How to Calculate Truss Span Load for Spigot Truss: A Practical Guide for Buyers
How to Calculate Truss Span Load for Spigot Truss
When planning a stage, exhibition, or lighting rig, one of the most critical steps is determining the correct truss span load for your spigot truss system. Spigot trusses (also called sleeve-block or cone trusses) are popular for their ease of assembly and structural reliability. However, improper load calculation can lead to dangerous failures. This guide explains how to calculate span loads using real, TÜV-tested data from our factory’s spigot truss range.
Understanding Distributed Load vs. Point Load
Truss load ratings are typically given in two forms:
- Distributed load (kg/m): The uniform weight per meter along the entire span.
- Point load (kg): A single concentrated weight applied at the center (or worst-case location) of the span.
For example, the WRF-29 Ladder Truss has a load table showing both values for spans from 1 to 6 meters. At a 3-meter span, it can support 168 kg/m distributed or 115 kg point load. Always check both values, as your actual load may be a combination.
Step-by-Step Calculation
- Determine the span – the distance between support points (e.g., 4 meters).
- Identify your load type – is it evenly spread (e.g., LED screen panels) or concentrated (e.g., a single lighting fixture)?
- Find the corresponding load rating from the manufacturer’s load table. For instance, the WRT-29 Triangle Truss at a 5-meter span supports 139 kg/m distributed or 348 kg point load.
- Apply a safety factor – industry standard is typically 4:1 or 5:1 for overhead suspension. Never exceed the rated load. If your load is 100 kg at a 5-meter span, ensure the point load rating exceeds 100 kg (it does: 348 kg).
- Consider deflection – even if load is within limits, excessive deflection may be unacceptable for aesthetic or functional reasons. Most aluminum trusses have a deflection limit of L/200 or L/300.
Real Data Examples from Our Spigot Truss Range
Below are load tables for key models. All data is TÜV-tested and certified.
WRF-29 Ladder Truss (50x3mm main tube, 25x2mm sub, 20x2mm brace)
| Span (m) | Distributed load (kg/m) | Point load (kg) |
|---|---|---|
| 1 | 990 | 990 |
| 2 | 340 | 340 |
| 3 | 168 | 115 |
| 4 | 87 | 43 |
| 5 | 51 | 20 |
| 6 | 26 | 10 |
WRT-29 Triangle Truss (50x3mm main, 30x2mm sub, 20x2mm brace)
| Span (m) | Distributed load (kg/m) | Point load (kg) |
|---|---|---|
| 3 | 371 | 557 |
| 4 | 250 | 500 |
| 5 | 139 | 348 |
| 6 | 109 | 327 |
| 7 | 85 | 298 |
| 8 | 67 | 268 |
WRS-29 Square Truss (50x3mm main, 25x2mm sub, 20x2mm brace)
| Span (m) | Distributed load (kg/m) | Point load (kg) |
|---|---|---|
| 1 | 1942 | 1942 |
| 2 | 976 | 1899 |
| 3 | 658 | 1766 |
| 4 | 488 | 1466 |
| 5 | 392 | 1150 |
| 6 | 317 | 948 |
WRS-30 Square Truss (same tube specs as WRS-29)
Same load table as WRS-29.
WRS-40 Square Truss (50x3mm main, 30x2mm sub, 25x2mm brace)
| Span (m) | Distributed load (kg/m) | Point load (kg) |
|---|---|---|
| 3 | 936 | 718 |
| 4 | 732 | 680 |
| 5 | 465 | 644 |
| 6 | 320 | 612 |
| 7 | 232 | 585 |
| 8 | 176 | 560 |
WRS-4060 Square Truss (50x3mm main, 50x2mm sub, 30x2mm brace)
| Span (m) | Distributed load (kg/m) | Point load (kg) |
|---|---|---|
| 4 | 805 | 1610 |
| 5 | 560 | 1400 |
| 6 | 403 | 1209 |
| 7 | 301 | 1054 |
| 8 | 247 | 988 |
| 9 | 210 | 945 |
WRS-52 520x520 Square Truss (50x3mm main, 50x2mm sub, 25x2mm brace)
| Span (m) | Distributed load (kg/m) | Point load (kg) |
|---|---|---|
| 7 | 460 | 1255 |
| 8 | 346 | 1130 |
| 9 | 303 | 1008 |
| 10 | 241 | 923 |
| 11 | 182 | 885 |
| 12 | 164 | 782 |
WRS-5060 500x600 Square Truss (50x3mm main, 50x2mm sub, 30x2mm brace)
| Span (m) | Distributed load (kg/m) | Point load (kg) |
|---|---|---|
| 4 | 805 | 1610 |
| 5 | 560 | 1400 |
| 6 | 403 | 1209 |
| 7 | 301 | 1054 |
| 8 | 247 | 988 |
| 9 | 210 | 945 |
Practical Tips for Buyers
- Always use the load table for the exact model you intend to buy. Never assume similar sizes have identical ratings.
- Consider the truss profile. Ladder trusses (WRF-29) are lightweight and best for low-load applications like LED walls. Triangle trusses (WRT-29) offer good strength-to-weight ratio for lighting. Square trusses (WRS series) provide higher load capacities and are ideal for heavy rigging.
- Factor in dynamic loads. Wind, movement, and suspended personnel increase risk. For overhead suspension, always use a safety factor of at least 4:1.
- Check material and welding quality. All our spigot trusses use 6082/6061-T6 aluminum with TÜV certification.
- Plan for connections. Spigot truss systems rely on cone connectors and locking pins. Ensure your span includes the truss length plus connector overlap (typically 10-15 cm per joint).
Common Mistakes in Span Load Calculation
- Ignoring point load limits. A distributed load may be safe, but a single heavy fixture in the center could exceed the point load rating.
- Using the wrong load table. Different truss profiles have different ratings even at the same span.
- Overlooking deflection. Even if the load is within limits, excessive sag can damage equipment or look unprofessional.
- Not accounting for truss self-weight. The load table typically excludes the truss weight, so add it to your total load.
FAQ
Q: What is the safety factor for spigot truss load calculations? A: Industry best practice is a safety factor of 4:1 for overhead suspension. Our load tables are based on ultimate strength, so divide the table values by 4 for working load limits.
Q: Can I mix different truss models in one span? A: It is not recommended unless the connection is designed for it. Always use the same model and manufacturer for consistent load capacity.
Q: How do I calculate the total load for a mixed setup? A: Sum all point loads and distributed loads. Convert distributed loads to total weight (distributed load × span) and add point loads. Then compare to the truss’s rated distributed and point loads.
Q: Where can I find the load tables for your trusses? A: Load tables are published on each product page. For example, see WRS-29 Square Truss for its table.
Conclusion
Calculating truss span load for spigot truss systems requires careful attention to span length, load type, and manufacturer data. By using the TÜV-tested load tables provided for our WRF-29, WRT-29, WRS-29, WRS-30, WRS-40, WRS-4060, WRS-52, and WRS-5060 models, you can confidently design safe and reliable structures. Always consult with a structural engineer for complex installations and never exceed rated capacities.