1. Loading Sand (cont.) Using Sand Hopper:
Control sand flow by how far you move handle back.
The sand chute directs sand into bucket.
Must release handle when failure, end of time, or max load is reached.
One student loads, one student stabilizes using the sticks provided.

2. Bucket Stabilization Rule 5.b. vii.
Team members must be allowed to safely and effectively stabilize the bucket from movement caused by loading of the sand.
Direct contact not allowed.
Must use stabilization sticks provided by event supervisor.
A bucket stabilization stick is made up of one piece of ½” dowel approximately 18 to 24 inches long with a spring type door stop screwed into one end. Two (2) sticks will be provided.

3. Bridge Scoring
Score = Load Supported (g) / Mass of Bridge (g) Ties are broken by: 1. Lowest Bridge Mass 2. Widest bridge (measured at the widest point prior to loading) Load Supported includes: loading block, eye-bolt, washers, wing nuts, chain, hooks, bucket, sand Does not include: Pieces of Bridge, sand loaded after end is reached

4. Scoring Tiers Within each Tier, teams are ranked by highest score:
Tier 1- Bridges meeting all construction
parameters and having no competition violations.
Tier 2- Bridges with one or more competition
violations.
Tier 3- Bridges with construction violations
or both construction and competition
Tier 4- Bridges unable to be loaded for any reason
(cannot cross the clear span, cannot accommodate
loading block, failure to wear eye protection) must
be ranked by lowest mass.

5. Test Stand Sand Hopper Sand Release Handle Test Base Test Supports
~15 kg of sand will be loaded into the sand hopper before the test.

6. Test Base Test base to be > 55.0 cm long x > 32.0 cm wide
Clear Span Lines are lines parallel to the Center Line.
For Division B it is 17.5 cm away.
(35.0 cm total width)
Opening to be
~ 20.0 cm x ~20.0 cm
For Division C it is 22.5 cm away.
(45.0 cm total width)
Bearing Zones are the areas
beyond Clear Span Lines
(ex. For C Division)
Bearing Zones are the areas
beyond Clear Span Lines
(ex. For B Division)

7. Test Supports Supplied by Event Supervisor.
There is only 1 (one) this year.
Must be 5.0 cm x 5.0 cm x 2.0 cm.
Must sit on one of the 2.0 cm x 5.0 cm faces.
Set up for Division C

8. Testing
Students place bridge on scale to measure mass to nearest 0.01 g.
Event supervisor measures bridge width prior to loading.
Students get 6 minutes to test bridge.
Students place bridge on Test Support that they set in the Bearing Zones.
Test supports must sit on a 2.0 cm x 5.0 cm face.
Students will place loading block approximately in the center of the bridge.
Students assemble the loading block assembly themselves.
Students may adjust bridge and bucket/chain assembly until they start loading .
While loading sand, students may only touch bucket with Stabilizing Sticks.

9. Testing
Bridge is loaded until it fails, the load is supported by something other than the bridge, the end supported by the Test Support touches the testing surface, or time has elapsed.
If sand is loaded after failure, the Event Supervisor must remove the extra sand.
Parts of the bridge that fall into the bucket must be removed prior to weighing the load.
The load supported will include the sand, bucket, chain, loading block.
Maximum load recorded will be 15,000 g.
If an appeal is going to be filed, the bridge must stay with the Event Supervisor.

10. Event Considerations
Bridge Types
Wood
Glue
Building Tips
Testing Day

11. Beam Bridge
• Direct descendant of the log bridge. Same as many interstate
overpasses
• In structural terms, the simplest of the many bridge types
• May be heavier than other bridge designs

12. Truss Bridge • Composed of connected elements (typically straight)
• Oldest types of modern bridges.
• Efficient use of materials

13. Arch Bridge
• Efficient use of materials
• Need to stabilize

14. Web Design Support Have students check out the
Building Big web site at:
Design your own bridge at:
And have them try the following:

15. Wood, Part 1 All parts of the Bridge must be made of wood and
bonded by adhesive.
No limits to sizes of cross
section or length
No other materials are permitted:
no particle board, wood
composites, bamboo, grass,
commercial plywood,
sawdust-adhesive members, paper price labels, or
paper.
Check for grain defects, cuts, chips, other damage.

16. Wood, Part 2
Consider laminating thin layers of wood to take advantage of multiple wood grains but REMEMBER that glue is heavy.
Unlimited lamination by students is allowed.
Check like-size wood pieces
for consistency of
density, especially balsa.
Use wood of higher density in
compression applications

17. STRENGTH OF BALSA WOOD COMPARED TO OTHER WOODS
Wood, Part 3
Balsa, strongest wood,
pound for pound!
STRENGTH OF BALSA WOOD COMPARED TO OTHER WOODS
  Weight  Stiffness  Bending Compression
Species Lbs./Cu. Ft. Strength Strength Strength
 Balsa
 Balsa  
 Balsa  
Spruce
Yellow Pine  
Douglas Fir
Hickory 50 
Oak  
Basswood
Black Walnut
NOTE ABOUT CHART: The strength of balsa varies in direct relation to its density or weight - the heavier the wood the stronger it is. The above chart was designed with 10 lb./cu. ft. balsa as the median. In other words, balsa at IO Ibs./cu. ft. has been tested given a value of 100. The other woods were then tested in the same way and given a figure that is numerically in proportion. By comparing the relative strength figures in the chart, it will be seen that balsa is as strong or stronger, pound for pound, than most of the species shown.

18. Cutting Balsawood