Rigging
Point Load vs UDL
Definition
A truss can carry weight as a uniformly distributed load (UDL) or as point loads. A UDL spreads the weight evenly along the span and gives the highest rating a truss can carry. A point load concentrates the weight at one spot and creates a bending moment that peaks at mid-span, so a truss rated 500 kg UDL may accept only 150 to 250 kg as a single centre point load. Several point loads are combined and checked against the manufacturer's load table for that span.
In the field
A truss UDL figure does not apply to a single heavy fixture hung at mid-span. Point loads are checked in the manufacturer's load table for the exact span, and the permissible point load is a fraction of the UDL.
Related lessons
Sources
- ANSI E1.2-2021 (ESTA), Design, manufacture and use of aluminum trusses and towers : conception, fabrication et usage des trusses et tours en aluminium · webstore.ansi.org
- EN 17115:2018, Entertainment technology — Specifications for design and manufacture of aluminium and steel trusses : conception et fabrication des trusses en Europe · knowledge.bsigroup.com
- Structural Basics, Beam moment formulas : M = F·L/4 (charge centrale) contre M = W·L/8 (charge répartie) · structuralbasics.com