Climbing Sequence Interrupted: Wind, Roller Gap and Wrong Counterweight
An internal climbing tower crane is being climbed inside a concrete core from level 8 to level 10 on its hydraulic climbing frame. The manual's climbing procedure requires the jib to be balanced per the configuration table, the guide rollers set to 3 mm ± 1 mm, and the climbing frame to carry the crane's weight at about 150 bar before the mast support is released. Today: the jib-head anemometer reads 11 m/s with gusts to 14 m/s; the climbing gauge holds 80 bar; the north bottom guide roller has a 9 mm gap; and the counterweight on the crane is 1.2 t lighter than the table requires for climbing, because the jib was shortened two climbs ago and the weights were never restored. The crew wants to finish the climb before the concrete pour at 14:00.
1. Give your go/no-go decision and the order of corrective actions.
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No-go, on three independent grounds:
- Wind. The manual's climbing limit is 10 m/s and the measured peak is 14 m/s. Limits are compared against the highest reading, not the average, and the jib head is the right measuring point.
- Roller gap. 9 mm against 3 mm ± 1 mm means the mast is not guided as the procedure assumes and the load path is not what the frame was designed for.
- Balance. The counterweight is not the configuration in the table, so the centre of gravity the climbing frame is designed to carry does not match the crane.
Order of work:
- Secure the crane in its current state and relieve the climbing frame exactly as the manual directs; do not leave it half-transferred.
- Restore the counterweight/jib configuration to the table for climbing.
- Re-set all guide rollers and re-check clearances.
- Wait for a sustained wind window below the limit, verify the anemometer is functioning and correctly sited, then restart the climb from the beginning of the manufacturer's checklist.
The 14:00 pour is not a factor in the decision.
2. What most likely explains the 80 bar reading, and how do you verify load transfer before releasing the mast support?
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Normal climbing pressure (about 150 bar) corresponds to the frame carrying the crane's weight. A reading of 80 bar alongside a 9 mm roller gap indicates the frame is not carrying the weight as designed: the mast is still partly supported by the structural connection or is binding against a guide, so the jack is pushing against a resisted path rather than lifting the crane.
Do not release the mast support on the strength of the gauge alone. Verify by the manual's method:
- Confirm the guide rollers are in contact and within tolerance.
- Check that the wedges/pins/shims are bearing and that the mast has lifted clear of its support.
- Watch for a gap opening between the mast and the support as pressure is applied, and confirm the frame's load-bearing surfaces are seated.
- Compare the gauge reading with the expected value for the actual configuration (jib length and counterweight).
Releasing the structural connection while the frame is not carrying the load is how climbing cranes drop. If load transfer cannot be demonstrated, stop and get the manufacturer's engineer involved.
3. The crew proposes to leave the counterweight as it is and 'make up the balance' by hanging the concrete skip on the hook during the climb. Evaluate.
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Reject it. Climbing procedures are configuration-specific and certified for a defined jib length and counterweight set. A hook load is not equivalent to counterweight:
- The skip load acts through the jib and hoist rope, adding moment with a different lever arm, plus dynamic effects from the swinging load and any rope stretch.
- The climbing frame, tie-in collars and hydraulic pressures quoted in the procedure were calculated without that load.
- The load can be lost, swung or snagged mid-climb, producing a sudden imbalance far worse than the original discrepancy.
- It turns a controlled configuration into an improvised one, with nothing to show the frame is within capacity.
Correct action: restore the counterweight called for in the table for this jib length, or obtain the manufacturer's written procedure for climbing in the lighter configuration. Then climb to that procedure only.