Do you want to know how concrete constructions should be in seismic zones?

Well, in this article we are going to try to influence this topic, and explain how concrete constructions in seismic zones will have to be. And, for this, we take as a source this article from El País: How to make buildings that resist earthquakes.

In the article we can read by way of introduction:

”Seismologists warn that earthquakes cannot be avoided. "Today they cannot even be predicted," says Amadeo Benavent, Professor of Structures at the Higher Technical School of Industrial Engineering of the Polytechnic University of Madrid. What can be done, explains the expert, is to prepare the buildings so that the damage caused by an earthquake is controlled and prevent people from dying. "

For this, it is very important to design new buildings and refurbish existing ones in accordance with the most current and advanced regulations," says Benavent. In Europe, the current regulation is Eurocode 8, a very complete standard although some countries, such as Spain, have not yet adopted it.

That is why it is important to adopt certain measures in concrete constructions in seismic zones, so that we ensure the least possible damage in the event of an earthquake. And, in particular, avoid loss of life.

Basic points in construction in seismic zones

As we can read in the article in El País:

Conventional buildings are prepared to resist their weight, that produced by gravity. Instead, when an earthquake occurs, the shaking causes the building to move in a horizontal direction. With this movement, the different floors of the building can collapse, one on top of the other, as happened in the earthquake in Amatrice (Italy) this week.

But another thing that can happen is that the structure is maintained but other non-structural elements collapse, such as walls. That was what happened in 2011 in Lorca. "The fall of walls is responsible for a high number of deaths," says the architect

The main objective in this type of construction is "to achieve an adequate combination of lateral resistance and ductility of the building against horizontal forces." And, the Eurocode 8 works on it, whose fundamental goal is to protect human lives.

In this way, in this code, a series of rules are established "to design buildings in such a way that they resist earthquakes in the area." Covering the construction of new buildings and the seismic adaptation of the old ones.

”In Spain, the current regulations are the NCSE/02 and the NCPSP-07, which regulate how new buildings and bridges should be undertaken, but say nothing about existing ones. The European seismic regulations have not yet been adopted in Spain and, in Benavent"s opinion, it is urgent to do so, especially since the national application document has already been approved by the competent body."

To which we can add that:

"Both the seismic project of new structures and the refurbishment of existing ones pursue the same objective: to achieve an adequate combination of lateral resistance and ductility of the building against horizontal forces", explains Benavent. Strength is achieved by making, for example, beams and columns larger and having more steel inside. "Only increasing resistance is economically unfeasible, so ductility is also used," says Benavent.

Structural reinforced concrete walls and diagonal bars to strengthen the strength of buildings

As we know, ductility is the ability of materials or structures to deform plastically, but without breaking. ”Plastic deformations cause damage and the problem is that, if the structures become too ductile, the damage in moderate earthquakes can be excessive. Therefore, "the goal is to achieve the appropriate combination of strength and ductility, we must find a balance between both properties," says Benavent."

And, to achieve this midpoint between resistance and ductility, Benavent advises:

”When we design buildings to resist earthquakes, we design them in a more permissive way than against other types of loads, such as gravitational loads. Permissive in the sense that we accept that the structure suffers damage, but not that it collapses, ”he explains. These damages can be cracks in the concrete or plastic deformations in the steel, but the structures would not collapse. ”The building would have to be repaired after a severe earthquake, but it would allow for a life-saving evacuation, which is what it"s all about,” he adds.

For his part, the expert provides some techniques, such as: adding structural walls of reinforced concrete blocks, diagonal bars, side walls on the pillars or reinforcing the pillars with steel clips.

And, work on the connection of the beams with the pillars, "so that with the movement they do not separate and the floors do not collapse."

What forces act on a building when an earthquake occurs?

Before finishing, we would like to focus on how the forces act on a building at the time of an earthquake. And it is that, as we know, the energy of an earthquake is released in the form of waves, which affect the ground and structures in various ways. In other words, the telluric movement does not damage buildings by impact, but by the force of inertia generated by the vibration of the mass of the building, what we know as seismic forces.

Well, these in turn are fired in three directions after the release of energy. The lateral forces are given by the superposition of the forces associated with each mode of vibration, being those that cause damage to the structures. Normally, causing columns and walls to bend and break. Hence the importance of the concrete used during construction.

To all of the above, we must add the great importance of the distribution of the horizontal components of the structure, to avoid collapse, since these are the least resistant to earthquakes. Remembering that the movement of the ground also affects the building in different ways, so the height will influence the force to which the structure is subjected in the event of an earthquake.