Tower crane tip capacity and wind limit
A hammerhead tower crane is being configured for a project. The jib is 55 m, the counter-jib is 18 m, and the load chart for the current free-standing height of 42 m shows 1.25 t at the jib tip. The site needs to lift a 1.15 t formwork bundle at a 52 m radius and a 2.0 t concrete skip at 30 m. The crane has a 6 t maximum capacity and is currently reeved in two-fall. The operator argues the bundle is acceptable because 1.15 t is below the 1.25 t tip rating. The lift plan lists the bundle at 1.15 t but omits a 90 kg spreader beam and 35 kg of slings. Wind at the top of the mast is forecast at 15 m/s; the load chart permits only 12 m/s for the bundle's 4 m² sail area, although the manufacturer's out-of-service limit is 20 m/s. The crane is free-standing and the tie-in design is not yet approved. Both lifts are scheduled for tomorrow.
1. Is the proposed configuration and reeving adequate for both lifts? Show the capacity check and identify the controlling issue.
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The bundle lift is not acceptable. The actual suspended load is 1.15 t + 0.09 t + 0.035 t = 1.275 t. At a 52 m radius the chart tip capacity is 1.25 t, so the load exceeds the rating by 0.025 t before any allowance for hook block, dynamic effects or unlisted rigging. The operator's comparison with the bare bundle weight is wrong because the spreader beam and slings are part of the load.
The wind check independently stops the lift. The forecast wind at the mast top is 15 m/s, but the chart limit for this 4 m² sail area is 12 m/s. The manufacturer's 20 m/s out-of-service figure is not a permission to lift; it is a different limit. The tie-in design is also unapproved, so I would not accept any change that relies on a higher tied-in configuration.
The 2.0 t skip at 30 m may be within capacity, but I would still check the exact chart for the current jib, counterweight, free-standing height and reeving. Two-fall reeving affects line pull and may suit the maximum capacity, but it does not correct a structural tip-capacity shortfall. The controlling issue is the bundle: it is over the tip rating and over the permitted wind limit. Options are to reduce the radius, reduce the bundle weight or rigging, use a crane with more capacity at 52 m, or wait for lower wind.
2. What would you require in the revised lift plan and crane configuration before the lifts proceed?
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I would require a revised lift plan that states the exact crane configuration: jib length, counter-jib, counterweight, free-standing height, tie-in status, reeving, hook block and the specific load chart page. The plan must list the actual weights of the bundle, spreader beam, slings and any other rigging, plus the radius at which each item will be lifted.
For the bundle, the plan must show a radius where the gross load is within the chart, or a different crane. It must also state the wind limit for the load's sail area and the method of monitoring wind at the load, not only at ground level. If the limit is 12 m/s, the lift should be stopped before that figure is reached; waiting for a calmer period is a valid control. The tie-in design must be approved by the relevant competent person if the configuration depends on it.
The skip lift should be treated as a separate planned lift with its own radius and chart check. Both plans need an exclusion zone, agreed radio signals, a lift director, tag lines and a trial lift where practicable. I would also confirm that the crane has been inspected for this configuration and that the operator has the correct chart in the cab. No lift should proceed on a verbal assurance that 'the tip rating covers it'.