Trusses::Fundamentals::Knowledgebase::SAFAS

Structure And Form Analysis System (SAFAS)

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Fundamentals

Trusses

Trusses are linear structures made of members that resist applied loads mainly through axial tension or compression rather than bending, and therefore they are structurally very efficient. However, this is valid only if the truss members are pin-connected and the loads act at the joints.

Deformation of a Truss Under Loads

Considering that the truss members are not subjected to any loads but at the joints (their ends), the internal forces of a truss member can be considered as shown below (note that there is no moment at the pins so the member can freely rotate):

Internal Forces in A Truss Member

Internal Forces in a Truss Member

where is the axial force and is the shear force.
Satisfying the equilibrium equation by taking sum of the moments about point A equal to zero :

Since is the length of the member and cannot be equal to zero, therefore,
This means that the truss members are subjected to axial forces(tension or compression) only.
There are various truss configurations. Some are shown below:

Pratt Truss

Howe Truss

Warren Truss

Common Types of Truss

Importantly, trusses are stable only if they are triangulated. This means that their configuration is made of triangles. If any member is removed such that this condition is violated, the truss becomes unstable. There is, however, one exception (Vierendeel truss).

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