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A Tower Crane Primer
For all practical purposes, there are six major parts that make up a tower crane: the base, the tower, the slewing unit, the jib, the machinery arm and the cab. Here is how those parts are put together.
- The base is bolted to a large concrete pad that supports the crane.
- The base connects to the tower (or mast), which gives a tower crane its height. A tower is usually built with 20-foot triangular sections.
- Attached to the top of the tower is the slewing unit (the gear and the motor) that allows the crane to rotate.
- On top of the slewing unit are three parts: The long horizontal jib (or working arm) is the portion of the crane that carries the load; a trolley runs along the jib to move the load in and out from the crane’s center. The shorter horizontal machinery arm contains the crane’s motors, electronics and counter weights. The last part is the operator’s cab.
The average tower crane is 150 feet in height. Once a crane exceeds 250 feet, it has to be tied to a building, which is the case with the crane used to build the River House.