Counterweight and Ballast Configuration Flashcards

Why are rated capacities typically different for over-rear versus over-front lifts on some crane models?

Answer: Over-rear lifts have the counterweight directly behind the load maximizing the stabilizing moment. Over-front or over-side lifts have the counterweight in a less optimal position, resulting in lower rated capacities for the same radius and boom length

The counterweight's stabilizing effect is maximized when it is directly opposite the load (over-rear). As the crane slews, the geometry changes and some cranes show different capacities for over-front, over-rear, and over-side sectors on their load charts.

When a crane manufacturer specifies that a specific counterweight configuration is rated for over-front lifts only, what does this mean operationally?

Answer: The specified counterweight amount and the capacities shown apply only when the boom is positioned within the specified over-front sector — using those capacities outside the specified sector would be unsafe

Sector-specific load chart configurations mean the published capacities apply only within the specified boom-swing zone. Using those capacities outside the specified sector could expose the crane to an overload condition in the non-rated sector.

How does a longer boom change the needed counterweight for the same rated capacity?

Answer: A longer boom increases the boom's own weight and shifts the boom CG farther from the crane center, increasing the overturning moment from the boom itself — requiring more counterweight to maintain the same stability margin

The boom itself has significant weight, and a longer boom places more weight farther forward. This increases the forward overturning moment even before a load is added, requiring additional counterweight to restore the stability balance.

What is a tipping load in crane engineering, and how is it related to the load chart's rated capacity?

Answer: Tipping load is the actual load at which the crane would begin to tip, determined by testing or calculation. Rated capacity is typically 75 to 85% of the tipping load, providing a safety margin against tipping

The tipping load is the theoretical or tested load at which the crane would actually tip. Rated capacity (the value shown in the load chart) is set at 75 to 85% of tipping load per ASME B30.5, providing a safety factor against tipping.

A crane is operated with its maximum counterweight for a heavy lift. After the lift is completed, the operator needs to travel the crane to its next location. Why is removing counterweight before travel often necessary?

Answer: Travel with maximum counterweight may exceed the crane's transport weight limits, axle load limits, or road and bridge capacity, making reduction of counterweight before travel necessary

Maximum counterweight configurations often exceed road weight limits, bridge capacities, or the crane manufacturer's travel weight limits. Reducing counterweight to the travel-permitted amount is required before moving the crane on public roads or across weight-limited surfaces.

What role does the carbody counterweight play in a crawler crane setup, and how does it differ from the rotating superstructure counterweight?

Answer: The carbody counterweight is installed on the non-rotating lower carbody and track frame to stabilize the machine without rotating with the boom, while the superstructure counterweight rotates with the boom and always stays opposite the load

Some large crawler cranes use both a superstructure counterweight (rotating with the boom, always behind the load) and fixed carbody counterweights (mounted on the non-rotating lower frame) to provide stable base ballast independently of boom position.