We’ve all seen tower cranes working on new high rises and skyscrapers. For those unfamiliar with tower cranes, their height may make one wonder how they’re built. After all, what other structure is tall enough to construct tower cranes? The answer is that these cranes build themselves from the foundation up. The key lies in the individual mast units that attach to each other. Keep on reading, and we’ll walk you through the entire construction process.
Laying the Foundation
Before the “tower” component of the crane can be built, the foundation needs to be set. Concrete is poured to form a solid block, typically with dimensions of 30 feet by 30 feet by 4 feet according to Deckrane. Included in this foundation are anchor bolts, which support the crane. For free-standing cranes, the base includes ballast weight, which stabilizes the crane while also spreading out the load weight. This is completed weeks before the crane’s components are delivered to the site.
The Initial Tower
When it’s time to construct the crane, the first step is to build the initial tower. This tower is comprised of a series of sections called masts. These square frames are connected by triangulated cross-sections. Typically two or three masts are fixed to the foundation with the use of a separate crane to construct the tower.
After the masts are set, the top climbing unit is added. This component is a special section that is set over the top mast, and allows for the insertion of more masts. Without this, the tower crane would not be able to grow.
The Slewing Assembly
Once the initial masts and top climbing units are added, it’s time to construct the slewing assembly. This consists of:
- Horizontal Jib: Also known as the working arm, the horizontal jib is used to carry loads with a trolley attached on its underside.
- Counter Jib: Also known as the counterweight, the counter jib is a balancing force for the horizontal jib. Drums, gears, and other electronics are located here, along with the counterweights themselves.
- Cab: The cab is where the crane operator sits. All communication, control, and monitoring systems are located here.
- Slewing Ring: Attached to a ball track, the slewing ring allows for the rotational movement of the slewing assembly.
- Tower Top: Used to provide additional stability to the crane, the tower top is placed above the cab. Pendant bars connect the tower top to both the horizontal and counter jibs.
After the slewing assembly is put together, a separate crane is used to lift and attach it to the mast.
Growing the Tower
As we mentioned earlier, the top climbing unit, initially set around the current top mast, is necessary for the crane to increase in height. When it’s time to grow the crane, this mast is disconnected from the slewing assembly. Through the use of a hydraulic jack, the climbing unit lifts itself and the slewing assembly. At this moment, the climbing unit is set between the slewing assembly and the top mast. The trolley on the crane’s horizontal jib then grabs a new mast unit, and slides it into the climbing unit. This new top mast is then encased by the climbing unit, just like the initial top mast. Once this new mast is secured to the mast underneath, the climbing unit raises the slewing assembly, and repeats the process.
The building of the tower crane can take one or two days, according to Crane Blogger, depending on the size of the crane.
Taking the Tower Down
Once the project is complete, disassembling a tower crane follows the aforementioned process in reverse. The crane removes the mast located inside the climbing unit. The unit then lowers itself and the slewing assembly, until it’s over the next mast to be removed.