Earthquakes reinforced concrete: usage and benefits in seismic contexts

Reinforced concrete is a material resistant to many types of stress, combining the stability of concrete with the elasticity of metal. A reinforced concrete structure is indeed both stable and elastic thanks to the compressive strength of concrete combined with the tensile strength of steel.

The structural part remains a particularly delicate step in the design workflow, especially if the construction takes place in a high seismic risk area. Fortunately, structural calculation software help us by implementing various solutions based on the material, including reinforced concrete, and ensuring the seismic analysis of the structure according to current regulations.

Let’s see together when a building is defined as earthquake-resistant and why reinforced concrete is the most used material in this field.

What happens to a building during an earthquake?

What happens to the building and its resistant elements when they are subjected to an earthquake?

As seismic forces stress the building, causing it to oscillate, the neutral axis of the columns, which by design nature is fixed at the center of the column itself, begins to enter the section. The more the horizontal seismic forces increase, the more the neutral axis moves towards the edges of the section, until it exits. This reaction is manifested by increasingly wider cracks on the tensile part and higher compressions on the compressed part.

The reason for these evidences can be found in the fact that in the subsequent moments of oscillation, the force of gravity and therefore the compression on the column section does not dissipate immediately but continues to act.

The techniques and materials used to cope with earthquake oscillations are multiple and are designed and sized based on the specific case and concrete needs. Some seismic interventions aim to safeguard human life but not necessarily the buildings, among these we certainly find tie rods or nets fixed on masonry. Other seismic interventions, of more recent implementation, aim to preserve not only people’s lives but also the integrity of the structure. Among these, we find seismic devices (dissipators and isolators).

Is reinforced concrete an earthquake-resistant material?

In the previous paragraph, we mentioned some seismic techniques, of more or less recent implementation, specifying that it will be the individual case to dictate the best design solutions. One thing is certain, regarding materials, reinforced concrete remains the best and most recommended material for the construction of earthquake-resistant buildings due to its strength and elasticity.

The main reason why reinforced concrete remains the most recommended material for earthquake-resistant constructions is that the shock waves of an earthquake are able, proportionally to their intensity, to literally crumble traditional load-bearing masonry structures. Reinforced concrete structures, on the other hand, characterized by the typical metal frame, are able to react to the earthquake by bending under the stress of the waves, without collapsing.

For this reason, the use of reinforced concrete is recommended for the design and construction of earthquake-resistant buildings or public works located in seismic risk areas.

Reinforced concrete structure – EdiLus

What are the advantages of reinforced concrete in seismic areas?

The reasons why regulations suggest the use of reinforced concrete for constructions in seismic areas lie in the intrinsic characteristics of this material. Reinforced concrete is indeed a material:

• ductile: a feature that gives it a high capacity to absorb seismic waves;
• lightweight: compared to load-bearing structures in traditional masonry, the load-bearing structure in reinforced concrete is less burdened and potentially undergoes less damage during an earthquake.

These characteristics already represent advantages that favor the use of reinforced concrete in seismic areas. In addition to these, there is an additional benefit, namely the possibility of building structures without structural constraints. The metal reinforcement and formwork can be shaped as desired without compromising structural stability. This potential of reinforced concrete frees from structural constraints and allows attention to detail in the execution phase.

Characteristics of reinforced concrete

When is a house defined as earthquake-resistant?

Reinforced concrete is therefore the recommended and most used material for the construction of earthquake-resistant buildings. But what characteristics must a house have to be defined as such?

The fundamental requirements that an earthquake-resistant house must have are:

• resistance even in situations of maximum stress;
• resistance to multiple successive shocks;
• habitability and usability even after an earthquake;
• ability to withstand damage or to be brought back to the initial safety conditions with interventions that are not too long or too costly.

In summary, a building to be defined as earthquake-resistant must have high resistance and must be able to maintain it both after a strong seismic event and after many years from its construction.

For professionals operating in a territory with such a high seismic risk, knowing the regulations, materials, and seismic design and retrofitting techniques is essential. For this reason, I recommend trying for free a structural calculation software which allows, among other things, structural design and seismic analysis in full compliance with current regulations.