Reading 1

Unit 5- Reading 1

Page 66

Skyscrapers

About 2.800 years ago. the tallest structure in the world was the Great Pyramid of Giza in ancient Egypt. It was 146 meters (479 feet) tall. Today, the Burj Khalifa building in Dubai is nearly six times that height.

It is 828 meters (2.717 feet) tall and has 163 stories.

The Burj Khalifa is one of many skyscrapers constructed in different areas of the world recently. Even though the Great Pyramid was very tall. It was not a skyscraper because people did not live or work inside. There is no exact definition of a skyscraper. It is simply a very tall building.

Today, millions of people live and work in skyscrapers.

A: EARLY BUILDINGS

Until the end of the 19th century, few buildings were taller than ten stories. One reason was because people could not easily climb any higher on stairs. Also, the entire structure of an old building was supported by its four outside walls. These walls were made of vertical piles of bricks or stones.

The piles had to be very thick or they would fall over. This restricted the height of the walls.

STEEL BEAMS

Two major inventions in the 19th century made the construction of taller buildings possible. One was a new process for making steel. This process was used to create strong beams (long, thin pieces) of steel.

Tall structures could be built with these beams. These structures used a new construction design. The walls were not made of stone or brick. Instead, thin steel beams were used to build a strong vertical framework for the walls. Later, the vertical beams were covered with concrete to create attractive walls. The thin walls gave much more area inside a building.

SAFETY ELEVATORS

The safety elevator was the other major invention that made possible the construction of taller buildings. Previously, elevators had been used for lifting things on ships or in factories. But they were too dangerous to use to lift people. The ropes often broke and the lifts fell to the ground. The invention of an elevator safety brake prevented elevators from falling.

This meant that people could safely ride up to high apartments and offices. And they could safely ride down.

However, elevators created certain building design problems. First, the vertical structure for elevators used valuable space inside a building. The engine room that provided power to the elevators also used valuable space. The area that could be used for offices or apartments was restricted by these necessary structures.

Skyscrapers have other design problems. For example, they need machinery to pump water up to high stories. They also need pipes to carry clean water up and wastewater down. Tall buildings also have complex systems for bringing electricity, heating, and air conditioning to the whole building. Finally, the top of a very tall building must be designed to be safe when strong winds blow high above the ground.

Is there a limit to the height of skyscrapers? We will probably learn the answer soon.