Beam tipping
Structural instability of bars

A bar loaded by end moments or loads transverse to its longitudinal axis is subjected to bending; a bar loaded in this way is usually called a beam.

Let's start with a beam whose cross-section is symmetrical with respect to the bending plane and is considered to be dimensionally stable, such as the I- or H-shaped cross-sections commonly used in structural steelwork for this purpose. The bending of such a beam around the low-inertia axis of its cross-section is manifested only by displacements v in the plane of stress, whatever the value of the stress.

If, on the other hand, the beam is bent around the axis of high inertia of its cross-section, it first undergoes displacements w in the bending plane. For a certain level of...