Elevated Bridge

Elevated BridgeInstructor

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 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