A king post is a part of a truss system used in construction to support roof elements. It has a decorative function and was evident in medieval Europe in churches and barns. King posts help distribute weight and prevent sagging, but have limitations for long spans. They are also used in bridge design and aviation.
A king post is part of a supporting structural element called a truss system, a structure used in construction to support roof elements. A truss consists of a horizontal beam connected at the ends to two beams which in turn rise diagonally to meet at the apex, or highest point, of a triangle, with the kingpost extending from the midpoint of the lower beam at the apex of the trellis. A king post truss is the simplest form of truss system and is an efficient support commonly used in buildings and bridges.
In medieval Europe, king truss systems were evident in Romanesque and Gothic period churches and tithe barns. King’s seats, or crown seats, originated in the late 13th century, becoming common after the 13th. During this period, architectural styles featured high ceilings and long aisled corridors.
These tall structures required many trusses to support the weight of the expansive roofs. Ceiling architecture during this period was often meant to be seen. The king posts adopted a decorative function as well as a structural one. Over the following centuries, this type of construction was increasingly common in large public buildings and smaller rural barns and parish churches, especially in Great Britain.
Structurally, the king posts help distribute the weight of the ridge beam to the other parts of the truss and prevent sagging of the tie beam, or horizontal beam. The two diagonal parts of the truss serve as the roof beams and the horizontal part is the ceiling joist. If two king suits are used next to each other, each is called a queen suit.
King posts can also be used in bridge design. While a king’s post system is highly efficient, it has its limitations. As the tie length gets longer, the truss must be built proportionately higher, making it unsuitable for long spans. A single kingpost can only be used on short span bridges. On a bridge with longer spans, additional diagonal support can be added, forming a multiple truss system.
In aviation, a king post refers to the vertical bracing posts used in wire-braced monoplanes and biplanes in the early 20th century. In the 1920s, the use of king poles on biplanes made wing-walking stunts possible, as the upright pole gave the walker something to grip during stunts. The use of king seats in aviation continues to be common, especially in microlights and other bolstered aircraft.
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