Today's buildings and their risks: researchers offer alternatives to mitigate the impact of potential seismic events

Bryan Castillo Torres, PhD student in Engineering with an emphasis on Solid Mechanics. In the background, a one-way seismic table used to carry out part of the experiments within the research. Credit: Communications Office, Faculty of Engineering.

The implementation of the industrialized system of housing construction (ISHC) is, at present, a highly used method in this region of the continent. The system, characterized by the use of concrete walls and thin structures, lacks adequate behavior in the face of possible seismic movement scenarios. 

Given the high concentration of seismic risk present in the Pacific region, especially in the city of Cali, a research conducted by the PhD student in Engineering with emphasis in Solid Mechanics, Bryan Castillo Torres, with the participation of the researcher Sharick Melissa Vides Quintero and the direction of the professors, researchers of the School of Civil Engineering and Geomatics and members of the research group Seismic, Structural, Wind and Geotechnical (G-7) Johannio Marulanda, Albert R. Ortiz and Peter Thomson, seeks to evaluate this behavior and offer an alternative to mitigate the risks derived from such scenarios. This research, the results of which were published in the specialized journal Building Engineering, is expected to stimulate the technical and technological development of the local construction industry, directly impacting the quality of housing construction in the immediate future of the region. 

Lea el artículo en español aquí.

The risks of the industrialized construction system

Although, at a macro level the most widely used construction system continues to be masonry, there has been a considerable increase in the implementation of the industrialized system in the construction industry in low-income and priority housing, due to its benefits related to lower labor costs and use of materials. Adopted from North American and Chilean buildings, these constructions are characterized by cast-in-place foundries, reusable metal forms and thin walls, ranging from 25 cm to 30 cm thick. This methodology, being industrialized, reduces construction times, favoring the construction of more structures in less time. 

However, there is a lack of research on the behavior of such structures once they are subjected to seismic movements of considerable magnitude. Since the thickness of the walls built in Cali is less than the international (about 10 cm), and given the risk of its inhabitants in the event of an earthquake, the need to implement models and mitigation structures for the effects that this scenario could cause, if it occurs, was born.  

"Accidents related to seismicity have shown that they are affected, even here in Cali with the Pizarro earthquake. Studies have been carried out. There is a lot of research and an institute fully dedicated to the investigation of this type of walls and their seismic behavior", says researcher Bryan Castillo, and clarifies that, although the benefits of this construction system should not be underestimated, the geographical location of the city requires a study to determine possible solutions to the problem, this time through a control system in the form of insulator, whose components were obtained after the joint work that has been doing the research group G-7, with discoveries and advances that have made possible the creation of these control devices locally. 

The role of the U-FREI device in the research and development of a local industry of seismic control systems for buildings

The research considered the use of unattached fiber reinforced elastomeric devices (U-FREI), a type of seismic isolators whose manufacture is low cost and allows for easier installation with respect to the structures, with the objective that the damage generated from the seismic simulation exercises developed in the laboratory would be concentrated on them and not on the structures as such.  

As it is an easily replaceable device, it is an important alternative to to take into account, in view of the cost that a seismic scenario may imply. "It is a fuse piece, which makes it much cheaper to replace compared to replacing or rehabilitating a structure again, which can often lead to collapse, losing all the heritage," explains researcher Bryan Castillo Torres. According to him, its use was also designed to promote the manufacture of this type of insulation systems locally in the future, since currently these devices are mostly manufactured and evaluated in foreign countries such as the United States and Chile. 

These devices also represent a step forward in the search for ways to take advantage of other eco-sustainable materials, since compared to previous versions (the SREI and the FREI), it has meant the replacement of materials such as lead and steel by geotextile elements, opening the door for the national industry. These decisions were key to the research, since they eliminated costs and testing times. "Being able to do this here is one of the advantages and one of the great contributions of the research. Saving the cost of transferring materials and evaluating it locally is fundamental for the implementation of these devices," says the researcher. 

In order to perform the analysis and experimentation with these devices, it was necessary to create a substructure that represented a real low-rise building system together with the isolator. With this substructure, it was proceeded to make the measurements, taking into account four high impact seismic events at international level: El Centro (USA, 1940), Kobe (Japan, 1995), Loma Prieta (USA, 1989) and Morgan (USA, 1984). The choice of these events was made, in turn, with the purpose of broadening the criteria to be evaluated. "We did not focus on a specific frequency content (power of the earthquake), but rather we had a range of options to evaluate the structure under different seismic conditions. This allowed us to broaden the range of analysis," says researcher Bryan Castillo. 

Subsequently, they worked with a hybrid simulation methodology, which allowed the research group to concentrate on analyzing them while examining the structural behavior of the building. "We took an experimental element, which in this case was the isolators, and at the same time we took an experimental structure (a full-scale wall). The methodology consisted of real-time feedback from a numerical model," explains researcher Bryan Castillo. According to him, the data were extracted to the model, then physically tested, to conclude with the re-input of such data to the numerical system.  

This allowed the researchers to have accurate information about what would happen in the structure in case of a seismic event, compared to the references mentioned above, presented through a hysteresis model where data related to the stiffness of the building behavior, the degree of dissipation, the degradation of stiffness, among other values, were evidenced. 

After comparing the isolation system developed based on the four international seismic events, it was shown that these devices reduced the displacement of the structure by 67.30% in the case of the Centro earthquake, 74.30% in the Kobe earthquake, 80.60% in the Loma Prieta earthquake and 49.30% in the Morgan earthquake. 

The innovative nature of the device 

For researcher Bryan Castillo Torres, the development of this hybrid analysis model represents an innovative bet at the research level, especially because it could be tested locally, thanks to the technological advances currently available: "Without this technology we would not have been able to test these systems. We would have the element, the wall, but we would not have been able to test them."

He also considers that the system developed is a great advance in the protection of buildings constructed based on the industrialized housing construction system. "With these systems we will be able to avoid major damage to buildings, reduce rehabilitation costs and be able to concentrate the damage on these elements. As the elements are replaceable, it means that you are taking care of your heritage and you are generating a higher level of safety for the people who live in these structures," he says, adding that the applicability of these systems depends on the country's development in terms of research and production of these elements.

If interested in being in touch with the PhD's student or any further information about the investigation, please write the Faculty of Engineering Communications Office: comunicaingenieria@correounivalle.edu.co.