A truss is a framework of triangles used to span large distances efficiently. The triangle is the key. It is the only polygon that cannot change shape without bending its sides. Arrange triangles in a row or a web, and you get a structure that is strong, stiff, and light.

Trusses are used in roofs, bridges, and floors. A roof truss spans from wall to wall and supports the roof covering. A bridge truss carries traffic across a river or valley. A floor truss supports a floor above an open space. Trusses can be made of timber, steel, or a combination of both.

The members of a truss carry either tension or compression. Top chords are usually in compression. Bottom chords are usually in tension. Diagonals and verticals transfer forces between them. The joints, called nodes, are where the members meet. In a pin-jointed truss, the members are assumed to rotate freely at the nodes, which simplifies the analysis.

Trusses are efficient because they place material where it is needed and remove it where it is not. A truss can span a distance that would require a much heavier solid beam. That efficiency is why trusses are everywhere, from the roof of a warehouse to the deck of a bridge.