Oak Valley Middle School Science Olympiad Elevated Bridge

1. Oak Valley Middle School Science OlympiadElevated Bridge Coach: Jay Trischman Phone: 858-312-1342 (home) 858-472-5651 (cell) E-mail: trischman2@cox.net trischmanj@saic.com

2. What is the Elevated Bridge Event ? • Teams of 2 will build a bridge prior to the competition. • It must be constructed only of wood bonded by glue • It must meet a set of size limits listed in the rules • During the competition, you will test how much weight the bridge will hold • You will add weight until it reaches 15 kg or until the bridge breaks • Score = weight held divided by the bridge’s weight Strength and Weight are Equally Important

3. Bridge Dimensions - 2010 Loading Block 20 cm 15 cm 15 cm clear area Test Platform 35 cm span 20 cm opening 5 cm 5 cm bearing zone Chain Sand Bucket (not to scale) Also see drawing at: http://soinc.org/elevated_bridge_b

4. Size Rules • Bridge must span at least 35 cm • Bridge can touch test surface only in “bearing zone” 5 cm on either side of span • Bridge must be less than 20 cm high • Bridge must have clearance for 15 cm x 15 cm block • Bridge must support 5 cm x 5 cm loading block centered over opening • Bridge must provide space for a chain or rod to extend below loading block • There is no restriction on the width of the bridge Bridges that don’t meet the rules are penalized

5. Materials • The bridge must be built of wood only • No bamboo, paper, particle board, composite material, or pre-laminated wood • We will have Balsa wood for you to use • You can get other types may be from hobby and craft stores • Thin pieces can be laminated (glued together in layers) to create stronger, thicker pieces if needed Remember, weight is important

6. Glue • Any kind of glue can be used • “Super” glue is strong and dries quickly( Use sparingly and Don’t glue your fingers together ) • White wood glue (must dry overnight) Remember, weight is important

7. Designing Your Bridge • Designing means creating plans of how your bridge will look and be built • Look for ideas in structures you see around you • The bridge must be elevated, so it might look different from the winners in other contests. • The bridge must be light and strong; you probably want to use a truss design Tower Bridge Truss Bridge

8. Your Design Ideas • Start with sketches in a notebook • Include notes about how thick each piece should be • After the bridge is built and tested you will add notes about what works and what doesn’t work • Your plans and notes let you rebuild a bridge that breaks • You can also make improvements each time so each bridge is better than the last

9. Hints: Building A Strong Bridge Weight • The vertical pieces are called columns • Columns break by buckling (bending in the middle) when loaded • To prevent buckling, attach cross-pieces to the columns • The angled pieces give stiffness by forming triangles Buckling Triangles are your friend !

10. Truss Design • A truss is a structure made of straight thin members connected to each other, usually forming triangles • Each member (piece) of a truss is either • under Compression (being squeezed) or • under Tension (being stretched) • Computer programs can tell you the amount and type of forces in each member of a truss

11. Example Truss Analysis Red pieces are under compression, black are under tension. Higher numbers mean larger force. Load

12. Construction Hints • The side sections (trusses) of your bridge can be built on top of your full-sized plans • Tape the plans to a piece of cardboard • Cover the plans with wax paper • Cut wood and check sizes against the plans • Use tape or pins on either side of the wood strips to hold them while the glue dries

13. Construction • Build two identical trusses and attach them together • One approach is to use stacks of books and tape to hold the trusses in place • Make sure the spacing and alignment is exact and the trusses are vertical • Glue in cross pieces on each end and the top • Once these have dried, remove the books and add the rest of the cross supports

14. Competition – Set up • On competition day the Bridges are weighed and placed on a test stand • The loading block with a chain or rod attached is put in place …

15. Competition - Loading The student adds sand to a bucket suspended from the bridge until the bridge breaks or the maximum weight (15 kg.) is reached. The loading technique is important too!

16. Testing • The best way to learn what works is to build bridges and then break them ! • Each failure teaches us something

17. On-line Resources • The Science Olympiad Site:http://soinc.org/elevated_bridge_b • Truss designerhttp://www.jhu.edu/virtlab/bridge/bridge.htm • Some pictures and ideas:http://www.bridgesite.com/funand.htm • Check out YouTube to see videos of bridges being tested • Notes that some bridge contests have different rules

18. Meetings / Practices • Competition: Saturday, Feb 6, 2009 atBernardo Middle School • Meeting / Building Sessions: • Place: Trischman House - 9647 Deer Trail Dr. • Days: Wednesday (alternating weeks) • Time: 4:30 – 6:00 pm • Possible Dates: • Oct 14, Oct 28, Nov 11, Dec 9, … • These weeks fall on Thanksgiving and Christmas • What are you conflicts and preferences?