Load Charts & Capacity Calculations Flashcards

A crane's load chart shows a capacity of 42,000 lbs at a 60-foot radius with a 120-foot main boom. The rigging weighs 1,800 lbs and the load block weighs 650 lbs. What is the maximum net load that can be lifted?

Answer: 39,550 lbs

The gross capacity from the chart is 42,000 lbs. However, the load chart capacity includes all suspended weight — the load itself PLUS the rigging and block. You must subtract both: 42,000 − 1,800 (rigging) − 650 (block) = 39,550 lbs maximum net load.

A crane load chart lists capacities for 'over-front' and 'over-rear' positions with significantly different values. When the chart shows 360° rotation capacity, which value is used as the basis?

Answer: The lowest capacity across all quadrants

When a load chart lists 360° capacity, it must be based on the most restrictive (lowest) capacity of any quadrant over which the crane can swing. Manufacturers use the minimum value to ensure the rating is safe regardless of where in the swing arc the load is held.

A mobile crane is set up on a 3% side slope. The load chart is based on level, firm ground. Which of the following best describes the appropriate action before consulting the load chart?

Answer: Use the load chart only after confirming the crane is leveled within manufacturer tolerances using outriggers or blocking

Load charts are only valid when the crane is level within the manufacturer's specified tolerance (typically ±1% or as stated in the manual). A 3% side slope exceeds standard tolerances, so the crane must be leveled — via outrigger extension, cribbing, or repositioning — before chart capacities apply. Simply derating by 3% is not a standard NCCCO-accepted practice.

A crane operator is using a jib extension. The load chart shows a main boom capacity of 28,000 lbs at 70 ft radius and a jib capacity of 9,500 lbs at the same radius. A 6,500 lb load must be lifted using the jib. What additional factor MUST be verified before accepting the jib chart rating as applicable?

Answer: That the jib offset angle matches the angle specified in the jib capacity chart

Jib capacity charts are specific to the jib offset angle (e.g., 5°, 15°, 25°). Using a different offset angle than what the chart specifies invalidates the rating. The jib angle affects the structural loading on both the jib and the main boom, and many operators overlook confirming the exact offset angle in use.

During a pick, an operator notices that the load radius has increased by 4 feet beyond the planned radius due to load swing. The load weighs 31,000 lbs including rigging. The original chart capacity at planned radius was 34,000 lbs, and the capacity at the new actual radius is 28,500 lbs. What is the correct assessment?

Answer: The lift is over capacity and the load must be landed immediately

Capacity is determined by the ACTUAL operating radius, not the planned one. At the 4-foot-greater radius, the chart capacity is 28,500 lbs — which is less than the 31,000 lb suspended load. The crane is over capacity at the actual radius and the load must be set down. Booming up to recover radius is tempting but increases instability with an overloaded condition.

A crawler crane's load chart has a footnote stating capacities are based on 'Class A ground bearing pressure with a minimum bearing capacity of 6,000 psf.' The available ground has a measured bearing capacity of 4,200 psf. Which approach is technically correct?

Answer: Distribute crane loads using engineered mats or cribbing to reduce pressure to within 4,200 psf before referencing chart capacities

When ground bearing capacity is less than the load chart's stated requirement, the solution is engineering — using mats, cribbing, or outrigger pads to spread the crane's load over a larger area until the pressure per square foot falls within the available 4,200 psf. Simply applying a percentage reduction to chart capacities is not a recognized engineering method and is not sanctioned by NCCCO or ASME B30.5.