Skyscrapers are very tall buildings, usually more than 20 storeys high. Their weight is supported by a steel frame rather than outside walls. They are a feature of many large cities, especially in North America and East Asia, where the high price of land leads developers to build tall, thin buildings that occupy the minimum amount of land space, rather than low-rise, sprawling ones.
The first skyscraper, the Home Insurance Building, was built in Chicago in 1884 following a fire that devastated the city. Soon, skyscrapers started to appear in New York as well as Chicago, often being built higher and higher in competition with one another. In recent years, Japan, Malaysia and China are among nations that have joined the race to build the world's tallest buildings.
The John Hancock Center in Chicago, USA, was completed in 1968. A skyscraper with both offices and residential apartments; it is the tallest multi-purpose building in the world and the seventh tallest skyscraper of all. It is 344 metres high but its twin antennae add a further 105 metres, making it a total of nearly 450 metres. It has a hull and core construction—a strong central concrete core with an open space between it and the steel frame. The frame has a triangular grid to give the structure maximum strength.
The John Hancock Center is like a city in a tower. It has shops, a bank, a post office, a restaurant, a swimming pool and a fitness centre. There are 50 lifts (it takes only 39 seconds to ascend to the 94th floor). A car park with spaces for 1200 cars takes up the first seven floors. Cars drive up a spiral ramp to get to it.
The building has more than 2000 kilometres of electric wiring, carrying enough electricity to supply the equivalent of a city of 30,000 people. More than 2.75 million litres of water are consumed each day. Computers warn of any fault in the skyscraper's service systems.
People have constructed buildings from ancient times as homes to provide shelter, monuments or places of worship. Earth, wood and stone have always been used as building materials. Bricks, hardened clay, were first used in the Middle East in about 3000 BC. Concrete is made by mixing sand, cement and water. Reinforced concrete dates from the late 1800s. Often used in modern buildings, it contains steel wires or rods to provide extra strength.
Buildings belong to one of two types. The first type has solid walls, called load-bearing walls that support the floors and roof of the building. The second type has a framework of wood, steel or concrete that bears the weight of the building.
Most buildings need foundations (a solid base) to prevent them from sinking into the ground or falling over. Foundations can be footings (underground walls), flat rafts, or underground supporting pillars called piles that are driven into the ground.
TALL STRUCTURES
The Great Pyramid at Giza in Egypt was the world's tallest structure for nearly 4000 years, until the great age of cathedral building began in medieval Europe. Lincoln Cathedral in England, which was built in 1311, had a great spire that made it slightly taller than the pyramid, although it was blown down in a storm in 1549. The Washington Monument in Washington, USA, became the world's tallest structure in 1884, before the Eiffel Tower in Paris, France, almost doubled the record five years later. The skyscrapers of the 20th century claimed the honour until the CN Tower, still the world's tallest self-supporting structure, was built in Toronto in 1976.
Picture Credit : Google
