Mobile Crane Load Chart

What is modelled

A crane on outriggers tips about the float at the front outrigger when the moment of the load and the boom about that line exceeds the stabilising moment of the crane body. The rear outrigger reaction falls to zero at the tipping load, so it shows how close the crane is to tipping. A slope towards the load increases the overturning arms, and a rope that is not perfectly rigid makes the force at pick-up larger than the weight.

Equations

• Moment about the front float M = ∑ mi (ui cosφ + wi sinφ), with slope coordinates (u, w) and slope φ.
• Tipping load where M = 0; rated load min(0.75 × tipping, Mboom / r, 60 t).
• Rear reaction Rr = −g M / Sp, front Rf = g ∑ mi cosφ − Rr.
• Pick-up shock 1 + √(1 + v2 k / (m g2)).

Checks run in the page

• The tipping load from the slope of the potential energy against the moment balance.
• The reactions at the tipping load and their sum.
• The slope effect by rotating every mass with a rotation matrix.
• An RK4 rope-and-load run against the pick-up factor.

Honest simplifications

The crane is a rigid body with one fixed weight and centre of gravity, the boom is a straight beam with uniform weight, the outrigger floats are points, and the soil does not settle or the boom bend. The 75 % rule and the boom strength limit are simple illustrative numbers, not a manufacturer chart or a standard, and wind, swing and slewing are left out.

• Press Long reach, low boom and watch the rated load fall with the radius.
• Press On a slope or Short outriggers and read the rear reaction approach zero.
• Press Snatch pick-up and compare the load at pick-up with the rating.