Internal and External Forces Act on Structures

 A force is a push or pull that causes an object to change its movement or shape

1) Magnitude  The stronger the force the more effect it will have on a structure 2) Direction  The direction of the force acting on a structure will determine its effect 3) Location  The location on a structure where the force acts will effect the outcome

 The unit used for measuring force is called a Newton (N)  1 Newton is the amount of force needed to hold a mass of 100 grams  How many Newtons would be needed to hold a 1 kg book?

 An external force is a force that is applied on a structure by something outside of the structure  Gusts of wind, waves in the ocean, and the Earth’s gravity are examples  Mass  The amount of matter in an object  Weight  The amount of gravity acting on an object

 Gravity acts on all parts of a structure  The Centre or gravity is the specific point where the mass of the structure is evenly distributed  To make a structure more stable, it must have a wider base  A wider base puts most of the mass near the ground, and lowers the Centre of gravity

 Static Load  The weight of a structure  These forces stay the same for long periods of time  Examples are the wood, nails, screws used to hold a bookcase together  Dynamic Load  An external force that moves or changes over time  Examples include the powerful gusts of wind that blow in Grande Cache or cars driving over a bridge

Beam Bridge Arch Bridge Suspension Bridge Truss Bridge

 An internal force is when one part of a structure puts force on another part of the same structure  Push the palms of your hands together and you can feel the internal forces within your muscles  There are 3 types of internal forces:  Compression  Tension  Shear  When more than one of these forces act on a structure they are called complementary forces

The Parthenon was built in 432 BC in Athens, Greece for the goddess Athena and stood intact until 1687 when gunpowder stored inside was detonated This Roman aqueduct was built between AD in Spain and stretches over 16 km. It is called El Puente which means “The Bridge”

TRIANGLE

 The arch can support a large load b/c the force of the load is carried down through the arch to the foundation  The keystone is the center piece of the arch and is the most important part of the arch

 I-beams are stronger than simple beams and have less mass  Girders are long, hollow rectangular prisms  A truss is a framework of beams usually arranged into interlocking triangles  A cantilever is a beam supported only at one end (a diving board)

 A solid structure that stands by itself or can support beams  Usually circular  Very common in ancient architecture

 Structural Stress  The combination of internal and external forces that act on a structure and weaken it  Structural Fatigue  A permanent change in the a structure caused by internal forces (compression, tension, or shear)  Cracks in a structure are a sign of this  Structural Failure  Occurs when a structure can no longer stand up to the forces acting on it  Think of the video of the collapsing bridge