trusses

n architecture, a truss is a structure comprising one or more triangular units constructed with straight members whose ends are connected at joints referred to as nodes. External forces and reactions to those forces are considered to act only at the nodes and result in forces in the members which are either tensile or compressive forces. Moments (torques) are explicitly excluded because, and only because, all the joints in a truss are treated as revolutes.
A planar truss is one where all the members and nodes lie within a two dimensional plane, while a space truss has members and nodes extending into three dimensions. The top beams in a truss are called top chords and are generally in compression, the bottom beams are called bottom chords and are generally in tension, the interior beams are called webs, and the areas inside the webs are called panels.[1]
Etymology of truss[edit]

Truss is derived from Old French trousse, around c.1200, which means "collection of things bound together."[2][3] The term truss has often been used to describe any assembly of members such as a cruck frame[4][5] or couple of rafters[6][7] but often means the engineering sense of "A truss is a single plane framework of individual structural member connected at their ends of forms a series of triangle (sic) to span a large distance."[8]
Characteristics of trusses[edit]

A truss consists of straight members connected at joints, traditionally termed panel points. Trusses are composed of triangles because of the structural stability of that shape and design. A triangle is the simplest geometric figure that will not change shape when the lengths of the sides are fixed.[9] In comparison, both the angles and the lengths of a four-sided figure must be fixed for it to retain its shape.Planar truss[edit]

Planar roof trusses

The roof trusses of the basilica di Santa Croce (Florence)
The simplest form of a truss is one single triangle. This type of truss is seen in a framed roof