BCGBC4010A Apply structural principles to residential low-rise constructions

Structural principles - Structural members

Beams

Internal moment of resistance
Beam load 1
A simple graph can be drawn to represent the internal stresses in the beam.
The graph shows a vertical line with a dotted horizontal line drawn midway along it. This midline is labelled 'N/A' (neutral axis). Above this neutral axis a triangle is drawn to the left of the line and an arrow labelled 'C' (for compression) points to the left. Below the neutral axis is another triangle, drawn to the left of the line, and an arrow labelled 'T' (for tension) points to the right. These triangles indicate that the amount of compression and tension in the beam increases in a linear way as you move further from the neutral axis.
Beam load 2
The maximum compressive stress C (from compression) and the maximum tensile stress T (from tension) occur where the beam bends the most. The neutral axis N/A is in the centre of the beam.
A diagram shows the beam under load bent into a U shape. The neutral axis (N/A) is drawn midway along the whole length of the beam. Compression forces (labelled C) are drawn above the beam pointing towards each other halfway along the beam. Tension forces (labelled T) are drawn below the beam, pointing away from each other halfway along the beam.
A graphical representation of this shows arrows for compression above the neutral axis, and arrows for tension (pointing in the same direction) below the neutral axis. These arrows are shortest near the neutral axis and increase steadily in length further away from the neutral axis.
Beam load 3
The final graph is the resultant graph which indicates the internal stresses.
This graph shows compressive stresses above the neutral axis, pointing to the left, and tensile stresses below the neutral axis, pointing to the right. In both cases, the stresses increase steadily in length further from the neutral axis.

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