How Skyscrapers Work

Skyscrapers are engineering and architectural marvels that tower above other city structures. Discover the innovations and building techniques that make keep these tall buildings standing safe against fire, earthquakes and high winds.

Skyscrapers are architectural marvels, rising hundreds or even over one thousand feet into the air. The tallest buildings, as of 2004, are the Petronas Towers in Malaysia, which rise to a height of 1,730 feet. Chicago also boasts several very tall buildings, including the Sears Tower at 1,454 feet, and the Hancock Building at 1,100 feet. The drive to build ever-taller structures dates far back into history, and modern-day competition to build the tallest structures in the world ensures that builders will be stretching ever higher for years to come.

In ancient times, pyramids rose to the greatest heights imaginable. Later, cathedrals and towers sprouted upwards as stone testaments to man's desire to build taller and taller structures. These were limited, however, by the sheer weight of the stones used for their construction. The heavy stones could only be lifted and stacked so high. As structures were built taller, two things had to happen to accommodate the laws of physics. The base of the building had to get wider as the height increased. Children quickly learn this concept when they build block towers. Those with wider bases can be built up taller. The tall, skinny structures are less stable and more likely to fall. Architects added stability to tall buildings and towers by making them wider at the base. They either made the bottom of the building wider than the top or added buttresses to support it. The sheer weight of the walls also necessitated making them thicker, as taller walls are heavier and need greater support to keep from crushing the lower parts. These two design necessities limited the possible size of buildings. If designers tried to build too high, the base would be too large to be practical, and the thick lower walls would take up too much interior space.

It wasn't until the late 1800's and the advent of inexpensive steel production that these limits could be surmounted. New materials prompted design innovations that shattered the old limits. The steel, lighter in weight and sturdier than previous materials like brick and stone, could be formed into long, thin pieces called girders. The first skyscrapers, built in the US in the 1880's, were constructed using vertical columns and horizontal beams made from steel girders. This supporting skeleton allowed buildings to rise to ten or more stories. Buildings reaching those heights also relied on a new invention, the elevator. Elevators made taller buildings more practical. Central heat and air conditioning systems helped maintain a comfortable environment in the big buildings, making them more desirable.



As population in larger cities grew, developers wanted to pack more and more people and places of business into smaller and smaller land areas. This necessitated building upward, since the amount of land in a city is limited. Taller buildings allowed more people to use the same land. Designers began to compete to build taller and taller buildings, and cities vied for the honor of having the world's tallest structures. This fueled the competition to find new ways to build ever taller.

Skyscrapers grew taller when designers began using bundled steel tubes instead of heavy girders. The lighter weight pieces need less support, and so the buildings could grow taller. Additional beams can be placed diagonally for additional support while adding little extra weight. Elevators could be housed in a strong central core that better supports the building. Very tall buildings and very long elevators are not always practical, so some buildings use one set of elevators to take passengers part way up the building and another set to service the upper floors. Innovation after innovation has allowed skyscrapers to break old limits and to be built taller and taller with the passing decades.

Taller buildings also pose new and different challenges for engineers and architects. Allowances must be made for wind speed and the sheer weight of the structure. Fires in a structure without ready exits to the ground can be devastating. Earthquakes, too, can cause peculiar problems for very tall buildings. Designers continue to develop new and better solutions to these problems, but current technology and building techniques are in use to minimize them.

High winds actually cause tall buildings to sway several feet from side to side, much like a tree moves in the wind instead of breaking at the slightest force. Many skyscrapers now have a strong central core that supports the building and braces it. The elevators are housed in this core, too. The girders and beams are not only bolted together but also welded on all sides to cause the building to sway from side to side as a unit instead of rippling. A few high-tech skyscrapers use complex hydraulic systems to push a huge concrete weight back and forth on a top floor to actually shift a portion of the building's weight and counter some swaying caused by the wind.

Skyscrapers are made from a skeleton of steel beams and girders. In such an arrangement, the weight of the structure is borne on the "legs." All of the weight is pushed downward on relatively small surfaces. In order to make this a workable situation, many skyscrapers have special structures that serve to brace these points of support. The substructure of the building, as it is called, has several parts. Each vertical column rests on an iron plate, which rests on at least two layers of horizontal beams. The beams are laid side by side to provide more support. The entire structure rests on a heavy concrete pad on the ground. The substructure is encased in concrete and serves to spread out the force of gravity acting on the building's support points.

Fires are a major concern for people living and working in high-rise buildings. There is no quick and easy exit from the fiftieth floor! Elevators are often not working in case of a fire, and the stairs take a very long time to use or are unusable by many people with even minor disabilities. Innovations in fire resistant and flame retardant building materials make these structures safer than they have ever been before. Advanced sprinkler systems generally contain and control most fires before they can cause much damage.

Skyscrapers add a unique and impressive look to the skyline of a city. They speak of wealth, power, and mastery of technology. Cities and businesses are continually vying for claim to the world's tallest building, and some will argue endlessly over minutia such as whether antennas count as part of the building's height or if one can consider decorative portions of a building if they are uninhabited. In any case, skyscrapers are likely to be attractions in major cities for years to come, and they certainly are the best way we've found so far to maximize land usage. As cities become more crowded, we can expect more and more impressive buildings to rise to increasing heights. The sky truly is the limit.

© High Speed Ventures 2011