Arcuated Systems

Arcuated structures were a major advance over posts and lintels. These systems of curved elements allow more space to be enclosed with supports that are less massive. An arcuated structure is based on the arch, a curved support that spans an opening between upright posts.

Arches

Arches are made from wedge-shaped stones known as voussoirs that are supported at their base by blocks called imposts. The earliest arches were built by stacking the voussoirs on a semicircular wooden framework. The stack of voussoirs was started from both ends and built up toward the top. When the largest wedge-shaped unit – a keystone – was placed on the top of the stack, the formwork was dismantled. Think of the arch as two weaknesses leaning against each other to make a strength (that’s how Leonardo da Vinci described the two halves).

Vaults

Extending an arch in the third dimension forms a structure with a curved ceiling known as a vault. Rounded like half a barrel, this type of vault is called, logically, a barrel vault. Many of the great structures designed by the ancient Romans rely on the barrel vault, such as the Colosseum in Rome. Vaults can span larger spaces than simple arches.

Domes

Another structure formed from arches is a half-spherical structure known as a dome. You can make a dome by rotating a series of arches 360 degrees around a vertical axis. The outward thrust is absorbed by a ring at the bottom and rings at various levels, called parallels that prevent the arches from moving in or out under the load. Because a dome’s arches, called meridians, are supported all the way to the top of the dome, they can be made much lighter than arches that are standing alone. A dome is a thin but strong structure that can span great distances.

H ypars

For some modern architects, breaking out of the box meant using saddle surfaces – or a hyperbolic paraboloid (hypar), as architects call them. While domes or barrel vaults have downward curvatures in all directions, a hypar has curvatures up in certain directions and down in others. This unique design gives it a soaring shape that resembles a butterfly or a bird. On your left, you can see the largest oceanographic aquarium in Europe that represents a hyperbolic/parabolic figure, resembling a water lily. It was designed by a master of the hypar, Spanish-born architect Felix Candela.

Thin Shells

Thin shells are a type of form-resistant structure in which strength is obtained by shaping the material according to the loads that it must carry. Thin shells are thin enough to avoid bending, but thick enough to support loads by compression or tension, or a combination of both. Although they can be constructed in a variety of materials, thin shells are best suited to reinforced concrete – a material capable of resisting both tension and compression. One of the most spectacular concrete shell structures is the Sydney Opera House designed by Jorn Utzon. Made of concrete segments, its soaring, sail-like roofs are Australia’s most famous architectural landmark.

Tents

Some of the most impressive contemporary buildings have returned to the most basic of all structures – tents. Like nomads pulling skins over wooden poles, today’s architects separate their tents into two components: 1) a membrane of fabric that is stretched over steel cables, 2) masts of steel and other materials that support the suspended cables and fabric. Tents are now made of Glass-reinforced fibers and self-cleaning Teflon coatings that boost the fabrics’ strength, fire-resistance, and insulating and reflective properties.

K han Shatyr entertainment center is a giant transparent tent in Astana, the capital city of Kazakhstan. The 150m-high tent has an elliptical base covering an area larger than 10 football stadiums. The roof is constructed from ETFE-cushions suspended on a network of cables strung from a central spire. The transparent material allows sunlight through which, in conjunction with air heating and cooling systems, is designed to maintain an internal temperature between 15–30 °C, while outside the temperature varies between -35 and 35 °C across the year.