Why Do Buildings Collapse During Earthquakes and Not Others?

Structural Weaknesses

Buildings that are designed and constructed with inadequate seismic resistance are more likely to collapse during earthquakes. This can be attributed to various factors, including the use of low-strength materials, insufficient reinforcement, and poor detailing. For instance, buildings with soft-story failures, where the first floor is not adequately reinforced, are particularly susceptible to collapse. In such cases, the first floor can become detached from the upper floors, leading to a collapse. The 2014 Port-au-Prince earthquake in Haiti is a classic example of a building collapse due to soft-story failure.

Soil Conditions and Liquefaction

The type of soil on which a building is constructed can also play a significant role in its vulnerability to earthquake damage. Buildings situated on soft or loose soil are more prone to soil liquefaction, a phenomenon in which the soil loses its strength and behaves like a fluid during an earthquake. This can cause the foundation of the building to shift or collapse, leading to structural damage or collapse. Soil liquefaction was a major contributor to the damage caused by the 1964 Alaska earthquake and the 1989 Loma Prieta earthquake in California.

Non-Structural Elements and Anchorage

Non-structural elements such as chimneys, water tanks, and ducts can also contribute to building collapse during an earthquake. When these elements are not properly anchored or secured, they can become loose and cause damage to the surrounding structure. In some cases, non-structural elements can even become projectiles during an earthquake, causing significant damage to the building and its occupants. To mitigate this risk, it is essential to ensure that all non-structural elements are properly anchored and secured to the main structure.