Rooftop Lifting | High Rise Development
Tower cranes working over 100 metres up in the air, can be a pretty awesome sight when you get up-close to them. But what about those cranes occasionally seen working from the very top of a new skyscraper. How does a crane get on top of a building, and how does it get down again when the project is complete?
Sometimes, even a standard tower crane isn’t high enough to be used to construct those increasingly tall buildings. At other times the size of the plot rules out the use of normal tower cranes. The following are three methods construction companies use to get cranes operating from the very highest points of a new high rise development.
The crane that grows itself
This crane is anchored into a large concrete slab laid next to the building. Smaller cranes are then initially used to construct the master crane’s legs and strengthening framework, allowing the main crane to start its own lifting operations. When the building has reached around 15 storeys (180ft) tall, engineers begin strapping the struts of the crane to the building using steel collars.
Now for the clever bit. The crane has a large metal sheath known as a climbing area, which stretches up the outside of the tower. This sheath can raise the crane’s arm above the last crane vertebra, and hold it there while a new steel segment is added by the arm, and bolted into place by the engineers. With each new segment added and bolted on, lifting operations using the main crane restart. The process is then repeated as often as required to complete the build.
The climbing crane is often the crane of choice on tall builds, due to the fact internal work can be continued without the need for safety breaks, as the height of the crane is adjusted.
The crane that hops up floors
On a growing number of high-rise buildings, where site space is at a premium, using large cranes which operate alongside the project is not always an option. In these situations, building engineers may well plumb for the hopping crane.
With the exterior lower shell of the building constructed, the crane is manoeuvred on the ground floor, into the centre of the building, and prepped for operation. As the hopping crane’s work progresses upwards, the steelwork for the higher floors is added. The hopping crane can work up to a height of around three or four floors and once there, lifting stops. The crane driver then operates a large hydraulic piston, which begins pushing against the base and lifting the crane skyward.
With the crane lifted slightly higher than the fourth-floor steel girders, steel beams are slid across by building staff, to provide the new base for the hopping crane to operate from, and lifting work continues. The process is then repeated every few floors, until the crane gets near the top, and can complete its tasks without further movement.
The Flying Crane
The third, and least popular method of getting a crane on top of a high rise development, is to fly it in. Large, heavy-lift helicopters are employed, and carry one strut at a time, slung underneath the machine, to the site.
When you consider one leg of a crane can weigh thousands of pounds, plus the weight of the helicopter, it is a method rarely used in the UK. The carnage that would occur if the strut broke loose, or the helicopter developed a mechanical fault operating over densely populated city centres, doesn’t bear thinking about. On top of all the logistical problems and massive safety concerns, it is also the most expensive way to undertake the project.
Getting a crane on top of à building down again
Not only are cranes expensive pieces of kit, who wants a city skyline full of crane jibs dotted around the area?
When the job is completed, the crane’s last job is to put together what is the forerunner of modern crane technology, a derrick. Whether an external crane, or the internal type, the derrick holds each strut while it is unbolted, and then lowers it down the side of the building, to be loaded onto a flatbed truck for transporting back to base.
If you require any additional information, do not hesitate to get in touch with our team here.