Earthquake Damage Prevention in Adobe Dwellings

Foto: ©

The Peru earthquake of August 15, 2007, leads us to recognize once again that preparedness is necessary, especially in the case of adobe structures. Peru has experienced powerful earthquakes throughout its history, most notably the earthquake of May 31, 1970 (Ms = 7.8), which left approximately 70,000 people dead and thousands more injured or displaced. More recently, the earthquakes of Nasca in November 1996 (Mw = 7.0) and of Atico-Arequipa in June 2001 (Mw = 8.4) and the latest, on August 15, 2007 (Mw = 7.9), have affected our coastal region (references 1 & 2).

As has been the case with past earthquakes, in this most recent event, many traditional adobe houses collapsed in Pisco, Chincha, Ica, and other towns, resulting in unfortunate human and material losses. These homes are extremely vulnerable due to the use of weak and poor-quality building materials, lack of reinforcement and maintenance, and poor construction, among other reasons. Despite this, the 2005 population and housing census indicates that over two million houses in Peru are built with adobe or tapial (mould for mud walls) and nine million people live in these structures. This leads us to the question: How can we help them?

While Peru has had technical standards for adobe since 1984 —renewed in 2000 (NTE E.080)— most adobe structures are built without consideration for the reinforcement necessary to withstand earthquakes. In contrast, very few homes had been equipped with such reinforcements and were therefore able to withstand the Pisco earthquake without damage.

In experimental research developed over the last 30 years at the Laboratory for Earthquake-Resistant Structures of the Pontifical Catholic University of Peru (PUCP), tests have shown that it is indeed possible to reinforce adobe houses to render them earthquake resistant.

“Seismic Reinforcement of Existing Adobe Housing in the Andean Countries” was a demonstration project of the International Decade for the Reduction of Natural Disasters (IDRND), sponsored by the United Nations at the end of the twentieth century. This project was carried out under the GTZ-CERESIS-PUCP Agreement, with financial support from GTZ in Germany and administrative support from CERESIS, to make adobe houses more resilient and malleable, thereby enabling the occupants to escape them and save their lives. The project stages included: 1) analysis of different reinforcements through seismic simulation tests in the Structures Laboratory of the PUCP; 2) installation of the reinforcements in 20 actual homes located in seismic areas of Peru in 1998 and 1999, work which was extended to other Andean countries; and 3) post earthquake evaluation of the effectiveness of the reinforcements (Ref. 3).

The first test took place with the earthquake of June 2001, in southern Peru (Mw = 8.4). Six houses (three in Moquegua, two in Tacna, and one in Arica) held up extremely well, without a single fissure, while neighboring houses were seriously damaged or collapsed completely. This was followed by the Tarapacá earthquake in June 2005 (Mw = 7.9) in northern Chile; once again, the house in Arica and the two in Tacna were unharmed.

Finally, the earthquake of August 15 2007 (Mw = 7.9) offered the third test of two pilot houses located in the Ica countryside. Both withstood the earthquake in perfect form, sustaining no damage, while neighboring houses tumbled or showed dangerous cracking.

The system of applied reinforcement consists of strips of welded mesh nailed and connected to the adobe walls and then covered with cement mortar to simulate beams and columns. This mesh is positioned at the corners of perpendicular walls, to fasten them, and along the top edges of walls to minimize the tremendous flexibility existing in the central area. The advantage is that these reinforcements can be installed in existing dwellings without affecting their foundations or their roofs and they are easily installed by local workers with very little training. The reinforcement manual and the limitations of the reinforcement system are available at the following reference [3] and [5].

What now remains is to spread word about this reinforcement technique and ensure that those living in such houses learn the lessons from the Pisco earthquake (and the preceding ones): traditional adobe houses crumble, while reinforced houses remain intact, at least during earthquakes similar to those described in this article. As the popular saying goes, “An ounce of prevention is worth a pound of cure.” During the launching of the GTZ-CERESIS-PUCP project, Alberto Giesecke, Director of CERESIS, referred to “vaccinating” houses: “Reinforcement protects your home just as vaccination protects your health.”

Following the 2001 earthquake, techniques similar to the one explained here were used in the construction of 400 new and improved adobe homes in the highlands of the Andean area of Arequipa, work carried out by COPASA-GTZ, after completing experiments at PUCP, for which local workers were trained and an instructional work manual was put together. [6]

Similar efforts are expected in the new situation created by the earthquake of 2007, given the magnitude of the destruction.

In conclusion, not only did the reinforced adobe houses successfully withstand the test of three actual earthquakes, but they did so without incurring any damage whatsoever. We are now faced with the task of publicizing what happened and working to convince the relevant authorities that the reinforcement system can be applied in a massive way in adobe dwellings to prevent further misfortune.

For further information, please contact:
Daniel Quiun and Ángel San Bartolomé
Professors, Engineering School, Civil Engineer Department
Pontifical Catholic University of Peru

Reference

1. Tavera H, Salas H., et.al. “El terremoto de Arequipa del 23 de junio del 2001.” Preliminary report, Geophysical Institute of Peru. Lima, June 2001.
2. Tavera H, Bernal I., Salas, H. “El Sismo de Pisco del 15 de Agosto 2007 (7.9 Mw) Departamento de Ica Perú.” Geophysical Institute of Peru. Lima, September 2007
3. http://www.ceresis.org/proyect/padobe.htm, 2000.
4. San Bartolomé A., Quiun D., Zegarra L. “Effective System for Seismic Reinforcement of Adobe Houses, 13th World Conference on Earthquake Engineering, Vancouver B.C., Canada, August 1-6, 2004, paper No. 3321
5. Website PUCP: http://blog.pucp.edu.pe/albanileria, 2007
6. Chuquimia, E. “Manual de construcciones sismo resistentes en adobe” GTZ-COPASA-Regional Government of Arequipa, PUCP, Arequipa, 2005.