Elevated Bridge
Jan 11, 2016
Elevated Bridge
Elevated BridgeInstructor
Andrew Roberts [email protected] 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 HeldBridge 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
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
Ideas
Ideas
Ideas
Ideas
Ideas