This document outlines the goals, constraints, materials, testing procedures, and engineering fundamentals for a student bridge design project. The goals are for students to learn the design process, practical applications of concepts like trigonometry and statics, and improve skills like prototyping, testing, and technical communication. Students will design and build bridges using tongue depressors and glue that can support at least 15 pounds using no more than 100 tongue depressors. Bridges will be tested and scored based on their load capacity divided by weight. The project involves component testing, prototyping, redesign, and a final competition. Guidance is provided on truss designs, mechanics of materials concepts, and construction hints.

1. Problem Definition: Design a Bridge to span a
given distance while supporting a maximum
load using a minimum materials.
Bridge Project

2. Project Goals
The goals for this project are for students to:
• Learn the design process.
• See practical applications for trigonometry, physics,
and engineering statics (force analysis).
• Improve skills associated with collecting data and
drawing meaningful conclusions.
• Experience the usefulness of prototype testing.
• Recognize the necessity of good communication
skills for engineers by completing memos, reports,
drawings, and presentations.

3. Introduction to Bridge
• Bridge Type
–Truss Bridge
–Arch bridge
–Suspension Bridge
–Cantilever Bridge

4. Truss Bridge
• Truss design is
to support the
bridge deck
• The truss may
have ompression
or tension
• The joint of truss
is important

5. Truss(force analysis)
• Loads members in tension and compression.
• Members are pinned at joints (Moment = 0).
• Triangles provide stability and strength.
•Top members in Compression.
•Bottom members in Tension.
Hint - Imagine entire truss wrapped in rubber skin, so you
have a large rubber box. When you bend it, where would the
wrinkles be? They indicate compression.

6. Beam
• Ways to strengthen members in bending.
– Decrease overall length (deflections).
– Cross section design (moment of inertia)
– Use stronger materials (elastic modulus).
Tension
Compression
Steel
=
Axis of
bending
vs.

7. Arch bridge
• Appear mostly
in Ancient time
• New arch
bridge is
modified to
reduce the
material

8. Function of Arch structure
• Puts members in compression.
• Need horizontal support at abutments.
Abutment

9. Suspension Bridge
• Replace the
Beam with
cable
• Reduce the
need for the
Pier , Girder
and Truss

10. Suspension
• Puts members in tension.
• Carries weight up to the top of the towers.
• Good for long spans.

11. Cantilever Bridge
• No support at
the bridge it
self
• The material
must be very
strong
• Or the structure
must be
different

12. Box Girder Bridge
• Box structure reduce
the weight and
material
• Increase the strength
on top and bottom to
resist compression
and tension

13. Project Constraints
Size: See above & 100 stick limit per bridge
Shape: Original ideas encouraged!
Strength: Must support a minimum of 15 lbs.

14. Constraints:
Building
Materials
• 100 Wood tongue depressors (6”)
• Glue guns and glue sticks and
wood glue
• String

15. Scoring Equation
Score = Load at Failure(performance)
Weight of Bridge(cost)
As engineers, you want to maximize the
load held using the least amount of
material.

16. Testing Procedure
2” dowel
2” x 6”
thin plate
testing jig

17. Project Break-down
• Project Intro (Problem Definition)
• Component Strength Tests (Information Gathering)
• Individual Brainstorming of Ideas (Idea Generation)
• Group Prototype Brainstorming (Idea generation)
• Prototype Selection (Idea selection)
• Full-Scale Prototype Construction (Implementation)
• Prototype Testing (Information Gathering)
• Engineering Analysis w/ software (Information Gathering)
• Redesign (Idea generation)
• Final bridge construction (Implementation)
• Final Test Competition! (Information Gathering)

18. Project Schedule
Timeline:
• Prototype Design, Build, Test – 1 week
• Final Design, Build, Test – 2 weeks
• Presentation and report – 1 to 2 classes
after Final Test

19. Grading
• Design and testing
– Bridge Ideas -10%
– Components test Memo-5%
– Prototype bridge performance-5%
– Draft Report-5%
• Project report
– Bridge Final Presentation-10%
– Competition-5%

20. Engineering Fundamentals
• Mechanics of Materials
• Construction Methods & Hints!

21. What is the easiest way to
break a tongue depressor?
• Pull?
• Push?
• Twist?
• Shear?
• Bend?
Engineering terms - tension, compression, torsion,
shear, & bending
Principle of Scissors

22. Bending! Thus bridge design Do’s & Don’ts:
• DON’Ts
– avoid bending bridge members when
possible.
– avoid compressing long bridge members -
causes buckling (a kind of bending).
• DO’s
– load members in tension and compression
(short) when possible.
– brace bending members when possible.

23. Bridge Type we have learned
• Truss Bridge
• Arch Bridge
• Suspension Bridge
• Cantilever Bridge
– Box Girder Bridge

24. Quiz
• Which orientation of a beam is stronger
under bending and why?
• Arch members are in T or C?
• Label members in T and C
I
I
vs.
Axis of
bending
C C
T T T

25. How can you improve your
bridge design?
• Incorporate truss structure (triangles).
• Design a 3-D structure from the start!
• Use short members in compression.
• Use string for tension members.(Reduce material and
weight)
• Avoid overloading joints.
• Strengthen base supports and load point.

26. Component Test-Compression
and buckle Test-1
• Compress your spaghetti until it start to buckle(When you don’t feel
you need to apply additional force but the structure still keep bending)
• Hold(use you hand) the center point to see how much force you need
to increase to have buckling
• Hold another two point to see how much force you need to increase to
reach buckling

27. Component Test-Compression
and buckle Test-2
• Cut the spaghetti in half and try again
• Cut the spaghetti in half again and try again
• Record all the force and Test
Situation

28. Tension Test on the joint
• Specimen preparation
– Use four depressor
• Two as a group. Glue them together
• Drill one hole on the each group
• Overlap two group according to
test procedure and glue them together
• Use hook to hold the structure
• Start tension and compression test by
force gauge and scale
• Do unit conversion if necessary
• Take your record home and make excel plot
and report

29. Fatigue Test
• Bend Paper clip and count how many cycle
it is needed to break it!
• Test 5 Paper clip

30. Torsion Test
• Twist a chalk and see how it break
• Explain why it happen(explain in
Components test Memo )