External and internal forces
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External and internal forces. There are TWO types of forces that designers MUST consider when designing structures. External Forces: forces that act on a structure from the OUTSIDE Internal Forces: forces that act a structure from WITHIN. External forces.

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External and internal forces

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External and internal forces

External and internal forces

  • There are TWO types of forces that designers MUST consider when designing structures.

  • External Forces: forces that act on a structure from the OUTSIDE

  • Internal Forces: forces that act a structure from WITHIN


External forces

External forces

  • What are some external forces you can think of?

  • The most obvious external force is gravity

  • External forces occur when……..

  • You push a swing, pull an elastic or throw a ball

  • External forces on buildings include…..

  • Wind, earthquakes, weight of people on the floors of the building and the weight of the building itself


Important things about external forces

Important things about external forces

POINT OF APPLICATION:

The precise point at which the force is applied

PLANE OF APPLICATION:

An imaginary flat surface through which an applied force passes

****the point and plane of application make a difference in how an applied force affects a structure. See page 278 in your text


Internal forces

Internal forces


Examples of the 4 internal forces

Examples of the 4 internal forces

  • Tension

  • Examples include: a stretched skipping rope, a trampoline, an electrical power line, a guitar string, the cables of a suspension bridge

  • Once the particles pass their breaking point the objects are unable to return to their original shape

  • Compression

  • Examples include: kicking a soccer ball, step on the sole of your shoe, lay your head on a foam cushion.

  • Compressed objects usually return to their original shape


Examples continued

Examples continued

  • Torsion

  • Examples include: when a skater twists in a jump, a washcloth is wrung out, a doorknob is turned.

  • Created when both ends of a structure are twisted or when one end is twisted and the other is left stationary

  • Shear

  • Examples include: scissors cutting paper, strong wind bending a tree


What do you remember

What do you remember?

The force acting within the rope is called?

shear torsion tension compression


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