Group 6Casey Ligrano

Hampton BrownNicholas Johnson

Xuan Nguyen

Presentation Outline• Introduction• Prototype Design

• Design Process• Reasoning for A-frame design• Prototype bridge discussion

• Final Design• Design presentation with changes made• Results of bridge improvements• Recommendations for the future

• Conclusion

Introduction

• Project Restrictions• Design a bridge solely out of tongue depressors

and fishing line• Must span a 16” gap and be 2.5” to 3.5” wide• Use no more than 125 depressors and 60 ft of

fishing line– The bridge must be as efficient as possible

Design Process

• Three original choices: Suspension, Arch, A-Frame– Suspension: Makes use of fish line anchors

• Can’t anchor them far enough away from bridge– Arch: Strong design, but hard to build– A-Frame: Strong like arch, easy to build

A-Frame Reasoning

• Easy to build• Less likely to be built wrong (keystone)• Very efficient in holding center weight• Makes good use of materials• Able to make solid walls

Prototype Bridge

Construction Difficulties

• Lack of time to work caused:– Poorly placed cross-braces– Warping in walls due to glue not drying

• No pre-drawn design– Time was not managed well– Cross-bracing not predetermined

Prototype Performance

• Weight: 0.638 lbs• Held: 478 lbs• Efficiency: 749.2• Break Points

– Top of bridge– Cross-brace cuts

Changes Made for Final Bridge

• Go from 4 depressor tall walls to 3 tall– 4 depressors weren’t adding additional

support– Using 3 depressors cut weight significantly

• Cross-bracing changed– Went from slots cut into walls to slots cut into

cross-braces– Hoped to decrease stress on bridge walls

• Top of bridge heavily reinforced– Top was the part that gave out first– Reinforcement of top would add to the weight

holding ability of the overall bridge

Final Bridge

Results of Bridge Improvements

• Weight: 0.531 lbs• Held: 622 lbs• Efficiency: 1171.4• Break Points

– Cross-bracing– Walls (warped under weight)

Bridge Discussion

• New design improvements over prototype– Top of bridge held completely– Shorter walls did not break

• Prototype points that were stronger– Cutting into the cross-braces made them next

to useless

Future Recommendations

• A-Frame bridge is a good design• Possibly use a 50-50 ratio of cuts into side

walls to cuts into cross-braces• More reinforcement of cross-bracing

Conclusion• Project Restrictions

• Design a bridge solely out of tongue depressors and fishing line

• Must span a 16” gap and be 2.5” to 3.5” wide• Use no more than 125 depressors and 60 ft of

fishing line– The bridge must be as efficient as possible

• Prototype-weight, held, efficiency: 0.638lbs, 478lbs 749.2

• Final-weight, held, efficiency: 0.531 lbs, 622 lbs, 1171.4

• Differences-weight, held, efficiency: -0.107 lbs, +144 lbs, +422.2