These structures rely heavily on torque and rotational equilibrium for their stability. This type of construction lends itself well to balanced cantilever construction where the bridge is built in both directions from a single support. Many box girder bridges are built segmentally, or in short pieces. Nearly all cable-stayed bridges are built using cantilevers as this is one of their chief advantages. Therefore, some truss arch bridges (see Navajo Bridge) are built from each side as cantilevers until the spans reach each other and are then jacked apart to stress them in compression before finally joining. This is very helpful when temporary supports, or falsework, cannot be used to support the structure while it is being built (e.g., over a busy roadway or river, or in a deep valley). The partially constructed structure creates a cantilever, but the completed structure does not act as a cantilever.
Temporary cantilevers are often used in construction. In the southern United States, a historic barn type is the cantilever barn of log construction. A cantilever in a traditionally timber framed building is called a jetty or forebay. The Forth Bridge in Scotland is an example of a cantilever truss bridge.
In cantilever bridges, the cantilevers are usually built as pairs, with each cantilever used to support one end of a central section. In bridges, towers, and buildings Ĭantilevers are widely found in construction, notably in cantilever bridges and balconies (see corbel). Ĭantilever construction allows overhanging structures without additional support. When subjected to a structural load at its far, unsupported end, the cantilever carries the load to the support where it applies a shear stress and a bending moment. Like other structural elements, a cantilever can be formed as a beam, plate, truss, or slab. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. The top and bottom example may be considered structurally equivalent, depending on the effective stiffness of the spring and beam element.Ī cantilever is a rigid structural element that extends horizontally and is supported at only one end. The bottom example is created by adding a Robin boundary condition to the beam element, which essentially adds an elastic spring to the end board. The middle example is created by an extension of a simple supported beam (such as the way a diving board is anchored and extends over the edge of a swimming pool).
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The top example has a full moment connection (like a horizontal flagpole bolted to the side of a building).
A schematic image of three types of cantilever.
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