POWER GENERAL SCIENCE BASLA BRIDGE BUILDING CONTEST
COMPOSITION OF TEAMS: 1-2 students per team
OVERVIEW:
Students will design and construct a model balsawood bridge from their own plans that
will carry a maximum load while using as little wood as possible, stressing neatness,
craftsmanship, and creativity.
MATERIALS:
1/8” x 1/8” square balsa wood (twenty sticks per group)
Pitsco Structures Glue
Wax Paper
Pitsco Bridge Book Student Guide
Exacto Knife and Miter Box
Cutting Board
Black Foam Pinning Board
"T" Pins
BRIDGE DIMENSIONS:
1)
Maximum Length
2)
Maximum Width
3)
Maximum Height of Super Structure
4)
Maximum Depth of Sub-Structure
5)
Minimum Span
6)
Minimum Distance of Sub-Structure from Abutment
6)
Maximum Bridge Weight
40 cm
10 cm
20 cm
10 cm
25 cm
1 cm
95 grams
RULES FOR CONSTRUCTION:
1.
Balsa Wood Bridge should be labeled with team members’ names, and school.
There will be a 10% penalty in the strength to weight score for failing to properly
label.
2.
No Kits are allowed.
3.
Joints must be at or within ¼” of the end of at least one of the sticks (members).
4.
No glue may extend beyond 3 mm of any joint.
5.
No more than two members can be glued together (laminated). The only
exception to this rule involves the gluing of the road bed to the roadbed beam.
There you may have no more than three members glued together.
6.
Members may be carved, notched, or cut anywhere along their length.
7.
Pins and/or gussets are not allowed.
8.
No material (e.g. paint, varnish, hairspray, etc.) may be applied to the bridge. Ink
or pencil to identify bridge is okay.
9.
10.
11.
12.
Maximum allowable weight of completed structure is 95 grams.
Bridge must support a 9 cm wide x 10 cm plate, which will bear the load for
testing. The test plate will be placed either on top of the structure or on the road
bed.
Bridge must have supports at least 25 cm apart, and must measure at least 10 cm
above a flat surface (an imaginary “river”) at least one point (may be more than
one point) between the supports.
Project must be the original work of student(s). Judges may ask questions to
confirm provenance.
JUDGING:
1.
Prior to load testing, the bridge receives a specifications check to determine
whether it conforms to the weight, dimension, and construction rules.
2.
Bridge is weighed and its weight recorded.
3.
Bridge will be tested for load bearing capacity using the a 9 cm x 10 cm plate
attached with an eye bolt to a bucket. The maximum load recorded by the loadtesting machine will be used as the load capacity of the bridge, regardless of
when failure begins.
4.
Disqualified bridges may be tested, time permitting.
GRADING:
1.
Bridge Design on graph paper (50 points).
Plans are due by 10-27-15.
2.
Daily Work (10 points per day).
3.
Bridge Construction (100 points).
Bridges are due 11-11-15.
4.
Bridge Performance (200 points).
Bridges will be tested 11-12-15 and 11-13-15.
Strength to Weight Ratio: Determined by dividing maximum load by weight of
bridge.
Bridge with greatest load bearing capacity compared to its weight wins.
Example:
Maximum load = 120.0 pounds
Bridge weight = 20.0 grams
Ratio
= 2724.0 = [(120 pounds x 454g/pound) / 20 g]
*subtract 10% if structure is improperly labeled:
e.g. 2724.0 – (2724x0.10) = 2724.0 – 272.4 = 2451.6
Bridge Performance Grade: Strength to weight ratio divided by 1000, then
multiplied by 200.
S to W Ratio
= 900
(900/1000) x 200 = 180
*Value of 1000 may change depending on strength to weight ratios of bridges.
SAFETY:
Appropriate safety measures will be used in testing. Safety glasses must be worn while
conducting the bridge tests.
BALSA BRIDGE BUILDING SPECIFICATION CHECKLIST:
This checklist is provided for you to “pre-inspect” your bridge to ensure that it meets
the rules specification. Please check-off each item after you have compared your
bridge’s dimensions with the rules.
o All rules were followed
o Bridge is properly labeled with team member’s names, and school
o Material is 1/8” x 1/8” balsawood
o Glue is PITSCO Construction Glue
o Maximum length ≤ 40 cm
o Maximum width ≤ 10 cm
o Maximum height of Superstructure ≤ 20 cm
o Maximum height of Substructure ≤ 10 cm
o Minimum distance between Substructure and Bridge Support System ≥ 1 cm
o Minimum clearance above “river” ≥ 10 cm
o Minimum Span ≥ 25 cm
o Maximum Bridge weight ≤ 95 grams
o All joints are at or within ¼” of end of one member
o No glue beyond 3mm from any joint
o No excessive gluing (i.e. members are glued only at the joints)
o No pins or gussets used
o Balsa wood is not painted or treated
o Load bed of Bridge has 10 cm x 10 cm area for placement of the test plate
o Bridge has supports suitable for placement on testing fixture
o No more than two members of balsa wood are laminated together, except
where road bed attaches to roadbed beam.