﻿ TRUSS CALCULATIONS - STAGECRAFT PRODUCTION SERVICE # CALCULATION OF LIGHTING TRUSS LOADS

### —How to hang a lighting truss—

Normally weight is computed in pounds or kilograms, lenths are coumputed in feet or meters. Always use the same unit of measure for all calculations.

As always, before suspending loads overhead consult a qualified engineer or rigger.
A speaker cabinet is an example of a single point load. In this case, the total weight of the cabinet, it's hardware and cabling is figured at 100%. An empty truss to be hung on two points is an example of an uniformly distributed load when all of the weight is between the two points. Here the weight is evenly divided between the two points. A uniformly distributed load on three points. When a third point is added, the center point carries over half of the load. The general formula for computing point loads. The following diagrams illustrate how the formula applies to various load configurations. Point loads between two hang points. As the point load approaches a hanging point, the load on that point increases while the load on the other point decreases proportionately. Cantilever point loads. When loads point loads are cantilevered, the net effect results in additional phantom load on both points that increases on both points the greater the cantilevered distance. Uniformly distributed cantilever loads. When the cantilevered load is uniformly distributed (say for example drapery), the calculation is the same as point load however, you treat the total UDL as centered on a single point in the mid point of the cantilever. Again, due to the leveraging, the net effect will result in additional phantom load on both points. Cite as: Stagecraft Production Service. "Calculation of Lighting Truss Loads". 30 January 2019. https://bit.ly/2TfBOKw