Skyscrapers appeared in places that had high population and high land prices. Invention of a civil elevator and improvement of materials like steel were conditions in improvement of building. First higher building appeared in 19th century but run into problems of height. If the building had more than 6 floors higher floors became impractical because people got tired of climbing the stairs. Elevator helped there. Second problem were the walls. Wall material is used to hold the weight of the building but as the building rises so does the weight and, if the walls are made from conventional materials like bricks or cinderblocks, as the walls raise so does the thickness of the walls at the base so the walls could hold the building. This way of building is called shear wall but for great heights is impractical because of the amount of material needed and the lessening of the floor-space. That is why skyscrapers “work” on different principle and in time that principle improved and changed.
The first idea that worked as a skyscraper was a steel frame which was basically a large steel box with many small boxes inside it. Idea is based on eliminating the part of a shear wall that did almost nothing - the central portion, and making support parts of the wall from much stronger material - steel. This method has drawbacks and can be used only on the lower skyscrapers. Main problem is that as height increases more material must be supported and the distance between supporting members must decrease. That makes more material that must be supported and so on. That is why this method is used only for buildings with 40 floors or fewer.
In 1963, a new method was invented: a framed tube introduced by Fazlur Rahman Khan. It was based on the idea that a building can be designed to resist lateral loads by designing it as a hollow beam vertical to the ground. In it, closely spaced interconnected exterior columns form the tube. This allows for fewer interior columns and so creates more usable floor space. It was used for the first time in the DeWitt-Chestnut Apartment Building which was completed in Chicago in 1963. Variant of the tube frame is a bundled tube, which uses several interconnected tube frames and is highly efficient in economic terms. It also changed buildings esthetically because they no longer had to be box-like but the tube-units could be combined as the designer wanted.
X-bracing, braced tube or trussed tube appeared in 1969 on the John Hancock Center. It reduces the lateral load on the building by transferring the load into the exterior columns. This method allows for much lower weight of steel per square meter which makes it more economic.
After the invention of the bundled tube and trussed tube, skyscrapers could again be made from reinforced concrete and of composite construction (the discrete use of both steel and concrete).
Today these forms and methods of building can be seen in many modern skyscrapers like the World Trade Center, Petronas Towers, Jin Mao Building and Burj Khalifa.