Why can the implementation of seismic resistance technologies be a critical factor for competitiveness? Chile, a country that has faced strong earthquakes, demonstrated its leadership during the event that occurred on February 27, 2010. Its tradition in the way it builds allowed it to protect both human lives and the country's heritage. 

* This article was published in Geociencias SURA Journal | Issue 1 | November 2016.

In the early morning of February 27, 2010, a magnitude XNUMX earthquake struckmagnitude 8,8 Mw sIt originated in the central area of ​​the Chilean coast, causing damage to structural and non-structural elements in buildings in the cities of Concepción, Viña del Mar, Constitución, Talca and Santiago de Chile. 

Although due to its magnitude it was considered the second strongest earthquake in the country's history, and the seventh in world history, most of the buildings were not damaged. This is a clear example of good seismic performance, and a sign that Earthquake-resistant engineering does have a direct impact on the mitigation of seismic risk and on the competitiveness and sustainable development of a country.. 

A good tradition: rigid structures

Chile is a country that has been forced to deal with very strong earthquakes. After the Chillán earthquake in 1939 (magnitude 7,8 Mw) it was observed that buildings constructed using the confined masonry technique (confined masonry), that is, with clay bricks, columns and reinforced concrete tie beams, performed better than those built without reinforced concrete beams and columns (unconfined masonry), explains structural engineer Patricio Bonelli. 

Later, when high-rise buildings began to be built, reinforced concrete walls began to be used. This idea was passed on to the following generations of engineers, who learned about the need to design structures with walls, since these guaranteed greater lateral rigidity and, therefore, better seismic performance. Finally, In the 1970s, reinforced concrete walls were put in place in Chile. 

This was decisive almost forty years later, in the 2010 earthquake, because according to engineer Bonelli, most of the buildings worked very well because, in addition to being very rigid, they were built on hard soils with very good characteristics, such as the gravel in Santiago. “This produced surprising results, with little or no incursion of the structures into the non-linear regime (low levels of deformation) and sometimes without cracks or damage,” he explains. 

In a recent work carried out by engineer Patricio Bonelli, with engineer René Lagos and other professionals, an evaluation was made of a sample of more than two thousand buildings in Chile, which presented very low relative deformations associated with the 2010 earthquake. It was concluded that the good performance of these was the result of good foundation soils, the distance to the fault where the earthquake originated and the high lateral rigidity of the buildings. 

One of the lessons that this natural phenomenon left to the Chileans was to continue with their traditional structuring of rigid walls., because, unlike buildings with frames or porticos, composed of beams and columns, these generate smaller displacements and, therefore, less damage. 

In addition, for engineer Bonelli, the key to reinforced concrete structural walls is to determine their thickness and the reinforcing steel required at the edges of the wall, in order to improve the seismic response of the building. 

What have been the lessons learned from the earthquakes in Chile?

According to engineer Bonelli, the earthquakes in Chile, and especially the one in 2010, have left several lessons: 

• Thin walls cannot be trusted, since containment is generally not effective and its behaviour tends to be very fragile. Buckling (bending due to compression) of the walls must be avoided. This depends on the characteristics of the structure and the deformation demand expected at the building site. 
• The deformation demand is not only related to the type of earthquake and the distance to the site of interest, but also to the amplification effects of seismic movements associated with soft soils and topographic conditions. 
• The soil is a decisive factor in generating damage from earthquakes. Therefore, depending on the characteristics of the soil, there are areas where certain types of buildings should be restricted, because they would entail a greater demand for displacement. According to the expert, current design practices in Chile are oriented towards the construction of rigid structures that behave appropriately and that have the greatest possible ductility, that is, the capacity to resist permanent damage without collapse, but without having to use it, which means having structures that deform little. 

“If you walk around Concepción and Santiago you would never think that an earthquake like the one in 2010 occurred.” 

Patricio Bonelli. Researcher at the Federico Santa María Technical University of Valparaíso, Chile.

 

Incorporate technologies

At the time of the 2010 earthquake, there were only a few buildings with seismic isolation in Santiago de Chile and Viña del Mar. All of them performed excellently during these movements. For this reason, the use of the system has become more widespread in recent years, because, as engineer Patricio Bonelli says, with the isolator “the earthquake is eliminated.” 

According to engineer Gloria María Estrada, Geosciences Manager at Suramericana, A base insulation system ensures that relative displacements between the floors of the building are small and therefore do not cause damage.. 

Another technology used is energy dissipation, which reduces deformation by around 30%. In the 2010 earthquake, several buildings that had this system performed adequately, however, The best solution, according to engineer Bonelli, is seismic isolation, which should be regulated and used massively.. 

Even if the building does not suffer structural damage (which would compromise its stability and resistance), it is important to consider that non-structural damage may occur which would prevent its occupation and immediate operation after the earthquake. Seismic isolation has the great advantage of being a solution to reduce damage of both types. 

For this reason, he considers it a success that in Chile this technology is being implemented not only in low-rise buildings, but also in taller buildings, with 20 or even 30 floors. When it was first implemented, costs increased by around 5%, but this has been reduced and currently the increase in the costs of the works is small. 

“We must continue to encourage the use of seismic isolation technology, because, as the relative displacement between the floors of the building is limited, we know that it will not be susceptible to damage,” says engineer Bonelli, adding that it is the best solution to reduce both structural and non-structural damage. 

Immediate occupation and operation

The major impact of the 2010 earthquake in Chile was the cost of lost profits and damage to non-structural elements, which made occupation and immediate use of the structures impossible after the event. For this reason, seismic risk management with a preventive approach is necessary. 

To the extent that companies manage seismic risk, they will have another indicator of competitiveness, which refers to the mitigation of losses associated with lost profits.. Since there is no damage to their facilities, either in structural or non-structural elements, they will be able to continue operating, since a partial or permanent closure of the same will not be necessary. 

Although Chilean seismic regulations specify that damage is accepted to a certain extent in earthquakes such as the one in Maule, engineer Patricio Bonelli points out that, in practice, people “do not accept any type of damage.” Hence the importance of being aware of how to avoid damage, as a key element of competitiveness and sustainability. 

Seismic risk management also involves resilience, that is, the ability to recover after an earthquake. This is a great example of Chilean engineering, as engineer Bonelli says: “If you walk around Concepción and Santiago, you would never think that an earthquake like the one in 2010 occurred.”

Fonts

• Patricio Bonelli. Civil engineer, specialist in structural calculation of reinforced concrete. Researcher and professor at the Federico Santa María Technical University in Valparaíso, Chile. 
• Gloria Maria Estrada Alvarez. Civil engineer, specialist in Environmental Engineering, specialist and M.Sc. in Earthquake-Resistant Engineering.