Bridge
Bridge Project Information for 2014 (pdf or google doc)
AVHS Bridge Building Contest & Analysis
The object of this activity is to build the strongest, lightest structure possible while following the specifications below. The Bridge is due prior to Winter Break and the Analysis is due after Winter Break.
Materials:
• 24 ft of 3/32” x 3/32” balsa wood given in eight 3 ft pieces. Please return any extra pieces!
• One tube of “Testor’s Cement for Wood Models” (green and white tube, small size)
Only these materials may be used, using other materials will result in a large point deduction. These materials are available from your teacher. It is advisable to pick them up after school to reduce the possibility of breakage.
Specifications:
• Bridge must be free standing; you cannot hold it and there will be no supports.
• Maximum mass allowed is 13 grams (as determined by your teacher’s balance)
NOTE: It is difficult to determine the amount of wood and glue actually used in a bridge by visual inspection, so a mass limitation has also been set. A bridge which uses no more than 24 ft of wood and 1 tube of glue will be within the mass limit.
• Length along the bottom will be no more than 20 cm and no less than 14 cm
• Length along the top will be no less than 12 cm and no more than 20 cm
• Width at all points will be 3 cm, no more, no less.
• Bridge height will be no more than 8 cm and no less than 5 cm
• Minimum vertical clearance at center of span: 5 cm for tall, 3 cm across the top, 14 cm long across the bottom and 3 cm width. See the trapezoid that much be clear on the back of this paper.
• Channel bottom must be clear, just like a real bridge something has to pass under your bridge.
NOTE: Bridge must have outer dimensions mentioned above, and must have a trapezoidal opening with minimum dimensions shown. Bridge may have an opening larger than the minimum if desired. There can be nothing underneath the trapezoid.
-6 points will be deducted for each length, width, or height dimension inside or out that is not to the specifications.
Lamination: No more than two balsa sticks may be laminated together, and there must be a minimum space equal to the width of one stick between laminated beams which run parallel to each other. Beams which meet in a joint, or which are in contact when crossing are deemed incidental to a rational design, and are not present primarily for lamenting. Three sticks glued lengthwise together would represent illegal lamination. -20 points will be deducted for illegal lamination
Testing:
Stage 1: A simulated paved roadway 3 cm wide cut from thick paper will be placed on the freestanding bridge and a 1 kg mass (2.2lb ) must be able to be rolled across the bridge. Any bridge not able to withstand this test will be unable to complete additional testing and suffer a 40 point deduction.
Stage 2: A vertical load will be applied to a 3 cm x 10 cm test block centered on the bridge. There are no blocks placed at the ends of the bridge to keep the bridge from spreading. Your bridge must hold 100 N (or ~22.5 lbs) vertical load. After 100 N is reached, bridges will be tested until failure of the structure. -5 points will be deducted for each 10 N shy of a 100 N load your bridge holds
Eligibility: Mandatory for Amador physics students, but other interested Amador students, staff, parents, etc., are also invited to participate
Determination of Winners: Winners must have bridges that meet all specifications and have the highest load held or the highest performance factor (total weight held divided by the mass of bridge).
Bridge Point Value: This is a project that is to be completed at home and is worth 100 points. There are deductions from 100 points for various infractions, or rule breaking:
-6 points for each length, width, or height dimension inside or out that is not to the specifications
-20 points for illegal lamination
-20 points if the bridge is not freestanding
-40 points if the bridge fails the 1 kg roll test
-5 points each 10 N shy of a 100 N load your bridge holds
Post-Test Analysis:
Analyze your bridge’s performance after testing. This analysis is worth 20 points and is due the first day back from Winter Break. Use the prompt and brainstorming questions below:
Write a full page, at least three age appropriate paragraphs, about what was good or bad about your bridge design. Your total point value will depend on your rationale, level of writing and evidence. Examine your bridge remains for evidence; look for breaking points and “popped” joints. Video taken during test will be available if possible. You may find drawings or simplified force vector diagrams helpful to your analysis.
Think about these questions while analyzing your bridge:
What would you do differently in order to improve its performance factor?
What part of your bridge was the “weak link”?
Was your bridge too light? Too heavy?
Were your joints clean (angled) or sloppy?
Did you make precise measurements? Did you “eyeball” it?
Where did your bridge fail? What could you do to reinforce that area?
Was the failure of your bridge symmetric? Did your bridge fail equally on each side?
Use the videos from your class to help you analyze your bridge as well as the bridge itself: