A seismic retrofit for an adobe church in the Peruvian Andes

The Peruvian countryside is dotted with earthen buildings dating back to the Spanish conquest of the Americas. The Spanish adapted traditional European building typologies to the locally available construction material: earth.Many of these earthen buildings have stood the test of time and have become of great monumental value to local communities and visitors alike. Some of them, however, have suffered extensive damage, or even fatal collapse due to one of the threats in the new world not so critically shared by Spain: earthquakes. While buildings were soon adapted and retrofitted to resist seismic action, the combination of the low-strength adobe (mud-brick) and high regional seismicity has remained a concern for many – if not all – subsequent generations.

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Remains of earth-cane barrel vault roof of a church near Ica, Peru that collapsed during the 2007 Pisco earthquake. (Image Tim Michiels, copyright The Getty Conservation Institute)

Today, relatively little attention is given within the academic community to the engineering and seismic design of earthen buildings. Despite the availability of advanced structural design codes, powerful calculation tools, and extensive material research labs, experts still struggle to characterize the behavior of masonry buildings, and especially earthen structures, during earthquakes. Thus, designing sensible and non-intrusive intervention techniques to preserve often languishing adobe monuments is a major ongoing challenge.

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Front facade of the church of Kuño Tambo (Image Sara Lardinois, copyright The Getty Conservation Institute)

Take for example the church of Kuño Tambo in Peru. Perched on a hilltop located two hours by dirt road from Cuzco, this small one-story adobe church was one of many built at the directive of Spanish missionaries in the late 17th century in the Peruvian Andes. Decorated with valuable wall paintings, the building has been at the center of community life in this rural village for approximately 350 years. Throughout its lifetime, the building has accumulated damage mainly due to the impact of earthquakes and the lack of resources to carry out basic maintenance, leaving the church in such a state of disrepair that it might not survive the next earthquake. Cracks caused by the rocking of the walls during past earthquakes separate the front façade and the transversal walls putting them at risk of overturning during a future seismic event. The ruble-stone base course has greatly suffered from erosion, buttresses supporting the lateral walls have disappeared, and recently the traditional roof system collapsed due to excessive water damage. Luckily, the church’s interior wall paintings have not yet been damaged beyond repair.

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View towards the choir loft of the church of Kuño Tambo. Note the vertical cracks separating the facade from the transversal walls in the corners of the wall paintings. (Image Mario Santana, copyright The Getty Conservation Institute)

The conservation needs of the church of Kuño Tambo illustrate many of the typical challenges encountered when attempting to preserve historic buildings in earthquake-prone areas. The preservation principles for historic buildings demand that any intervention should be based on a complete understanding of the monument and should be as minimally intrusive as possible. Engineers thus face the difficult task of designing a minimal structural intervention plan, while still guaranteeing that the building will not collapse during an earthquake, endangering the lives of its occupants. Furthermore, in the case of the church of Kuño Tambo and adobe structures like it,  they also need to ensure that any new intervention is compatible with the building’s earthen materials and guarantee that the use of modern techniques does not endanger the valuable wall paintings. Finally, engineers should always act with great humility, understanding that techniques that might seem state-of-the-art today, can be proven wrong in the future, and thus any of the proposed retrofits should be able to be reversed.

Enter the Getty Conservation Institute. This Los Angeles based philanthropic research institution is dedicated to advancing conservation practices in often overlooked fields. In 2009, it initiated the Seismic Retrofitting Project in Peru to address the challenges of and develop guidelines for seismically retrofitting traditional earthen buildings. The Getty’s conservation architects assembled a diverse international group of engineers, architects and conservation specialists who selected the church of Kuño Tambo and three other prototype buildings representative of Peruvian earthen colonial heritage on which to perform in-depth investigations ranging from historical research to wall-painting conservation and advanced structural analyses. In order to design appropriate seismic retrofitting techniques, engineers at the Pontifical Catholic University of Peru (based in Lima) conducted an extensive material testing campaign, which was complemented by a set of non-destructive dynamic tests performed at the University of Minho (Portugal). The results were then used by the University of Minho researchers to make nonlinear finite element models of the buildings to predict their load-bearing capacity under seismic action and to test the effectiveness of the various strengthening measures proposed by the entire project team.

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Results of a nonlinear finite element push-over analysis showing that the lateral wall of the church will overturn for an equivalent acceleration of 0.19g (analysis and image by Giorgos Karanikoloudis, copyright The Getty Conservation Institute)

Ultimately, for the church of Kuño Tambo the Getty’s Seismic Retrofitting team decided that employing traditional strengthening techniques would be best because they would minimally impact the authenticity of the earthen building, while still providing a crucial intervention without damaging the interior wall paintings. They recommended the addition of buttresses to prevent overturning of the longitudinal walls, the insertion of timber corner keys to stitch the façades to the transversal walls and the placement of a timber collar beam along the top of the walls. These proposed interventions aim to restore the box-behavior of the structure and were confirmed to be effective by the project’s structural models.

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Proposed retrofitting design for the church of Kuño Tambo. A timber bond beam (orange) is added on top of the adobe wall. This bond beam is connected to tie-beams (yellow) some of which are original. Additionally, buttresses are added to the lateral wall and these are interlocked with timber corner keys. (Image Giorgos Karanikoloudis, copyright The Getty Conservation Institute)

In 2016 architects from the Getty Conservation Institute worked with the Peruvian Ministry of Culture to begin implementing these proposed changes at Kuño Tambo. Firstly, mud grout was injected to secure portions of the wall paintings that had become detached and the conservation of the various religious objects in the church was started. Currently, the rubble-stone masonry of the foundation is being repaired using a lime-based mud mortar to provide a solid base for the forthcoming seismic retrofitting work detailed above. Last week, the Getty gathered a group of local and international experts in Peru to evaluate the analysis methodology, discuss the proposed intervention techniques and to visit the restoration efforts at the church of Kuño Tambo. The experts agreed that once complete, the successful retrofitting of the church of Kuño Tambo should serve as an important tangible model of best practices that can be applied to scores of other community churches in South-America.

Some images of the welcoming of the Getty’s peer review group by the community of Kuño Tambo (Images Tim Michiels, copyright The Getty Conservation Institute)

Author: Tim Michiels

Tim Michiels is a PhD candidate at the Form Finding Lab whose research focuses on the design of masonry shells in seismic areas. Tim has been contributing to the Getty’s Seismic Retrofitting Project since 2012.

More information about the Seismic Retrofitting Project can be found here.

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