Load Charts & Capacity Calculations Flashcards

A crane's load chart shows a capacity of 28,000 lbs at a 40-foot radius with a 100-foot main boom. The rigging weighs 1,200 lbs and the load itself weighs 24,000 lbs. The crane is set up on outriggers and the chart is based on 360° rotation. What is the net load capacity remaining after accounting for the rigging?

Answer: 2,800 lbs

The chart capacity is 28,000 lbs. The total suspended load includes the rigging (1,200 lbs) plus the load (24,000 lbs) = 25,200 lbs. The remaining net capacity is 28,000 − 25,200 = 2,800 lbs. Rigging hardware is part of the lifted load and must always be deducted from the chart's rated capacity before determining available lifting capacity for the payload.

A load chart footnote states 'capacities are based on freely suspended loads.' The operator is using a jib with a 15° offset and a load line reeved through the jib tip. Which factor most directly invalidates the freely-suspended-load assumption and requires a capacity reduction?

Answer: The load line angle caused by horizontal jib deflection under load

When a load line runs through an offset jib tip, the line is no longer plumb — it forms an angle relative to vertical. This creates a side-load component on the jib and increases the effective load on the hoist line (due to the cosine effect), meaning the freely-suspended assumption is violated. The angular deviation of the load line directly adds resultant forces that standard load charts do not account for, requiring a derating.

A crawler crane load chart shows a capacity of 45,000 lbs when traveling with a load, with the load over the front. The operator must instead travel with the load over the side. According to ASME B30.5 operating principles, what must occur before the crane travels?

Answer: Traveling with a load over the side is only permitted if the manufacturer's chart includes a specific side-travel capacity rating

ASME B30.5 and manufacturer load charts govern travel-with-load operations. Traveling with a load over the side is only permissible when the manufacturer has specifically rated and published side-travel capacities. Without an explicit side-travel capacity in the load chart, the operation cannot be performed at any percentage of the front-travel rating — the entire operation is prohibited. A blanket 75% rule does not exist in the standard for this scenario.

A crane is rated at 30,000 lbs at a 35-foot radius on outriggers fully extended. The operator extends only the two front outriggers fully and leaves the rear outriggers retracted. The load chart has a separate section for 'on rubber' and 'outriggers extended.' Which capacity applies, and why?

Answer: The 'on rubber' capacity applies because stability is determined by the weakest support configuration

Load chart ratings assume a specific, complete configuration. Outrigger capacity requires ALL outriggers to be fully extended and set per manufacturer specifications. With rear outriggers retracted, the crane is not in the outrigger configuration — it is in a mixed state closer to 'on rubber.' The controlling capacity defaults to the most restrictive applicable chart section. Stability is governed by the worst-case support point, not the best, so the 'on rubber' rating must be used to ensure safe operation.

A load chart references a 'load radius' of 30 feet. The boom is at a 70° angle from horizontal and the boom pin height is 6 feet above ground. The load has been rigged and the hook is directly below the boom tip. After the lift, the load swings outward and the radius increases to 33 feet. What is the crane operator's primary concern regarding load chart compliance?

Answer: The increased radius reduces the load chart capacity, and the operator must verify the actual load does not exceed the rated capacity at 33 feet

Load chart capacities decrease as radius increases, typically significantly. If the load swings outward to 33 feet — a 10% radius increase — the operator must immediately check whether the actual load weight remains within the rated capacity at 33 feet. Crane structural safety factors do not excuse operating beyond the chart-rated capacity at the actual working radius. The operator cannot assume any percentage increase is automatically safe; they must verify against the chart at the new radius.

A lattice boom crane's load chart specifies a maximum capacity at a given radius using a specific boom length. The operator adds a 10-foot boom insert to increase the boom length by one section. The radius and operating conditions remain identical. How does the added boom section most likely affect the crane's rated capacity at that same radius?

Answer: Capacity decreases because the additional boom section adds structural dead weight and increases bending moment on the boom

Adding a boom insert increases the boom's dead weight (reducing net capacity), increases the bending moment along the boom structure, and changes the geometry of load-line angles. At the same radius, a longer boom must operate at a shallower angle, which increases the horizontal component of boom compression and may reduce structural ratings. The manufacturer's load chart for the longer boom configuration will reflect these factors, typically showing reduced capacity at the same radius compared to the shorter boom chart. Always use the load chart page corresponding to the exact boom length configured.