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A truss plate is a device used to connect the different components of a truss, which is used to carry weight over a span of space. Truss plates are flat pieces of metal placed across the point where two or more different pieces meet. A plate is attached to each of the pieces and carries the load between them, making the connection stronger than it would be by connecting them together directly. A truss plate is often used with wooden members, such as two-by-fours, in home construction to facilitate the building of roof trusses; however, they are also used in many other types of construction such as with bridges and steel-framed structures.
In home construction, roof trusses are often pre-built at a factory or workshop, and then taken to the site where the home is being built. At the facility, the wooden components of the roof trusses are laid out in the correct pattern to distribute the weight of the roof properly to the load-bearing walls of the structure. A truss plate is cut to the shape of each of the connection points of the boards that make up the roof truss. Each truss plate is nailed or stapled into place, connecting the boards to one another in a single unit.
Truss plates tend to make the structure of the roof truss much stronger than it would be by nailing the boards directly together. When directly connected, there are relatively few nails in a small area of the truss, and the nails are inserted in the same direction that the weight of the roof will pull on the trusses. Therefore, when under stress, the nails connecting the truss will be pulled out.
A truss plate can extend as far down the board as needed to give the desired amount of surface area to connect the boards. With a much larger area, many more nails or staples can be used. In addition, the angle of the nails or staples is not in line with the direction of force, but directly opposed to it. The stresses on the connection joint are carried by the metal truss plate instead of the wooden framework.
Truss plates are also used to construct the trusses used for bridges, steel roofs, and other structures. With steel structures such as a railroad bridge, truss plates can be bolted, welded, or riveted into place, making the structure much stiffer and stronger. Other structures, such as the frameworks for large pieces of industrial machinery, also make use of truss plates, which are usually welded into place across the steel frames.