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

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
There are three major types of bridges:
The beam bridge
The arch bridge
The suspension bridge
The biggest difference between the three is the distances they can cross in a single span. A span is the distance between two bridge supports, whether they are columns, towers or the wall of a canyon. A modern beam bridge, for instance, is likely to span a distance of up to 200 feet (60 meters), while a modern arch can safely span up to 800 or 1,000 feet (240 to 300 m). A suspension bridge, the pinnacle of bridge technology, is capable of spanning up to 7,000 feet (2,100 m).
What allows an arch bridge to span greater distances than a beam bridge, or a suspension bridge to span a distance seven times that of an arch bridge? The answer lies in how each bridge type deals with two important forces called compression and tension:
Compression is a force that acts to compress or shorten the thing it is acting on.
Tension is a force that acts to expand or lengthen the thing it is acting on.
A simple, everyday example of compression and tension is a spring. When we press down, or push the two ends of the spring together, we compress it. The force of compression shortens the spring. When we pull up, or pull apart the two ends, we create tension in the spring. The force of tension lengthens the spring.
Compression and tension are present in all bridges, and it's the job of the bridge design to handle these forces without buckling or snapping. Buckling is what happens when the force of compression overcomes an object's ability to handle compression, and snapping is what happens when the force of tension overcomes an object's ability to handle tension. The best way to deal with these forces is to either dissipate them or transfer them. To dissipate force is to spread it out over a greater area, so that no one spot has to bear the brunt of the concentrated force. To transfer force is to move it from an area of weakness to an area of strength, an area designed to handle the force. An arch bridge is a good example of dissipation, while a suspension bridge is a good example of transference.
Reference web sites:

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

7. Truss

8. Deck

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

10. Function of Arch structure
Puts members in compression.
Need horizontal support at abutments.
Abutment
Arch reduce the bending on the member !

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

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

13. Tower Design

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

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

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

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

18. 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.

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

20. 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)

21. 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
Prototype test: 10/10
Final design test 10/19

22. 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%

23. Engineering Fundamentals
Mechanics of Materials
Construction Methods & Hints!

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

25. Bending! Thus bridge design Do’s & 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.

26. Bridge Type we have learned
Truss Bridge
Arch Bridge
Suspension Bridge
Cantilever Bridge
Box Girder Bridge

27. Quiz
Axis of bending
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
vs. I
C C
T T T

28. 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.

29. 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

30. 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

31. 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

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

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