Rooftop HVAC Unit with the Jib Deployed
A 60 t capacity all-terrain crane is set up on a concrete pad at a distribution centre to place a rooftop packaged HVAC unit. The unit weighs 8,200 kg; the hook block weighs 480 kg and the four-leg sling assembly with shackles weighs 170 kg. The crane is configured with a 30.5 m main boom and a 9.2 m jib offset at 15 degrees. The required radius to the centre of the unit is 16 m, and the crane must swing through 360 degrees because the unit is picked from a truck at the rear of the building and set on the roof at the side. The load chart shows 9,900 kg for main boom only at 16 m, 6,400 kg for the boom-and-jib configuration at 16 m on the 360 degree chart, and 6,900 kg on the over-the-front chart. The site supervisor says the crane is a 60-tonner, so 8.2 tonnes is nothing.
1. Calculate the gross load and determine whether the lift is permitted. Show your working and explain which chart line applies.
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Gross load = 8,200 + 480 + 170 = 8,850 kg. Everything suspended below the boom tip that is not already in the chart must be added: hook block, slings, shackles, master links, and any jib that is not built into the chart line.
Which chart line? The crane is in the boom-and-jib configuration (jib offset 15 degrees), so the main-boom figure of 9,900 kg does not describe the machine as it stands. The 9,900 kg line would only apply if the jib were removed or stowed in the transport position in accordance with the manufacturer's notes. The over-the-front figure of 6,900 kg does not apply either, because the pick is at the rear and the set is at the side, so the load passes over the side and the 360 degree chart governs.
Available capacity = 6,400 kg (boom and jib, 360 degrees, 16 m).
Utilisation = 8,850 / 6,400 = 138% of rated capacity. The lift is not permitted. The 60 t nominal rating is only achieved at minimum radius, shortest boom, full counterweight and the correct outrigger spread; at 16 m with a jib this machine is effectively a 6.4 t crane.
2. The supervisor wants to keep the crane where it is and just shorten the radius. What options would you evaluate to make the lift legal, and what must be checked before any of them are accepted?
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Any of these could work, but each must be verified against the actual chart for the actual configuration:
- Reposition the crane to reduce radius. Both the pick radius at the truck and the set radius at the roof must fall inside the chart, not just the final radius. Read the boom-and-jib 360 degree line at the new radius.
- Remove the jib and use main boom only, provided the boom length still gives the required tip height and the geometry works. Only then does the 9,900 kg line become valid: 8,850 / 9,900 = 89%. Even then, add the manufacturer's radius-increase allowance for boom deflection and check the chart notes.
- Use a larger crane or split the unit into lighter sections if the site geometry cannot change.
Before accepting any option: confirm the weight from shipping documents or a weigh ticket rather than the drawing, confirm the counterweight and outrigger spread match the chart line, check the swing path and tail swing, and confirm the ground can carry the outrigger reactions. Never interpolate between chart lines or apply a margin that is not written in the notes.
3. What should be documented and communicated before this lift proceeds, and what is your responsibility if the supervisor insists?
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Before the lift: a written lift plan identifying the crane configuration, the exact chart page and line, gross load build-up, rigging arrangement, ground bearing check, exclusion zone, wind reading and the designated signalperson. Hold a pre-lift meeting with the rigger, signalperson, supervisor and anyone in the swing path. Confirm radio communication works on the agreed channel.
If the supervisor insists on proceeding at 138% of the chart, do not operate. State the refusal plainly, with the numbers, and stop the job. Record the refusal and the reason, and escalate to the lift supervisor, the competent person or the site safety representative. A load chart is a limit, not a target, and no verbal assurance from a supervisor transfers the chart limit or the responsibility for the lift to them. The operator who moves the lever owns the consequences.