Once you have a working solution for each of your rotation increments, you'll want to check that your weight distribution assumption was reasonable.Assess the wind and weather to ensure the safe operation of the multiple crane. Determine communication methods and test those communication methods prior to commencing the lift. Select personnel with appropriate qualifications and experience to undertake the lift. Any imbalance means the assumed sling angles (e.g. Assign cranes that meet the lift criteria specified in the planning. Check statics (sum of vertical and horizontal forces) for each of your components.You will often need to assume a weight distribution between the rigging points to eliminate another variable. With rolling blocks, the total load in any sling has to be constant, which eliminates one variable.For a two-level rigging problem like this, you'll need to start with a guess at the locations of the middle-level blocks. Next, geometry (sling lengths and rigging points) will suggest the angles of each sling at any given rotation.The crane hook will always be aligned with this CG. Find the CG of the pick, and how it will relate to the load geometry as the load is tripped up (at least 15 degree increments, if not smaller).If a more detailed solution is warranted, start from the basics. Instability can be addressed through using fixed length slings, but use of a tagline from the ground or auxiliary line ("whip line) from the crane is more common for tripping operations. The load won't be evenly distributed between all the points either, but somewhere in between. That said, snatch blocks do pretty much prevent the weight from being split between only 2 attachment points (as can happen with fixed length rigging). Rarely do you save a lot of time and money by optimizing rigging.
PhamEng's approach works, and can be a good starting point. RE: calculation of load distribution on multi-lifting points with multiple snatch blocks I'd say the first set should be static slings, and then a system of blocks could help balance the load.Īgain, all this is just shooting in the dark because I don't know the specifics. It creates an awfully unstable arrangement. I also question the use of blocks at every juncture. I imagine your arrangement might warrant some reduction, but how much I don't know. 1) A static crane lifts a mass from solid ground using a 4-leg lifting system with the load equally distributed between each leg: Winch operating speed (v) is 0.3m/s (17 seconds to raise a load 5m) Young's modulus (E) for the wire rope (see CalQlata's Wire Rope calculator) used for your lifting legs is 2.7E+10N/m. Given the consequences of failure, it's a good idea to be extra conservative.Ĭertain lifting devices - spreader bars, lifting beams, load compensators, etc. There are a lot of variables here and it's entirely plausible that through wear and tear on the rigging equipment, slight variations in length from the manufacturer, an error on the part of the rigger or crane operator, or a hundred other little things you could end up with all the weight on just 2 attachment points. This may seem extreme, and it is, but for good reason. There isn't anywhere near enough information here to go with, but in general I'd start with 1/2 of the weight of the panel for each lift point, all hardware and the connections having a factor of safety of 5. I see now this is for precast and the other is for a truss. The writer hold no responsibility to any misdeeds.Sorry - very similar topics. The details obtained by using this method will allow you to ensure that the whole lifting was performed well inside the cranes radius.ĭisclaimer : The above stated information is solely for the purpose of reference additional factors such as ground conditions,Proximity hazards all are to be taken into account for. Work out the obtained data along with the cranes rated duty charts while preparing the lift plan.Take account of the radius, boom length and other contributory factors(See my Blog on Selection of cranes and calculating the Gross load). Now u have the value of F1 to calculate F2, Subtract "F1" from "P" (weight of load) '''c''' is the distance between the leftmost to the position of the cog (center of gravity) (M)ġ.- The resultant force acting on the object is zero.Ģ.- The sum of the moments acting on an object must be zero.į1 x (c-a) = (P x (l-b-c)) - (F1 x (l-b-c)) '''b''' is the distance between the rightmost to the position of the sling from crane number 2 (M) '''a''' is the distance between the leftmost to the position of the sling from crane number 1 (M) '''F2''' is the weight soported by crane number 2 (Tons) '''F1''' is the weight soported by crane number 1 (Tons) '''P''' is the weight of the piece (Tons)
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