"...according to the 1993 Peruvian National Census data, 51.1 percent of all dwellings in the country, housing 48.7 percent of the total population, have soil as the predominant material of external walls....It is evident that some technical solution has to be developed to protect those people from the destruction of their houses during a severe earthquake. "

• Historical background
• Present situation of adobe constructions
• Experimental research
• Reinforcement of prototypes
• Conclusions
• Reference
• Bibliography
• Author information
• Additional web resources

Historical background

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In Peru, as in most Third World countries, a great percentage of the current population lives in houses made mainly with soil. Among the various traditional building construction techniques used in Peru, the most common is adobe, which is a sun-dried mud brick. Other traditional earthen construction systems include rammed earth and "quincha" (wood frame with cane and mud covering), known in many other Latin American countries as "bahareque."

Image link, prehispanic adobes (~31K file)

Remains found in the Rimac Valley, where Lima is located, show that the rectangular adobe blocks typical of current construction have been in use since at least 900 B.C.E. Variations of block shapes and material additions were typical of the different regions where adobe was used. Some prehispanic civilizations fabricated adobe bricks by hand-molding the clay soil. Others, mainly in the coastal areas, added eggshells and seashells to the soil. In the highlands, small stones and "ichu" were added to the soil used to fabricate adobe. Ichu is the straw of a very common plant found over 2000 meters (6,600 feet) above sea level.

Image link, Chan Chan (~19K file)

The main characteristics of pre-Inca adobe construction can still be appreciated in various ruins. The most outstanding are those of Chan Chan, capital city of the Chimu civilization on the north coast of Peru, which flourished between 1250 and 1470 CE. It has been considered the biggest adobe citadel of the prehispanic world, because it covered over 18 square kilometers (seven square miles) and lodged around 75,000 people. The whole city was protected by a very tall perimeter wall of adobe, three meters thick at the base and one meter thick at the top. Typical adobe constructions of that time had walls built on stone foundations and roofs, both horizontal and pitched, made of cane and mud. They were typically massive buildings with rectangular symmetrical plan views and very small wall openings.

Image link, Colonial house (~22K file)

With the arrival of the Spaniards in Peru, adobe construction continued, maintaining its basic characteristic of massiveness and incorporating typical features of the Spanish culture of that time. Thus, these buildings included elaborate gypsum moldings, carved wooden doors and windows, forged gratings, and a second floor made of quincha. After the earthquake of 1746 damaged most two-story adobe houses in Lima, a royal decree prohibited the use of adobe on the second level. Many examples of this architecture can still be appreciated in beautiful colonial houses both in Lima and Trujillo.

Adobe constructions have excellent thermal and acoustic properties which make them appropriate for areas with severe weather and high temperature range variation. For the poorest people, these constructions are the only option because of their low cost and the possibility of self construction. However, these advantages disappear when adobe constructions are subjected to earthquakes.

Peru is located in the Circum-Pacific Belt region, where around 75% of the world's seismic activity takes place. Plate tectonics theory explains the reason of such activity in Peru. It is at the border of two active plates: the Nazca plate and the Continental plate, and their relative movement generates earthquakes. As a result, Peru has always been subject to seismic activity. However, there is written evidence of it only since history has been recorded. Giesecke and Silgado (1981) mention a chronicle which describes several earthquakes as occurring in the 15th century, during the rule of Inca Sinchi Roca, causing destruction in Cuzco and Arequipa.

The most significant Peruvian earthquakes include among others:

• 1586, July 9: Complete destruction of Lima.
• 1604, November 24: Earthquake followed by tsunami, destroying the south coast, especially Arequipa, Moquegua and Tacna.
• 1619, February 14: Destruction of Trujillo: 350 people died.
• 1664, May 12: Complete destruction of Ica: more than 300 people died.
• 1746, October 28: Earthquake in Lima and tsunami in main port Callao, 1,141 people died, 2,275 houses collapsed, complete destruction of Callao.
• 1868, August 13: Earthquake and tsunami in southern Peru.
• 1940, May 24: Lima was severely damaged: 23% of adobe houses collapsed, 179 people died.
• 1970, May 31: Earthquake in Huaraz and landslide in Yungay: 50,000 people died, 20,000 disappeared and 150,000 were injured. All adobe constructions of the affected area were destroyed.
• 1974, October 3: Lima and the south coast were affected: 78 people died, many adobe and quincha houses collapsed.
• 1996, November 12: Nazca, 400 km south of Lima, was practically destroyed. Many adobe constructions of the area collapsed.

As can be seen, much death, destruction and material loss has resulted from seismic activity in Peru, especially when adobe constructions are involved.

Present situation of adobe constructions

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Adobe buildings have poor seismic behavior. On one hand they are massive and heavy, thus they attract high levels of seismic force; on the other hand, adobe is brittle and has practically no tensile strength by itself. Poor construction practices often decrease the bond between adobe and mortar. Besides, the architectural concepts of the past have changed and, at present, the typical thickness of adobe walls has been greatly reduced to make them externally similar to brick masonry. These factors, together with lack of maintenance, contribute greatly to increased adobe vulnerability.

Image link, damage patterns (31K file)

The usual failure pattern of adobe structures during an earthquake starts with vertical cracks at the corner of front and lateral walls. These cracks develop very fast and the walls separate. Once each wall is free, the front wall falls; this causes the collapse of the roof, which is the main cause of human and material loss.

In spite of this danger, according to the 1993 Peruvian National Census data, 51.1 percent of all dwellings in the country, housing 48.7% of the total population, have soil as the predominant material of external walls. Dwellings with soil walls represent 83.4% of dwellings in rural areas and house 82.3% of rural population, whereas dwellings with soil walls represent 36% of all urban houses and house 34.2% of the urban population.

Image link, seismic test results (~40K file)

Local research on adobe construction systems started in 1970. The Catholic University of Peru took an important step in this direction, studying ways to reinforce traditional adobe construction by including vertical and horizontal cane reinforcement in the interior of the walls and adding a crown beam to integrate the structure. These research results were derived from tilting table tests and were later verified with seismic simulation tests on natural-scale adobe modules at the Aseismic Structures Laboratory of the Catholic University.

This internal reinforcement solution is applicable only to new adobe constructions. However, as the data from the latest census show, a large percentage of people are currently living in traditional, unreinforced adobe houses and are consequently highly vulnerable to seismic activity. It is evident that some technical solution has to be developed to protect those people from the destruction of their houses during a severe earthquake.

This article presents the results of a research project designed to develop a means of reinforcing and better protecting existing traditional adobe houses.

Experimental research

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This research project was carried out by Engineers Luis Zegarra, Angel San Bartolomé and Daniel Quiun, Professors of the Engineering Department of the Catholic University of Peru. The project was developed through an agreement between the Centro Regional de Sismología para América del Sur (CERESIS) and the Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ), with the participation of the Pontificia Universidad Católica del Perú.

The purpose of this research was to provide existing adobe house with some reinforcement to delay the formation of vertical cracks in the corner of the walls. At a minimum, this delay should give enough time to permit the evacuation of the people inside the building. Since local construction patterns often involve houses that share common walls, any type of protection added to an existing house can only be applied to its interior walls and to the exterior front wall.

Image link, reinforcement methods (~68K file)

The following reinforcement techniques were tested with full-scale specimens at the Aseismic Structures Laboratory of the University:

• a wooden board fixed at the top of the wall with steel nails.
• 1/2-inch (1.25-cm) diameter rope inserted and tensioned in the upper part of the wall.
• "chicken-wire"" mesh placed in horizontal and vertical strips. electrically welded wire mesh also placed in strips.

Image link, seismic tests (~25K file)

The test specimens were U-shaped walls with the different reinforcing alternatives. They were tested on the seismic simulator using a signal derived from the May 30th, 1970, earthquake. The test program included movements of increasing intensity, to represent light, moderate and severe earthquakes.

These tests showed that all the specimens collapsed during a moderate earthquake except those reinforced with chicken-wire mesh and welded wire mesh, which collapsed during a severe earthquake. The conclusion of this first series of tests was that the reinforcement with welded wire mesh made of 1 mm (0.03 inch) galvanized wire every 2 cm (3/4 inch), covered with cement:sand mortar in proportion 1:4, proved to be the most effective for the intended purposes.

Image link, 'test' house (~24K file)

The next step was to test this solution on full-scale adobe modules with architectural characteristics representing one-story houses both of the coast and of the highland areas of Peru. The idea was to test the traditional modules with no reinforcement in order to observe their behavior, and after that, to test similar modules with the electrically welded mesh placed in strips: vertically in the corners of all interior perpendicular walls, simulating columns; and horizontally surrounding the upper perimeter, simulating a crown beam for the wall. The mesh strips were connected by means of wire that crossed the wall through a hole that was later covered with mortar. Externally, only the front wall was reinforced in a similar manner.

The results of this series of tests confirmed the effectiveness of the welded wire mesh reinforcement and gave important information as to the quantity of reinforcement needed. This factor is relevant because of the cost of the reinforcing materials.

Reinforcement of prototypes

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After the experimental research concluded, it was important to discover any possible problems that might result from the application of the reinforcement technique in real houses. Another objective of this stage of the research was to disseminate information about the repair system among potential users and to study the seismic behavior of the protected houses during the next earthquake.

Therefore, the second stage of the project consisted in the reinforcement of 19 pilot houses located in the Departments of Ancash (central highland), Cusco (south highland), Tacna, Moquegua and Ica (south coast) and La Libertad (north coast).

Image link, plan drawing index (~K file)

The conditions which determined the selection of a house for this reinforcement were:

• they should be located in seismic areas; and
• they should have sustained minimum damage on walls and roof (Undamaged houses were not included in the project).

Image link, highland house (~23K file)

Some two-story houses, typical of the highlands, were also selected. They were completely covered with horizontal mesh strips on the first floor, while on the second floor, where less shear force is present, the mesh was placed, as described before, only in a top horizontal strip and in vertical position at the interior corners.

Image link, wall with mesh (~24K file)

1. Remove the existing gypsum or mud plastering.
2. Open 5-cm (2-inch) square holes every 50 cm (20 inches) at the intersection of vertical mesh strips.
3. Insert small steel connectors into each hole, moisten the interior and fill them with 1:4 cement:sand mortar.
4. Fasten the vertical mesh strips to the adobe wall with nails, and then the horizontal strips. The usual width of mesh strip was 45 cm (18 inches).
5. Bend the ends of the connectors 90° and nail them to the adobe wall.
6. Moisten the area and plaster it with cement sand mortar applied in two layers.

A construction technician from the University was in charge of the reinforcement, with the help of local masons who were trained in the repair procedures.

During the visits to evaluate existing adobe houses for potential inclusion in the project, many common defects were found. Some of these defects could be repaired before the application of the proposed technique, others made such techniques inapplicable unless additional reinforcement was applied, and others were not repairable, leaving the houses highly vulnerable to collapse during the next major earthquake.

During the visits to evaluate existing adobe houses for potential inclusion in the project, many common defects were found. Some of these defects could be repaired before the application of the proposed technique, others made such techniques inapplicable unless additional reinforcement was applied, and others were not repairable, leaving the houses highly vulnerable to collapse during the next major earthquake.

Image link, reinforcement (~37K file)

Among the repairable defects, the most common were:

• Lack of mortar in vertical joints. Before placing the mesh, those joints were sealed with cement mortar.
• Lower part of the walls slightly eroded because of humidity or weather conditions.
• These areas were cleaned, moistened and sealed with cement mortar.
• Short perpendicular walls with no connection to main walls. These had to be removed and built again using the same adobes with concrete mortar joints.
• Damaged timber or log roof beams. The beams were removed and replaced by new ones.
• Very tall walls, up to five meters. This situation is very common in old houses and meant that an additional horizontal mesh strip had to be placed at mid height.
• Very long walls with no buttress in almost seven meters (23 feet). It was necessary to add an additional vertical mesh strip at the middle point of the wall's length. In the longest wall, this strip could be twice as wide as usual (0.90 m, or 3 feet).

Among the defects that required additional reinforcement were:

• Lower part of the walls severely eroded. A concrete foundation should be carefully provided for these walls, supporting the roof by external means during the process.
• Severely damaged roofs. This condition requires completely rebuilding the roof. If this is done, a concrete crown beam could be added on top of the walls instead of the upper horizontal mesh strip.
• Walls more than seven meters long without buttressing. In these cases one or two intermediate concrete columns should be added.
• Bulging walls, deviating from the vertical more than one centimeter. These walls should be rebuilt using the same adobes with cement mortar and adding a column at the intersection with the existing wall.
• Low wall density. Wall density is calculated as the total wall length multiplied by its thickness and divided by the roofed area. For best seismic behavior, wall density in each direction should be more than 0.07 m²/m². When this factor is lower, additional masonry walls should be added, connecting them to the roof beams.

The non-repairable defects found included:

• Houses built over soil of poor quality such as loose sand, expansive clay, and sand susceptible to liquefaction, among others.
• Houses with no foundation at all, that is, where the walls stand directly on natural soil (especially if the soil is of poor quality).
• Houses with more than two floors and low wall density.

Conclusions

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The reinforcement technique was easily understood and applied by the masons in each area where the project was conducted. However, it is important to have technical assistance in order to point out the areas where reinforcement is needed.

The electrically welded wire mesh could be purchased in the main city of each Department of the country.

Many structural problems were found in existing adobe houses in all the places that were visited. Most of them were capable of being repaired but others unfortunately were not suitable for repair of any kind.

CERESIS and the Catholic University promote the use of this reinforcement technique among anyone who wants to use it, providing all technical information and specific assistance.

Even though this project has dealt with houses made of adobe, with some creativity and engineering criteria, this reinforcement system can be applied to the protection and repair of historical monuments as well.

Reference

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Giesecke, A. and E. Silgado. 1981. Terremotos en el Perú. Lima, Peru: Ediciones Rikchay.

Bibliography

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Cárdenas, M. 1998. Material diagnóstico del Periodo Formativo en los valles de Chao y Santa, costa norte del Perú. Boletín de Arqueología PUCP, Volume II.

Hartkopf, V. 1985. Técnicas de Construcción Autóctonas del Perú. Washington, D.C.: USAID.

Instituto Nacional de Estadística e Informática (INEI). 1993. Censos nacionales 1993, IX de población. IV de vivienda. Lima, Peru: INEI.

Zegarra, L., D. Quiun, A. San Bartolomé and A. Giesecke. 1997. Reforzamiento de viviendas de adobe existentes. Primera parte: Ensayos de muros preliminares "U". Report presented at the XI National Congress of Civil Engineering. Trujillo, Peru.

Zegarra, L., D. Quiun, A. San Bartolomé and A. Giesecke. 1997. Reforzamiento de viviendas de adobe existentes. Segunda parte: Ensayos sísmicos de módulos. Report presented at the XI National Congress of Civil Engineering. Trujillo, Peru.

Zegarra, L., D. Quiun, A. San Bartolomé and A. Giesecke. 1999. Reforzamiento de viviendas existentes de adobe. Proyecto CERESIS-GTZ-PUCP. Report presented at the XII National Congress of Civil Engineering. Huánuco, Peru.