so yeah i know that cranes do the main work but i guess there are no such really toll cranes to do that with skyscrapers ?
They put a crane on the ground, and they build 5 stories, say. Then they put the crane on top of the 5th story, and build another 5 stories, then they put it on the 10th story and build 5 more, etc. Or it's hanging on the side of the building, moving upwards as the building rises.
The cranes hook to the side of the building and climb the steel frame as it is being built. The crane can only reach a few stories so it has to climb each story's steel frame as it is finished.
That is a good answer. Ordinary cranes build the steel frame to a height of perhaps 60 feet. The frame is designed so a specially designed crane can climb up the side (like climbing a ladder) to about 50 feet where the climbing crane can complete the frame to about 100 feet, then the crane can climb to the 90 foot level and build the frame to about 150 feet etc. Another method is the floor at about the 60 foot level is completed and extra strong. A crane is assembled on that floor and can complete the steel frame to about 100 feet where another extra strong floor is built. The crane at 60 feet is then dismantled and moved to the floor at the 100 foot level, or perhaps this is a second crane. Repeat until the full height of the building is frame work. As cranes are removed at the lower levels, more floors can be installed and some of the finishing work done. Either way, you can see why very tall buildings are very expensive. Likely both methods are used for some very large and very tall buildings. Neil
