How do they put together a big tower crane? How does it grow taller during construction? --- Tom, Kansas City, MI
Marshall Brain Answered:
A tower crane is an amazing thing because it has the ability to grow. You can see the entire process of putting the crane together in this video, along with the system that lets it get taller:
If you read How Tower Cranes Work you can see that the piece that makes the growth possible is called a "climbing frame". The article puts it this way:
Here's the process:
1) The crew hangs a weight on the jib to balance the counterweight.
2) The crew detaches the slewing unit from the top of the mast. Large hydraulic rams in the climbing frame push the slewing unit up 20 feet (6 m).
3) The crane operator uses the crane to lift another 20-foot mast section into the gap opened by the climbing frame. Once bolted in place, the crane is 20 feet taller!
See How Tower Cranes Work for details.