Truss bridges are one of the oldest types of modern bridges. 19th- and early 20th-century engineers. A truss bridge is economical to construct because it uses materials efficiently. Timber truss design pdf purposes of analysis, trusses are assumed to be pin jointed where the straight components meet.
If the top member is sufficiently stiff then this vertical element may be eliminated. The ability to distribute the forces in various ways has led to a large variety of truss bridge types. Some types may be more advantageous when wood is employed for compression elements while other types may be easier to erect in particular site conditions, or when the balance between labor, machinery and material costs have certain favorable proportions. The inclusion of the elements shown is largely an engineering decision based upon economics, being a balance between the costs of raw materials, off-site fabrication, component transportation, on-site erection, the availability of machinery and the cost of labor.