Soft footing.The ground condition must have enough stability and bearing capacity to support all loads placed on it by the crane. Extreme caution should be used when performing lift operations beside buildings, especially if newly constructed with uncompacted backfill, along trenches, or in areas where water mains, sewer pipes or steam lines are buried. Improper use of outriggers. If lifting on outriggers, the load chart rating applies only when all the outrigger beams are fully extended and all tires are clear of the ground. If these two conditions are not met, then the “on rubber” capacity charts should be used. If lifting on rubber, the load chart ratings apply only when tires are in accordance with the manufacturer’s specifications and in good condition, and the specified tire pressure is maintained. Some mobile cranes have load charts for mid-extended outrigger beams. For such cranes, the outriggers should still be extended to the proper point and all of the tires must be clear of the ground. Unbalanced rope reeving occurs whenever the main hoist line is reeved to one side of the boom tip. This condition causes the boom to twist, which subsequently reduces the rated capacity of the crane. Full chart ratings may only be applied when the boom tip is symmetrically rigged. On singleline reeving, when the hoist line runs along the center sheave or on the sheave beside the centerline of the boom, the boom twist is minimized. On multi-part reeved systems, if the parts of the line are evenly distributed on either side of the boom centerline, the boom twist will also be minimized. Be sure to check the manufacturer’s reeving diagrams to ensure proper reeving. Most important, operators must know the configuration of the crane, ensure the configuration is correct, and use the appropriate load chart. What is the configuration of the hoist reeving?.What counterweights are used? Are they configured according to the manufacturer’s specifications?.What type of boom is used? What is the boom length? Where are the boom insert locations?.Load chart ratings may only be applied if the machine is rigged according to the manufacturer’s specifications. Some of these factors are described below. The first step in creating a lift plan is to understand the factors affecting the strength and stability of mobile cranes.
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