Today we’ve got a fun little holiday that fits well into the world of metals – Skyscraper Day!
That’s right! A lesser known holiday that falls on Labor Day, the origins of the holiday are unknown. But now it’s taken as an opportunity to celebrate the amazing engineering, art, and ingenuity that go into even the simplest skyscraper.
When did they come about?
The term was coined in the early 1880s in the United States. It was applied generically to all of big new buildings popping up in Chicago, New York City, Philadelphia, Detroit, and St. Louis. These buildings, about 10-14 stories tall, were massive for their day.
1885 saw the creation of the internal steel frame, which changed building design forever. The 138′ tall Home Insurance Building in Chicago was the first skyscraper made with this revolutionary structure.
Traditionally, buildings rely on their walls to provide most of their structural support. Due to the danger of walls collapsing under their own weight, this limits how big they can be. The internal steel frame is designed with a strong core in the middle, and the frame branches out from that. This means that the frame bears the weight. Consequently, walls are thinner, windows are bigger, and fewer structural supports are needed. Large, open floor spaces also suddenly were an option.
Between the 1880s-1920s, those few US cities were the only places that had such tall buildings. But in the 1930s, skyscrapers began to spread across the US and the rest of the world. They initially gained popularity in South America, before spreading to Europe and Asia, then Africa and Australia.
The end of World War II saw a big boom for skyscrapers. Many European and Asian cities were rubble. Therefore it was a good time to start fresh and design new buildings for a bright new future. Skyscrapers began popping up all over Europe and Asia in the 1950s and 1960s.
The 1960s saw further development that made it possible to go even taller. Bangladeshi-American architect Fazlur Rahman Khan developed a tubular structural design. These are even stronger than the internal steel frame design, as the entire tower is designed to act like a bundle of steel tubes. It gives the skyscraper extra strength and the ability to resist wind pressure. This lead to the development of high-rises and other tall but very narrow buildings.
Though the rate of skyscraper construction slowed a bit in the 1970s – 1990s, they still became ubiquitous in cities around the world.
However, the last 20 years have also seen an unparalleled number of skyscrapers built. This is especially the case in east Asia and the Middle East. The list of the tallest skyscrapers in the world only counts for buildings over 350 m tall. There are presently 59 buildings on that list, and of those, 28 are in China, 6 more in east Asia. 16 of the remaining towers on the list are in the Middle East. Likewise, of the 59 towers, only 9 were built before 2000.
The tallest skyscraper in the world, the Burj Khalifa in the United Arab Emirates, was built in 2010. It is 829.8 m (2,722′) tall. It is so tall that on the floors above the 150th, it stays light for 3 minutes longer than at ground level during sunset.
What counts as the first modern skyscraper isn’t really certain. Because the old definition was a bit fuzzy. Nowadays, architects have agreed on a cleaner definition. To count as a skyscraper, the building must be at least 40 stories tall (about 492′ or 150 m). It must also be designed for business or residential use.
Buildings have also gotten so tall that engineers have made special terms to describe them. Any tower that is over 984’/300 m is described as “supertall.” While anything over 1969’/600 m are classified as “megatall.”
What are they made from?
Alloys steels, aluminum, composites, and reinforced concrete are the most common materials used in skyscrapers.
Steel is used for the main structure and support. Its strength is the single most important attribute of steel. The weight of the metal is somewhat of a liability, but modern alloys often have excellent strength-to-weight ratios and so that issue is lessened. Stainless steel is often used for aesthetics or specific pieces. But it is less ductile and more brittle, which reduces the value in skyscrapers.
Concrete is typically used for the foundation and filling in the structure between the steel supports. While reinforced concrete is less strong than steel, it still has its uses. It is inexpensive, easy to pour large quantities, and it is strong. Raw concrete was very popular for Brutalist skyscrapers, but that has largely fallen out of favor.
Steel and concrete made up the vast majority of older skyscrapers. However, modern skyscrapers increasingly are using aluminum. The high strength, light weight, and corrosion resistance has made aluminum desirable. It is not strong enough to act as main structural supports, but it performs well as a secondary support and smaller parts.
The broadest category by far, these next generation materials are becoming more common. As buildings get taller, weight becomes a bigger concern. Newer composites such as carbon fiber offer strength, low weight, good rigidity, and good corrosion resistance. The main concerns at the moment are that composites tend to be expensive. Also, since they are still pretty new, engineers aren’t always sure how they will age in the long term. Regardless, expect to see more composites in future skyscrapers!