The third step also involves building the steel skeleton.
This steel frame has outer walls (or curtain walls) that support almost all the weight of the building .
The weight from all the floors gets transferred directly to the vertical columns .
This sends forces through the steel skeleton down into the building's base.
In modern skyscrapers, these exterior curtain walls are made almost entirely of glass which gives more floor space for tenants to live or work.
Once the skeleton has been built, the fourth step is much easier.
The floors are then added to a new skyscraper, often one to two a day.
A fifth and final step is stabilizing the skyscraper.
Some buildings have huge weights controlled by computers .
The weights glide back and forth in the opposite direction than that which the building moves during an earthquake or high winds