In Peru, as in many other countries straddling the Andes Cordillera, earthquakes make you literally tremble with fear, and with good reason.

The 1970 earthquake, for example, left behind only ruin and misery: 50,000 people dead, 20,000 missing and 150,000 injured, in addition to 60,000 homes destroyed. Although nobody can prevent this type of natural disaster, one factor that adds to the death toll in the wake of an earthquake is the fragility of adobe houses. Something can be done to improve this.

For several years, a team of researchers from the Civil Engineering Department of the Pontificia Universidad Católica del Peru in Lima have been working toward this goal. In cooperation with the Building Research Centre at Concordia University in Montreal and with IDRC funding, the team has developed a simple, inexpensive construction technique for adobe buildings that significantly increases their resistance to earthquakes.

"Most of the loss and damage resulting from earthquakes is due to the collapse of adobe houses, where traditional construction methods make them as unstable as a house of cards," says Gladys Villa Garcia, an engineer and researcher at the Peruvian university's Laboratory for Earthquake­Proof Structures. "That is why the primary goal of our work is not to find a means of preventing every kind of crack in the adobe and the mortar, but rather methods of framing the walls so as to prevent them from crumbling in the wake of intense seismic pressure."

Adobe brick is an inexpensive and readily available construction material. Its use is widespread in Latin American countries, especially in rural areas where it offers excellent heat resistance and acoustic properties. These solid and rigid bricks tend to crack and break apart during an earthquake, causing walls to collapse and ceilings to fall in - the primary cause of injury and death.

A Homogeneous Unit

The researchers subjected an adobe structure to the vibrations produced by a full­size seismic table. They studied the structure's reaction and developed a technique for reinforcing the walls and tying down the roof more firmly, using materials that are inexpensive and readily available and techniques that do not unnecessarily complicate house-building.

Mrs Villa Garcia says that it does not matter what kind of mortar is used to cement the adobe bricks: whether it is good quality or not, it will not prevent the housing from collapsing during a strong earthquake, unless each wall has a vertical and horizontal frame that acts as a skeleton for keeping the bricks in place. "The wall must function as one homogeneous unit and not as a fragile assembly of a hundred or so bricks which crumble at the slightest shock," explains Mrs Villa Garcia.

The frame designed by the researchers consists of vertical bamboo poles anchored to a cement foundation 45 cm apart. Lattice cane is then placed horizontally on the mortar every four or five rows of bricks. The cane is attached to the bamboo poles. At the top of the walls, the vertical poles are fastened to two parallel wooden beams to which the roof joists are attached.

One weakness of traditional construction methods is that the roof rafters are attached directly to the walls, says Mrs Villa Garcia. When these crack, there is nothing left to hold up the roof. That is why it is important not only to strengthen the walls with a grid of vertical and horizontal joints but also to provide beams to help the roof absorb the seismic shock.

To promote the adoption of the new construction methods, the researchers worked with various government and community organizations in Peru to create five prototype adobe houses and test a variety of methods for disseminating the techniques in the field. "If our type of construction should prove too complex or difficult to teach, people will go back to the old way of doing things," says Mrs Villa Garcia. "That's why our work also included evaluating the most appropriate teaching methods. To date, the use of scale models and photographs showing step­by­step how to frame the adobe has produced the best results."

Contact:

Gladys Villa Garcia
Laboratorio de Estructuras Antisismicas
Pontificia Universidad Católica
Casilla de Correo 1761
Lima 100
Perú

Telex: 20300 PE PB SMGL
Fax: (51­14) 611­785

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