POWER GENERAL SCIENCE BASLA BRIDGE BUILDING CONTEST COMPOSITION OF TEAMS: 1-2 students per team OVERVIEW: Students will design and construct a model balsawood bridge from their own plans that will carry a maximum load while using as little wood as possible, stressing neatness, craftsmanship, and creativity. MATERIALS: 1/8” x 1/8” square balsa wood (twenty sticks per group) Pitsco Structures Glue Wax Paper Pitsco Bridge Book Student Guide Exacto Knife and Miter Box Cutting Board Black Foam Pinning Board "T" Pins BRIDGE DIMENSIONS: 1) Maximum Length 2) Maximum Width 3) Maximum Height of Super Structure 4) Maximum Depth of Sub-Structure 5) Minimum Span 6) Minimum Distance of Sub-Structure from Abutment 6) Maximum Bridge Weight 40 cm 10 cm 20 cm 10 cm 25 cm 1 cm 95 grams RULES FOR CONSTRUCTION: 1. Balsa Wood Bridge should be labeled with team members’ names, and school. There will be a 10% penalty in the strength to weight score for failing to properly label. 2. No Kits are allowed. 3. Joints must be at or within ¼” of the end of at least one of the sticks (members). 4. No glue may extend beyond 3 mm of any joint. 5. No more than two members can be glued together (laminated). The only exception to this rule involves the gluing of the road bed to the roadbed beam. There you may have no more than three members glued together. 6. Members may be carved, notched, or cut anywhere along their length. 7. Pins and/or gussets are not allowed. 8. No material (e.g. paint, varnish, hairspray, etc.) may be applied to the bridge. Ink or pencil to identify bridge is okay. 9. 10. 11. 12. Maximum allowable weight of completed structure is 95 grams. Bridge must support a 9 cm wide x 10 cm plate, which will bear the load for testing. The test plate will be placed either on top of the structure or on the road bed. Bridge must have supports at least 25 cm apart, and must measure at least 10 cm above a flat surface (an imaginary “river”) at least one point (may be more than one point) between the supports. Project must be the original work of student(s). Judges may ask questions to confirm provenance. JUDGING: 1. Prior to load testing, the bridge receives a specifications check to determine whether it conforms to the weight, dimension, and construction rules. 2. Bridge is weighed and its weight recorded. 3. Bridge will be tested for load bearing capacity using the a 9 cm x 10 cm plate attached with an eye bolt to a bucket. The maximum load recorded by the loadtesting machine will be used as the load capacity of the bridge, regardless of when failure begins. 4. Disqualified bridges may be tested, time permitting. GRADING: 1. Bridge Design on graph paper (50 points). Plans are due by 10-27-15. 2. Daily Work (10 points per day). 3. Bridge Construction (100 points). Bridges are due 11-11-15. 4. Bridge Performance (200 points). Bridges will be tested 11-12-15 and 11-13-15. Strength to Weight Ratio: Determined by dividing maximum load 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 Ratio = 2724.0 = [(120 pounds x 454g/pound) / 20 g] *subtract 10% if structure is improperly labeled: e.g. 2724.0 – (2724x0.10) = 2724.0 – 272.4 = 2451.6 Bridge Performance Grade: Strength to weight ratio divided by 1000, then multiplied by 200. S to W Ratio = 900 (900/1000) x 200 = 180 *Value of 1000 may change depending on strength to weight ratios of bridges. SAFETY: Appropriate safety measures will be used in testing. Safety glasses must be worn while conducting the bridge tests. BALSA BRIDGE BUILDING SPECIFICATION CHECKLIST: This checklist is provided for you to “pre-inspect” your bridge to ensure that it meets the rules specification. Please check-off each item after you have compared your bridge’s dimensions with the rules. o All rules were followed o Bridge is properly labeled with team member’s names, and school o Material is 1/8” x 1/8” balsawood o Glue is PITSCO Construction Glue o Maximum length ≤ 40 cm o Maximum width ≤ 10 cm o Maximum height of Superstructure ≤ 20 cm o Maximum height of Substructure ≤ 10 cm o Minimum distance between Substructure and Bridge Support System ≥ 1 cm o Minimum clearance above “river” ≥ 10 cm o Minimum Span ≥ 25 cm o Maximum Bridge weight ≤ 95 grams o All joints are at or within ¼” of end of one member o No glue beyond 3mm from any joint o No excessive gluing (i.e. members are glued only at the joints) o No pins or gussets used o Balsa wood is not painted or treated o Load bed of Bridge has 10 cm x 10 cm area for placement of the test plate o Bridge has supports suitable for placement on testing fixture o No more than two members of balsa wood are laminated together, except where road bed attaches to roadbed beam.