Crane Types, Configurations and Load Charts for Cranes over 100 t
Know the machine
Large slewing mobile cranes include all-terrain and rough-terrain truck cranes, lattice-boom crawler cranes, and telescopic-boom crawlers. Each has a load chart specific to boom configuration, counterweight, outrigger or track spread, and optional equipment such as jib, fly, luffing jib, superlift or boom extension. The chart you use must match the machine as configured on the day.
Reading the chart
The chart gives rated capacity for a given radius, boom length and configuration. Deduct the mass of all lifting gear below the hook, and any hook block or auxiliary head allowance the chart requires. Rated capacity already includes the crane's structural and stability limits and a design factor; it is not a suggestion to be exceeded. Working radius is measured from the slewing centre to the vertical line through the hook, not to the boom tip. Boom deflection increases radius as the load comes on, so the loaded radius is what matters.
Configuration traps
Common question traps: using a chart for the wrong counterweight; ignoring the difference between 360-degree and over-the-front or over-the-side ratings; forgetting that pick-and-carry ratings are far lower than static ratings; and mixing metric tonnes with short tons. Also watch for charts that require a specific outrigger spread or pad size, and for derated zones near the chart's edge.
Worked example
A crane's chart shows 42 t at 18 m radius with full counterweight and 8 m outrigger spread. The load is 36 t and the rigging below the hook weighs 2.5 t. Total 38.5 t, which is within 42 t. Now the boom deflects and radius grows to 19 m, where the chart shows 36 t. The lift is now over capacity. Rule of thumb: always plan to the radius you will actually have under load, and keep a margin below the chart line.