Crane Types, Components, Terminology and Load Charts
Types
Bridge cranes span between runway beams and travel along the runway; gantry cranes carry their own legs on rails or wheels at ground level, so they can run outdoors or over long spans. Variants include semi-gantry (one leg on a rail, one end on a building runway), monorail hoists, jib cranes (not CB) and portal cranes. Know the difference: a bridge crane's end trucks run on elevated runways; a gantry crane's legs carry the load to the ground.
Components and terminology
Key parts: bridge girder, end trucks, runway rails, festoon or conductor bar for power, hoist, wire rope or chain, hook with safety latch, trolley, limit switches (hoist high, hoist low, travel), overload protection, brakes, pendant or radio control, and the load chart or rated capacity indicator. Terminology: span, wheelbase, hook height, headroom, duty classification, and rated capacity.
Load charts
The rated capacity is the maximum load for a given configuration, including the hook block, slings and lifting gear. Capacity can reduce as the trolley moves toward the end of the bridge or as the boom/jib extends (for jib types). Never exceed the chart. Traps: forgetting to subtract the weight of slings and spreader beams; assuming capacity is constant across the span; confusing the rated capacity with the proof load test figure.
Worked example
A 10 t crane has a chart capacity of 10 t at mid-span but 8 t near the end truck. A load of 7 t plus 0.5 t of slings and a 0.4 t spreader beam totals 7.9 t - within 8 t, but only just. Confirm the trolley position before lifting.
Rule of thumb
Chart capacity minus all lifting gear equals the maximum payload. If the answer is close to the limit, treat it as over.