https://orcid.org/0000-0001-5442-5950
ABSTRACT
The challenges posed by conserving historical earthen structures in seismic-prone regions prompted the initiation of the Seismic Retrofitting Project (SRP) by the Getty Conservation Institute (GCI) and the Ministry of Culture of Peru. Since 2009, the SRP has aimed to enhance the structural performance and safety of historic earthen buildings while preserving their historical fabric by combining traditional techniques, local materials, and technical expertise with advanced computational tools. The project has focused on four Peruvian earthen buildings as case studies, including the seventeenth-century adobe church of Kuñotambo. An intervention was carried out between 2016 and 2019 by the regional branch of the Ministry of Culture in Cusco based on techniques developed by the SRP. The GCI is now working on a monitoring and maintenance plan for the site, collaborating with local stakeholders, including the Ministry of Culture of Peru in Cusco, the Archdiocese of Cusco, and the community of Kuñotambo. This paper primarily discusses the practical aspects of on-site monitoring, including the tools and techniques used to track changes in the building and its decorated surfaces. It also outlines the implementation of a structural health monitoring system and the development of capacity-building activities for Latin American engineers. The overarching goal is to provide a sustainable framework for the long-term preservation of historic earthen structures in seismic-prone regions, highlighting the importance of community involvement and multidisciplinary collaboration.
Los desafíos que plantea la conservación de estructuras históricas de tierra en regiones sísmicas impulsaron el inicio del Proyecto de Estabilización Sismorresistente (SRP, por sus siglas en inglés) por parte del Getty Conservation Institute (GCI) y el Ministerio de Cultura del Perú. Desde 2009, el SRP tiene como objetivo mejorar el desempeño estructural y la seguridad de los edificios históricos de tierra y al mismo tiempo preservar su material histórico mediante la combinación de técnicas tradicionales, materiales y experiencia técnica locales con herramientas analíticas avanzadas. El proyecto se ha centrado en cuatro edificios de tierra peruanos como casos de estudio, incluida la iglesia de adobe de Kuñotambo del siglo XVII. La oficina del Ministerio de Cultura del Peru en Cusco restauró la iglesia entre 2016 y 2019 empleando las técnicas de estabilización sismorrestente desarrolladas por el SRP. El GCI ahora está trabajando en un plan de monitoreo y mantenimiento para el sitio, colaborando estrechamente con las partes interesadas locales, incluido el Ministerio de Cultura del Perú en Cusco, la Arquidiócesis de Cusco y la comunidad de Kuñotambo. Este artículo analiza principalmente los aspectos prácticos del monitoreo in situ, incluidas las herramientas y técnicas utilizadas para rastrear los cambios en el edificio y sus superficies decoradas. También describe la implementación de un sistema de monitoreo de la salud estructural, la organización de actividades de desarrollo de capacidades para ingenieros latinoamericanos y la importancia de la participación comunitaria y la colaboración multidisciplinaria.
Introduction
This contribution outlines the implementation and dissemination of the multidisciplinary monitoring and maintenance plan for the church of Santiago Apóstol of Kuñotambo (church of Kuñotambo), located in a small rural community in the Department of Cusco and under the jurisdiction of the Archdiocese of Cusco.
The plan was collaboratively designed by the Getty Conservation Institute (GCI), Peruvian stakeholders, and international consultants, considering the site’s unique features and the needs of stakeholders. Its objectives encompass the long-term preservation of the monument, the assessment of the outcomes of treatment, and the establishment of a participatory framework for sustained care of similar heritage sites in the region. Besides defining practices to be shared through publications and capacity-building initiatives, the plan also presents a set of inspection and data collection protocols. These protocols, initially created to work in an integrated manner for Kuñotambo, are adaptable for independent use at other heritage sites, based on their distinct characteristics and existing resources.
The church of Kuñotambo is one of four case studies in the GCI’s Seismic Retrofitting Project (SRP), a collaboration with the Ministry of Culture of Peru seeking to validate the effectiveness of seismic retrofitting solutions for earthen historic buildings using traditional techniques, local materials, and available expertise (Getty Citation2023). The SRP used four Peruvian historic earthen buildings that exemplify common architectural typologies across Latin America and their frequent modes of failure so that the results would be applicable to similar sites in the region (Cancino and Lardinois Citation2012). Built in the Andes during the viceroyalty period, the church of Kuñotambo exhibits thick adobe walls, a wooden truss roof, and extensive wall paintings ( and ).
Figure 1. Exterior view of the church of Kuñotambo and the bell tower, after the completion of the restoration and seismic retrofitting. Image: Elena Macchioni. ©2019 Getty Conservation Institute.
Figure 2. Interior of the church of Kuñotambo. Image: Anna Flavin ©2019 Getty Conservation Institute.
Studies by SRP consultants from the Pontificia Univesidad Católica del Peru and University of Minho (Lourenço et al. Citation2019; Torrealva, Vicente, and Michiels Citation2018) assessed materials and structural systems, identified seismic vulnerabilities and provided recommendations for retrofitting, for each of the four case studies.
Within the SRP’s implementation phase, the regional branch of the Ministry of Culture of Peru in Cusco (Dirección Desconcentrada de Cultura Cusco (DDC–C)) joined the SRP to develop technical specifications and construction drawings for the restoration and seismic retrofitting of the church of Kuñotambo; works started in 2016. Detailed information on the implementation of earthquake-resistant retrofitting techniques can be found in Cancino et al. (Citation2020). The completion of the works in June 2019 marked the beginning of the post-intervention phase, including regular monitoring and maintenance, under the responsibility of the Archdiocese of Cusco, owner of the building.
This contribution highlights the significance of developing a monitoring and maintenance plan for the church of Kuñotambo. It outlines the materials and methods used for monitoring, provides insights about the structural health monitoring system (SHM) installed at the site, presents the results of the monitoring to date, and covers the creation of capacity-building activities for Latin American professionals who will take charge of implementing similar strategies at heritage sites with comparable characteristics. Ultimately it discusses the broader implications of such a plan in the context of sustainable heritage conservation.
Materials and methods
The importance of regular care of historic sites, including monitoring systems and maintenance actions, is recognized in most international charters, although the approach to preventive conservation, especially in relation to architectural heritage, has gained prominence in the last decades. This corresponds to a shift in perspective from restoration as an ‘event’ led by experts, to conservation as a cyclical ‘process’ considering the perspective of the users (Della Torre Citation2020).
Monitoring involves the collection of qualitative and quantitative data and the periodic verification of any signs of change that may affect the site, its environment, and its cultural significance, with attention to the various elements that compose it. Periodic inspections with qualitative and quantifiable methods, covering both the pre- and post-intervention phases, as well as regular maintenance, are considered essential to ensure site integrity and to mitigate risk for existing and historic structures (ISO Citation2010). Monitoring therefore represents a diagnostic tool, essential to the cyclical process of conservation, which must be seen in relation to education and awareness-raising practices (Van Balen Citation2015).
Within this framework, the monitoring plan created for the church serves as a vital tool for the preservation of the site and the mitigation of damage caused by various risks (including, e.g. earthquakes) by enabling early damage detection and identification of lack of maintenance. It also allows to check the results of the interventions, both the seismic retrofitting techniques and consolidation of wall paintings in situ. This data will contribute to evaluate the SRP results and refine the final guidelines of the project, conceived to be applied in heritage earthen buildings in Latin America. Finally, the plan empowers the local community and local stakeholders to be active actors in the long-term care of their heritage.
The stakeholders identified for the development of the plan are the DDC–C, which needs to establish a participatory protocol for the long-term care of the religious buildings in their remit, and the small technical team of the Archdiocese of Cusco, in charge of managing a scattered heritage over a large territory. Then, the Municipality of Rondocan, encompassing the town of Kuñotambo, is responsible for various maintenance activities at cultural sites within its district. Finally, the involvement of the local community is essential; in fact, the conservation of earthen architectural heritage can often count on the permanence of traditional knowledge, and a system of continuous care guarantees the transfer of these skills, alongside decision-making and communal work systems, such as those that exist in the Andean region (Heras et al. Citation2019; Vázquez, Achig, and Cardoso Citation2018).
A fundamental activity for the development of the monitoring plan was to carry out and provide the parties involved with a survey of the site after the completion of the works. At the end of 2019, a team from Carleton Immersive Media Studio (CIMS), GCI consultant, carried out a campaign to document the church, its wall paintings, and the bell tower. The obtained drawings have served as the foundation for all monitoring activities, and the point cloud allows for precise comparison with subsequent 3D acquisitions, to evaluate even the smallest modifications in the geometry of the site. In addition, CIMS contributed to the definition of guidelines for the monitoring of wall paintings (Reina Ortiz et al. Citation2021).
The team collaboratively designed three short-, medium- and long-term analysis and inspection protocols tailored to the main components of the construction, assigning roles and responsibilities to separate groups of stakeholders, based on their skills, equipment, and time availability (). Each protocol underwent several rounds of refinements based on inspections conducted on site since 2020, and included the development of capacity-building activities.
Table 1. The monitoring plan.
The first monitoring protocol involves trained members of the community of Kuñotambo responsible for the regular control of the church. If any alarming conditions are detected, the community contacts the Archdiocese of Cusco. To this end, integration between the community and civil and religious entities has been strengthened. Community members are in charge of the appropriate use of the site and basic maintenance, with roles assigned to individuals holding specific positions according to the traditional system in place (e.g. president of the community, keeper of the keys).
As part of the second monitoring protocol, the technical team of the Archdiocese of Cusco and the DDC–C carry out a rapid inspection of the site once a year, after the rainy season. This makes it possible for the Archdiocese of Cusco to plan maintenance activities during the dry season. The same protocol can be implemented after an alert from the community or the occurrence of major natural events. The rapid protocol includes a visual inspection, the completion of a detailed inspection form, and simplified mapping of conditions on site plans, as well as a production of photographic records ().
Table 2. Outline of the annual inspection form with main sections and content required.
Currently, the Archdiocese team uses a printed version of the form, but the same is also available digitally. The conclusions of the inspection should detail the planned actions: additional investigations, interventions with different priorities (with a maximum period of 3 months; for the next inspection cycle; desirable long-term actions), and/or small renovation works to be carried out by the community without the need for approval documents from the authorities. The Archdiocese implements any other intervention, collaborating with the Municipality of Rondocan and DDC–C, where applicable.
The third monitoring protocol for heritage specialists should take place every 5 years. It includes a detailed condition survey, using the documentation produced after the completion of the works, as-built drawings, and the monitoring forms from previous years, complemented by photographic records and documentation of the site. It is envisioned that the GCI will be involved for at least the first 5 years of monitoring, when the responsibility will be given to the Archdiocese of Cusco. Whitin the protocol for heritage specialists, the University of Minho installed a permanent SHM in 2022, to assess the structural and environmental conditions of the structure after its seismic retrofitting.
SHM can be defined as the recording, data collection, and statistical correlation of structural conditions, seismic actions, and other environmental parameters, establishing a clear relationship between causes and effects (ISO 13822 Citation2010). A crucial part of the process is the association between the qualitative data obtained during monitoring activities (visual analysis, condition mapping, etc.), with the quantitative data obtained by the SHM. Information from assessments and non-destructive testing conducted before the design and implementation of retrofitting techniques, alongside the update of the finite element model of the retrofitted building, are critical to effectively design the SHM ( and ) (Ahmadi et al. Citation2022).
Figure 3. Worksite and implementation of retrofitting techniques of the church of Kuñotambo. (a) Typical section and plan of the lateral walls showing tie beam, bond beam, and roof rafter connections. (b) Lateral bracing in the upper walls and connection with roof rafters. (c) New roof with double rafters. Images: Juan Carlos Mellado ©2019 Getty Conservation Institute and Dirección Desconcentrada de Cultura Cusco.
Figure 4. Modelling of the retrofitted church. (a) Configuration of the finite element model (FEM) with timber reinforcements. (b) Three principal mode shapes obtained from ambient vibration tests, during December 2019. (c) The same, from the updated FEM. Images first published in Ahmadi et al. (Citation2022).
The SHM for the church of Kuñotambo aims to record alterations in the shape and formation of cracks in relation to environmental and seismic data, to analyze structural capacity and deformation in the structure, and thus understand the probable causes. This type of monitoring has proven to be appropriate for damage detection, especially after earthquakes (Alban et al. Citation2019; Zonno et al. Citation2021).
The system installed at the church includes five elements (). First, sensors for temperature and relative humidity (RH) which have a direct effect on cracks, outward rotations, and dynamic properties, including interior and exterior data loggers, interior surface thermocouples, and a temperature and RH probe for the external ambient conditions. Their readings are integrated with static and dynamic sensors, to investigate the effect of seasonal cycles. Second, a system of accelerometers for the detection of natural vibrations and seismic events. The main objective is to monitor the out-of-plane modes of the side walls and main façade, in correlation with seismic events, parameters indicative of the effectiveness of bracing and anchoring systems. Third, crack meters are located at selected points, such as interfaces between different materials or existing cracks. Fourth, tilt meters in walls to detect out-of-plane rotations, a type of damage common in unreinforced load-bearing masonry structures. Finally, an integrated system for the acquisition, storage, and processing of the SHM data. Data acquisitions are continuous, with appropriate sampling frequencies. Data from the sensors is collected by a laptop on site and then uploaded to a storage cloud, using automatic procedures for large data series, to be processed remotely.
Figure 5. Schematic representation of the SHM system at the church of Kuñotambo. Images: Georgios Karanikoloudis ©2023 Getty Conservation Institute.
Results
Inspections have been carried out since 2020, with the GCI staff initially providing guidance and receiving feedback via conference calls, due to the team’s inability to travel during the Covid-19 pandemic, and in person from April 2022.
Basic monitoring by community members enabled detection of lost roof tiles, damage to the roof eaves, and the presence of bird droppings inside the church. This served as an early warning system for the Archdiocese of Cusco to plan for site visits and repairs. The community has been conducting basic maintenance activities such as cleaning of the church and its surroundings. Annual inspections were carried out by staff of the Archdiocese of Cusco and the DDC–C. The protocol and form were progressively simplified, allowing the team to complete the inspection in half a day. The Archdiocese planned and implemented maintenance works in 2021 and 2022, before the rainy season, including localized tile replacement, seal of minor cracks in interfaces between parts, and stabilization of small detachments in specific areas of the wall paintings using earth-based injection grouts. Another issue encountered by the team was the condition of the exterior paint, which presented detachment and losses. This was attributed not only to the material, a lime-based paint with several additives commonly used by the DDC–C, but also to the meteorological conditions suffered by the church, which is on the ridge of a mountain exposed to extreme rains and winds. The GCI and consultants conducted several tests and subsequent evaluations to identify an alternative material for the finishes of the church and bell tower (Marcus et al. Citation2022). As a result, and considering additional factors such as availability, durability, cost, and ease of application, a new earth-based mortar slur and silicate-based paint was applied in 2022 and is currently being monitored.
The permanent SHM has been recording hourly acquisitions since 2022 with few downtimes due to power failures.
As part of the protocol for heritage specialists, the GCI staff, consultants in engineering and wall painting conservation, alongside the staff from the Archdiocese of Cusco, performed a complete condition assessment of the site in April 2022. Originally planned for early 2020, the assessment was delayed by the Covid-19 pandemic. Digital records of the detailed mapping were shared with the Archdiocese and DDC–C to establish a repository for ongoing monitoring acquisitions.
Much of the structural damage found in the church since 2022 is related to the construction process and foundation or soil settlement in the northeast part of the building. This includes cracks in the top parts of the gable of the main façade, the staircase leading to the choir loft, and the northeast section, including the baptistry. Cracks were observed in the adobe walls, stone base course, and intrados of the gypsum plastered roofs, with discontinuities in the interior and exterior pavement.
Non-structural cracks in the interior surfaces of the roof structure are likely due to deformation of the timber elements from hygrothermal variations. Weather-related damage, such as water ingress from missing tiles after the rainy season, in roof eaves, and at the intersection between roofs and adjacent walls is connected to the implementation of traditional tiles without proper waterproofing or flashing. Significant water damage is also evident in many exterior areas near the base course, possibly due to exposure to heavy rainfall patterns.
Environmental conditions in Kuñotambo are characterized by a drier and colder season (May–October) and a wet and rainy season (November–April). Internal air temperature and RH were found to be much less variable than the exterior, and the wall temperatures exhibited a time lag due to the thermal inertia of the adobe walls. The internal RH varies from 15% to 77%, while values higher than 65% and lower than 40% can affect decorative surfaces and artworks.
Continuous monitoring of a crack in the staircase with a linear variable differential transformer (LVDT) crack meter showed seasonal fluctuations. In general, this crack has shown a steady increase during the dry seasons, when adobe is expected to shrink, while the widening slows or reverses during the wet season, alongside the expansion of adobe; its overall, non-recoverable progression is 3 mm per year. Additionally, a seismic event of magnitude 7.2 and with epicenter at 200 km from the church on 26 May 2022 caused a non-recoverable crack increase of 0.14 mm, which corresponds to 5% of the yearly positive progression.
Two highly sensitive tilt meters have been monitoring vertical rotations at the gable end of the baptistery and at the north lateral wall of the nave, with thermocouples in the walls to evaluate temperature effects. Vertical rotations exhibited seasonal fluctuations with maximum positive outward drifts of 0.1% and 0.5% degrees respectively.
Three natural frequencies and mode shapes were identified and monitored continuously over time, based on hourly acquisitions of the five uniaxial accelerometers at the top of the walls in the nave and the façade. The natural frequencies remained stable, with minor variations linked to seasonal cycles, mainly under a slight increase during the wet season. Following the earthquake on 26 May 2022 there was a sudden decrease in natural frequencies by approximately 0.1–0.2 Hz, indicating a loss of stiffness and minor structural damage.
Overall, the collected monitoring data shows oscillating variations due to seasonal effects, sometimes under complex nonlinear correlations with the environmental parameters. Processing of data from more seasonal cycles is therefore needed. The team is also considering some additions to the monitoring system: installing a weather station, given the influence of RH on structural response and the impact of rainfall on the church conditions, and conducting regular measurements to monitor settlements in the northeast part.
Finally, capacity-building has been a fundamental component of the monitoring and maintenance plan. Since 2020, activities have been conducted for community members responsible for basic inspections, cleaning, and small repairs. A manual for the appropriate use of the site (including for example, instructions for avoiding any damage to the decorated elements and surfaces), together with an annual maintenance calendar was prepared by the GCI and updated based on feedback from the community.
Then, staff from the Archdiocese of Cusco and the DDC–C worked alongside the GCI team to refine the methodology for the annual inspection and to test it on site every year after the rainy season.
Furthermore, the GCI and DDC–C convened civil engineers and graduate students of civil engineering from Latin America for a 4-day workshop in Cusco in June 2023. The workshop centered on diagnosis and structural monitoring of historic buildings, with a focus on earthen and masonry constructions. Staff from the University of Minho and the Pontificia Universidad Católica del Perú led the activities, alongside GCI staff. The 22 participants attended lectures on topics such as methodology for inspection, analysis and structural diagnosis of historic buildings, in situ testing, and some of the most advanced tools and techniques for the evaluation and monitoring, including the interpretation of data generated by the SHM. Half of the curriculum of the workshop was practical, with site visits to historic buildings in Cusco to discuss structural damage, as well as exercises and field sessions. Participants performed non-destructive and micro-destructive testing on one traditional earthen residential building in Cusco and visited the SHM at the church of Kuñotambo. The workshop raised awareness of the latest developments in terms of SHM, as well as deepening expertise among participants on monitoring tools and techniques.
Discussion
The development and implementation of a monitoring and maintenance plan for the church of Kuñotambo exemplifies an integrated approach to heritage preservation, emphasizing the importance of long-term sustainability and the rising role of communities and social entities as active caretakers of their heritage.
The primary goal of the monitoring plan is the preservation of the site for future generations. Changes in buildings after construction can happen, especially in the case of earthen structures; some of these changes may be linked to material adjustments, customary building practices that prove inadequate for a changing environment, or limitations during construction. By tracking changes in the building, the plan ensures that the site remains usable, perpetuating and adding to its significance for the local community. To this end, the commitment of the Archdiocese of Cusco to provide religious services to all communities in the region, regardless of their geographical accessibility, is pivotal.
Safety is paramount for all heritage sites located in seismically active regions. Not only does the church of Kuñotambo demonstrate the possibility of intervention with earthquake-resistant repairs using traditional techniques and local materials, but the monitoring plan provides an additional layer of safety by continually assessing the structural integrity of the monument.
The use of an advanced SHM, complementing a regular three-tier monitoring protocol, facilitates the early detection of problems. Any damage is identified promptly, allowing for proactive responses. Additionally, the retrieval and processing of information from the SHM enables verifying the effectiveness of the retrofitting techniques implemented, providing scientific data to support their broad dissemination.
The engagement of the community of Kuñotambo and local stakeholders in the monitoring and maintenance plan enhances public awareness and trust in the preservation of heritage, and stems from the sense of pride for their conserved church. The clear three-tier system offers a transparent record of the church’s condition and need for maintenance actions, fostering cooperation between stakeholders. Timely maintenance, such as replacement of missing roof tiles, is more cost-effective and less disruptive than addressing major interventions. Moreover, the plan was created having considered the capacity, availability of time and equipment by each group responsible for the monitoring and maintenance actions. While the three protocols described are intended to be integrated, they can also operate independently so that they can be used, in whole or in parts according to available resources, in other comparable sites.
One notable aspect of the project is dissemination and capacity-building. The GCI has organized activities for professionals responsible for the conservation of similar buildings in the region, offered training to Latin American engineers on advanced tools for structural monitoring, and produced publications available to the larger conservation community.
Preventive and planned conservation have undeniable benefits in terms of resources and impact for communities, owners, authorities, as well as cultural properties (Vandesande et al. Citation2018). Within this framework, two key sub-themes play a crucial role. First, the implementation of the monitoring and maintenance plan for the church of Kuñotambo is an example of collaborative international and interdisciplinary work. This is a powerful model for addressing complex preservation challenges when expectations and responsibilities of all parties are well set. Second, the focus on preventive conservation is often intertwined with the empowerment of communities and social entities as active caretakers of their heritage. This commitment fosters a sense of belonging and reinforces the idea that the protection and management of cultural properties is a shared responsibility among all interested parties, including institutions, owners, and users (ICOMOS Citation2014; Van Balen and Vandesande Citation2015; García et al. Citation2021). The active involvement of different members of the ‘heritage community’ (Council of Europe Citation2005) helps to safeguard the spirit of the place (Cˇebron Lipovec and Van Balen Citation2008) and at the same time ensures the sustainability of conservation actions in the long-term.
Acknowledgements
The Seismic Retrofitting Project (SRP) is a partnership between Getty Conservation Institute (GCI) and the Ministerio de Cultura del Peru. The authors would like to thank the DDD-C, Arzobispado del Cusco, Municipalidad Distrital de Rondocan, and Comunidad Campesina de Kuñotambo, as well as the following individuals, who have been collaborating to the design and implementation of the monitoring and maintenance plan at the church of Kuñotambo, and related capacity-building activities: Andres Arce Campos, Felícitas Ttito, Cesar Chacara Espinoza, Angela Delgado Gibaja, Mauricio Gonzales Paliza, Juan Carlos Mellado Flores, Claudia Miranda Sotomayor, Violeta Paliza Flores, Margherita Rago, Rony Reategui Arrue, Miquel Reina Ortiz, Mario Santana Quintero, Leslie Rainer, Alex Ramos, Juana Segura Escobar, Alessandra Sprega, Clemencia Vernaza Albisser, Luís Andrés Villacorta Santamato, and Carlos Yaya Miranda.
Disclosure statement
No potential conflict of interest was reported by the author(s).
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