Pick and Carry Operations Flashcards

A rough terrain crane's load chart has separate capacity columns for 'stationary on outriggers,' 'stationary on rubber,' and 'pick and carry.' At the same 20-foot radius, the pick and carry rating is lower than the stationary-on-rubber rating. What is the PRIMARY engineering reason for this derating?

Answer: Dynamic inertial forces generated by travel motion increase the effective structural load on the crane beyond what the static chart accounts for

Pick and carry ratings are derated compared to stationary-on-rubber ratings because traveling with a suspended load introduces dynamic forces not present in static lifts. Inertia, travel vibration, and load pendulation all amplify the effective structural loading on the crane's boom, slewing ring, and chassis. Manufacturers test for these dynamic conditions and publish lower ratings to account for them. The other options describe real crane phenomena but are not the primary basis for the pick and carry derating methodology.

During a pick and carry operation, a crane operator notices the suspended load has begun to pendulate (swing) perpendicular to the direction of travel. Which action is MOST appropriate as the immediate corrective response?

Answer: Stop travel immediately and allow the load to stabilize before reassessing travel conditions

Stopping travel immediately is the correct first response. Perpendicular swinging is especially dangerous because it creates lateral tipping forces that act against the crane's narrowest stability axis. Continuing to travel or attempting dynamic corrections (slewing, accelerating) can amplify the swing through resonance or introduce compound forces. Once stopped, the operator must wait for the load to come to rest before reassessing whether travel can safely continue. The other options risk compounding the instability.

A crane operator is configured with a lattice boom crane that has a swing-away jib stowed in the travel position along the main boom. The manufacturer's pick and carry load chart provides ratings for the main boom only and contains no jib configuration entries at all. How must the operator interpret this?

Answer: Pick and carry operations are NOT permitted in any configuration with the jib physically attached to the crane

If a manufacturer's pick and carry chart does not include ratings for a jib-attached configuration — whether stowed or deployed — that configuration is simply not rated for pick and carry. The absence of data is not a gap to be filled with operator-calculated derating; it means the manufacturer has not certified that configuration for travel with a suspended load. Attaching the jib alters the crane's mass distribution and structural dynamics in ways that may not be safe during travel. Only configurations explicitly listed in the load chart are permissible.

A mobile crane manufacturer's pick and carry specifications state a maximum travel speed of 0.5 mph with a suspended load. An operator on a smooth, level concrete floor argues the restriction is unnecessary in ideal conditions and proposes traveling at 1 mph. Which engineering concern MOST directly justifies the manufacturer's speed limit?

Answer: The risk of resonant frequency coupling between the load's natural swing period and the crane's travel motion increases significantly above rated speed

The primary engineering concern behind pick and carry speed limits is resonant frequency buildup. A suspended load behaves as a pendulum with a natural swing frequency determined by the rope length and load radius. If the crane's travel cadence (speed over terrain irregularities) approaches that frequency, the oscillations can amplify each cycle — a phenomenon called resonance — leading to runaway load swing that the operator cannot control. The manufacturer's speed limit is specifically calibrated to keep travel-induced excitation below the load's natural frequency. Ideal surface conditions do not eliminate this risk.

A rough terrain crane is performing a pick and carry operation over the front, traveling uphill on a 2% grade (within the manufacturer's maximum allowable grade). Compared to a level surface at the same boom angle setting, what happens to the effective load radius as the crane ascends?

Answer: The effective load radius decreases because the boom rotates toward vertical relative to gravity as the front of the crane rises

When a crane travels uphill nose-first with a load over the front, the entire chassis pitches nose-high. Because the boom is mounted on the rotating superstructure, pitching the crane's nose upward effectively rotates the boom toward the vertical — reducing the horizontal angle between the boom and plumb. Since load radius is the horizontal distance from the centerline of rotation to the load (and the load hangs vertically by gravity), a boom that is more upright yields a smaller horizontal radius. This is why crane manufacturers specify that if grade reduces radius below the chart's minimum, the operator must re-evaluate using the new geometry.

A pick and carry load chart shows a capacity of 14,000 lbs at a 15-foot radius for a specific crane model. The operator has a rigged load of 13,200 lbs and begins travel. Midway through the route, the operator must make a 90-degree turn. During the turn, which condition is MOST likely to create an exceedance of the rated capacity even though the load weight has not changed?

Answer: Centrifugal force during the turn acts outward on the suspended load, effectively increasing the load radius beyond 15 feet

During a turn, the suspended load behaves like a pendulum bob subject to centrifugal (outward) force. The load swings outward relative to the crane's turning center, effectively increasing the horizontal distance from the centerline of rotation to the load — i.e., increasing the load radius. If the load swings out far enough to push the effective radius beyond 15 feet, the crane is now operating at a radius that exceeds what was used to verify capacity. Even a modest radius increase from 15 to 16 or 17 feet can push the operation over the chart limit. This is why pick and carry turns require reduced speed and pre-planned turning radii.