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For more truss types, see truss types used in bridges. A large timber Howe truss in a commercial building. There are two basic types of truss: The pitched truss, or common truss, is characterized by its triangular shape. It is most often used for roof construction. Some common trusses are named according to their "web configuration".
Most trusses have the lower chord under tension and the upper chord under compression. In a cantilever truss the situation is reversed, at least over a portion of the span. The typical cantilever truss bridge is a "balanced cantilever", which enables the construction to proceed outward from a central vertical spar in each direction.
Two king post trusses linked to support a roof. Key:1: ridge beam, 2: purlins, 3: common rafters. This is an example of a "double roof" with principal rafters and common rafters. A timber roof truss is a structural framework of timbers designed to bridge the space above a room and to provide support for a roof.
A hammer-beam is a form of timber roof truss, allowing a hammerbeam roof to span greater than the length of any individual piece of timber.In place of a normal tie beam spanning the entire width of the roof, short beams – the hammer beams – are supported by curved braces from the wall, and hammer posts or arch-braces are built on top to support the rafters and typically a collar beam.
Illustration of a single intersection Pratt truss. An illustrated pamphlet, dated 1882, is available online.In this pamphlet, Wrought Iron Bridge claims that "during the past 18 years this firm have erected nearly 4,300 spans, varying in length from 20 to 300 feet."
The king post is the central, vertical member of the truss. Crown posts in the nave roof at Old Romney church, Kent, England. A king post (or king-post or kingpost) is a central vertical post used in architectural or bridge designs, working in tension to support a beam below from a truss apex above (whereas a crown post, though visually similar, supports items above from the beam below).
William Howe was a construction contractor in Massachusetts when he patented the Howe truss design in 1840. [3] That same year, he established the Howe Bridge Works to build bridges using his design. [4] The first Howe truss ever built was a single-lane, 75-foot (23 m) long bridge in Connecticut carrying a road. [1]
The Belfast truss is a cross between Town's lattice truss and the bowstring truss. It was developed in Ireland as a wide-span shallow rise roof truss for industrial structures. McTear & Co of Belfast, Ireland began fabricating these trusses in wood starting around 1866. By 1899, spans of 24 metres (79 ft) had been achieved, and in the 20th ...