FAQ >> Wind and Tower Cranes

Wind and Tower Cranes

Like most mobile rigs, self-erecting cranes can fold up on short notice. All other tower cranes must ride out severe storms. That requirement has induced engineers to identify two principal classes of load combinations germane to the design of these machines: hi-service loads act on the crane in operation, and out-oj-service loads occur under the influence of high winds when the crane is unmanned. Some cranes have an additional load case that applies only when the crane is in the process of climbing. Each load case combines the dead weight of the crane with an appropriate dose of wind and other relevant factors. In-service loading is composed of the dead load, a permissible wind for operation, stewing torsion, the tilled load and impact. Out-of-service loading combines dead load and a storm wind that ideally should be suited to the locale where the crane is operating. Designed to European codes and standards, freestanding toner cranes are generally evaluated for storm winds of 94 mi/h (42 m/s) at jib elevation, but design practices with respect to wind may vary with the manufacturer or country of origin. Some areas are prone to more extreme winds. In the United States, these regions are on the Atlantic, Gulf, and Northwest coasts as well as some river valleys and mountain passes. Installation practices should be adjusted for those regions. A heavier mast and foundation might be used or the freestanding height reduced. Alternately, a contingency plan to guy, brace, or remove the crane might be considered. When in the midst of climbing, a tower crane is in a balanced stance that may be particularly sensitive to disturbance from wind (Figure 2.4l ). In order to assure that the climbing operation is well-controlled, the wind limitation is often set particularly low, usually 20 to 25 mi/h (9 to 11m/s).

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