In something less than ten years the placing of concrete for high buildings has been revolutionized by the self-climbing tower cranes. Without these cranes these is some doubt as to whether many complicated high structures could have been economically justified under present-day construction conditions. There are many reasons why the tower cranes have been so well accepted. Chief advantages lie in their speed plus their ability to pinpoint materials- forms, reinforcement, concrete- exactly where needed. This adds up t immense savings in time and labor. On restricted city sites the cranes take up little room; they can operate virtually at the center of a structure and thus avoid any need for turning or maneuvering space. This can often mean that the problem of traffic jams and detours disappears. Additionally, the tower cranes are silent. Since the driving and hoisting mechanism is electric powered, there is none of the growling, vari-powered noise associated with conventional diesel-powered crawler cranes, especially under heavy loads.