Weights and lifting
Lift weight of a steel piece with rigging and hook block
- where
- piece weight with fittings (kg)
- section mass per metre (kg/m)
- member length (m)
- fittings allowance (%)
- total lifted weight (t)
- rigging below the hook (kg)
- hook block if not deducted on the chart (kg)
- lifted load as a force (kN)
Explain this equation
Gives the total weight on the crane hook for one steel piece. Use it before every lift to compare with the crane’s load chart.
m_p is the piece itself: mass per metre w times length L, plus the fittings allowance f_a. r is everything rigged below the hook, such as slings, shackles, a spreader beam and tag lines. m_hb is the hook block, which only counts if the chart does not already allow for it. W is the total in tonnes and F_k is the same load as a force in kilonewtons.
The crane carries everything hanging from it, so all the parts simply add up. Dividing by 1000 turns kilograms into tonnes, and 9.81 converts a tonne of mass into kilonewtons of force under gravity.
Sense check: an 8 m length of 67 kg/m beam with end plates is about 560 kg; with 40 kg of rigging the hook sees about 0.6 t, roughly 6 kN.
Watch out: a heavy spreader beam or a hook block left out of the sum can be a large share of the load on light picks near the limit of the chart.
Total weight on the crane hook for a single steel piece: the member with its fittings, plus everything rigged below the hook.
Enter your values to see the result.
Good to know
BS 7121-1 requires the whole load on the hook to be counted: the piece, slings, shackles, spreader beams and the hook block where the chart does not already allow for it. Use the fabricator’s marked piece weight when available. 1 t is taken as 9.81 kN.
Common mistake
Leaving out the rigging and spreader, or using the bare section weight without the end plates and cleats.
Limits
Weight only. Sling angles, centre of gravity and lifting points must be checked separately as part of the lift plan.
Sources
- BS 7121-1:2016 Code of practice for safe use of cranes – General (lift planning, appointed person, total load on the hook)
- The Lifting Operations and Lifting Equipment Regulations 1998 (SI 1998/2307), reg. 8: lifting operations planned by a competent person, supervised and carried out safely
- HSE L113 Safe use of lifting equipment (LOLER Approved Code of Practice and guidance)
- SCI / Steel for Life Blue Book: section dimensions and properties (533 × 210 × 82 UKB: h 528.3, b 208.8, tw 9.6, tf 13.2, r 12.7 mm, A 105 cm²)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Always work to the engineer’s drawings and bending schedules, BS 8666, BS EN 1992, BS EN 1090-2, BS 5531/the BCSA National Structural Steelwork Specification and manufacturers’ data. Lifting must be planned under LOLER by a competent person.