The tower crane is the most expensive and most decisive piece of equipment on a site. A wrong choice means not only wasted money but a blocked construction programme. The questions to answer are few — but they must be asked in the right order.
1. Where will you lift the heaviest load?
A tower crane's capacity is not constant; it decreases with radius. The further along the jib you go, the less you can lift. What matters is therefore not the crane's maximum capacity but its capacity at the point where the heaviest piece must be placed.
On a project using tunnel formwork the heaviest piece is usually the formwork set. When dimensioning formwork, check whether it can be carried to the furthest point of the site.
2. How high will you go?
Building height alone is not enough when calculating hook height. Add:
- Final structure height
- Length of the longest piece to be lifted
- Height of slings and lifting gear
- A safe clearance allowance
3. Where will you erect the crane?
Mast position determines coverage. It must also avoid clashing with the excavation boundary, neighbouring plots, power lines and traffic routes. Minimum clearances to power lines are set by regulation and must be observed without exception.
Mast position also drives the foundation design. Deciding a crane foundation without a ground investigation is among the riskiest choices on a site.
Formwork and crane must be planned together
The mistake we meet most often on site is formwork and crane being selected separately. The formwork supplier optimises the panel, the crane company sets the capacity, and the formwork that arrives cannot be handled. These two decisions must be made at the same table.
Erection, climbing and dismantling
Erection, climbing and dismantling of a tower crane must be carried out only by authorised, trained crews following the manufacturer's instructions. During these operations the crane enters loading conditions different from normal service. Periodic inspections, load tests and operator certification must not be neglected.
In summary
Crane selection is a planning task, not a catalogue task. If you would like to work out a crane arrangement compatible with your formwork system, our engineering team is available.
