9.+Structures

 =AHL. Topic 9. Structures .=





**__Structures are designed to:__**

 * **Support. ** || **Protect. ** ||
 * [[image:http://www.asd.co.uk/special_needs/options/leg_supports/leg-rest2_240.jpg align="center"]] || [[image:http://shoei.motorhelmets.com/shoei-crash-proof-dummy-head.jpg align="center"]] ||
 * **Cover.** || **Span.** ||
 * [[image:http://www.bdonline.co.uk/Pictures/468xAny/l/k/v/Foster_smith_roofC_ready.jpg width="292" height="251" align="center"]] || [[image:Bridge.gif width="282" height="253" align="center"]] ||



__**Structures can be natural or manufactured****.** __
Can you see recognise that parts of your skeleton have evolved to do some very specific things. Skull? Rib Cage? Legs? Feet? What have these specific parts eveloved to do? || ||
 * Your skeleton is a very good example of a natural structure.

**__When manufatcured structures fail, the results can be catastrophic. __**

 * **Twin Towers.** || **Tacoma Narrows Bridge.** ||
 * [[image:http://dnowlan.ca/VM/science7/structures/wtc_collapse5.jpg width="320" height="241"]] || media type="youtube" key="P0Fi1VcbpAI" height="344" width="425" ||

  <span style="font-family: 'Comic Sans MS',cursive;">
 * <span style="font-family: 'Comic Sans MS',cursive;">**Youngs Modulus.**
 * <span style="font-family: 'Comic Sans MS',cursive;">**Forces.**
 * <span style="font-family: 'Comic Sans MS',cursive;">**Strength and Stiffness.**
 * <span style="font-family: 'Comic Sans MS',cursive;">**Beams.**


 * media type="youtube" key="YdqvGGFIbfc" height="344" width="425" || [[image:http://www.geom.uiuc.edu/education/calc-init/static-beam/img/stress-strain.gif link="http://www.geom.uiuc.edu/education/calc-init/static-beam/img/stress-strain.gif"]] ||
 * //[|Tensile test]// || //What is stress and strain?// ||

<span style="font-family: 'Comic Sans MS',cursive;">Useful Links.

[|Visual structures data base.]

<span style="font-family: 'Comic Sans MS',cursive;">The key term you must know here is "**youngs modulus**", you must understand that this is "**__the stiffness of a material__**".

Formulae that you must know linked to this topic.

The stiffness, //k//, of a body is a measure of the resistance offered by an elastic body to deformation (bending, stretching or compression). where //P// is a steady force applied on the body δ is the displacement produced by the force (for instance, the deflection of a beam, or the change in length of a stretched spring)
 * Youngs modulus =**


 * Stress =** Stress is a measure of how strong a material is. This is defined as how much pressure the material can stand without undergoing some sort of physical change.



where σ = stress and F = force (in Newtons) and A = the cross sectional area of the sample.

Geometrical measure of deformation representing the relative displacement between particles in a material body. Strains are produced by [|stresses] induced on the material body by external forces or temperature changes.
 * Strain =**


 * Lchange =** Change in Length.
 * L=** Original Length.


 * Stiffness =

Factor of Safety = Design Factor = Failure Load / Design Load**