Counterweight and Ballast Configuration Flashcards

A crawler crane is configured with a superlift counterweight system. The operator notices the crane's actual lifting capacity at a given radius is LESS than what the load chart shows for that configuration. Which condition most likely explains this discrepancy?

Answer: The superlift counterweight tray is not fully extended to its rated horizontal offset distance from the crane centerline

Superlift load charts are calculated assuming the counterweight tray is positioned at a specific horizontal offset (radius) from the crane's centerline. If the tray is not fully extended to that rated offset, the stabilizing moment arm is shorter than the chart assumes, reducing the effective counterbalancing moment and therefore the allowable lift capacity. The chart's rated capacity is only valid at the exact counterweight offset specified.

During a critical pick, a lattice boom crawler crane operator must travel the crane with a suspended load. The manufacturer's load chart permits traveling with loads, but specifies a maximum counterweight configuration of 'Option B' for travel. The crane is currently rigged with 'Option C' (heavier) counterweight for the lift. What is the CORRECT procedure?

Answer: The counterweight must be reduced to Option B or less before any travel with a suspended load is attempted

Manufacturer specifications for traveling with loads are configuration-specific. A heavier counterweight increases the machine's overall weight and affects dynamic stability differently during travel — particularly over uneven ground — than the manufacturer's travel charts account for. The counterweight must be de-rigged to the maximum permitted travel configuration (Option B) before traveling with a suspended load, regardless of the fact that more counterweight might seem intuitively 'more stable.'

A tower crane's ballast (base ballast) is specified at 40,000 kg in the manufacturer's documentation for a standard mast height. The crane is erected to a taller freestanding height than the base configuration. Which statement correctly describes how this affects ballast requirements?

Answer: Additional base ballast must be added to compensate for the increased overturning moment from the taller mast

As a tower crane's freestanding mast height increases, the overturning moments from wind loading on the mast itself and from eccentric loads become greater. Manufacturers specify increased base ballast amounts for taller freestanding heights to ensure foundation stability. Using the standard ballast specification for a taller-than-standard mast is a serious engineering error that can result in foundation failure or crane collapse.

A hydraulic all-terrain crane is rated for a specific lift with its full 78-tonne counterweight installed. The job site has a soft soil condition requiring outrigger pad loads to stay below a set threshold. Engineering calculates the full counterweight configuration exceeds this threshold. The rigger proposes removing 20 tonnes of counterweight and adjusting the lift plan accordingly. What is the PRIMARY concern with this approach?

Answer: The crane's load charts for reduced counterweight configurations may show significantly lower capacities, potentially making the lift impractical

Load charts for hydraulic cranes are specific to each counterweight configuration. Reducing counterweight by 20 tonnes means the crew must use the load chart for that specific reduced-counterweight configuration — not the full-counterweight chart. The reduced-counterweight chart will show lower rated capacities, often dramatically so at longer radii, which could make the intended lift impossible or require significant changes to the lift plan (shorter boom, reduced radius, etc.).

During a crawler crane assembly sequence, the manufacturer's procedure requires installing the car body (carbody) counterweight BEFORE attaching the upperworks counterweight. A supervisor suggests reversing this sequence to save time. What is the primary technical reason the manufacturer's sequence must be followed?

Answer: Installing upperworks counterweight first causes the crane's slewing ring to be loaded asymmetrically before the car body can resist the moment

The assembly sequence is engineered to maintain structural and stability balance throughout the erection process. Installing upperworks counterweight before car body counterweight creates an overturning moment on the slewing ring and car body that the undercarriage is not yet stabilized to resist. The car body counterweight provides the foundation-level ballast that allows the upperworks assembly to proceed safely — reversing the sequence can cause structural overload on components or crane instability during assembly.

A crane operator is reviewing a load chart for a luffing jib configuration. The chart footnotes state: 'Capacities apply with counterweight at Position 1 only. Counterweight must not be repositioned while jib is erected.' The operator needs to convert to a standard boom configuration mid-project, which requires moving counterweight to Position 2. What is the correct sequence?

Answer: The luffing jib must be fully disassembled and removed before repositioning the counterweight to Position 2

The manufacturer's footnote is an absolute restriction — the counterweight must not be repositioned while the luffing jib is erected. This restriction exists because the luffing jib structure, pendants, and boom geometry are designed and rated only for the Position 1 counterweight configuration when assembled. Moving the counterweight changes moment loads on structural components in ways that may exceed their design limits, regardless of jib angle or hook load status. Full disassembly of the jib is required before reconfiguring the counterweight.