Truss is a structure of connected elements forming triangular units, and a bridge whose load-bearing superstructure is composed of a truss is a truss bridge.
From the mechanical point of view, truss structures are highly efficient in using the strengths of construction materials due to the fact that only axial forces are resisted in truss members.
Trusses are generally assumed as pinned connection between adjacent truss members. Therefore, truss members like chords, verticals and diagonals act only in either tension or compression.
Moreover, a truss is generally more rigid than a beam because a truss is composed of a variant of triangles and it has the ability of dissipate a load through the whole truss. The truss bridge is also called a beam bridge with braces.
Owing to its simple design method and efficient use of materials, a truss bridge is economical to design and construct.
Short-span truss bridges are built as simply supported, while the large-span truss bridges are generally built as continuous truss bridges or cantilever truss bridges.
All these truss configurations can be used as an under-slung truss, a semi-through truss, or a through truss bridge.