Earthquake proof buildings- where are we?

Every year media brings us more news about seismic events. We have no control over naturally occurring earthquakes. We can, however, reduce their impact by clever engineering and constructing earthquake proof buildings.

Prevention research

The aftermath of an earthquake is simply devastating. But it is not the earthquake itself that results in damage. Falling buildings and structures entrap thousands of people. Places such as Hawaii, are known for being under particular danger. Their current architecture is very susceptible to earth movements and with no advances in earthquake engineering, it is not possible to reduce seismic effects. Earthquakes result in ground shaking, tsunamis, surface rupture and landsliding to mention just a few. Most buildings, even in seismically active areas, are not built to resist such effects.

There has been an increase in earthquake engineering research in the past years. It is mainly based in several centres, such as National Science Foundation and Earthquake Engineering Research Institute. Many universities offer postgraduate courses in Earthquake Engineering. Even though UK is not under threat, universities such as UCL or Cambridge still offer related courses.

Hazard assessment is an important part of earthquake engineering. It measures the probability and size of an earthquake. Design takes into consideration loads and regularity with distribution of mass. Choice of connections and reinforcements, as well as specific material is vital. Detailing plays a crucial role as well. Movements and dynamic structures also have to be considered during planning and design processes.

Technologies for earthquake proof buildings

There are several technologies being used to construct earthquake proof buildings. One of them is tune mass dampers used in skyscrapers. Big mass structure suspended at the top of tall buildings prevents its oscillation. This technology has been first used in other industries, such as aeronautics and automobiles.

Japan engineers have used base isolation to reduce impact of ground movement on building structure. Isolation is essentially an air cushion, which lifts building up to 3cm off the ground when seismic danger is detected. Building then returns to its original position.

Mechanical energy of an earthquake can be transformed into heat by dampers. They work as shock absorbers. Another technology is known as Controlled Rocking system. It uses steel frames to make structure more elastic and hence less prone to damage. Rocking-core walls are introduced to prevent permanent deformation of concrete. In this structure, two lower levels are reinforced with steel. The entire height is additionally reinforced with post tensioning. Seismic waves can also be trapped by concentric rings, which act as ‘invisibility cloak’. Waves are guided around a building making them invisible and leaving structure unaffected. On the rise is research into smart materials that will potentially be able to return to their original shape.

Commonly used technologies

Earth-made building materials, such as adobe mud bricks, have been used for centuries. They are very vulnerable to earthquakes but can now be strengthened. Limestone and sandstone, popular in North American and European architecture, is prone to damage due to its heavy weight. Timber framing has been used for a long time to improve general durability of buildings. It is also helpful in partially reducing effects of seismic waves. Concrete structures can be reinforced with steel bars. Prestressing of bridges and other structures increases their general stability and integrity. Interestingly, highest earthquake-resistance is found among steel structures. However, even they can be affected. Moment-resisting frames had been considered safe until 1994 when the Northridge earthquake occurred.

Another technology is seismic retrofitting. Earthquake proof buildings are made this way with some extra supports, such as on the picture below.The techniques include external post-tensioning, supplementary and tuned mass dampers. In developing countries the effort is put into use of naturally available sources and materials.

Challenges and future

The current challenge is to bring these technologies into developing countries, which are very likely to experience earthquakes. Expensive solutions will not work due to many current buildings being in need of extra earthquake proof adjustments. With more universities offering research degrees in earthquake engineering and worldwide centres, the advances are hopefully on the rise.