4. Concept
● Warren Truss design
● Hand Calculations and SAP2000
Analysis
● Seven triangle design most
efficient
● Safety Factor of 2
5. Design Methods
● Warren Truss design
● 69 Total Members
○ 27 on each side of truss
○ 15 connecting the two sides
● Deflection decreases with increased cross-sectional area
Cross Sectional Size Number of Members Pieces Laminated
1/4" x 1/4" 38 4 x (1/8" balsa wood)
1/8" x 1/8" 8 4 x (1/16" balsa wood)
3/8" x 3/8" 4 4 x (3/16" balsa wood)
1/4" x 1/8" 4 2 x (1/8" balsa wood)
6. Construction techniques (1) - Cutting
● Materials used: X-Acto blades, T-squares or metal rulers
● Followed table to keep track of amounts, lengths, sizes
● Rounded up for consistency
7. Construction techniques (2) - Laminating
● Super glue used to form members with larger cross-sectional areas and
greater strength
○ Ex. using ⅛” wood pieces, four were laminated together to create a ¼”X¼” member
● Extra pieces added to small members at connection joints so heights were
equal
8. Construction techniques (3) Building Frame
Comparison of hand and CAD templates; second frame built on top of first
10. Construction techniques (5) Lateral Bracing
● Tongue depressor and screw system to align
frames
● Gusset plates added on small members
● Cross-bracing cut and placed one at a time at
the end
11. Testing/Performance (1)
Testing Method
● Metal bar laid on platform at
top center of bridge
● Chain hung over bar then
attached beneath bucket
● Began at ten pounds then
weight was added until failure
12. Testing/Performance (2)
The bridge met all design requirements
● Minimum 36” span with no more than ½” at
each support
● Minimum height 5”, width 4” for truck to pass
● Less than 0.25” deflection
● Did not exceed 30% over-order
Weight of
load at failure
53.5 lb
Length 40”
Height 6”
Width 4”
Weight of
bridge
135.6 g
16. Post Test Evaluation (3)
Length 40”
Height 6”
Width 4”
Weight of bridge 135.6 g
Weight of load at
failure
53.5 lb
17. Post Test Evaluation (4)
● More efficient design can be achieved
○ Underestimation of elastic modulus
Trial Length
(cm)
Width
(cm)
Moment of
Inertia
(cm4
)
Load
(N)
Length
(cm)
Deflection
(cm)
Elastic
Modulus
(GPa)
1 0.318 0.318 8.468E-04 0.196 25.000 1.800 6.704
2 0.318 0.318 8.468E-04 0.196 25.000 2.200 5.485
3 0.159 0.159 5.293E-05 0.098 10.000 1.000 6.178
4 0.159 0.159 5.293E-05 0.098 10.000 1.500 4.119
Our data (left), researched data (right)
18. Conclusions
- The bridge met all design requirements
- The bridge was over designed
- What we would improve
● Use larger gusset plate
● Take into account the thickness of each member
● Measure the actual elastic modulus of the material
