1949

Tower Crane

Hans Liebherr (1915–1993)

Anytime a new skyscraper is being erected, we see a tower crane helping the process. But when we watch a tower crane in action, it almost looks impossible. We see this thin, leggy truss forming the “tower,” and then another thin, leggy truss forming the arm, and then this arm appears to be able to hold a huge load that should, seemingly, cause the whole thing to collapse. How did German inventor Hans Liebherr, in conjunction with many design engineers, make a tower crane work?

One key to the whole process is the foundation, which normally is hidden. A month before the tower crane arrives, builders pour a huge reinforced concrete block. This foundation might measure 50 feet (15 meters) or more on a side, could be 10 feet (3 meters) thick, and can weigh many thousands of tons. The tower bolts to this foundation.

The vertical truss, although it looks leggy, is quite sturdy by design. It does have a maximum safe height however. It usually clips into the structure it is erecting for support as it grows taller.

The arm or jib is the same kind of truss—extremely strong despite appearances. It is counterweighted on one side to balance the tipping forces on the tower. There are usually cables employed as well, in a manner similar to a cable-stayed bridge.

With all of this in place, the tower crane is strong and stable despite appearances to the contrary. But there are definitely limits. There is a maximum load that changes as the load moves out toward the end of the jib. A crane might be able to pick up fifty tons if the load is near the tower, but only one ton if the load is out near the end of the jib.

It is that ability to slide the load horizontally as well as vertically that makes the tower crane especially useful. The sliding action makes the tower crane unique, and well suited for the work it was originally meant to do, rebuilding post-war Germany and setting the foundation for what would become the international manufacturing company, the Liebherr Group.

SEE ALSO The Great Pyramid (2550 BCE), Woolworth Building (1913), Kinsol Trestle Bridge (1920).

A tower crane enabled builders to tackle new projects.