Cantilever

Cantilever, in Engineering, is a special type of girder which, since its introduction on the Forth Bridge, is being generally adopted on girder bridges of large span all over the world. Essentially it means a girder fixed at one end and free at the other. The free ends of two cantilevers pointing towards each other may be connected by placing a smaller girder across, each free end supporting half the weight of the girder. The greatest strength of section is wanted at the fixed end, and consequently large cantilevers cannot be made uniform for their whole length, but must taper towards the free end. They are usually made of steel, and, as with ordinary metal girders, open lattice-work is used to brace the top and bottom booms together. On the Forth Bridge cantilevers are placed back to back so as to form three double brackets and therefore four spans, each bracket being balanced by the symmetrical disposition of its two cantilevers.