Book 25, Question 2
Why do tall buildings have a steel skeleton?
Tall buildings have a steel skeleton because a frame of steel columns and beams can carry the weight of the whole building, so the walls do not have to.
A skyscraper's strength comes from a frame of steel columns and beams, like a skeleton. The frame carries the weight of the floors, walls, and people down to the foundation. Steel is strong and can bend a little without breaking, which helps in wind. The walls hang from the frame, so they can be thin and light.
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Quick answers
What holds up a skyscraper?
A skeleton of vertical steel columns and horizontal beams supports the weight of the entire building.
Why can skyscraper walls be thin?
The outside wall is really just a skin to keep out the weather, because the steel skeleton does the heavy lifting.
Is steel better than thick stone walls?
Thin pieces of steel can support a tall building as well as thick stone walls can, and they weigh much less.
Why do skyscrapers have to fight the wind?
As skyscrapers grew taller, wind became a new enemy, so engineers design them to be lighter and stiffer.
Sources: PBS Building Big: Home Insurance Building, PBS Building Big: Skyscraper Basics
More fun facts
- The word skyscraper was coined in the 1880s, shortly after the first tall buildings were built in the United States.
- Before steel, towers were made of heavy stone with thick walls, so their rooms were dark and cramped.
- The 10-story Home Insurance Building in Chicago, finished in 1885, was the first tall building held up by a skeleton of steel columns and beams.
- The steel for that 10-story building weighed only one-third as much as a 10-story building made of heavy stone or brick.
- In 1857 the first passenger elevator was put into a New York City department store, which made taller buildings practical.
- Today's tallest skyscrapers must be 50 times stronger against wind than the typical 200-foot buildings of the 1940s.
Sources: PBS Building Big: Home Insurance Building, PBS Building Big: Skyscraper Basics
Questions kids ask
Who built the first skyscraper with a steel skeleton?
Engineer William LeBaron Jenney, for the 10-story Home Insurance Building in Chicago.
Why did the steel frame give buildings more windows?
The steel skeleton carried the weight of the whole building, so the outside wall was just a skin to keep out the weather and could have many windows.