Group 3 designed and constructed a Warren truss bridge made of balsa wood with a total of 69 members. Through testing, the bridge met all requirements by supporting over 50 pounds without failing and having less than 0.25 inches of deflection. While the bridge was successful, post-evaluation found the design could be improved by using larger gusset plates and more accurately accounting for member thickness and the material's elastic modulus in the calculations.

1. TRUSS FINAL
PROJECT
Group 3: Arman Yosal, Josia Tannos,
Maya Goldman, Savannah Brooks

2. Completed Bridge

3. Introduction
-Concept
-Design Methods
-Construction Techniques
-Testing and Performance
-Post Test Evaluation
-Conclusion

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

9. Construction techniques (4) Second Frame
Second frame build 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

13. Testing/Performance (3)
https://youtu.be/X-wvcwi89wY
Video of testing

14. Post Test Evaluation (1)
Bridge main failure points

15. Post Test Evaluation (2)
Gusset plate and member shear failures

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

19. Questions?