
One of the most challenging and devastating consequences of earthquakes is the destruction of buildings in seismically active zones. This leads not only to the loss of homes and material possessions but also to the loss of life for those caught inside collapsing structures. Earthquakes can cause the destruction or damage of homes, industrial facilities, transportation infrastructure (bridges, roads, and railways), water supply networks, power lines, and other communication systems.
The number of casualties and the extent of destruction can be greater if the main shock is followed by aftershocks, capable of completely collapsing weakened structures that have not yet fully lost their integrity. Therefore, after the first series of tremors, people often leave buildings and remain in open spaces until seismic activity subsides.
How and why do buildings collapse from seismic tremors, and where is the safest place to be inside a house during an earthquake? Which type of house is safer β reinforced concrete monolithic, block, or brick? Are residents of upper or lower floors exposed to greater seismic risks? To answer these questions, it’s important to understand the effects of earthquakes on buildings.
Why Buildings Collapse During Earthquakes
Ground motion caused by an earthquake primarily affects a building’s foundation, which in turn begins to vibrate. During a seismic event, the entire structure is subjected to horizontal loads due to the inertia of its mass, which shifts under the influence of ground vibrations. Inertial forces create deformations in the load-bearing elements of the structure β walls, floors, columns, and beams. Buildings are typically designed to withstand the force of gravity. However, additional horizontal loads can destabilize the structure and exceed the permissible strength of the load-bearing elements.
In some cases, the main structures cannot withstand the level of deformation imposed on the building by vibrations, leading to the collapse of walls and floors. Also, certain soil types are very sensitive to dynamic loads and can lose their load-bearing capacity during seismic waves. As a result, supporting elements settle and tilt. These phenomena cause damage to buildings β from the appearance of cracks to their partial or complete collapse. Therefore, without proper anti-seismic design, which takes into account dynamic loads from vibrations during an earthquake, a building may face situations that threaten its stability.
How Buildings Collapse During Earthquakes
During earthquakes, reinforced concrete buildings suffer a variety of damages, but the most common are:
- Soft-story collapse (piano effect): This type of deformation occurs when one plane of a building is significantly less rigid than the others. This is a relatively common occurrence, often arising not from structural flaws, but from architectural choices. Seismic risk increases for buildings where the ground floor is occupied by commercial spaces with large windows, while the upper floors are residential. During seismic activity, deformations concentrate in the plane subjected to the greatest stress β the lower floors. Occupying the upper residential floors in such a building during an earthquake is extremely dangerous; the building could collapse, trapping its inhabitants.
- Cracking of joints and supports: Earthquake-resistant buildings are constructed using the principle of “hierarchy of resistances,” creating levels with deformation buffers. This technology of compensating for and dampening vibrations from one floor to the next prevents cracks in supporting structures, making the building earthquake-resistant. Conversely, buildings constructed using traditional methods will transmit vibrations through the floors, leading to cracks in load-bearing elements and eventual collapse.
- Inter-story drift and torsion: This occurs in buildings where reinforced concrete shear walls and stairwells are offset from the center. During seismic events, buildings with this eccentricity in plan are subjected to additional torsional forces. Vertical supports furthest from the center of rigidity can shift, causing an entire floor to collapse, regardless of the building’s height.
- Failure of backfill and soil: Unlike a steel frame, the ground beneath a foundation lacks plasticity. During an earthquake, the ground is subject to vibrations and can lose strength. This reduction in the foundation’s load-bearing capacity can cause the entire building to tilt and collapse during a seismic event.
Therefore, when choosing a building for business or residential purposes in a seismically active zone, mitigating risk and ensuring survival during an earthquake requires purchasing property built with modern protective technologies.Β Seismic design significantly reduces building movement during tremors and dissipates vibrations. Without these safeguards, excess energy will propagate through the building’s primary structure, leading to structural deformations, failure of load-bearing elements, and ultimately, collapse.