Mexican Scientists Develop Cost-Effective Earthquake Protection for Buildings

At the UNAM Engineering Institute (II), experts are developing seismic energy dissipators that reduce the effects of earthquakes on buildings, which is why the goal of ensuring that building structures are not damaged by earthquakes, even those of greater magnitude, and are very safe, is close to being achieved.

The team headed by Héctor Guerrero Bobadilla has innovated various devices—one of which has already been patented, transferred, and marketed by a company—that have advantages such as their cost, that they can be installed in existing or new buildings, and, in some cases, that they do not need to be replaced, due to their great dissipation capacity.

In several cases, in addition to offering greater security against earthquakes, this technology allows savings of close to 10 or 15 percent compared to conventional structural systems. The reason is that it makes it possible to use materials more efficiently, since a structure equipped with the technology becomes a dual system, where one part is dedicated to resisting the weight of the building and the other to taking seismic actions, he explained.

Unlike others used in countries such as Japan and the United States, university systems are distinguished because they take into account the specific conditions of Mexico; for example, the seismic movements of soft soils in Mexico City.

In 2016, Guerrero Bobadilla began to conduct research so that, in the event of an earthquake, buildings, bridges, stadiums, airports, or hospitals could reduce damage significantly.

The first device he created, together with his work group, was a type of bracing restricted to buckling. This model helps reduce relative displacements in structures caused by lateral movements.

These are bars with a metal core and “jacket” and a reinforced concrete or mortar filling that are placed on each floor of the building, and capture most of the tremor energy, deforming. The university device has a great advantage over other available instruments: it physically shows when it should be replaced.

The innovation was patented by the II and its use was licensed to a spin-off company run by young graduates called Dampo Systems. It is currently being marketed and has been installed in at least 20 buildings. In addition, the company has ISO-9000 certification; “this means that they are doing the job well, and that the buildings are being protected responsibly.”

Similarly, other devices have been developed that work based on a viscous fluid, similar to car shock absorbers, whose objective is also to attenuate seismic energy. “We are doing tests in the laboratory to validate their behavior,” he added.

In addition, additional dissipation accessories are fitted to them; This makes them “a completely new system that combines two sources of energy dissipation with very different properties from each other, making it very efficient,” Guerrero Bobadilla said.

Added to this is the work with a PhD student to create dissipators for prefabricated connections between beams and columns, which are essential elements in buildings. After four years of research, a patent application was filed that is currently in process.

In this regard, the expert explained that although there are similar devices on the market, these are normally used in steel constructions; however, one was needed for concrete, one of the most widely used materials in Mexico.

Additionally, the university team uses the principle of car brakes, that is, friction between materials, to obtain another type of seismic protection technology.

In addition to all these types of dissipators, there are seismic isolators, where the building is “disconnected” from the ground and is supported by flexible systems that allow the structure to move slowly, even if the ground moves a lot due to the earthquake, which reduces damage. In this case, it is better to use the technology in new constructions, because it is a technical challenge that is expensive for those already built, he said.

The innovations dissipate so much energy that they are not easily damaged, they are stable, and based on laboratory tests, it has been proven that they can withstand several large earthquakes, unlike elements such as columns or walls that, when affected, must be repaired or replaced at great cost and over long periods of time.

“There is a tendency to think that dissipators are very expensive, and that is why they are not used, even though when they are installed, thanks to their efficiency, they can even reduce the investment,” the university student emphasized.

Although the technology to have highly secure buildings already exists at UNAM, since the knowledge, software, and computing power to perform the corresponding calculations are available, the construction industry needs to assimilate it and make it its own, so that it can really be applied to the benefit of the inhabitants.

The energy released by an earthquake is enormous: an earthquake of magnitude 8 is 32 times larger than a magnitude 7, a thousand times larger than a magnitude 6; 32 thousand times larger than a magnitude 5, and so on.

The amount that “enters” a building depends on its properties, such as: height, construction materials, weight, and the type of soil on which it is built, among others; it has been estimated that devices can dissipate up to 70 percent of it.

Devices such as buckling-restricted bracing, which are normally installed diagonally, work better for frame structures (i.e., those made from beams and columns), whether steel or concrete; “Instead of facing an earthquake, technology must be used to ‘dodge’ it and prevent it from fracturing the ‘bones’ of the building,” the expert advised.

The deformation during an event is mainly due to two parameters: the type of soil and the characteristics of the structure. A rigid surface, such as the rocky one at Ciudad Universitaria, moves less; but in the center of the country’s capital, where it is very soft, it is amplified and can cause greater damage. If the building and the soil are flexible, the former can enter into resonance, which would be disastrous. The technologies developed at UNAM help to avoid these problems.

The seismic energy dissipators are placed where it is most convenient for the use of the spaces; in some cases, they are placed on the façade because they do not invade interior areas, and in others, behind a false wall. This depends on the architectural project.

What is important is to install them symmetrically, because that avoids the problem of torsion and the building behaves better, Guerrero Bobadilla specified.