Case Study: Kuñotambo
This project is a collaboration between the Getty Conservation Institute and the Dirección Desconcentrada de Cultura-Cusco.
The Church of Santiago Apóstol is located in the Comunidad Campesina Kuñotambo, a remote village of 500 inhabitants located southeast of the city of Cusco. Constructed in 1681, the church was built with thick mud brick walls and buttresses over a rubble stone masonry base course and a wood-framed gable roof. The one-story, 500 m² church consists of a large rectangular mass oriented along a North–South axis and a baptistery and sacristy located along the east lateral wall of the main church. Rich wall paintings depicting saints and various decorative elements adorn the interior.
The main church is a single room containing five different functional spaces: a sotacoro, choir loft, nave, presbytery, and altar. Prior to intervention, the structural performance of the building was severely compromised by a leaking roof, inadequate or broken connections of the roof framing, the loss of several exterior buttresses causing structural vulnerability of the walls, and settlement of the foundations due to the erosion of the site which had led to cracking at wall junctions.
Following structural assessment, numerical modeling, and testing of various seismic retrofitting techniques, a series of interventions was proposed to preserve and strengthen the church against future earthquakes. Proposed measures include the reconstruction and reinforcement of the roof, including a ring beam and tie beams, the insertion of wooden corner keys to strengthen the connection of wall planes, and the reconstruction and addition of buttresses to the exterior. The new buttresses are linked to the historic masonry through wooden reinforcement keys and layers of geomesh. The exterior masonry of the building is to be strengthened including the reconstruction of stone foundations and filling areas of loss on the adobe exterior. Finally, a layer of limewash will protect the exterior plaster.
The stone and adobe walls of the church are reinforced starting with the stone foundations, strengthening of existing buttresses, and construction of additional buttresses. All new buttresses are linked to the historic structure via three wooden keys constructed of half-lapped 4 x 4" timbers, and geomesh inserted horizontally every three rows of adobe brick. Modeling showed that due to lack of lateral support, the western wall of the church was the most susceptible to catastrophic failure in an earthquake. Therefore three new buttresses were proposed for this wall. On the west elevation the existing buttresses needed to be widened to provide adequate lateral support. Another important intervention is the insertion of wooden corner keys on all angles of the church. These ensure that the church acts as a structural unit and that wall planes do not separate in the event of a strong earthquake. All wooden elements must be inserted from the exterior to avoid damage to the wall paintings on the interior of the church.
The existing roof is a recent replacement and was poorly tied into the walls causing structural vulnerability. The proposed new roof is a par y nudillo system where rafters sit on wall plates (arrocabe or collar beam) embedded into the walls, which connect to existing and newly inserted tie beams. The tie beams are anchored on both sides of the adobe walls with wedge shaped anchor keys. The exterior keys are partially embedded into the wall. The roof structure elements are all wood and the connections are half-lapped joints. This system ties the upper walls together, resisting lateral movement in the event of an earthquake.
The bell tower of Kuñotambo has suffered from erosion of its exterior masonry and basal erosion of the walls. The proposed intervention will replace the lost width of the adobe masonry with new adobe masonry. Eroded stone masonry at the base of the tower will be replaced to strengthen the foundation. The tower will be then be wrapped in geomesh to seismically reinforce the structure and plastered with earth plaster and a layer of protective limewash.