Cantilever

CANTILEVER, a beam supported at one end and carrying a load at the free extremity, or distributed evenly all along the exposed portion. The upper half of the thickness of such a beam is subjected to tensile stress, tending to elongate the fibres; the lower half to compressive stress, tending to crush them. Canti levers are employed extensively in building, steel constructional work, and machines. In the first specified any sort of wood or steel or masonry or concrete beam built into a wall and with free end projecting forms a cantilever ; brackets of braced type are also used in small and large dimensions. The longer cantilevers have to be incorporated in a building when clear space is required below, the cantilevers carrying a gallery, roof, canopy, part of the building above or a runway for an overhead travelling crane.

A good example of a cantilever sustaining a portion of a workshop

out over a yard appears in fig. 1.

In bridge building a cantilever construction is employed for

large spans, the classic type being that of the Forth bridge, having girders connecting up the ends of the huge cantilevers, fig. 2. The clear span between the piers is nearly one-third of a mile. Cantilever cranes are necessary when a considerable area has to be served, as in steel stockyards, and shipbuilding berths. In the lighter types a central travelling tower sustains the cantilever girders on either side : the big hammer-head cranes (made in capacities up to 30o tons) for fitting-out basins have a fixed tower and revolving pivot reaching down therein, to rotate the cantilever in a circle. These cranes are outlined in fig. 2. Block setting Titan cranes have a very large reach of the cantilever, besides being mounted on a travelling carriage, to move out to sea as the block-setting proceeds.

In motor-car construction a cantilever spring was formerly much used for rear suspensions. Such a spring is anchored to the frame at the centre and at the forward end, the rear end being sup ported by the axle housing.