The mast has a large triangulated lattice structure, which gives the crane its strength. In turn, the slewing unit consists of three parts:. A typical tower crane has the following specifications, but note there are differences depending on the model and manufacturer:.
Note that the maximum load is 18 metric tons, but the crane cannot lift that much weight when the load is positioned at the end of the jib. The closer the load is located to the mast, the more weight the crane can lift safely. Weather monitoring in construction sites is important, but especially when tower cranes are used. A strong gust of wind can destabilize the load and structure, causing a collapse.
Project managers should constantly check weather forecasts, and avoid lifting operations with unfavorable weather. A weather monitoring system at the project sites can warn about dangerous wind conditions that are not covered in forecasts.
One of the first questions that may be asked by someone looking at a tower crane is these structures stand upright. Typical measurements for the pad are 30x30x4 feet 10x10x1. Large anchor bolts are deeply embedded in the concrete pad, and these elements support the base of the crane.
Tower cranes are delivered to construction projects in parts, which are then assembled on-site. Qualified installers assemble the jib and the machinery section, these horizontal elements are then positioned on the mast, which is only 40 feet tall initially. Once this assembly is completed, the counterweights are placed by a mobile crane.
The mast rises from the concrete pad, and it remains upright thanks to its triangulated structure. To increase the crane height, the crew adds sections to the mast with a climbing frame:. These steps are repeated continuously until the desired height is achieved. Once it is time to remove the tower crane from the construction site, the crane disassembles its own mast and smaller cranes are used to disassemble the rest. Then workers slide steel beams underneath the crane to give it a sturdy new footing, and the crane begins building again.
However, because of the cost, and because flying a load-bearing helicopter over a populated area is logistically very difficult, this method is the most rare, used only a few times a year nationwide.
Bonus Explainer: How do cranes get back down? Often by constructing the very gallows that will destroy them. To disassemble themselves, tower cranes construct derricks on the rooftop of the finished project. These derricks then help dismantle the tower cranes, and — in the case of internal climbers — lower their parts one by one to the ground using extremely long cables. External climbers, however, can jack themselves all the way back down.
By comparison, the lug nuts on most cars torque to ft lbs. The process continues as mast sections are added until the needed height is achieved. The turntable operator cabin included is added in the same manner and is often the heaviest piece of the crane.
In some applications this section is split to reduce weight on the mobile crane. This may add two hours to the crane erection process, so it is avoided when possible. After the Turntable is installed the Tower Top is added and four large pins are added as the connecting members.
The Counter Jib is erected as one piece. It is connected by large gates or pins at the turntable. After this connection is made it is elevated by the mobile crane to around 15 degrees above horizontal.
The pendants are connected by pins with cotter pins. Then the Counter Jib is lowered to horizontal. After this, any needed Erection Ballast is installed in the Counter Jib. The Working Jib of the crane is installed at the turntable and elevated with the Mobile Crane.
After it is elevated the Tower Crane hoist is connected to the pendant attached to the jib and pulled up to the Tower Top and connected with a pin.
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