Elevated Bridge

Elevated Bridge Instructor Andrew Roberts ajrober4@gmail.com 7 year participant in Science Olympiad Multi event medal winner in regional and State competitions Coached State Champions in Wright Stuff. 4 year SO Summer Camp Instructor. Science Olympiad Student Intern

Process Read and understand the rules Research Brainstorm Design Build Supplies & Tools Test Analyze…Repeat last 4 steps

Rules Make several copies of the rules and always have one with you while working Identify important measurements Measure your drawing as you design to be sure you meet the rules.

Rules Efficiency is actually all that matters. Efficiency = A 30g structure holding 15kg(15,000g) has an efficiency of 500 Mass Held Bridge Mass

Test Board Setup

Division B Testing Board

Division C Testing Board

Important Measurements (B) Must span 35-40 cm Must clear 15x15 cm in center Max height of 20cm

Important Measurements (C) Must span 45-50 cm Must clear 30x12.5 cm in center Max height of 20cm

Other Important Rules Can only touch the testing board in Bearing Zone There is no maximum wood size. Must support 5x5x2cm block on top mid span Must be wood (no bamboo or commercial laminates)

Research / Bibliography www.sciencenc.com www.turnertoys.com/G1/science_olympiad www.garrettsbridges.com http://abcdpittsburgh.org http://www.jhu.edu/virtlab/bridge/bridge.htm www.scioly.org www.soinc.org West Point Bridge Design

Brainstorm Take a field trip and look Bridges Ask students to draw what they liked Discuss sketches Make sure they understand the device that holds the most weight does not necessarily win.

Supplies/Tools Copy of the Rules Drawing Board Paper/drafting Pencils Eraser Metal ruler T-square Testing equipment Balsa Razors Saw Glue Accelerator Packaging Tape Building Board Acetone Sanding block Level

Balsa Has the highest strength to weight ratio of all woods Has a greater tensile strength than compression strength Is easy to shape and work with It is cheap

Balsa

Adhesives Wood Glue Green Tube Glue () Super Glue/CA glue Accelerator Mix with rubbing alcohol 1part to 1part Green Tube Glue () Super Glue/CA glue Accelerator Glue can be a major weight factor, but it doesn’t have to be. You can easily use 1-2 grams of glue (or less) on a 10-gram bridge.

Design Everything must be square, level, and symmetric. Draw your plan on paper and tape it to a rigid, flat surface. Cover the plans in a non stick surface. Clear packaging tape works best.

Tensile Advantages The tensile strength of balsa is much greater than its compression strength(19.9MPa compared to 12MPa) This means you can use a smaller piece to hold the same weight if that member is in tension.

Construction Build two sides and then connect them to each other. You can hold pieces down with scotch tape or by crossing T-pins over them (don’t put pins through the wood). If pins are used, keep pins away from glue joints.

Joints Lap Joint: The lap joint is one of the strongest, and you should use it whenever you can. It strengthens compression members because it adds stiffness. The lap joint has one drawback, however. The joint is only as strong as the face of the wood.

Joints End Joint: The end joint is not a very strong joint, especially for tension members. In tension, the two pieces of wood will just pull right away from each other.

Joints Notched Joint: The notched joint gives more strength than the end joint, but less than the lap joint. It is more difficult to build, so it is not very common.

Joints Gussets: If you have to use an end joint, it is a good idea to add a gusset to make it stronger. The gusset creates a lap joint, which is strong in both tension and compression.

Joints On your X braces, they must be connected in the middle. Glue here!

Trusses Warren Truss

Trusses Pratt

Trusses Howe

Trusses K Truss

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