Crane types and configuration
Crane types and configuration tests whether you can select a machine and a setup that suit the lift, then prove it on paper. Expect questions on the mobile, crawler, tower and gantry families, outrigger and counterweight options, boom and jib combinations, and the ground pressure that decides whether the chart is usable at all.
Know the families
- All-terrain and truck cranes travel fast but need outriggers for their main chart; on-rubber capacity is a fraction of it.
- Rough-terrain pick-and-carry only on the manufacturer's travel chart: short distance, load low, slow, correct tyre pressure, no slewing while travelling.
- Crawlers travel with a load on their own chart, spreading load over the track area, and need a prepared level pad.
- Tower cranes lose capacity as jib radius grows; erection, climbing and tie design follow the manufacturer's manual.
- Gantry and portal cranes are limited by span, wheel loads and runway beam capacity, not just hoist capacity.
Configuration controls
Select the chart for the actual outrigger spread (full, mid or retracted), counterweight state, boom, jib or fly jib, and reeving. Parts of line can be limited by rope and block capacity as well as by the chart. Follow the manufacturer's assembly procedure and torque checks, and have a competent person inspect before the first lift.
Worked example
A 52 t crane lifting 8 t carries 60 t total. The manufacturer's maximum outrigger load, with the load slewed over that corner, is 65% of 60 t, or 39 t. On 1.5 m square mats: 39 / (1.5 x 1.5) = 17.3 t/m2, about 170 kPa. The compacted fill on site is rated at 100 kPa, so the mat area must be at least 39 / 10.2 = 3.8 m2, roughly 2.0 m square. Trench backfill and service pits must be bridged or avoided.
Traps that cost marks
- Quoting a chart without stating the spread, counterweight and boom configuration.
- Using the outrigger chart while set up on wheels.
- Mats too small, or a steel plate used over a void.
- Ignoring how a fitted jib or fly jib reduces main boom capacity.