BCGBC4010A Apply structural principles to residential low-rise constructions

Structural principles - Structural members

Beams

Types of beams
Simply supported beams
Simply supported beams are supported at each end only.
A diagram of a simple beam supported at each end is shown. If downwards pressure is applied bending would occur at the middle of the beam.
Continuously supported beams
Continuously supported beams are supported by three or more support points. They deflect less than simple beams of the same span because the positive and negative bending cancel each other out. Generally a continuous span is 20% more efficient than a simple span as it is able to span longer distances.
A diagram of a simple beam supported at each end and in the middle of the beam. Bending downwards occurs in between the first support and the middle support, and again between the middle support and the end support. The beam bends upwards at the middle support. 
Cantilever beams
Cantilever beams overhang their supports. The cantilever section of the beam cannot support the same loads as the back span which is the section of beam between the supports. A typical allowance for the amount of cantilever in a beam is 30% of the back span therefore a 45 m beam could have a cantilever section 15 m long.
A diagram shows a simple beam supported at one end and at 30% from the other end. For this beam the bending occurs between the support.

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