Crane Types, Components, and Load Charts
What the exam tests
This domain checks whether you can identify crane configurations and read the chart for the exact setup in front of you. Questions often give a boom length, radius, quadrant, outrigger condition, and deductions, then ask for the allowable load.
Core rules
- Mobile crane families include truck-mounted, rough-terrain, all-terrain, crawler, and boom trucks. Lattice booms are pinned; hydraulic booms telescope. Each has different chart assumptions for stability and structure.
- Key components: boom, jib, boom extension, counterweight, outriggers and floats, swing system, hook block, sheaves, wire rope, anti-two-block device, load moment indicator (LMI) or rated capacity limiter (RCL), and boom angle/radius indicators.
- Load charts are configuration-specific. Variables include boom length, radius, boom angle, counterweight, outrigger spread, quadrant (over front, side, rear), jib use, reeving, and travel/pick-and-carry mode.
- Radius is the horizontal distance from the crane's center of rotation to the vertical line through the load's center of gravity, not the distance to the boom tip.
- Gross capacity is the chart value before deductions. Net capacity equals gross capacity minus the weight of the hook block, slings, shackles, jib, stowed boom sections, auxiliary head, and other attachments. The load itself must not exceed net capacity.
- Charts assume static, freely suspended loads, level ground, and no wind. Dynamic loads, side pulls, and wind require reduction or a stop.
Worked example
A 50-ton hydraulic crane is set on fully extended outriggers, over the side, with 60 ft of boom at 30 ft radius. The chart gives 18,000 lb gross. Deductions are 800 lb hook block, 300 lb slings and shackles, and 1,200 lb stowed jib. Net capacity = 18,000 - 800 - 300 - 1,200 = 15,700 lb. The load weighs 15,800 lb, so the lift is 100 lb over the net capacity. It is not acceptable. Moving closer to 28 ft radius may raise the chart value, but only if the new chart line and all deductions are checked.
Traps
- Using boom angle as a substitute for radius.
- Forgetting stowed jib or auxiliary head deductions.
- Reading the on-tires chart while the crane is on outriggers, or the reverse.
- Assuming 360-degree capacity when the chart is limited to over-front.
- Treating chart capacity as allowable load without deducting rigging.