BRIDGE BUILDING ASSIGNMENT

1. Work with a partner to construct 1 bridge.2. Choose Partners.3. Draw a full size truss pattern from one of the

six truss examples.4. Construct the bridge using balsa wood.5. Test the efficiency & applied force of the

bridge.

BRIDGE SPECIFICATIONS• Work as a team to design and construct a balsa wood bridge.• You may use no more than 7 - 24”x1/8” balsa sticks. (14 ft.

total)• The bridge must have two identical trusses, a roadbed & a

top.• The bridge must be exactly 10” in length.• The test block must fit between the two trusses.• No excessive glue blobs.• Support weight = Over 50 lbs.• Tape may only be used to hold pieces while glue dries.• Only two pieces of balsa wood may be laminated together.

EXAMPLES OF TRUSS BRIDGES

UNDERNEATH DECK TRUSS

THROUGH TRUSS

TRIANGULAR TRUSS

K TRUSS

WARREN TRUSS WITH VERTICAL SUPPORTS

BALTIMORE TRUSS

TRUSS BRIDGEINTERCONNECTED TRIANGLES

The truss bridge...consists of an assembly of triangles. Truss bridges are commonly made from a series of straight, steel bars.

WATER

RIGHT ABUTMENT

LEFT ABUTMENT SPAN

ROADBED

BRIDGE TERMS

SUBSTRUCTUREBELOW ROADBED

SUPERSTRUCTUREABOVE ROADBED

1

2

3

10981 2 3 4 5 6 70

0

1

10981 2 3 4 5 6 70

Warren Truss with Vertical Supports

1

2

3

10981 2 3 4 5 6 70

Baltimore Truss

0

1

10981 2 3 4 5 6 70

K Truss

1

2

3

10981 2 3 4 5 6 70

Through Truss

0

1

10981 2 3 4 5 6 70

Triangular Truss

Underneath Deck Truss

TRUSS EXAMPLES

EXAMPLES OF JOINTS USED IN BALSA BRIDGE BUILDING

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3

2

1

0

1

980 1 2 3 4 5 6 7 10

Total inches for vertical pieces in.+

Total inches for horizontal pieces in.+

Total inches for diagonal pieces in.

=

Total inches for one truss 12 = # of feet to build one truss (round to the tenth place)

x 2

= # of feet to build two trusses (round to the tenths place)

Wood Usage Calculations: GRADING PROCEDURE

Lines are drawn with ruler (no wavy lines)

Lines are 1/8” thick.

Appearance of drawing (Easy to read)

Complete wood usage calculations.

Joints are clearly drawn. GRID SIZE = .25

DO NOT SHADE IN THE LINES!

TRUSS VIEW Drawn by: __________________________________ Block #_____ Date: ____________

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3

2

1

0

1

980 1 2 3 4 5 6 7 10

Total inches for vertical pieces in.+

Total inches for horizontal pieces in.+

Total inches for diagonal pieces in.

=

Total inches for one truss 12 = # of feet to build one truss (round to the tenth place)

x 2

= # of feet to build two trusses (round to the tenths place)

Wood Usage Calculations: GRADING PROCEDURE

Lines are drawn with ruler (no wavy lines)

Lines are 1/8” thick.

Appearance of drawing (Easy to read)

Complete wood usage calculations.

Joints are clearly drawn. GRID SIZE = .25

DO NOT SHADE IN THE LINES!

TRUSS VIEW Drawn by: __________________________________ Block #_____ Date: ____________

Bad jointGood joint

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3

2

1

0

1

980 1 2 3 4 5 6 7 10

Total inches for vertical pieces in.+

Total inches for horizontal pieces in.+

Total inches for diagonal pieces in.

=

Total inches for one truss 12 = # of feet to build one truss (round to the tenth place)

x 2

= # of feet to build two trusses (round to the tenths place)

Wood Usage Calculations:GRADING PROCEDURE

Lines are drawn with ruler (no wavy lines)

Lines are 1/8” thick.

Appearance of drawing (Easy to read)

Complete wood usage calculations.

Joints are clearly drawn. GRID SIZE = .25

TRUSS VIEW Drawn by: __________________________________ Block #_____ Date: ____________

10”

8.25”

2.25”2.25”2.7

5”

2.75”2.75”

2.75”2” 2”2”2” 2”

1018.2515.5043.75 3.6

7.2

BALSA BRIDGE CONSTRUCTION

Two trusses must be standing vertically. ____ pts. (15) No excessive glue blobs. ____ pts. (15) Tight joints. ____ pts. (15) Roadbed & top pieces do not over hang trusses. ____ pts. (15) Over 50 lbs. = 40 pts. 40 – 49 lbs. = 30 pts. Below 40 lbs. = 20 pts. ____ pts. (40)

____ pts. (100)

BRIDGES GRADESHEETTRUSS VIEW DRAWING GRADE

Lines are drawn with ruler. No wavy lines ____ pts. (20) Lines are 1/8” thick. ____ pts. (20)Drawing should have neat appearance. ____ pts. (20) Joints are clearly drawn. ____ pts. (20) Complete wood usage calculations. ____ pts. (20)

____ pts. (100)

WHAT IS WRONG WITH THISTRUSS VIEW DRAWING?

- WAVY LINES.

- LINES ARE NOT 1/8” THICK.

- MESSY APPEARANCE.

- JOINTS ARE NOT CLEARLY DRAWN.

- DID NOT COMPLETE THE WOOD USAGE CALCULATIONS.

50%

AN EXCELLENT EXAMPLE OF A TRUSS VIEW DRAWING!

- NO WAVY LINES.

- LINES ARE 1/8” THICK.

- NEAT APPEARANCE.

- JOINTS CLEARLY DRAWN.

- COMPLETED THE WOOD USAGE CALCULATIONS.