What is Earthquake Engineering?

Earthquake construction is an important discipline that contributes to minimizing damage by using pile foundations, base isolation, and other techniques. Evaluation of soil conditions is also important.

Earthquake Engineering is a specialised field within Geotechnical Engineering. Earthquakes are simply a series of vibrations due movements below the Earth that have the potential to cause immense damage and destruction at the Earth’s surface. Earthquake Engineering is the application of the study of earthquakes and the vibrations generated at the surface in order to protect the built environment and people from being harmed.

What Is Earthquake Construction?
Earthquake construction ensures that structures resist earthquake shocks by the integration of seismic designs throughout their expected life, in conformity with the building codes applicable in the region. Earthquakes destabilize buildings either by direct effects of the seismic waves, or indirectly through soil liquefaction and landslides.

Simulation and failure mode analysis are important tools that help Earthquake Engineers to design structural elements that can withstand earthquake exposure without major structural damage. Earthquake Engineering is a small niche that provides opportunities in a limited number of countries.

Most structures fail laterally by an earthquake, meaning the the walls may fall down, or movement of the walls may cause displacement of the roofs, and result in the collapse of the structure. Therefore, to ensure safety of human life and property, earthquake-resistant techniques should be used, including the utilization of proper design and materials.

The condition of soil at the site of construction
Soil conditions is an important factor, since the state of soil can significantly alter the motions of an earthquake. The condition of the soil should be thoroughly evaluated. Soils that consist of loose sand and gravel possess poor earthquake-resistant characteristics, and should be reinforced. Seismic waves are amplified in soils that are saturated with water, and change the form of soil from a solid to a liquid upon the occurrence of earthquakes.

Such soils acquire the characteristics of quicksand and make the ground incapable of supporting a foundation due to cracks and weakening. Deep and firm soils are good since they allow only minor vibrations to be transferred from the foundation to the construction above.

Pile Foundations
Pile foundations are a structural part used for the transfer of the structure load to the solid ground located at some depth. Piles are extended and thin elements that transmit the load to a lower soil of greater bearing capability, penetrating the shallow soil. Piles can be used in earthquake construction to minimize earthquake effects, especially with soft surface soils that may easily liquefy, by resisting vertical and lateral loads.

A structure is raised on piles if the soil is unstable, weak, does not possess sufficient bearing capacity, and the likely settlement is not advisable. The design of the piles should be proper, by binding the pile caps with reinforced concrete slabs that can function in tension as well as compression, so that the foundation may perform as a unit. In addition, the piles should be designed to carry axial, shear, and bending loads that may be occur because of the horizontal movements between the layers in the soil.

Base Isolation
Base isolation techniques are a recent development in the structural design of buildings and bridges in highly seismic regions. They function on the principles of oscillation and damping. Rubber isolation bearings are used that minimize the earthquake damage to the buildings by decoupling the building from the horizontal component of the ground movement.

This is achieved by making the bearings rigid in the vertical direction and elastic in the horizontal direction. The earthquake energy is not absorbed by the base isolation techniques but is deflected due to the system. Rubber bearings can be manufactured easily, do not have any moving parts, and are not affected by time or the environment.

In areas that are significant risk of being exposed to earthquakes, a team of Earthquake Engineers are called in to prevent disaster from occurring. Importantly, they make significant use of design and construction techniques to ensure that buildings and infrastructure are able to withstand such considerable damage.

The main objectives of earthquake engineering are:
  1. Foresee the potential consequences of strong earthquakes on urban areas and civil infrastructure.
  2. Design, construct and maintain structures to perform at earthquake exposure up to the expectations and in compliance with building codes.
A properly engineered structure does not necessarily have to be extremely strong or expensive. It has to be properly designed to withstand the seismic effects while sustaining an acceptable level of damage.

What causes earthquakes and where do they happen?
The earth has four major layers: the inner core, outer core, mantle and crust. The crust and the top of the mantle make up a thin skin on the surface of our planet. But this skin is not all in one piece – it is made up of many pieces like a puzzle covering the surface of the earth.  Not only that, but these puzzle pieces keep slowly moving around, sliding past one another and bumping into each other. We call these puzzle pieces tectonic plates, and the edges of the plates are called the plate boundaries. The plate boundaries are made up of many faults, and most of the earthquakes around the world occur on these faults. Since the edges of the plates are rough, they get stuck while the rest of the plate keeps moving. Finally, when the plate has moved far enough, the edges unstick on one of the faults and there is an earthquake.

Why does the earth shake when there is an earthquake?
While the edges of faults are stuck together, and the rest of the block is moving, the energy that would normally cause the blocks to slide past one another is being stored up. When the force of the moving blocks finally overcomes the friction of the jagged edges of the fault and it unsticks, all that stored up energy is released. The energy radiates outward from the fault in all directions in the form of seismic waves like ripples on a pond. The seismic waves shake the earth as they move through it, and when the waves reach the earth’s surface, they shake the ground and anything on it, like our houses and us! (see P&S Wave inset)

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