Constructing Today’s Skyscrapers Require the Use of Tower Cranes

Tower cranes are essential to constructing the extremely tall skyscrapers being built today such as the Wilshire Grand Center in Los Angeles.  Capable of lifting very heavy loads of steel, concrete, generators and other building materials, tower cranes can be erected taller and taller as the building moves skyward.  Wikipedia cites the typical maximum unsupported height of a tower crane is 265 feet; the maximum reach of the jib is 230 feet, and the maximum lifting strength is 19.8 tons.   

Before it is ready for use, a tower crane is stabilized at the jobsite by constructing a concrete pad that is embedded with large anchor bolts used to secure the base of the crane.  When the crane reaches its maximum height, it is tied to the side of the skyscraper with steel collars so it can move upward as needed. 

The gears and motor of the crane are contained in the slewing unit, which is attached to the mast and allows the crane to rotate.   Set on top of that is a long jib used to lift the heavy materials and a counter-jib that is used as a counter-weight to keep the crane balanced.  A crane operator controls the unit from the ground or in a cab located on the top of the tower.

The mast of the crane is comprised of a series of vertebras generally 10 square feet in size.  Once the crane is fastened to the exterior of a building, or in some cases to the interior, a process is started to build the crane taller by adding new vertebra pieces.  The climbing frame, which sits just below the slewing unit and on top of the tower, temporarily supports that section of the mast as the jib moves a new segment into place.  After the new piece is bolted down, the climbing frame moves up higher along the mast to get ready to repeat the process. 

Conco’s mission is to be the best supplier of concrete services in the Western United States and to bring expertise, experience and quality to each project.  We continue to upgrade and expand facilities to better serve the growing market for public works projects, commercial, parking structures, educational, and other construction development. We serve California, Washington State, Oregon, Colorado and Nevada.

Source: en.wikipedia.org/wiki/Crane_(machine)#Tower_crane