Rigging
Truss
01 — Definition
The structural framework that carries lighting, audio and video equipment overhead. Three families: box truss (the most common, four chords), triangle truss and ladder truss. Its capacity depends on the span, the position of the point load and the number of support points. A truss rated 500 kg as a uniformly distributed load (UDL) will not necessarily carry 500 kg as a centre point load: point load capacity is typically 25 to 50% of the UDL.
02 — In the field
Never hang point loads on a truss without calculating the actual bending moment. A 200 kg point load at the centre of a 10 m span creates a peak bending moment of about 4,900 N·m at mid-span (M = F·L/4, with F = 200 kg × 9.81) — a stress with nothing in common with a uniformly distributed load.