Box truss

Box truss is a four-chord aluminium lattice, built in straight lengths with corner blocks and bolted or coned together on site. It is the structure a lighting rig, an LED wall or a line array is attached to, and it is designed and documented under a published standard for aluminium trusses and towers.

Its capacity is not a single number. A truss is rated for an allowable load that is in addition to its own weight, and that allowance falls as the span between supports grows. The same length of truss that will carry a heavy rig on two points a short distance apart will carry far less across a wide opening, and will deflect visibly before it is anywhere near failure. This is why a truss quote is tied to a drawing, not to a length.

How the load sits on it matters as much as how much there is. A truss is designed for loads applied at its nodes, spread along its length. Hanging a concentrated weight at mid-span between panel points is a different problem from hanging the same weight at a joint, and a heavy point load in the middle of a long span is the arrangement most likely to be wrong.

Truss is also inspected on a documented cycle rather than when it looks bent. A dented chord or an elongated bolt hole is a repair decision, not a cosmetic one.

Staging and rigging — owned inventory, our own crew, and a site survey before anything is specified.

• Ground support Towers standing on the floor to hold a rig up, used when the building has no points to hang from or there is no building at all — and engineering rather than equipment.
• Chain motor The electric hoist that lifts truss and scenery into the air on a loop of chain — rated by capacity, and not by itself a licence to leave a load hanging over people.
• Rigging point One place where a load is attached to the building — counted and rated individually, because the building cares where the weight is, not how much is in the room.