greater than the SWL of the wire rope, the test weightwill be computed from the SWL of the wire rope or ifthe winch capacity is less than the SWL of the wirerope, the test weight will be computed from thecapacity of the winch. The winch capacity is eitherdocumented on the load charts or in themanufacturer’s manual.The formula for computing the SWL for a hoistrope is the diameter of the rope squared multiplied by8 or (D x D x 8 = SWL in tons).Example: The wire rope on a crane is 1/2 inch indiameter. Compute the SWL for the rope.The first step is to convert the 1/2 into a decimalnumber by dividing the bottom number of the fractioninto the top number of the fraction: (1 divided by2 = .5). Next, compute the SWL formula: (.5 x .5 x 8= 2 tons). The SWL of the l/2-inch wire rope is2 tons.The next factor to compute is the breakingstrength of the wire rope. On some wire rope spools,the nominal breaking strength of the wire rope ispublished; however, if the breaking strength isunknown, a break test can be performed on the wirerope. This is accomplished by cutting off sections ofthe wire rope and placing each section of the rope ona wire rope break test machine. The machine pulls thewire rope apart and computes the breaking strength.By testing several sections of the wire rope, you candetermine the average breaking strength for that typeof wire rope.Overseas, Public Works Centersnormally have wire rope break test machines that canbe used by the NCF.If the break test cannot beperformed, the rule of thumb used for finding thebreaking strength is to multiply the SWL by 5(SWL x 5 = B.S.). For example, a l/2-inch wire ropewith a SWL of 2 tons has a breaking strength of 10tons (2 x 5 = 10 tons).REMEMBER: When thesingle line wire rope end connection is assembledwith a wedge socket, the wedge socket only develops70 percent of the breaking strength. Example: Thecrane is rigged with l/2-inch wire rope with a wedgesocket end connection. The wedge socket onlydevelops seventy percent of the l/2-inch wire ropeB.S. of 10 tons, which gives the wire rope a B.S.determined by an end connection of 7 tons. Swagedsocket, cappel socket, and the zinc (spelter) socket allprovide 100 percent of the breaking strength whenproperly made.The next factor to compute is the AWL by usingthe factor of safety (F.S.). To compute the allowableworking load (AWL) of a wire rope, you must firstunderstand the following wire rope safety factors:1. Rigging ropea. 5 to 1 under operating conditionsb. 10 to 1 when used to lift personnel2. Pendants or standing ropea. 3.0 to 1 under operating conditionsb. 2.5 to 1 when erecting the boom3. Ropes that wind on drums or pass oversheavesa. 3.5 to 1 under operating conditionsb. 3.0 to 1 when erecting the boomFor the auxiliary line, use the F.S. of 3.5 for wirerope that winds on drums or passes over sheaves. Theformula for the F.S. is the breaking strength (B.S.),determined by the type of end connection divided byF.S. (Example: B.S. = 7 divided by 3.5 = AWL of2 tons.)The next factor to compute is the test weight.This is done by multiplying the AWL of 2 tons by 110percent (2 x 110% or 2 x 1.10 = 2.2 tons). Your testweight for the l/2-inch wire rope is 2.2 tons. After thetest weight is figured, you must remember that thehook blocks and rigging gear are weight that are partof the test weight.Leveling a crane cannot be overemphasized.Cranes must be set up as per manufacturer’sinstruction, with the outriggers fully extended and thecrane leveled. Crane capacity is lost when the craneis out of level by a few degrees (fig. 3-14). MostFigure 3-14.-Crane capacity lost by crane out of level.3-15

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