A truss span is the measurement of the length of a truss. A truss is a rigid architectural framework comprised of one triangle or a series of triangular units used to displace weight in structures such as roofs, floors, and bridges. A variety of truss forms are used in architecture and engineering. The measurement of the truss span depends on the size of the structure it is designed to support.
In a standard truss, the truss span is measured from end to end or from the butt cut to the opposite butt cut. This is the term for a small 90-degree cut at the end of the truss. The truss span is calculated based on the material used to create the truss, the truss configuration, the greatest amount of weight it is meant to carry, also known as its load condition, and the load duration of the truss.
Trusses come in a variety of shapes. The most common form is called a common truss, a triangular shape most often associated with the typical roof line. Variations on the common design include the amount of triangular or zig-zag supports within the frame, as well as allowances for roof overhangs. The longer the truss span, the more triangular or zig-zag supports appear within the framework.
The cathedral truss is another variant on the truss form. It is similar to the common truss but makes allowances for vaulted, raised, or open ceilings within the architecture. Some truss shapes allow for the angle or pitch of the roof or support structure to differ from the norm, while other trusses allow for flat areas, such as a floor, within the form.
Engineering as well as architecture uses trusses, usually in the form of truss bridges. The same basic forms are used for bridges as for architecture, although the material can differ. In the case of larger geographical areas that need to be spanned, multiple trusses will be lined up one after the other, supported by pylons from below where they meet. Truss bridges became a popular building technique from the 1870s to the 1930s. The earliest truss bridge dates back to a design by Stephen H. Long in 1830.
Trusses are most often used in architecture and bridge construction. Trusses are also found in early aviation design. The truss was used in smaller biplanes, like those used in World War I, as a means to support the double wing structure.
