Design Guide: Trusses

What is a Truss?Trusses comprise of individual members connected at joints or nodes, creating a system of interconnected triangular elements that work together to form a rigid structure. 
All loads and reactions are assumed to act only at pinned nodes, so no shear or moment is transferred between members. As such, truss members are subject to axial loading only which is beneficial because it means section sizes can be greatly reduced. Pin connections found in trusses are also much cheaper compared to moment connections, making trusses a relatively cheap option for a structure.
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Truss Components
This guide will discuss truss forms, their features, and how to design them. But first, check out the activity below to understand how triangular elements work in a truss.
✏️ Quick Activity
Understanding from First PrinciplesWhy are triangles and resulting trusses so effective at resisting load? 
These shapes perform well since no shear or bending develops in the system’s individual members when the load is applied at nodes. As the nodes are pinned, equilibrium at the connection is achieved through opposing vectorised loads in each connecting member.
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Vectors
Each member connected to the node will take a percentage of the imposed load in axial force proportional to its angular position. In the example above, the horizontal members take no vertical load, given they're at 90 degrees to the force F, but they take the horizontal reaction load induced by the angled chords. 
💪Let's take a look at a 2D Truss in action!
As you can see, there is no shear or bending in any of the members. The only force is axial!
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Loading Condition on a Warren Truss
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Axial Force (T = tension, C = compression, 0 = zero force member)
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Shear Force Diagram
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Bending Moment Diagram
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Magnified Deformed shape
Trusses, the triangular marvelSo in short, trusses - the triangular marvel - are great because they:
Achieve long-span structures such as bridges and stadiums.
Minimise the weight of the structure by efficiently distributing loads through the triangular arrangement and thus enabling a lean member design.
Carry heavy loads and provide robust support.
Resist lateral load, such as wind or seismic forces. See our Design guide: Steel Bracing Systems for more information about how steel bracing can be effectively used in a lateral stability system.
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Stadium roof trusses
Explore more on TrussesTake a deep dive into the world of trusses and check out:
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Common Truss Types
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Truss Analysis
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Steps for Designing Truss Members to Australian Standards
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Also check out our 2D Truss Analysis using OpenSeesPy calculator!
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