Climbing Sequence and Wind
A self-erecting crane is being climbed from 12 m to its maximum free-standing height of 21 m to serve a three-storey building. The climb is carried out using the crane's own jacking system with the mast sections added from the base. The manufacturer's manual states that climbing must not be carried out when wind speed at the jib exceeds 10 m/s, and that the crane must not be left in a partially climbed condition overnight. The forecast is for 7 m/s gusting to 13 m/s in the afternoon. The climb is scheduled to start at 13:00 and is expected to take four hours. The site has an anemometer at ground level only, reading 5 m/s. The erector proposes to start, monitor the ground reading, and 'stop if it gets bad'.
1. Assess the proposed plan against the manufacturer's requirements and identify the critical errors.
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Critical errors:
- Wind measurement at the wrong height. The manual's limit is at the jib, not at ground level. Wind speed increases with height, and a 5 m/s ground reading is not evidence that the jib is below 10 m/s - at 21 m the wind will be materially higher. A ground anemometer cannot be used to authorise a climb.
- Forecast exceeds the limit. Gusts to 13 m/s exceed the 10 m/s limit. The climb is scheduled to run through the afternoon when gusts are forecast, so the plan is starting into a known exceedance.
- The 'stop if it gets bad' approach is unsafe. Once climbing has begun the crane is in a transient, less stable condition. Stopping partway leaves the machine in a configuration the manual prohibits overnight, and reversing a partial climb under gusting conditions is itself hazardous.
- Duration. A four-hour climb starting at 13:00 runs into the gusty period and possibly beyond daylight; there is no contingency for abandoning safely.
Correct judgement: do not start. Re-schedule the climb to a period when the forecast, measured at jib height, is comfortably below 10 m/s with margin for gusts, and plan the climb so it can be completed - or safely returned to a stable, manual-compliant condition - within the window. Use an anemometer at jib height or a calibrated mast-mounted sensor, and record readings throughout.
2. If the climb must proceed, what controls and decision points would you put in place?
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Controls:
- Obtain a forecast for the specific site and height, and set a go/no-go threshold below the manual's 10 m/s (e.g. abort if jib-height wind exceeds 8 m/s, giving margin for gusts).
- Fit an anemometer at or near jib height, calibrated, and log readings at agreed intervals during the climb.
- Define hold points: before starting, after each mast section, and before final pinning. At each, the supervisor confirms wind is within limit and the crane is in a stable, pinned condition.
- Brief the whole team on the abort criteria and the safe abort procedure - how to return the crane to a stable, fully pinned configuration if the wind rises mid-climb.
- Confirm the crane will not be left partially climbed overnight; if the climb cannot be completed, it must be returned to a compliant state before the team leaves.
- Exclude other work and personnel from the slew and drop zone during the climb, and control access.
- Record the climb, wind readings, and any deviations in the lift plan and in the crane's log.
Decision point: if at any hold point the jib-height wind is at or above the abort threshold, stop and stabilise rather than press on. The manual's limit is a maximum, not a target.