Supremely tall buildings present architects and engineers with special challenges. How will the building stay upright and not sink into the ground or blow over in a strong wind?
Before the late 1800s, the tallest buildings were rarely higher than 10 stories. The solid brick walls at the bottom needed to be very heavy and thick to support the weight of the upper floors. And thick walls used up a lot of space. Once advances were made in the iron and then beams of solid steel (which is stronger and lighter than iron). The development of the fire-resistant building materials and invention of a passenger elevator also changed the future of architecture. Elevator shafts take up a lot of space. In modern skyscrapers, people going to the top floors will often take one elevator part of the way up and then switch to another.
Cool FactsAbove street level, the Petronas Towers, in Malaysia, are 1,483 feet (452 m) tall. They have a foundation that is 394 feet (120 m) deep.
All buildings sway a little bit in the wind, but this motion can make the people inside feel uncomfortable. A building’s structure must be tight so the whole thing moves together. This prevents different floors from moving differently or twisting, which might weaken the building. Some tall buildings have enormous weights at the top that shift depending on the wind outside to keep the structure from swaying too much and making the people inside feel queasy.
At the Shanghai World Financial Center, in China, there is a large hole built in the top of the building, which allows wind to flow through the building rather than just push on it.
Builders must know a lot about the land that will support a building. In New York City, much of the ground below skyscrapers is bedrock, the solid sturdy rock makes up Earth’s crust. This makes laying a foundation simpler. In Chicago, the ground is clay, which is softer. So it is more expensive to create solid foundation there.
The vertical beams of structures attach to an underground plate made of cast iron. This plate sits atop groupings of heavy horizontal steel beams, called grillage. Each layer of beams in the grillage is wider than the one above it, making hefty underground pyramid. The grillage rests on an even wider concrete pad. The tallest building in the world is the Burj Khalifa, in Dubai, United Arab Emirates. It is 2,722 feet (829.7 m) tall above street level and has a foundation that’s 164 feet (50 m) deep.