Load dynamics, stability, and capacity determination
Domain 5 tests the physics behind the chart: radius, load moment, stability, and dynamic effects. Questions often ask why a legal static lift becomes unsafe once the load moves.
Core concepts
Capacity is the lower of structural strength and stability. Load moment is load times radius. Any increase in radius lowers capacity: booming down, telescoping out, swinging the load outward, or boom deflection all increase it. Quadrants and boom length matter; the chart is configuration-specific. Dynamic loads add to the static weight: hoist acceleration, swing centrifugal force, wind, shock loading, and sudden braking. Ground slope, outrigger settlement, and tire deflection change the tipping axis.
Worked example
A crane is rated 10,000 lb at 30 ft radius. The load weighs 8,000 lb and rigging 600 lb. Static load is 8,600 lb, apparently legal. During the swing, boom deflection and load swing increase effective radius to 31.5 ft, where the chart gives 9,000 lb; wind and acceleration add about 10 percent, so effective load is 9,460 lb. The lift is now over capacity. The correct action is to reduce radius, reduce load, or use a larger crane; do not "slow down a little" and proceed.
Traps
Using only the load weight and ignoring rigging; reading the chart at the static radius while the boom is flexed; ignoring wind sail area; swinging too fast; side-loading the boom; picking on rubber when the chart requires outriggers; assuming a level indicator is optional; using a chart for a different counterweight.