What it takes to build supertall structures

In order to construct new supertall buildings, some new building techniques are used:

Wind is the “dominant force” in tall buildings, says Baker. Over time, engineers and architects have become more and more sophisticated when it comes to shaping a building to account for gusts that can, on very rare days, reach 100 miles-per-hour at the crown of a 90- or 100-story skyscraper. Early in the design process, different shapes for a proposed tower are workshopped and run through wind tunnel testing to determine which one is most efficient. Computer simulations for complex wind patterns still take a long time, so model testing often works best to determine factors such as lift and cross-breezes. Baker says, “the wind tunnel is a giant calculator.”

Skyscraper designers want to “confuse the wind,” says Baker. Air pushing against the surface of a tall tower creates vortices, concentrated pockets of force that can shake and vibrate buildings (the technical term is vortex shedding). The aim of any skyscraper design is to break up these vortices. Facades often have rounded, chamfered or notched corners to help break up the wind, and sometimes, open slots are grooves will be added to let wind pass through and vent, in effect disrupting the air flow…

To help counter the shifting and swaying of building, engineers also utilize dampers, massive devices that shift and help stabilize tall structures like counterweights. Think of them like the weights in a grandfather clock; engineers attach 300-800 ton pieces of steel or concrete on a floor near the top of a tower, tuning and adjusting chains to balance them so they move out of phase with local wind patterns, steadying the tower. Two main types of dampers are used today; tuned mass dampers, which function like swinging pendulums, and slosh dampers, or slosh tanks, large pools of water that help absorb vibrations. The technology isn’t new; it’s been used on buildings such as the Seagram Tower, completed in 1958. But it’s become more common and more sophisticated. Some tuned mass dampers even use actuators, or small motors, to shift and move in opposition to the wind. The engineers of the Shanghai Tower even devised a damper system with powerful magnets…

Even with carefully engineered facades and vibration-canceling technology, supertalls still need to support massive amounts of weight. While we haven’t moved past concrete and steel, technological advances means the elemental ingredients of skyscrapers can support much larger loads with much less material. “Concrete is amazing these days,” says Baker. “We should call it something new, since it’s so different than concrete from a few decades ago.” More workable and up to five times stronger, concrete today has gained these powers due to a more complex chemical composition. In many cases, industrial by-products, such as fly ash, slag from steel mills and microsilica left over from silicon manufacturing, are added to strengthen the mix, allowing it to be stiffer and support heavier loads.

That’s a lot of work and we would want to make sure this is done right from the beginning. (If people are worried about all the computer code in cars, imagine an article written from the angle of what could go wrong is building these tall structures.) Just putting all the appropriate pieces together – in addition to the new technologies that evolve to help make this possible – requires dealing with an impressive amount of complexity.

Just a reminder from a post earlier this year: the engineering can get us to even taller buildings (3,000-5,000 feet) but the economics haven’t caught up yet. Yet, with the luxury end of the market continuing to thrive, perhaps we aren’t that far away…

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