A swinging derrick rotates its boom and suspended load about the mast axis. This calculator multiplies an entered load by entered horizontal radius and compares that moment with a user-entered reference. OSHA requires approved derrick load ratings for corresponding boom angles or operating radii; the entered reference is not such a rating.
Swinging Derrick Crane Interactive Calculator
Vary entered load, horizontal radius, moment reference and illustrated boom length. Results show W times R and reference quotients only, not a crane rating.
Equation Used
- Load acts vertically at the entered horizontal radius.
- The entered moment reference is not treated as certified capacity.
- Boom length controls the illustration. The outputs use load, radius and entered moment reference; a straight boom requires R no greater than L.
- Boom, hook, block and rigging weights, reeving, dynamics, side load, wind, mast, guys, foundations, stability, structure and safety factors are omitted.
Ideal Swinging-derrick Moment Scenario
OSHA defines swing as horizontal rotation of a crane's upper structure or a derrick's mast and boom about its axis of rotation. A vertical load W at horizontal radius R creates a moment magnitude W times R in the vertical plane of the boom, about the reference point at the mast. It is not torque about the vertical swing axis.
Actual rated loads depend on the approved derrick configuration and load chart, including boom angle or operating radius. The calculator's entered moment reference is not an approved rating.
What This Explanatory Model Is Useful For
The calculator makes load-times-radius scaling visible and reports simple comparisons with a user-entered reference. The illustration also flags an entered radius greater than the entered straight-boom length as geometrically inconsistent.
Actual operation must use the manufacturer-approved load chart, configuration, reeving and procedures. OSHA requires rotation speed to keep the load within a controllable radius.
Ideal Moment and Reference Comparison
The displayed Mref/R quotient and max(0,M-Mref) excess are arithmetic consequences of the entered reference. Neither is a certified capacity or overload limit.
Worked Example: Entered Scenario
For W = 50 tons and R = 40 ft, ideal load moment is 2,000 ton-ft. Against an entered 3,000 ton-ft reference, M/reference is 66.7 percent, reference/R is 75.0 tons and excess over reference is zero.
Those values do not include the boom, hook block, rigging or dynamic effects and do not establish a safe hook load.
Model Boundary
- Calculated: entered load times entered radius, a percentage of entered reference, reference/radius quotient and nonnegative excess.
- Regulatory boundary: actual rated load comes from the approved chart for the derrick's boom angle or radius, length, configuration and reeving.
- Not calculated: component weights, dynamic amplification, side loading, wire rope, hoist, boom, mast, guys, foundations, stability, wind, structure, acceleration, braking or controllability.
Frequently Asked Questions
Is M/reference a crane utilization ratio?
No. This tool treats the reference as a user-entered scenario value and does not establish crane utilization or capacity.
Is reference/R the maximum load?
No. It is an arithmetic quotient and omits the factors behind a rated load chart.
Why flag R greater than L?
A straight boom's horizontal projection cannot exceed its length. The tool accepts independent radius and length entries and flags this inconsistency.
Does boom length affect the outputs?
No. Boom length controls the illustration here. Actual load charts depend on boom length and configuration.
Are hook block and rigging weights included?
No.
Can this replace the load chart?
No. Use the approved chart and operating procedures.
References
- OSHA 1910.181, Derricks: swing definition, approved load ratings and charts by boom angle or operating radius.
- OSHA 1917.45, Cranes and derricks: durable rating charts over operating radii and boom lengths; manufacturer ratings not to be exceeded.
- OSHA 1926.1417, Operation: rated-capacity compliance and controlled rotational speed.
- OSHA 3433, Cranes and Derricks in Construction: load-chart and operating requirements.
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