To earthquake-proof a building, diaphragms must be placed on their own deck and strengthened horizontally to share forces with vertical structures. Trusses strengthen the diaphragm where the deck is weakest. Simply put, they are diagonal structures that are inserted into the rectangular areas of the frame.
Engineers incorporate a variety of columns, braces, and beams to transfer seismic forces back to the ground. Cross braces incorporate two diagonal sections in an X-shape to build wall trusses.
To help resistance swaying forces, engineers use vertical walls, known as shear walls, to stiffen the structural frame of the building. These can be used in place of braced frames or in addition to them. When this happens, multiple waves at the resonant frequency pass through the structure, their effects amplifying each other. This makes for a very destructive force. The impact of resonance was very apparent after a large quake in Mexico City in Mid-range buildings of stories were in resonance with the seismic waves, causing those buildings to sufer more damage than shorter or taller ones.
As quake waves pass through the earth, they are filtered in different ways by different kinds of soils. Mexico City sits on a mud plain, which happened to allow waves of a particularly devastating frequency to strike the buildings. Surprisingly, Mexico City is quite far from the epicenter of the quake. But because of this resonance phenomenon, the city suffered much more damage than some other towns closer to the fault.
So, the ground below a structure can be as important a safety consideration as its construction. Bedrock absorbs more wave energy than sandy soils or landfill, so buildings on solid rock will be much less affected than those built on softer soils. And if softer soils have water in them, they can become a little like quicksand during an earthquake. When seismic waves pass through saturated soil, they give it a strong squeeze. The soil loses its strength and behaves like a liquid, a process called liquefaction.
Buildings on top of liquefied soil sink, and often topple. Testing, testing. Earthquake-resistant buildings also need features to help absorb shocks. People more commonly refer to them as seismic dampers. Engineers worked with NASA to develop damper systems for swing arms on its rockets in the s.
Seismic dampers absorb destructive energy, protecting the building from sustaining it. One manufacturer of these dampers sells products to withstand from 25 to 1, tons and sells customized options, too. Another approach involves putting a thin layer of graphene on top of a natural rubber pad. Researchers believe this will be a low-cost damper option for commercial and residential buildings.
Pooled water can create structural complications. Engineers achieve positive drainage with 1. Drainage is also crucial to help structures tolerate earthquakes. When the disasters occur in places with loose, sandy soils, the shaking can result in a phenomenon called liquefaction. It makes buildings sink or move to one side, and sewage pipes may rise to the surface.
When the soil solidifies again after an earthquake, the buildings stay in their sunken, tilted positions. However, earthquake drains help collected water escape, preventing liquefaction. They are prefabricated pieces wrapped in a filtering fabric.
Each drain measures between 3 and 8 inches in diameter. A successful installation requires a grid-style placement. The Tokyo Skytree Credit: Alamy. Other methods involve the layout and design of the building itself. But often the designers of spectacular skyscrapers are reluctant to make those kinds of compromises, and tensions between the seismic standards required by engineers and the creative visions of architects are common.
The Skytree Tower in Tokyo is the second tallest building in the world. Sato has worked on developing seismic engineering solutions that are both functional and elegant.
If one part buckles, having a close neighbour helps stop it bending and distributes the energy absorption. As a result, mesh structures — which can also be very beautiful — help to fortify buildings.
The Naoshima pavillion Credit: Sou Fujimoto. The goal of creating earthquake-proof buildings is not static. Researchers estimate how future earthquakes might impact a building by observing active faults.
But the magnitude of earthquakes in the region appears to be getting larger, so prediction becomes even more difficult, says Ejiri.
The answer lies in gradually testing all the known technologies we have to stabilise buildings, while trialling ever more creative designs, such as mesh structures. Construction for Olympics Credit: Getty Images.
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