Truss and Layher Systems for Stage Structures

Box truss, with its square cross-section, offers high torsional rigidity and is ideal for long-span applications like main PA hangs, roof structures, and heavy lighting grids. Its four-chord design distributes loads evenly, making it the go-to for flown arrays and ground-supported towers where lateral stability is critical.

Triangular truss, lighter and more aerodynamic, is commonly used for horizontal runs, catwalks, and smaller spans where weight savings matter. Its three-chord geometry provides excellent strength-to-weight ratio but less torsional resistance than box truss. For SSOUNDS line array deployments, we typically specify box truss for main hangs and triangular truss for delay towers or side fills, balancing load capacity and rigging speed.

Spigot connections (also called cone or pin connections) use tapered pins and quick-release mechanisms, enabling fast assembly and disassembly—critical for touring and festival setups. They are common in triangular truss and some box truss systems, but require precise alignment and can be less rigid under heavy dynamic loads.

Bolt connections, using grade 8.8 or 10.9 bolts through flanged joints, offer superior strength and fatigue resistance. They are standard in heavy-duty box truss and Layher-style modular structures where long-term stability and high load ratings are required. SSOUNDS recommends bolted connections for flown arrays exceeding 12m span or any structure supporting more than 500kg point loads, as they eliminate the micro-movement that can cause fretting over extended events.

Every truss system must be used within its published span and loading tables, which specify maximum uniform and point loads for given spans. These tables are derived from structural analysis considering material (typically 6082-T6 aluminium), chord diameter, wall thickness, and bracing pattern. For example, a 12m box truss with 50mm chords may support a uniform load of 800kg, but only 300kg point load at mid-span.

SSOUNDS engineers use these tables to design PA rigging grids, ensuring that the combined weight of loudspeakers, cables, and any additional equipment stays within a 4:1 safety factor (or local code requirement). We also account for dynamic loading from wind, crowd movement, and vibration—especially in outdoor festival settings. Always consult the manufacturer's current load charts; never exceed the rated capacity, and factor in the weight of the truss itself.

Ground-supported structures (goalpost towers, ground support roofs) rely on base plates, outriggers, and ballast to resist overturning. They are simpler to install and do not require building tie-offs, making them ideal for outdoor events without existing rigging points. However, they occupy stage footprint and limit sightlines.

Flown systems, suspended from a venue's roof or dedicated truss grids, offer unobstructed stage areas and better sightlines but demand rigorous engineering of the hanging points, steelwork, and fall protection. SSOUNDS often designs hybrid solutions: ground-supported delay towers for front-of-house and flown arrays for main PA, optimising coverage while maintaining structural integrity. For flown systems, we always verify the venue's load capacity and use certified rigging hardware.

Layher-style modular scaffolding systems, with their wedge-lock connections and standardised components (verticals, horizontals, diagonals), have become the industry standard for temporary stages, roofs, and grandstands. The all-round system allows rapid assembly without tools, and its high load capacity (up to 45kN per leg in some configurations) supports large audiences.

For stage decks, Layher decks (e.g., 1.5m x 1.5m or 2m x 1m) are laid on a grid of transoms and bearers, with adjustable base jacks for uneven ground. Roof structures use truss-like girders or lattice beams to span up to 30m, often with a fabric or solid roof covering. Grandstands are built using stepped frames and handrails, with load capacities designed for seated or standing audiences. SSOUNDS works with certified structural engineers to integrate PA hang points into these systems, ensuring that loudspeaker loads are transmitted directly to the main vertical supports.

The engineering process begins with a site survey and structural analysis using software like Autodesk Robot or Dlubal RFEM. Load cases include dead loads (truss, speakers, lighting), live loads (wind, rain, crowd), and dynamic loads (wind gusts, crowd sway). Connections are modelled as pinned or rigid, and deflection limits (typically L/200 for truss) are checked.

Assembly follows a strict sequence: base plates and outriggers first, then vertical towers, then horizontal trusses, with diagonal bracing installed progressively. All bolts are torqued to spec, and spigot pins are secured with split pins or clips. After assembly, a load test may be performed using water bags or calibrated weights to verify the structure's capacity. SSOUNDS recommends that all rigging be supervised by a qualified rigger or structural engineer, and that a full inspection log is maintained for every event.