Construct a Truss Tower

1. Construct a Truss Tower Graphic retrieved from, http://www.world-city-photos.org/Paris/Eiffel_Tower/Pictures_of_Eiffel_Tower_black_and_white.jpg, on 5/11/2010 Graphic retrieved from, http://www.atlaso.com/images/bridge.jpg, on 4/09/2010

2. Construct a Truss Tower • Performance Objective: Given VEX parts construct a truss tower a minimum of 12” tall, and that will hold a weight ( > 5 lbs) without collapsing. • Enabling Objectives: • define the following terms: force, compression, tension, and shear • identify the forces acting on an object • explain how the geometric shape and orientation of an object can affect the strength of that object or assembly • explain the benefits of using certain geometric shapes over other shapes in the construction of a structure • design a truss bridge

3. Forces acting on a structure Force is a pressure on a body or structure If the force is great enough it will produce a change in movement or in shape of the body or structure Conceptually, a force can be thought of as a push or a pull acting on a structure or system In constructing a truss tower, the forces acting on members are compression, tension, and shear

4. Compression Graphic retrieved from, http://library.thinkquest.org/06aug/02102/Forces%20acting%20on%20Bridges.html, on 3/27/2010 Compression is a force or pressure that attempts to flatten or squeeze an object

5. Tension Graphic retrieved from, http://library.thinkquest.org/06aug/02102/Forces%20acting%20on%20Bridges.html, on 3/27/2010 Tension is a force that attempts to pull apart or stretch an object

6. Shear Graphic retrieved from, http://library.thinkquest.org/06aug/02102/Forces%20acting%20on%20Bridges.html, on 3/27/2010 Shear force attempts to cause the internal material of an object to slide against itself

7. Interaction of forces compression tension shear Graphic retrieved from, http://www.masstec.org/teched/mcasquestions.html, on 3/27/2010 When weight is applied to the beam below it experiences compression, tension, and shear forces

8. Forces Applied to Structures • Various geometric shapes can be used in the construction of a structure • Arcs, • Rectangles, • Triangles, • etc. • Different shapes react to forces in different ways

9. Arches keystone The Gateway Arch, St. Louis, MO Graphic retrieved from, http://upload.wikimedia.org/wikipedia/en/7/79/Gateway_Arch.jpg, on 4/09/2010 Graphic retrieved from, http://www.dkandsons.com/images/arch%20with%20keystone.JPG, on 4/09/2010 Arches have a keystone in the middle, that allow the sides of the arch to lean inward, applying a force to the keystone

10. Rectangles Graphic retrieved from, http://jouleconsultingengineers.co.uk/bigimages/640x480shed.jpg, on 4/09/2010 Modular apartment buildings are constructed using rectangles

11. Triangles Truss bridges Graphic retrieved from, http://www.prhs.k12.ny.us/fac/HerskowitzM/images/cascade_teft_truss_bridge_476_1971_ampprn.jpg, on 4/09/2010 Graphic retrieved from, http://www.atlaso.com/images/bridge.jpg, on 4/09/2010 Truss bridges use triangulation to support the weight or force

12. Combinations Graphic retrieved from, http://www.thetravelpeach.com/europe-vacations/france/eiffel-tower.jpg, on 4/09/2010 What shapes are used in the Eiffel Tower?

13. Strength and orientation of geometric shapes angle channel bar • Which shape and orientation gives the most structural strength when a force is applied?

14. Shape and Orientation • horizontally the bar has very little strength when force is applied • vertically the bar has goodstrength when force is applied A beam placed vertically is stronger than if placed horizontally

15. Bends add support • An angled shape has strength in two directions due to the bend in the material, minimizing flex as a force is applied. bend in bar Notice how this bar flexes or bends when force is applied

16. Additional bends • the strength is increased in this channel piece bend in bar Additional bends in the material create even more strength.

17. Strength of Geometric Shapes in structures • Which shape gives the most structural strength when a force is applied?

18. Squares No Force Applied What happens when you apply a force to the side of a square?

19. Squares Force Applied The square collapses, because it has no strength from side to side.

20. Squares No Force Applied What happens when your structure utilizes only square and rectangular shapes?

21. Squares Force Applied The structure is not able to hold its shape, and it collapses.

22. Triangles No Force Applied What happens when you apply a force to the side of a triangle?

23. Triangles A B Force Applied When force is applied to the side, member A is in tension, while member B is in compression, this allows the triangle to hold its shape.

24. Triangles No Force Applied What happens when you use triangulation in your square structure?

25. Triangles Force Applied When a force is applied, the structure will be able to hold its shape and not collapse.

26. Triangle vs. Square Notice how the triangle did not lose its shape as the square did when force was applied to the side. Using triangles in construction offers more structural support for an object than simple squares.

27. How does this apply to a robot? Here is a robot that won a regional competition What is good about the structural design? Why? What could be improved? Why?

28. Robot design Identify various shapes and structures used in this design.

29. Robot design • Here are various structures Bar with bend Channel Here are four possible triangles

30. The end Now don’t get bent out of shape over building your truss tower!