Why do buildings fall during Earthquakes? : 4 Reasons

In this article, we will discuss why do buildings fall during Earthquakes? We will discuss the main 4 reasons.

An earthquake is the sudden shaking of the earth that releases the energy in the earth’s lithosphere causing the creation of seismic waves.

✔ It may be due to volcanic eruption, moving of tectonic plates, formation of the cave in a small area, or explosions.

✔ It is also called a quake( or tremor or temblor).

✔ It is measured with a Richter Magnitude scale.

Despite the continuous efforts of constructing earthquake-proof structures, it is practically not possible to provide complete immunity to the buildings from earthquakes due to their unpredictable intensity of occurrence.

✔ With the growing cities, the risk of collapsing of buildings during the earthquake has increased and due to this, constructing earthquake-resistant buildings have become a prime area of concern for engineers throughout the world leading to the development of a new field of engineering i.e. Earthquake Engineering.

  1. Why do buildings fall during Earthquakes?  

The main causes behind the falling of buildings during an earthquake can be summarized as follows:

a. Failure of Soil:  

Earthquake causes shaking of the ground simultaneously particularly due to the passage of the seismic wave.

The lateral forces imposed are so strong that they can easily turn the soft soil into a loose mass of sand-like particles abandoning its ability to bear weight.

Such sand-like mass can transform sloppy sides into mudslides posing the risk of landslides.

Thus, buildings that have been constructed in such soft soil or sloppy areas have a greater threat of collapse during the earthquake.

During the motion of the ground in the event of an earthquake, the building also moves in a back and forth direction.

After the shaking stops, the buildings may sometimes slump to the ground.

The buildings that are well-built and intact may remain erect but will topple in case of unstable soil on account of the failure of the soil.

According to the reports, during the Mexico earthquake, in 1985; about 4 billion $ damage was caused due to the collapse of buildings owing to the failure of soil.

b. Failure of Foundation:  

One of the main causes behind the collapse of buildings during an earthquake is the failure of the foundation.

When the foundation is not able to withstand the seismic stresses imposed, it fails thereby causing the falling of the building.

The mass of a building can resist normal lateral forces like force exerted by the wind. However, in most cases, the buildings are not designed to resist the intensive multi-directional lateral forces.

The foundations of the buildings, in particular, may shake from their original position and may not be able to hold the structure above.

c. Failure of Soft Floors:  

Soft floors are those floors that consist of large open spaces, minimal shear walls on the interior side, and additional floor-to-floor height.

In many cases, it has been observed that often the upper floors remain intact but the lower floors are either crushed or crumbled. This is because the seismic forces are maximum on the ground floor where most of the soft floors are located.

The soft floors are also less intact than the building structure as a whole and thus are more prone to failure.

One such example of the collapse of a building due to the failure of soft soil was the Leaning Tower collapse during the Taiwan earthquake.

d. Failure of Building Itself:  

The strength of the building depends upon the materials that have been used during its construction.

In general practice, buildings made up of wooden materials are less susceptible to collapse than concrete buildings. This is because concrete buildings are highly rigid.