1. Structural Analysis of Truss Bridges
Triangles, Forces, Labeling, and Designing!

2. Structural Analysis
Structural analysis is a mathematical examination of a complex structure
Analysis breaks a complex system down to individual component parts
Uses geometry, trigonometry, algebra, and basic physics

3. What Makes this Truss Bridge Strong?
A structural analysis is used to determine the load carrying capability of this truss bridge.
This is pretty close to the bridge the students just constructed. Challenge the students to identify if there are any differences in this bridge and the one they just completed. (The two center diagonals are in opposite directions than the manila folder bridges)

4. This Truss Bridge is Built from Right Trianglesc θ1 θ2
Stress the simple concepts stated before will be used to complete the structural analysis of the truss bridge. It is made of right triangles, an object they have seen over and over again in math class.
Ask students how many geometric shapes they can recognize. There are right triangles, isosceles triangles, rectangles, parallelograms, trapezoids, etc. Also ask them to identify angle bisectors, parallel and perpendicular lines, and right angles. If you get bold, ask how many triangles they can find.

5. How many triangles?
15!
A structural analysis is used to determine the load carrying capability of this truss bridge.
This is pretty close to the bridge the students just constructed. Challenge the students to identify if there are any differences in this bridge and the one they just completed. (The two center diagonals are in opposite directions than the manila folder bridges)

6. Forces

7. 3 Types of Forces
Push
Pull
Torque

8. Identify the Forces

9. Balanced Forces Balanced forces mean no movement.
Think of two people who kick a soccer ball at the same time in opposite directions.
The ball won’t move!
Why?
The force were balanced!

10. Break it into Parts:
A structural analysis is used to determine the load carrying capability of this truss bridge.
This is pretty close to the bridge the students just constructed. Challenge the students to identify if there are any differences in this bridge and the one they just completed. (The two center diagonals are in opposite directions than the manila folder bridges)

11. What does each piece do?

12. Why have the green piece?
Spreads out forces.
Fewer forces spread out means the bridge won’t turn into a board ready to be karate-chopped.

13. Balancing Forces

14. Sum up: Triangles divert weight to edges.
Have supports in the triangles (to make them right triangles) to spread out forces on the roadway and truss.

15. Drawing your Design
A structural analysis is used to determine the load carrying capability of this truss bridge.
This is pretty close to the bridge the students just constructed. Challenge the students to identify if there are any differences in this bridge and the one they just completed. (The two center diagonals are in opposite directions than the manila folder bridges)

16. Labeling your Design, and then Labeling the Wood Itself
Label Joints
Wood pieces will be named by their joints.
This helps you communicate to your partner, and to transfer designs from paper to real life!
Name the pieces! A C D B E F
A structural analysis is used to determine the load carrying capability of this truss bridge.
This is pretty close to the bridge the students just constructed. Challenge the students to identify if there are any differences in this bridge and the one they just completed. (The two center diagonals are in opposite directions than the manila folder bridges)

17. Keep in mind:
Spread out your forces (don’t leave too much push force on 1 joint without counterbalancing with a pull force on the same joint!)
Try to divert forces to the sides of the bridge with plenty of triangles.
Minimize torque! It will twist and break your bridge!

18. What NOT to do.
Poor form

19. Paper on joints (adds too much strength)

20. Poor angles

21. Beams too short

22. Check it out.

23. Leaning Bridge of Balsa