final presentation (balsa wood bridge design)
TRANSCRIPT
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TRUSS FINAL PROJECT
Group 3: Arman Yosal, Josia Tannos, Maya Goldman, Savannah Brooks
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Completed Bridge
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Introduction-Concept
-Design Methods
-Construction Techniques
-Testing and Performance
-Post Test Evaluation
-Conclusion
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Concept● Warren Truss design
● Hand Calculations and SAP2000
Analysis
● Seven triangle design most
efficient
● Safety Factor of 2
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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 areaCross 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)
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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
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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
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Construction techniques (3) Building Frame
Comparison of hand and CAD templates; second frame built on top of first
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Construction techniques (4) Second Frame
Second frame build on top of first
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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
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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
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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
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Testing/Performance (3)https://youtu.be/X-wvcwi89wY
Video of testing
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Post Test Evaluation (1)
Bridge main failure points
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Post Test Evaluation (2)
Gusset plate and member shear failures
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Post Test Evaluation (3)
Length 40”
Height 6”
Width 4”
Weight of bridge 135.6 g
Weight of load at failure
53.5 lb
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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)
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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
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Questions?