UNIT ZERO – STRUCTURES & GRAVITY

SkyscrapersSquare vs. Triangle

Skyscraper Basics

• 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.

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.

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.

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.

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 fives stories tall.

Skyscraper: Forces

The skyscraper pushes down into the ground.

But when the wind blows, the columns on the windy side stretch apart, and the columns on the other side squeeze.

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 skyscrapers to resist 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.

• In new skyscrapers, 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.

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, such as the Petronas Towers in Malaysia.

Structures of buildings

When constructing buildings like skyscrapers, it’s important to think about the following:

1. Cost – How can we use less material while still ensuring that the structure is strong and stable?

2. Strength – The structure must not only support its own weight, but also withstand as much external force as it can.

Which one is strongest?

Most Stable Shape

Triangle

Why?

• Because the triangle does not easily deform and is able to balance the stretching (tension) and compressive forces inside the structure.

• For economic reasons: since the triangle obvious only has 3 sides, it requires little material to make a support, thus minimizing the costs.

Why triangle is strongest shape?

• The angle cannot change once the triangle is built.

• The load from the structure will transfer smoothly.

Geodesic Dome

Disney Epcot Center, Florida

Bicycle

The Great Pyramid, Egypt

Sydney Harbour Bridge, Sydney

Petronas Towers, Malaysia

Infosys Mysore Development Center, Mysore

Square vs. Triangle

Strengthening Squares

• Add a diagonal between opposite corners.

BrainstormingSpaghetti and Marshmallow Challenge #2

STEM Notebook, page 5

End of Presentation