Load Charts and Capacity Calculations Flashcards

A crane's load chart shows a capacity of 18,500 lbs at a 30-foot radius with a 60-foot main boom. The rigging hardware weighs 850 lbs and the load itself weighs 16,400 lbs. The lift is being made over the rear quadrant. If the manufacturer's chart is based on 75% of tipping capacity for structural ratings but 85% of tipping for stability ratings at this configuration, and the controlling limit is structural, what is the maximum additional load the crane can pick before exceeding its rated capacity?

Answer: 1,250 lbs

Gross load = rigging (850 lbs) + net load (16,400 lbs) = 17,250 lbs. Rated capacity at this configuration is 18,500 lbs. The remaining margin is 18,500 − 17,250 = 1,250 lbs. The structural vs. stability distinction in the question is a distractor — operators use the published rated capacity directly from the chart regardless of its derivation basis. Exceeding 18,500 lbs is the violation threshold.

When using a load chart that references 'on outriggers fully extended,' a crane operator sets outriggers to only 75% extension due to a ground obstruction. The chart capacity at the required radius is 24,000 lbs. Which action correctly reflects NCCCO and ASME B30.5 requirements?

Answer: Contact the crane manufacturer or a qualified engineer to obtain a derating factor for the non-standard outrigger position

ASME B30.5 and NCCCO standards require that lifts made on outriggers not fully extended must use capacity information obtained from the manufacturer or a qualified engineer — you cannot simply pro-rate the chart value by the percentage of extension. The pick-and-carry chart and the 25% reduction method are not sanctioned engineering approaches. The lift cannot proceed until an appropriate derating is obtained.

A mobile crane is performing a tandem lift. Crane A is rated for 30,000 lbs at the required radius and Crane B is rated for 22,000 lbs at its required radius. The total gross load including all rigging is 44,000 lbs. A lift director assigns 60% of the load to Crane A and 40% to Crane B. Which statement is correct regarding this load distribution?

Answer: The distribution is acceptable but load transfer must be monitored continuously because dynamic forces during tandem lifts can shift loading unpredictably beyond planned percentages

Crane A (60% × 44,000 = 26,400 lbs) is at 88% and Crane B (40% × 44,000 = 17,600 lbs) is at 80% — both within rated capacity on paper. However, the critical concern with tandem lifts is dynamic load transfer: out-of-sync movements, boom flex, or ground settlement can redistribute loading well beyond planned shares. ASME B30.5 and NCCCO require continuous load monitoring and coordination specifically because real-time load shares deviate from plans. Equal distribution and 100% individual capacity are not absolute requirements.

A crane's load chart has a footnote stating: 'Capacities are based on the crane being level within 1% of grade.' The site has a 2% slope and the crane is positioned with the slope running from left to right (side slope). The operator levels the upperworks using the swing brake on high ground. Which statement is most accurate?

Answer: The crawler or carrier remains on the 2% grade, so structural and stability assumptions in the chart are violated and capacity must be derated per manufacturer guidance

Leveling the upperworks does not address the slope's effect on the crane's carrier, outrigger float loading asymmetry, or the travel path of the center of gravity during a swing. The load chart's 1% level requirement applies to the entire machine setup, not just the upper structure. With a 2% grade, the manufacturer or a qualified engineer must provide derating guidance — the full chart cannot be used simply because the boom and cab appear level.

A lattice boom crane's load chart shows capacities for a 120-foot main boom at various radii. The operator needs to pick at a 45-foot radius, but this exact radius does not appear in the chart — the table shows 40 feet (capacity 19,200 lbs) and 50 feet (capacity 15,800 lbs). The operator interpolates linearly to calculate 17,500 lbs for 45 feet. Is this method acceptable under NCCCO standards?

Answer: No — when the exact radius is not listed, the operator must use the capacity from the next longer radius in the chart (50 feet at 15,800 lbs)

ASME B30.5 and standard NCCCO practice require that when an exact working radius is not listed in the load chart, the operator must use the capacity corresponding to the next longer (greater) radius — in this case, 50 feet at 15,800 lbs. Interpolation is not a sanctioned field method because load chart capacity curves are not necessarily linear between data points; using the next longer radius is the conservative, code-compliant approach. Using the shorter radius (40 ft) or interpolating could allow lifts that exceed actual safe capacity.

A crane is making a lift using a jib (fixed offsetted fly) attached to a 100-foot main boom. The load chart for 'main boom + jib' shows rated capacity at the maximum working radius. The operator notices the load chart footnote reads: 'Jib capacities DO NOT include the weight of the jib.' The jib weighs 1,100 lbs and the headache ball and hook block weigh 420 lbs. The desired net load is 8,200 lbs. What is the correct gross load to compare against the jib chart capacity?

Answer: 9,720 lbs (net load + hook block + jib weight)

When the load chart footnote states that jib weight is NOT included in the rated capacity, the jib's weight must be treated as part of the gross load along with all other suspended components. Gross load = net load (8,200) + hook block/headache ball (420) + jib weight (1,100) = 9,720 lbs. This total must not exceed the chart's rated capacity for that configuration. Failing to account for the jib weight is a common and dangerous error that can result in an overload.