final presentation (balsa wood bridge design)

TRUSS FINAL PROJECT

Group 3: Arman Yosal, Josia Tannos, Maya Goldman, Savannah Brooks

Completed Bridge

Introduction-Concept

-Design Methods

-Construction Techniques

-Testing and Performance

-Post Test Evaluation

-Conclusion

Concept● Warren Truss design

● Hand Calculations and SAP2000

Analysis

● Seven triangle design most

efficient

● Safety Factor of 2

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)

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

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

Construction techniques (3) Building Frame

Comparison of hand and CAD templates; second frame built on top of first

Construction techniques (4) Second Frame

Second frame build on top of first

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

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

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

Testing/Performance (3)https://youtu.be/X-wvcwi89wY

Video of testing

Post Test Evaluation (1)

Bridge main failure points

Post Test Evaluation (2)

Gusset plate and member shear failures

Post Test Evaluation (3)

Length 40”

Height 6”

Width 4”

Weight of bridge 135.6 g

Weight of load at failure

53.5 lb

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)

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

Questions?