Mexico is a territory with a vast seismic history, with seismic records dating back to 1500, in which high-intensity earthquakes stand out, such as those of September 7 and September 19, 2017. Considering that the reduction of seismic vulnerability is fundamental for development sustainability of a country, or Mexico concentrated efforts on the development of knowledge, in the evolution of two construction regulations and the preparation of professionals suitable for its application, which are essential elements to increase its resilience capacity. 

* This article was published in Geociências SURA Magazine | Edition 3 | March 2018. 

The learning of two earthquakes in Mexico throughout its history has encouraged the development of research that has changed in the Earthquake Resistance Standards, or that has been implemented in all stages of the development, such as, for example, detailed studies of the characteristics of the And the local effects of it on buildings, greater knowledge of two methods of analysis and structural design, use of seismic-resistant materials and greater controls during the stage of the construction process. 

The evolution of the Earthquake Resistance Standards in Mexico deixa A positive balance from the 19S 2017 earthquake, noting that only a small percentage of buildings built in Mexico City collapsed or suffered significant damage, or that demonstrates that the changes made in the standards are essential to achieve a reduction in seismic vulnerability.

SURA is currently supporting the development of structural assessment studies and repair/rehabilitation projects for approximately 40 buildings in Mexico City, the State of Mexico, in Puebla and in Morelos.

Management of buildings affected by earthquake 

The magnitude and severity of the damage that a structure can suffer from an earthquake depends on various factors, such as the characteristics of the support only, the quality of the structural design, the structural typology, the construction materials and the presence of irregularities. 

The presence of damage to a building implies carrying out a detailed review of it, in order to determine whether it can be repaired, rehabilitated or, depending on the severity of the damage, it is advisable to demolish it and construct it again.

Structural systems with the best performance during the 19S 2017 earthquake:

• Low-height alvenaria structures with continuity of foundation wall and coverage. 
• Structures with parking spaces outside the building, eliminating the possibility of weakness in the base of the structure. 
• Double or combined systems. Rigid structures with displacements only smaller than those of concrete columns and strips. 
• Steel structures that, due to their modern design and height, present a very different way of vibrating than the predominant one. 
• Buildings built after 1985.
• Structures in reinforced concrete walls.

The rehabilitation techniques most used for the reinforcement of medium-rise buildings, which suffered damage such as the 1985 earthquake, formed the casing of reinforced concrete columns and beams. In taller buildings, the predominant technique was the insertion of reinforced concrete walls and metal profiles.

Currently, The great development of new technologies used in different parts of the world has been highlighted in the search for improvements in seismic design of buildings.

A positive balance

The earthquake of September 19, 2017 shows that the damage caused to buildings depends, mainly, on the structural system and the area where the building is located. If a detailed analysis is carried out, in which we consider which structures behave appropriately in Mexico City, both in the 1985 earthquake and in the September 19, 2017 earthquake, we can easily conclude that The double and combined systems form some of the typologies that provide the best seismic performance.

According to the opinion of Mr. Francisco García Álvarez, the earthquake of September 19, 2017 has different characteristics from the earthquake that occurred in 1985, although it is a great distance between the epicenter and Mexico City (400 km) and the high contents The frequency of the earthquake disappears and only as low frequencies, which excite structures between 8 and 15 times, remain.

Regarding the 2017 earthquake, which has an epicenter closer to the city (approximately 120 km), it was possible to filter out the high frequencies and, therefore, affect buildings of lower height, as the disadvantage is that these are only more predominant.

For a megacity, such as Mexico City, the number of buildings damaged by the earthquake of September 19, 2017 was low. The path to seismic resilience marks a challenge that seeks to substantially reduce the vulnerability of the built environment, which implies interconnections with the communication mechanisms of society.

In conclusion, the global effort to achieve greater resilience has been focused on the use of new technologies, both for the development of new buildings and for the implementation of rehabilitation alternatives, such as energy dissipation systems and seismic isolation, which require increase in initial investment costs, but it means a considerable reduction in structural damages associated with interrupting businesses, translating into a lower total cost distributed over the expected useful life of the building.

Sources

• Elizabeth Cardona Rendon. Civil Engineer and specialist in Earthquake Engineering at Eafit University.
• Francisco Garcia Alvarez. Civil engineer, master in engineering. President of the Mexican Society of Structural Engineering.
• Francisco Garcia Jarque. Civil Engineer and Master in Engineering.
• Gloria Maria Estrada Alvarez. Civil Engineer, specialist in Environmental Engineering, specialist and master in Earthquake Engineering.
• Juan David Rendon Bedoya. Civil engineer and specialist in structures of the National University of Colombia. 
• Mario Rodriguez Rodriguez. Civil engineer, master and doctor in Structures, exclusively dedicated researcher of the UNAM Engineering Institute. 
• Victoria Luz Gonzalez Perez. Civil Engineer at the University of Medellin, specialist and master in Earthquake Engineering at the Eafit University.