Crane Outrigger Reaction from Lift Geometry
The maximum single-outrigger reaction over a corner from the gross load and radius, counterweight.
Example
You enter
- Gross suspended load (kip) 40
- Counterweight (kip) 30
- Load radius R (ft) 30
- Counterweight radius Rc (ft) 12
- Outrigger spread (ft, center to center) 20
You get
- Even quarter-share 17.5 kip
- Net overturning moment 840 kip-ft
- Max outrigger reaction (over corner) 59.4 kip
Checked against published worked examples from: Crane load-moment method / SAE J1063 stability.
Details, formula, and sources
ScopeThe maximum single-outrigger reaction over a corner from the gross load and radius, counterweight, and outrigger spread (R_max = (W+Wc)/4 + M/(sqrt(2) spread) while all four pads are down, and sqrt(2) M/spread once the far one lifts; it reports an overturned crane as such). Not a quarter-share -- swinging over a corner can concentrate well over half the load into one outrigger. The load a crane ground-bearing check asks for but never derives.
Formula or tableeven = (W + Wc)/4; overturning M = W x R - Wc x Rc; R_max = even + |M|/(sqrt(2) x spread) while the far outrigger stays in compression. When even is less than |M|/(sqrt(2) x spread) that pad has lifted, the crane stands on three, and R_max = sqrt(2) x |M| / spread. At |M| >= (W + Wc) x spread / sqrt(2) the resultant is over the corner and the crane overturns.
Source and editionCrane load-moment method / SAE J1063 stability, by name.
Free accessThe over-corner outrigger-reaction estimate is a public statics result; the crane manufacturer's load-moment chart governs.
What governsEstimate. Head rigger and manufacturer working-load-limit charts govern. Inspect every piece of hardware before the show.
API field namesgross_load_kip, counterweight_kip, load_radius_ft, cw_radius_ft, outrigger_spread_ft, even_share_kip, overturning_kipft, reaction_max_kip
- Over-corner concentration R_max = (W+Wc)/4 + M/(sqrt(2) x spread); the diagonal outrigger takes the overturningcrane load-moment method
- Chart governs the crane manufacturer's load-moment chart and published outrigger reaction data are authoritativeSAE J1063