #2. The maximum load recorded by the load testing machine will be used as the load capacity of the bridge, regardless of when failure begins.
  3. Individual's bridges are not limited in the number of categories they can win.
  4. Disqualified bridges will not be tested.

AWARDS:

Awards are given in each of the following three categories:

    a) Strength to Weight Ratio: Determined by dividing load at failure by weight of bridge. Bridge with greatest load bearing capacity compared to its weight wins.

Example: Maximum load=120.0 pounds
Bridge weight=20.0 grams
Total score:=(120/20 x 454 g/lbs or 2724)
    b) King Kong: Greatest load bearing capacity.
    c) Creativity: Finest workmanship, including neatness and innovation of design.

SAFETY: Appropriate safety measures will be used in testing.

ATTACHMENTS:

  1. Sample Joints
  2. Testing Apparatus
  3. Official Entry Form

BALSAWOOD BRIDGE CONTEST

SENIOR HIGH SCHOOL

ATTACHMENT #1: SAMPLE JOINTS

(Please attach page with illustration)

BALSAWOOD BRIDGE CONTEST

SENIOR HIGH SCHOOL

ATTACHMENT #2: TESTING APPARATUS

1) FIGURE 1a:
Overall Dimension Test: The bridge must fit inside a box with the following dimensions to be considered legal; bridge must also pass the 10cm clearance test.
2) FIGURE 1b:The bridge must be supported on both of the blocks as shown:
3) FIGURE 2:
The bridge is tested for strength by applying weight to a 12cm square plate placed on top of the bridge. The bridge is tested for strength while sitting on the blocks.

BALSAWOOD BRIDGE CONTEST

SENIOR HIGH SCHOOL

OFFICIAL ENTRY FORM

BRIDGE NUMBER ________________________________
MESA CENTER ________________________________
SCHOOL ________________________________
BUILDERS ________________________________
________________________________
________________________________

FOR JUDGES USE ONLY

WEIGHT OF BRIDGE   	___________________________________



CREATIVITY OF DESIGN	1   2   3   4   5   6   7   8   9   10

(craftsmanship & neatness)



TOTAL LOAD		_______________________________________



STRENGTH OF LOAD/	_______________________________________

	WEIGHT RATIO



COMMENTS



______________________________________________________________



______________________________________________________________



______________________________________________________________



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Last updated: 7 June 1997.