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Rigging Formulas Pdf
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2 lifting calculation method index stress determination on sleeves, spherical head anchors and flat head anchors 1. Weight of precast unit.
Rigging math • 1. Rigging MathCalculating our WLL from catalog WLL • BasicallyWLL=UL(d) • BasicallyWorking Load Limit Design Factor WLL=UL(d) Ultimate Load • But More LikeWorking Load Limit Design Factor WLL=UL(d)(e) Ultimate Load Efficiency UL(Force Ratio) • And Actually My Working Load Limit My Design Factor WLL=UL(d)(e) Ultimate Load Efficiency UL(Force Ratio)Catalog WLL/(d) Vendor Design Factor • OrWLL=(Catalog WLL/Vendor Design Factor)(Force Ratio)(Design Factor)(Efficiency) But I can’t remember ever using precisely that formula. • Terms• WLL – Working Load Limit – Safe Working Load – Maximum Allowed Force – A derived strength value based on the Ultimate Load and the Design Factor • Terms• UL – Ultimate Load – Failure Load – Minimum Failure Load – Breaking Strength – Minimum Breaking Strength – The applied force that causes failure • Terms• Design Factor – Safety Factor “saferty factor”• A mathematical value applied to provide appropriate capacity for unknown influences• Usually expressed as a ratio, i.e. “10:1” • Terms• Efficiency• The nature of the application may require the load capacity to be reduced• Some things that change efficiency – D/d Ratio – Type of termination • Terms• Force Ratio• The nature of the application may require the applied load to be increased• Something causing a force ratio – Accelerations • 16 FPM Chain hoists add 25% on stop and start • Work In Steps• Remember – Is this really the load? – Do I get full capacity?
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– Am I comparing apples & apples • Apples = Breaking Strength • Oranges = Vendor Working Load Limit • Peaches = My Working Load Limit – Do Not Exceed Vendor Working Load Limit • Work In Steps• To derive your WLL for a given component – Multiply UL by your Design Factor • Include efficiency calculation if necessary• To find UL – Look it up in the vendor information – Multiply vendor WLL by their Design Factor • Example• If the catalog WLL of a given ¼” screw pin anchor shackle is ½ Ton, what is the maximum applied force I can apply using a 10:1 Design Factor? • Example• ¼” Shackle has a WLL of 1/2t or 1000#• If you follow the asterisk you see this:• “Maximum Ultimate Strength is 6 times the Working Load” • Example• Vendor WLL=1000#• Vendor Design Factor = 6:1 Strip their design• Ultimate load = 6000# factor to get to breaking strength and then apply our more conservative• My Design Factor = 10:1 design factor to get to our WLL.• My WLL= 6000#/10• My WLL= 600# • Example• What is the maximum load I can apply to a sling of ¼” 6x19 IWRC Cable terminated at each end with wire rope clips used in a “basket” over a 1 ½ Schedule 40 pipe.
