After the earthquakes in Turkey, Iran and Syria, and significant destruction of buildings, there were doubts about the quality of construction. Strong tremors of magnitude more than 7.0 caused thousands of deaths and injuries due to the collapse of buildings.
Earthquakes in these regions were expected, as they hit areas with high seismic risk located on the edge of active tectonic plates. At the same time, the events were unpredictable, as well as the victims. This was partly due to the fact that geophysicists cannot determine the exact time, place and strength of the earthquake.
If a person cannot prevent and deal with natural disasters, he has only one way to protect himself from destructive earthquakes – to learn how to build seismically resistant houses. Such buildings are able to resist Earth’s vibrations without destruction, saving the lives of everyone who was inside during an earthquake.
What happens to buildings during an earthquake
Typical buildings are designed taking into account the loads from structural elements. During an earthquake, the nature and indicators of loads on load-bearing structures of the building change:
- strong rises and falls of the ground during tremors cause an increase in vertical load on the structure, which was not designed to withstand double the weight of the house;
- chaotic movement of the soil under the building in the horizontal plane causes powerful shifts that the frame cannot absorb. The building does not just move left and right, its foundation fluctuates with the soil, which eventually leads to the destruction of the frame.
Since the building cannot stretch, it begins to bend and straighten during seismic shocks. In some cases, the structure begins to resonate with horizontal waves from the earthquake, which increases the amplitude of vibrations and leads to its rapid collapse.
What types of structures are seismically resistant
According to statistics, medium-rise buildings are most often destroyed during an earthquake. This is due to the fact that houses of this height resonate during seismic tremors. One-or two-storey houses bend less during earthquakes.
High-rise buildings bend during seismic tremors, but without an amplifying effect, since they are designed to withstand strong winds. Therefore, in cities located in areas with high seismic risk, it is recommended to avoid building that are four to ten stories high. Other methods to build earthquake-resistant buildings include:
- projects with simple forms. The most seismically resistant buildings have a symmetrical, simple cubic or rectangular shape. L or Z – shaped structures, as well as buildings in the shape of a cross, are the least stable. To ensure their seismic resistance, it is recommended to divide buildings into several simple shapes that can be freely deformed;
- the integration of rigid structural elements, such as elevator shafts and staircases, with the core of a building;
- preserving the integrity of vertical load-bearing structures. For example, this applies to reconstruction of interfloor ceilings or projects allowing for significant floor heights. Vertical openings can significantly increase the building’s vulnerability during seismic tremors.
At the same time, the integration of asymmetrical buildings and buildings with vertical openings into a single structure enhances the seismic resistance of the facility.
Materials for earthquake-resistant buildings
Brick and stone walls are most susceptible to horizontal shifts during strong earthquakes. Reinforced concrete and metal are the materials that are best able to withstand a seismic shock without much damage.
In the design of metal structures, it is recommended to use deformable steel capable of absorbing the energy of seismic vibrations. Attention should also be paid to the quality of fasteners, especially anchor bolts. Reinforcement bars should be chosen with a periodic profile, as they provide better adhesion with concrete.
General requirements for earthquake resistance
The earthquake resistance of a building does not guarantee that cracks will not appear during a strong tremor. Seismic building codes provide two levels of safety:
- I – the building after the earthquake should not only remain standing, but also maintain its functionality. This includes hospitals, communication centers, fire stations, and those that could cause environmental disasters (nuclear power plants, storage tanks for toxic materials and power plants). These buildings must retain operational water supply, electricity and communications. Such structures are often designed and built with dampers и seismic isolation features;
- II – buildings whose main function is to save the lives of people inside during an earthquake.
The consequences of the earthquake in Turkey on February 6, 2023, showed that ignoring earthquake resistance requirements during the construction can result in significant human casualties. Tremors of magnitude 7.8 and 7.5 killed 14,000 people and about 110,000 were injured due to numerous building collapses.