What a safe lift study actually calculates
A lift study is not a form, it is a set of calculations that prove a specific crane can make a specific lift on specific ground in specific weather. The four numbers that decide whether the lift is safe, and what tandem lifts change.
8 min read · 2026-08-09
By EHLL Lifting Desk · Editorial, crane operations
A lift study is not a form to be filled in, it is a set of calculations that prove a specific crane can make a specific lift, on specific ground, in specific weather. The parts people picture, the pick radius and the rated capacity, are the easy half and largely read straight off the load chart. The study earns its place in four numbers that decide whether the lift is actually safe, and most lifts are won or lost on the third of them, the one about the ground, not the one about the crane.
The capacity margin, and when a lift turns critical
Capacity is not a single line on a chart, it is a percentage you are working at, and it changes the whole process. A lift is normally treated as critical once it exceeds about 75 to 80 percent of the crane's rated capacity at the working radius, or when it is over people, a tandem lift, or a complex rigging arrangement. A critical lift needs an engineered plan reviewed and signed by a qualified person. So the first thing the study establishes is where you sit against that line, because it decides how much engineering everything else needs.
Ground bearing pressure against the soil's capacity
A crane does not exert its weight as a number, it exerts a pressure, a force spread over the area of its outriggers or tracks. If that pressure exceeds what the ground beneath can safely carry, the crane settles or tips, and it does so under load, at the worst possible moment. The study calculates the bearing pressure at each outrigger for the worst case of the lift and sizes mats or steel plates to spread it below the soil's safe capacity. On made ground, fill, or near an excavation, this is the calculation that actually keeps the crane up, and it is the one most often skipped.
The dynamic load factor
The load is never purely static. Lifting it off the ground, a sudden stop, a swing, all add dynamic force on top of the dead weight, and that force can briefly exceed the static limit. Standards such as AS1418 apply a dynamic load factor so the crane is never planned right up to its static rating and then surprised by the snatch as the load leaves the ground. The study applies the factor rather than treating the load as a still number on a scale.
The wind limit, set by sail area not a single figure
Wind is not one number that applies to every lift. The limit falls as the load's sail area grows and as the boom is extended, because a light load with a large face catches wind like a sail and can swing the hook or overturn a crane long before the rated capacity is reached. A common working envelope is in the order of 20 to 40 km/h, with many manufacturers advising a stop as sustained wind approaches about 22 miles per hour, and lower thresholds for large light loads or long boom configurations. The study sets the limit for this specific load and a rule to monitor and stop.
What a tandem lift changes
When two cranes share one load, the share is not fixed at half each. As the load tilts, as one crane swings, or as the geometry shifts during the move, the share moves between them, and a crane that started at half can find itself carrying far more. So each crane in a tandem lift is deliberately derated, often well below its solo rating, and the study controls the movement and the load share rather than assuming an even split. This is the case where the four numbers above all interact at once, which is why tandem lifts are critical lifts by default.
| Number | What it proves |
|---|---|
| Capacity percentage | Whether the lift is routine or critical |
| Ground bearing pressure | The ground will hold the crane under load |
| Dynamic load factor | The snatch and swing stay within limits |
| Wind limit for this load | The lift stops before wind makes it unsafe |
The study is only as good as the ground and weather data
A perfect calculation on a wrong soil bearing value, or a wind limit nobody monitors on the day, is not a safe lift. The numbers depend on real ground investigation and a real plan to watch the wind and stop.
Send us the load, the radius, the ground conditions and whether the lift is over people or in tandem, and we will produce the study that proves it, including the mats and the wind limit, before anything leaves the ground.
Sources
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