Basic beam behaviour
Beam analysis is generally based on simplifying assumptions.
The detailed behaviour of a beam is complex and exact analysis requires considerable mathematical sophistication. However, the vast majority of beams can be designed using engineering beam theory. This is based on a number of simplifying assumptions.
The structural action of a beam is represented by internal forces called bending moments and shear forces.
A beam is subjected to two sets of external forces. These are the loads applied to the beam and reactions to the loads from the supports. The beam transfers the external load set to the external reaction set by a system of internal forces.
Engineering beam theory identifies two types of internal force – bending moments and shear forces. The behaviour of any beam is characterised by the magnitude and distribution of these forces. At any point in the beam, the internal shear force and the internal bending moment can be represented as pairs of forces.
The bending moment and shear forces vary along the beam length and are often represented diagramatically.
These internal forces may vary along the length of the beam and are usually represented as separate bending moment and shear force diagrams.
The calculation of bending moments and shear forces is traditionally part of structural analysis and is beyond the scope of this unit.
