🕑 Reading time: 1 minuteThere are a number of properties of a beam that an Engineer should be aware of as they dictate beam behaviour when subject to a load and ultimately represent possible areas or mechanisms for failure. The main ones being:
- Second moment of area (also referred to as the second moment of inertia): this depends on the cross section profile of the beam and is a measure of the resistance of the shape of the beam to bending.
- Bending moment: usually illustrated on a bending moment diagram, and often related the deflection of the beam, can be used to calculate regions subject to maximum bending forces and consequently most likely to yield. It also illustrates which sections of the beam are in compression or tension.
- Beam deflection: beam deflection tends to be undesirable and correlates to the bending moment.
- Shear diagrams: these are used to illustrate stress concentrations along the beam and provide a means to identify areas of maximum shear forces where the beam is more likely to fail by shear.
Figure 7 – Box section cross-section profileThe box section has the most efficient profile in loading both horizontally and vertically. It has a lower value for second moment of area so is less stiff. It can be calculated by using the formula: