BCGBC4010A Apply structural principles to residential low-rise constructions

Structural principles - Structural members

Beams

Actual deflection
Span
The longer the span, the greater the deflection. The load on the beam is 2 kN and the beam is supported at both ends. As the beam increases in length the deflection also increases.
Load
Point loads and uniformly distributed loads have different effects on the deflection of a beam. However, in both cases an increase in the load results in a greater deflection.
A diagram shows a beam supported at both ends. With a 2 kN load there is a slight deflection. With a load of 4 kN the deflection is greater.
Beam shape
This property is represented by the second moment of area (or moment of inertia) which evaluates the resistance of a shape to bending. The same beam resting on its edge will bend differently to the beam resting on the flat side as the beam on edge has more resistance to deflection. 
A diagram shows two beams, each resting on two supports. Each beam has a 2 kN load being applied at its central point. Both beams have an 'I' shaped cross-section, but for the first beam the 'I' is longer and thinner. The first beam is not deflected as much as the second beam.
Note that although the cross-sectional area is identical for both beams, they function differently in different positions.
Material 
This is the relative strength of the material represented by the modulus of elasticity (also known as Young's modulus and is a measure of the stiffness of material), eg mild steel is stronger than aluminium and will bend less under load.
A diagram shows two beams, one of steel and one of aluminium. Each beam is supported at both ends, with a 2 kN load. 
The deflection of the steel beam is not as great as the deflection of the aluminium beam.

End fixity
The way the beam is attached to the supports will affect the amount of deflection. A beam that is rigidly held in place will deflect less than one that is free to slide or rotate.
Image 1
A picture of a beam supported by two brick members. There is a 2 kN load on the beam. Deflection does not affect the ends of the beam that is connected to the brick wall. Deflection affects the middle of the beam only.
Image 2
A beam is placed on two round members and is free to slide. There is a 2 kN load and the deflection is much greater than in image 1.
Camber
A designer may deliberately incorporate camber (a bend) into a beam knowing that there will be some degree of deflection in the beam. The camber is placed in the opposite direction to the deflection and is equal to the amount that the beam is expected to deflect.
The deflection in the first beam is shown relative to its original position before the load has been applied. This deflection is the same as the amount of camber built into the second beam so that when deflected the second beam will flatten out.
Image 1
A picture of a beam after a load has been applied. The beam is deflected in the middle so it forms a slight 'U' shape.
Image 2
A picture of a beam that starts off curved upwards so when the load is applied it flattens out.

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