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Load Radius

Radius is just a straight line measurement…from the very center of any circle to the outside edge of that same circle.

With respect to cranes, radius is the horizontal (level) distance from the center pin of the crane to the center of gravity of the load being lifted. You measure, with your tape measure stretched flat and level, from the middle of the load to the middle of the crane. Usually, the longest reach or ‘radius’ required is to where the load is to be placed or installed, so you have to make that measurement as if the load were already there- to the center of where its weight is going to be. Just remember, all ‘radius’ is is a horizontal measurement in feet from where the middle of the crane is set up to where the the middle of the load needs to be.

The center pin of the crane is generally about in the middle of the deck of the crane and is usually, nowadays, a stump containing dozens of hydraulic and electrical connections rather than a pin. By definition any mobile construction crane can swing a load, in other words, the whole upper structure including the boom with the load hanging from it can be easily and smoothly made to rotate about a center point on the job site. That center point is directly under the middle of the crane where the center of the big ring gear would be. All future crane operations from that crane set up site are relative to that center point. The decisions about weight and reach are all based on the distance from where the load needs to be placed back to that center point… the load radius!

The “center of gravity” is just a term for the very middle of the weight of the load. This is not always the tape measured middle of the unit. If the load is a bundle of 12 foot long 2X4s then the center of gravity (c.g.) is indeed pretty close to 6′ from one the end and about half way across the bundle. If the load is a 50′ steel wide flange beam, the c.g. is pretty much exactly 25′ from the end, go ahead and choke it right there-it’ll pick 9 times out of 10. Most rooftop HVAC units, on the other hand, have heavier internal components concentrated toward one end/side or the other. You can’t accurately determine the c.g. of most HVAC units with a tape measure. Use a good long chain four way and test lift it, then adjust chain links to satisfactory level for your crew.

The exact location of the c.g. notwithstanding, if you are so close to overloading your crane that one or two feet internal weight distribution makes a difference, it is usually best to move the crane closer to the load destination.