The seventeenth-century colonial Church of Kuño Tambo sits four thousand meters above sea level in the Peruvian Andes and is the most important building in its small town of five hundred inhabitants. Two hours’ drive from the city of Cusco, the town’s 150 or so earthen houses, together with the church, represent a historic rural settlement typical of the Andean region found from Colombia to Chile.
Built with thick adobe walls and a wooden truss roof covered with clay tiles, the church has preserved most of its original architectural features, including its three hundred-year-old mural paintings. Nevertheless, during its history the church has suffered from a series of earthquakes and a lack of maintenance. These factors have resulted in the structure’s partial collapse and, sadly, the cessation of its ecclesiastical use.
Four hundred kilometers northwest of Kuño Tambo, near the Peruvian coast, is the city of Ica, founded by the Spanish in 1563. Fronting the city’s main square is the Cathedral of Ica, originally built in 1759 by the Jesuits. Throughout its history, the cathedral has hosted the city’s important religious events and has been Ica’s central place of worship. Its design follows the Jesuit typology established by the Church of the Gesù in Rome—a rectangular base plan consisting of a central nave, two side aisles, a transept crowned by an impressive dome, and an altar—and is thus typical of many cathedrals found on the west coast of South America. Its facade, probably from a later period, has two towers. On August 15, 2007, a 7.9–8.0 magnitude earthquake with an epicenter eighty kilometers northwest of Ica caused widespread damage to the cathedral, which suffered partial collapse of the vaulted roof and the main dome, as well as extensive loss to its adobe walls, wattle and daub pillars, and other architectural elements, including its towers and facade. In 2009 another earthquake led to the total collapse of the dome.
Earthen buildings such as the Church of Kuño Tambo and the Cathedral of Ica are typically classified as unreinforced masonry structures, which are extremely vulnerable to earthquakes and subject to sudden collapse during seismic events—especially if a building has been poorly or inadequately maintained. Identifying methods to seismically upgrade historic buildings such as the Church of Kuño Tambo and Ica Cathedral could help reduce the risk of damage to or destruction of similar historic earthen sites located in seismic regions.
In the context of its extensive multiyear Seismic Retrofitting Project (SRP), designed to address the seismic threat to historic earthen buildings in the South American region, the Getty Conservation Institute (GCI) has been working at both Kuño Tambo and Ica Cathedral. The community of Kuño Tambo has supported and facilitated efforts that the Cusco branch of Peru’s Ministry of Culture and the GCI are undertaking to design and implement retrofitting techniques for the Church of Kuño Tambo that could be applied to similar churches across the Andes, in order to make them seismically safe.
Ica Cathedral structurally resembles other churches along the Peruvian coast, including the Cathedral of Lima in that city’s historic center, a World Heritage Site. These coastal colonial churches have brick facades; timber frame structures; thick adobe walls and vaults; and domes supported by pillars of timber, cane, and mud—a construction technique known as quincha. In collaboration with the Ministry of Culture and the Diocese of Ica, the GCI designed a shoring system for the cathedral, implemented in 2012. Beyond that, the GCI and the ministry are—as with the Church of Kuño Tambo—using the cathedral as a case study to design seismic retrofitting techniques that can be applied to similar churches along the South American coast.
The Seismic Retrofitting Project
During the 1990s the GCI carried out a major research and laboratory testing program—the Getty Seismic Adobe Project (GSAP)—to investigate the performance of historic adobe structures during earthquakes and to develop effective retrofit methods that preserve the authenticity of these buildings. Results of this research were disseminated in a series of publications in both English and Spanish.1
In April 2006 the GCI hosted a colloquium for an interdisciplinary group of sixty international specialists to assess the impact and efficacy of the GSAP seismic retrofitting recommendations and to discuss where and how GSAP guidelines had been implemented. The participants concluded that the methodology was reliable and effective but that its reliance on high-tech materials and professional expertise was a deterrent to its wide implementation in many seismically active places with large numbers of historic earthen buildings, such as throughout South America.
In response to these conclusions, the GCI in 2010 initiated a new seismic retrofitting research project with the objective of adapting the GSAP guidelines to better match the equipment, materials, and technical skills available in many countries with earthen buildings. The project includes the development of lowtech, cost-effective seismic retrofitting techniques and recommendations on easy-to-implement maintenance programs that improve the seismic performance of historic earthen buildings while preserving their historic fabric.
Peru was selected for the project’s location because of its wealth of current and historical knowledge, the interest there in retrofitting earthen buildings, and its potential research partners and organizations that could implement new techniques through model conservation projects. Thus the GCI joined the Ministry of Culture of Peru and the School of Sciences and Engineering at Pontificia Universidad Católica del Perú—along with the Department of Architecture and Civil Engineering at the University of Bath in the United Kingdom—to launch the Seismic Retrofitting Project, which receives support from the GCI Council. The SRP aims to design appropriate retrofitting techniques; to verify their efficacy through scientific testing and modeling; to develop a methodology and guidance for implementing suitable retrofitting techniques for practitioners, including conservation professionals, building officials, site managers, and local builders; and to work with regulatory authorities to gain acceptance of these methods, thereby ensuring they are embedded in practice.
The project involves a number of phases: (1) identifying prototype buildings that represent key earthen historic buildings in South America; (2) undertaking detailed site inspections, structural assessments, and material assessments of each prototype, followed by laboratory testing of key building elements and developing numerical models of the prototypes to understand their response to seismic activity; (3) designing, testing, and modeling of potential retrofitting strategies for each prototype building; (4) implementing the retrofit strategies on selected prototypes; and (5) disseminating the results and methods.
The Case Study Buildings
The first phase of the SRP, as mentioned above, included identifying important building types representing the historic earthen heritage of Peru and of South America in general—and thus with priority for seismic performance improvement. Four buildings exemplifying the identified typologies were selected, each demonstrating significant historic, social, or architectural value as well as retaining a high level of integrity. Developing solutions for a range of prototypes will ensure their relevance across South America and provide lessons for other seismic regions of the world. The partners evaluated a number of buildings in Peru and selected the following:
• Hotel El Comercio, a nineteenth-century three-story adobe and quincha building in the historic center of Lima, representing colonial houses in the historic centers of towns and cities along the coast;
• the Cathedral of Ica, an eighteenth-century church with thick adobe walls and quincha vaults and domes, representing colonial churches built in coastal cities;
• the Church of Kuño Tambo, a seventeenth-century building constructed with thick adobe walls and a wooden truss roof, representing colonial churches built in the Andes;
• Casa Arones, a seventeenth-century two-story adobe house with a wood truss roof located in the historic center of Cusco, representing colonial houses built in the historic centers of Andean cities.
Both Ica Cathedral and Hotel El Comercio include a considerable amount of timber structural elements, which is a direct reflection of their physical environment. Despite its tropical location, the coast of Peru is extremely arid owing to a cold, lowsalinity ocean current (the Humboldt Current) that flows north from the southern tip of Chile to northern Peru. The Peruvian coast is also part of the Pacific Ring of Fire, an area that encircles the basin of the Pacific Ocean, where some 90 percent of the world’s earthquakes and 81 percent of the largest ones occur.
These two characteristics of the Peruvian coast—its aridity and its seismic vulnerability—determined the construction techniques of the buildings erected by the Spanish. The lack of rainfall meant that lightweight quincha roofs—timber and cane, plastered with mud and/or lime mortars—could substitute for the heavier stone roof structures and tile covering used elsewhere. This adaptation reduced the inertial seismic forces, and it is thought that the colonial builders deliberately chose this method to improve earthquake resilience.
Hotel El Comercio is located in this coastal zone. The first story has thick adobe walls; the second and third stories are made of quincha. The floors are constructed of lightweight flat timber. Over 50 percent of the building’s mass is concentrated in its first story; the second and third stories are more lightweight and more flexible. In an earthquake, the second and third stories vibrate differently than does the much heavier first floor. The lightweight floors, roof, and upper story walls have helped this type of building resist strong earthquakes and survive as part of the urban conglomerate of the historic center of Lima. Experimental testing on new and historical quincha panels, coupled with numerical model analysis, both undertaken as part of this project, supported the anecdotal and evidentiary confidence in the resilience of this construction system in withstanding seismic movement.
Further down the coast is Ica Cathedral, a timber frame structure with adobe side walls. Its timber structure is concealed by a cane and sand-lime mortar plaster system, which is decorated on the inside with high reliefs and paintings. Because of the building’s configuration, the majority of the timber roofing elements are curved and composed of several lapped timbers connected by iron nails. Mortise and tenon connections are commonly encountered in the coupling of timber beams and posts, as well as of timber posts and arches. Since the lightweight roof structure follows the same principle of seismic resilience as the flat roof of Hotel El Comercio and would therefore be expected to be fairly resistant to seismic activity, the SRP team did not initially understand its failure during the 2007 earthquake. One explanation is that because the roof timbers were plastered both internally and externally and were thereby inaccessible, they had not been inspected or maintained over time. On-site evaluation and numerical analysis supported the hypothesis that a critical timber element across the barrel vault—which proved to be severely decayed—was responsible for its partial collapse. Numerical analysis also showed that the interaction between the adobe masonry side walls and the timber structure heavily influenced the seismic behavior of the building’s different elements.
In contrast to the coastal buildings, the historic buildings along the Andes are located in a lower earthquake risk zone. However, while Andean faults that trigger earthquakes have a small radius of influence, the earthquakes are nevertheless extremely intense near their epicenter. Because the environmental conditions in the Andes differ greatly from those on the coast—lower temperatures in winter that reach minimums of –15ºC and heavy seasonal rain—buildings were constructed with thicker walls and heavy roofs. Unfortunately, the large mass of the roof, with its heavy structural components, increases the inertial earthquake forces that trigger collapse. To address this challenge, local masons developed construction techniques for houses and churches designed to stabilize the thicker adobe walls and enhance their resistance to earthquakes. These techniques included the use of buttresses in long unsupported walls, the installation of tie beams to stabilize parallel walls, and the use of “corner keys” to help maintain the connection between perpendicular walls.
Experimental Testing and Modeling
The second phase of the SRP, carried out between 2011 and 2013, focused on research about and investigation of the selected prototype buildings. This included: (1) historical research and on-site surveys; and (2) experimental and analytical investigations, including laboratory testing of materials and structural composite systems, and development of numerical models to help understand each prototype building’s behavior. The data acquired through historical research and on-site surveys are available for conservation professionals to consult and can be found at the GCI website as part of the SRP publications.2 The analytical and experimental information will be available in 2016.
The methodology used in the SRP’s second phase required close interaction among the on-site surveys, the experimental testing, and the numerical analyses. Each activity informed the others. The testing helped guide the building of the models and demonstrate their efficacy, and the results of the modeling in some cases directed the team to further testing. The experimental testing proposal and rationale were extensively discussed by the partners and then presented to an international peer review committee. The proposal originally comprised more than two hundred tests on materials (historic and new) and structural characterization of the building prototypes.
As noted, the Hotel El Comercio and Ica Cathedral structures rely heavily on timber; part of the study therefore focused on the structural behavior and material properties of the timber and its interaction with the adobe masonry under earthquake forces. To a lesser degree, brick and stone masonry were present in all building prototypes, so testing for these materials was also carried out.
Three traditional constructions for improving seismic behavior were studied and validated either by numerical analysis (buttresses) or by experimental testing (tie beams and corner keys). The information generated by the experimental testing was fed into the numerical analysis of one of the prototype buildings, the Church of Kuño Tambo. The numerical model, adjusted to include these traditional retrofitting elements, demonstrated significant seismic behavior improvement.
Numerical models for all four building prototypes were developed at the University of Bath, discussed by all partners, and presented to peer review members. The objective of the models was to represent the behavior of the building prototypes as found and, in the case of the Ica Cathedral, to determine the reasons for the collapses during the 2007 and 2009 earthquakes. In 2013 the modeling work was transferred from Bath to the Civil, Environmental, and Geomatic Engineering Department of University College London, which has published papers describing its partial results from this phase. Currently the GCI is working with engineering consultants to continue developing numerical models to guide the project’s next phase. This work will seek to confirm the efficacy of traditional retrofitting techniques already tested experimentally, using the numerical models, currently being developed, of the building prototypes.
The third phase of work includes the design and modeling of new, low-tech, and easy-to-implement seismic retrofitting techniques using locally available materials and expertise. The numerical models will then be used to test the proposed techniques and demonstrate their potential response.
The fourth phase of the SRP involves implementing the retrofitting approaches established by the project. Conservation and retrofitting designs for two of the buildings, Ica Cathedral and the Church of Kuño Tambo, will be developed. The GCI is working closely with local authorities and professionals to produce the construction documents and technical specifications for these two sites, with construction to start in 2016. The construction documents and the implementation of the retrofitting technique designs on these two sites (all of which materials will be available to the professional community) will serve as model case studies for similar earthen historic buildings in the region. Another goal of this phase will be gaining the support of building officials for these suggested techniques.
The SRP provides new information on the characteristics of the materials used in earthen heritage buildings; the effectiveness of traditional retrofitting techniques; the seismic behavior of traditional construction systems; and the appropriate methodology to evaluate, diagnose, and implement seismic retrofitting projects in Peru and other countries in seismic zones. The final phase of this initiative will include the production of guidelines to be used by conservation professionals, building officials, site managers, and local builders—whose traditional knowledge has been an essential source of information for this project—to retrofit earthen historic buildings located in seismic areas, helping ensure that this heritage can survive the threat from earthquakes that it perpetually confronts.
Daniel Torrealva is former dean of the Escuela de Ciencias Ingeniería at the Pontificia Universidad Católica del Perú and a team member of the Seismic Retrofitting Project. Claudia Cancino, a GCI senior project specialist, is the project manager for the Seismic Retrofitting Project.