A truss main chord is the primary structural member running along the top and bottom edges of a truss. The top chord mainly carries compression forces, while the bottom chord mainly carries tension forces. Together, they form the main load path of the truss and determine its strength, span capability, stiffness, and overall structural performance.
In most aluminum stage trusses, the main chord is the large-diameter tube visible on the outside of the truss. It is often called the main tube in manufacturing drawings and product specifications.
What Is a Main Chord?
Every truss consists of three primary elements:
Component | Function |
|---|
Top Chord | Carries compression force |
Bottom Chord | Carries tension force |
Web Members (Braces) | Transfer loads between chords |
Visualized simply:
Top Chord
──────────────
\ /\ /
\ / \ /
\/ \/
──────────────
Bottom Chord
The top and bottom chords form the primary structural skeleton of the truss.
Without these members, the web braces alone cannot carry significant loads.
Why Does the Main Chord Carry Most of the Load?
When a truss supports lighting, LED screens, speakers, or roofing systems, the structure bends slightly under load.
This bending creates:
Structural principle:
M→Top Chord Compression+Bottom Chord TensionM
Instead of resisting bending like a solid beam, a truss converts bending forces into axial forces inside the chords.
This is why trusses can achieve large spans with relatively low self-weight.
Why Main Chord Diameter Matters
For aluminum stage trusses, the main chord diameter is usually the first factor affecting load capacity.
Typical examples:
Main Chord Tube | Common Application |
|---|
30 × 2 mm | Light decorative truss |
50 × 2 mm | Medium-duty event truss |
50 × 3 mm | Professional stage truss |
50 × 4 mm | Heavy-duty roof systems |
Although the difference may appear small, structural capacity increases significantly with tube wall thickness and section properties.
This is why professional roof trusses almost always use larger main chords than simple exhibition trusses.
How Main Chords Determine Truss Span
One of the most important design limitations is span length.
As span increases:
The main chord must be strong enough to resist these effects.
A larger main chord allows:
Longer unsupported spans
Higher load capacity
Better stiffness
Reduced deflection
This is why large concert roof systems often use 520 mm, 760 mm, or even larger truss sections.
Related reading:
What is the Maximum Load Capacity of an Aluminum Lighting Truss System?
Main Chords in Modular Event Truss Systems
In modern stage and event structures, the main chord is not only a load-carrying member.
It also serves as:
Connection point for spigots
Bolt connection location
Rigging attachment position
Support for roof systems
Interface for accessories
Examples include:
Lighting truss systems
Roof truss systems
Exhibition truss systems
Speaker towers
LED support structures
Related guide:
What Is Lighting Truss? (Ultimate Guide for Stage, LED & Event Systems)
Material Selection for Main Chords
Most professional aluminum trusses use:
EN AW-6082 T6
Advantages:
High strength
Excellent fatigue resistance
Good corrosion resistance
Suitable for heavy-duty structures
Some lighter-duty systems use:
EN AW-6061 T6
Advantages:
Easier fabrication
Lower cost
Good overall performance
Material selection directly affects:
Yield strength
Deflection
Fatigue life
Maximum allowable load
Related reading:
Aluminum Material Guide
Common Misunderstandings About Truss Strength
Myth 1: More Braces Mean Stronger Truss
Not necessarily.
The primary strength usually comes from:
Main chord size
Material grade
Structural geometry
Braces mainly transfer forces between chords.
Myth 2: Larger Truss Width Always Means Higher Capacity
A wider truss helps stiffness, but capacity still depends heavily on chord design.
Myth 3: All 290 mm Trusses Have the Same Capacity
False.
Two trusses with identical external dimensions may have completely different load ratings if their chord thicknesses or materials differ.
Main Chord vs Web Members
Feature | Main Chord | Web Members |
|---|
Primary Load Path | Yes | No |
Compression/Tension | High | Moderate |
Controls Span | Yes | Limited |
Controls Capacity | Yes | Partial |
Structural Importance | Critical | Important |
The main chord is the backbone of the truss.
The web members help distribute and transfer loads, but the chords carry the majority of structural forces.
Conclusion
The main chord is the most important structural member in a truss system. By carrying compression and tension forces, it forms the primary load path that allows trusses to achieve long spans, high load capacities, and efficient material usage.
Whether designing a concert roof, lighting truss, exhibition structure, or speaker tower, understanding the role of the main chord is essential for selecting the correct truss system and ensuring structural safety.
