MOBILE CRANES
Heavy lift planning and simulation for mobile cranes Planning and preparation before performing any high-risk activity is always good practice, and particularly when lifting heavy equipment, preparedness ensures that there are no surprises, and the lift is performed according to plan, and performed safely. Some of the planning tools that can be used for heavy and complex crane lifts, are Computer Aided Design (CAD) software and crane manufacturer simulation systems allow the user the ability to simulate the crane set up and simulate the lift virtually, using the specific crane’s load chart and specifications. To lift a 3ton air conditioner unit, on top of a building 60m high, and pace the unit 20m into the building, from the building’s edge. Crane positioned on roadway ensuring outriggers jacks are not positioned above electrical and other services beneath the road surface. Using simulation software for a 200-ton crane, we are able to select the best boom and fixed fly combination to ensure boom clearance with the building edge, and ability to reach the desired placing radius and height. Using the outrigger loading calculator, the point loads under each outrigger can be calculated, in tons, in order to ensure that ground conditions are adequate to support the high loadings generated by the crane during the lift. Based on this calculation, the crane supplier can determine what size of outrigger support plate should be used to spread the loading. Typically, an outrigger pad measuring 2m x 2m should be used under each outrigger, thereby generating pressures of 47 ton / 4m2 = 11.75 tons per m2. If these pressures are still too high, by using a larger outrigger pad of say 3m x 3m = 9m2 the pressure would be
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Lifting Africa - Nov/Dec 2021
reduced to 47 ton / 9m2 = 5.2 tons per m2 which is substantially reduced. The planning software can also be used to establish maximum allowable wind speeds for crane to operate, based on the size of the load. For load (air conditioner module 2m x 2m = 4m2 (Ap) the maximum allowable wind speed of the crane is reduced from 7m/s down to 6.06 m/s due to the relatively large surface area of the load and compared to the relative light mass of the load. Lifting operations performed in wind speeds exceeding 6.06 m/s could exert excessive wind load forces on the crane, and cause a failure.
Johnson Crane Hire (Pty) Ltd, +27 (0) 11 455 9222, PeterY@jch.co.za, www.jch.co.za
