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The first joist in 1923 was a Warren truss type, with top and bottom chords of round bars and a web formed from a single continuous bent bar. Various other types were developed, but problems also followed because each manufacturer had their own design and fabrication standards.
Closed/open distinction is used in two ways to describe truss roofs. Closed truss: A truss with a tie beam; or; Roof framing with a ceiling so the framing is not visible. Open truss: A truss with an interrupted tie beam or scissor truss which allow a vaulted ceiling area; or; Roof framing open to view, not hidden by a ceiling. [4]
In the truss pictured above right, the bottom chord is in tension, and the top chord in compression. The diagonal and vertical members form the truss web, and carry the shear stress. Individually, they are also in tension and compression, the exact arrangement of forces is depending on the type of truss and again on the direction of bending.
Engineered components are commonly used to form floor, ceiling and roof structures in place of solid wood. I-joists (closed-web trusses) are often made from laminated woods, most often chipped poplar wood, in panels as thin as 1 cm (0.39 in), glued between horizontally laminated members of less than 4 cm by 4 cm (two-by-twos), to span distances ...
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.
Plank framed truss was the name for roof trusses made with planks rather than timber roof trusses. In the 20th century, it was typical for carpenters to make their own trusses by nailing planks together with wood plates at the joints. Today similar trusses are manufactured to engineering standards and use truss connector plates.
A truss roof with tongue and groove sheathing. The gap in the sheathing at the ridge is the space designed to allow natural ventilation. Pre-manufactured roof trusses come in a wide variety of styles. They are designed by the manufacturer for each specific building. Timber trusses also are built in a variety of styles using wood or metal joints.
True cruck or full cruck: The blades, straight or curved, extend from a foundation near the ground to the ridge. A full cruck does not need a tie beam and may be called a "full cruck - open" or with a tie beam a "full cruck - closed". [7] Base cruck: The tops of the blades are truncated by the first transverse member such as by a tie beam. [7]