DOE-STD-1090-96, DOE Standard Hoisting and Rigging Manual ...

DOE-STD-I090-96 (Rev-I)11.3 SLINGS11.3.1 Generala. Slings shall have a minimum design factorappropriate to the type ofmaterial as specified inthe appropriate section. Features that affect therated capacity of the sling and that shall beconsidered in calculating the design factor are:1. Nominal breaking strength ofmaterialfrom which it is constructed.2. Splicing or end-attachment efficiency.3. Number ofparts in the sling.4. Type ofhitch (e.g., straight pull,choker hitch, or baskethitch).5. Angle ofloading and load center ofgravity.6. Diameter ofcurvature around whichthe sling is bent.b. Published working loads for chain slings areusually based on 25-33 percent ofthe breakingstrength.c. The center ofgravity of an object is a pointaround which the entire weight may beconcentrated. To make a level lift, the crane hookorpoint ofsuspension must be directly above thispoint. While slight variations are usuallypermissible, ifthe crane hook is too far to one sideofthe center ofgravity, dangerous tilting willresult and should be corrected at once. For thisreason, when the center ofgravity is closer to onepoint of the sling attachment than to the other, theslings must be ofunequal length. Sling stressesand sling angles will also be unequal (seeFigure 11-6).d. Slings shall be secured or terminated at thecrane hook so that the sling does not reeve or slipthrough the hook. To attach the load, locate thecenter ofgravity, position the crane hook directlyabove the center ofgravity, and then rig the loadso that it will lift level and true.11.3.1.1 Load Angle Factora. The following is an example ofselecting asling using the load angle factors shown in Figure11-7.1. Load=1,000 lb.2. Sling=2-legged bridle.3. Angle with horizontal=45 degrees.4. Load angle factor from Figure 11-7 =1.414.b. Each ofthe two legs would lift 500 Ib ifavertical lift were made. However, there is a 45sling angle involved. Therefore, the 500-lb loadwould be multiplied by the load-angle factor in thechart, giving a total of7071b (500 lb x 1.414)tension in each sling leg. Each sling leg, therefore,must have a rated capacity ofat least 707 lb.11.3.1.2 Safe Loada. The rated capacity or working load limit(WIL) of a sling varies depending on the type ofhitch. The rated capacity tables in this sectionshow the applications for which the various safeloads apply when the slings are new. All ratingsare in pounds (lbs).b. Figures 11-8 and 11-9 provide informationfor determining the total rated capacity of3-legand 4-leg bridle slings. Select multiple-leg slingsso as not to introduce a working load in directtension in any leg greater than that permitted.Two legs should be considered to carry the loadbecause in normal lifting practice, the load will notbe uniformly distributed on all legs. Ifriggingtechniques, verified by a qualified rigger, ensurethat the load is evenly distributed then full use ofthree legs is allowed. Special rigging techniquesverified by a member of a qualified engineeringorganization shall be required to prove that a loadis evenly distributed over four or more sling legs.Chapter 11Wire Rope and Slings 11-8