Why they don’t make skyscrapers from only traditional bricks
Seems boring really, to keep using steel and concrete to make skyscrapers. However, building a building is a little more complex than picking a material and starting to build up. The main reason we use steel and concrete won’t really surprise anyone; they are strong but cheap. A skyscraper need a lot of stuff to build it no matter how you look at it. However, the costs are one of many problems that come with building higher.
Stress is not just experienced by university students cramming for exams. Stress is an engineering term for the force for a specific area. A building that is tall is also very heavy, so it creates a high stress on the ground. A strong foundation is needed to stop a building literally sinking into the ground. The Burj Khalifa the world’s tallest building needed to build a concrete foundation that went 50m into the ground.
If a building sinking into the ground was worrisome enough if the building is too heavy the material at the bottom can become crushed under the weight of the building above. But bricks are quite strong and can resist being compressed, this is not the problem with building with bricks. Bricks major disadvantage they can be compressed but they can’t be stretched, when something is stretched it is under tension.
Forces don’t just compress they can also cause shear, anyone who has seen a tree sway in the wind has seen the effect of a shear force. Higher up winds can reach very high speeds. This can cause a shear stress, where stress is pressing across the surface and this causes the building to also sway in the same way as a tree. With a tall building there is a larger shear stress the higher it is built, this means as the wind blows the building can start to sway, even if it’s only a little.
The shear stress on an object via Wikimedia Commons
Here lies the problem with bricks with they do very well under compression but can’t handle this the shear stress. This means that if you tried to make a brick wall too high the wind would blow it down, like a house of cards. Saying that walls collapsing is a safety concern is an understatement. The only way they can be built is if they are reinforced with another material, which is most likely to be steel. Steel is strong under tension that’s why you could hang objects from steel wires. The Chrysler Building has over 3.5 million bricks, but it uses a steel frame to reinforce it. By reinforcing the bricks with steel, the force can be dissipated through it keeping the structure stable.
The Chrysler Building via Wikimedia Commons
Why we’re building it up
Despite the challenges of building up buildings are becoming taller and this has some merits. The cost of land is fixed but building multiple floors mean more space within the building, and this means more people can fit inside. This is particularly the case for countries like Singapore, where there isn’t much space to build out; the only way to go is up. In the end, it’s the need for space that will take us higher.