Tuesday, June 21, 2005

How was a Skyscraper built?, a basic knowledge approach


The term "skyscraper" was coined in the 1880s, shortly after the first tall buildings were constructed in the United States -- but the history of tall buildings dates back hundreds of years. Since the Middle Ages, engineers have engaged in a battle for the sky.

Image of the San Gimignano towers
San Gimignano towers
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Before there were skyscrapers, there were towers.
Made of heavy stone, towers had thick, sturdy walls, but the rooms were dark and cramped -- too many windows would have weakened the structure.


Image of Flying Buttresses on a Gothic Cathedral
Flying buttresses:
Notre Dame Cathedral
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Soon Gothic cathedrals joined the quest for height.
Long, stone arms, called flying buttresses, supported the cathedral's heavy weight, allowing the walls to be filled with colorful glass windows.


Image of Home Insurance Building
First steel skyscraper:
Home Insurance Building
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With steel came the first modern skyscrapers.
During the Industrial Revolution, engineers began experimenting with two new materials -- iron and steel. The 10-story Home Insurance Building in Chicago was the first tall building to be supported by a steel skeleton of vertical columns and horizontal beams. But even with windows, the closely spaced columns and deep beams made rooms in the Home Insurance Building feel tight and cramped.


Image of an early elevator
Early elevator
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Who wants to climb all those stairs?
In 1857, the installation of the first passenger elevator in the Haughwout Department Store in New York City made it possible and practical to construct buildings more than four or five stories tall.

Chek out the forces that act on the Skyscraper!

Skyscraper: Forces


The skyscraper pushes down (compression) into the ground
The skyscraper pushes down into the ground.
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But when the wind blows, the columns on the windy side stretch apart (tension) and the columns on the other side squeeze together(compression)
But when the wind blows, the columns on the windy side stretch apart, and the columns on the other side squeeze together.

Comparison image of 2 different styles of skyscrapers
Minneapolis skyline
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New structural designs made skyscrapers even lighter and stiffer.
As skyscrapers grew taller and taller, engineers were faced with a new enemy: wind. Today's tallest skyscrapers, which are almost 1,500 feet tall, must be 50 times stronger against wind than the typical 200-foot buildings of the 1940s.


How do engineers design the Skyscraper to resist the wind?

By clustering steel columns and beams in the skyscraper's core, engineers create a stiff backbone that can resist tremendous wind forces. The inner core is used as an elevator shaft, and the design allows lots of open space on each floor. Stiff backbone

In newer skyscrapers, like the Sears Tower in Chicago, engineers moved the columns and beams from the core to the perimeter, creating a hollow, rigid tube as strong as the core design, but weighing much, much less. columns on the perimeter

Image of Petronas Towers
Petronas Towers
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Today, the sky's the limit!
As architects and engineers experiment with new styles and building methods, taller and more innovative structures are springing up around the world. The tallest buildings in the world, the Petronas Towers in Malaysia, are connected by a flexible skybridge on the 42nd floor -- a design that improves the circulation of people between the towers and provides an escape route from one tower to the other in case of emergency.

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