Structural Engineering & Statics
where the load goes
Concept

Rigging — where it appears

The arrangement of slings, spreaders and lifting points by which a load is picked up. Each leg is a two-force member whose force is its share of the weight divided by the sine of its angle, so shallow slings multiply the force and push the horizontal components through whatever is being lifted.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

1015202530354045500510152025beam length (m)factor of safety against rolling1.5, a working factorpast 42 m30 m: 13.3

Hung from above and still unstable

A rigid body hanging from a point above its centre of gravity is a pendulum and cannot fall over. A beam is not rigid, and tilting it puts a component of its own weight sideways — which bows it, which moves its centre of gravity further out. Past a length there is no hook height at which it hangs stably at all, and the length arrives as a fourth power.

stability · lift stability 20004000600080001000012000140000200400600800distance between lateral restraintsthey cross at 4086the plastic capacity of the sectionelastic critical momentSt Venant torsion alone — what is left at long lengthswarping dominates here

The load that moves with the twist

A beam about to buckle sideways is beginning to rotate, and everything attached to it rotates with it. A load hung from the top flange swings out over the side and drives the rotation on; the same load hung underneath swings back and stops it. Two identical beams, two different capacities, and the only difference is a height.

stability · load height

Named alongside it

The objects these essays reach for when they reach for this one.

ImperfectionStabilityBracingCentre of gravityCompression flangeCritical loadEigenvalueEquilibriumErection stabilityFactor of safetyLateral stiffnessLateral torsional

All concepts