Types of Tower Cranes
Large building construction projects increasingly use tower cranes for lifting and placing materials. Their configuration offers several advantages over more traditional cranes, including reduced space requirements, higher vertical lift, increased capacities and quiet electrical operation.
In high-rise buildings, tower cranes can route through the elevator shaft, further easing space requirements. Tower cranes are available in several common types, each with its own advantages.
A hammerhead crane is the configuration most often associated with a tower crane. A long horizontal jib is attached to a vertical tower. One end of the jib extends horizontally over the worksite, while the other end has a counterweight. A trolley, which holds the lifting cable, travels along the length of the jib, and a tower crane can operate anywhere within the jib's radius. The operator rides in a cab at the intersection of the jib and tower. Hammerhead cranes typically require a second crane to assemble and disassemble them at the worksite. Self-lifting hammerhead cranes can insert and remove sections to their tower and change their height.
Self-Erecting Tower Cranes
A self-erecting crane can completely assemble itself at the job site without the need for a second crane. This provides an advantage in setup time and equipment costs. While some versions have an operator cab on the jib, self-erecting cranes are often remote-controlled from the ground. Self-erecting cranes are usually freestanding, and can be equipped to move around the job site. Some self-lifting cranes also have a telescoping tower, which allows the crane to work at multiple heights without reconfiguring the tower.
Luffing Jib Tower Crane
In tight urban work spaces, there is often insufficient clearance for the jib to rotate without being blocked by existing buildings. For such spaces, a luffing jib tower crane is used. While most tower cranes have a fixed horizontal jib, the operator can raise or lower a luffing jib to allow the crane to swing in a reduced radius. A luffing jib does not use a trolley like a conventional tower crane, but rather raises or lowers the jib as needed for lifts closer to the tower. Because of the added complexity, luffing cranes are more expensive, and only used when needed.
Andrew Hazleton has been writing on a freelance basis for more than 20 years, and his work has appeared in national, regional and in-house publications. His work has appeared in "Sports Illustrated," "IEEE Spectrum," "Popular Photography" and several newspapers. Hazleton has a Bachelor of Science in engineering from Lehigh University and a master's degree in management from Pepperdine University.