Case Study: Ica Cathedral
St. Jerome Cathedral, known as Ica Cathedral, overlooks the main plaza of Ica, one of the most important cities on the Peruvian coast. Originally built in 1759 by the Society of Jesus, the typology of Ica Cathedral is a remarkable example of Jesuit architecture in Latin America. Following severe damage caused by an earthquake in 1813, the front facade was rebuilt in the neoclassical style by the Mercedarian Order who took possession of the cathedral after the expulsion of the Jesuits from Peru in 1767.
The cathedral plan has a cruciform, or rectangular, shape and consists of a choir loft, one central nave with four structural bays, a transept, and an altar all covered with barrel vaults. Either side of the nave is flanked by an aisle covered with a series of small domes, and the crossing of the nave and transept is covered by a large dome with a lantern. The thick lateral walls are constructed with mud brick masonry (adobe) over a fired brick base course and stone foundations. The side aisles are separated from the central nave by a series hollow quincha pillars and arches which are covered with painted mud and gypsum plaster. The barrel vault and domes are also constructed with wood arches, or ribs, and quincha.
The structural damage incurred during the 2007 earthquake was mainly caused by the lack of connection between the main architectural elements and the different seismic behaviour of the various constructive materials.
The structural assessment highlighted that the most vulnerable macro elements were the tympanum, the longitudinal walls, and the roof structure. In contrast, the front wall and the towers were found to be less vulnerable.
Therefore, the seismic retrofitting proposal aims to increase the connection between the different architectural elements by following the main conservation principles of minimal intervention, reversibility, and authenticity.
Proposed measures include the use of steel anchoring systems connecting the internal timber structure with the front facade, the reinforcement of the longitudinal walls with wooden ties and brick columns, and the strengthening of the roof.
Longitudinal Abode Wall
The intervention in the longitudinal adobe walls has two key objectives:
The first is to replace part of the adobe wall with brick column in the locations coinciding with the lateral pillars, so that they provide rigidity and lateral resistance to the wooden structure. Timber anchoring systems are embedded in these new brick columns along the lateral longitudinal walls to improve the connection between the internal timber frame and the external masonry envelope. The wooden ties and the insertion of the arrocabe beam ensure the connection between the pillar, the adobe wall and the roof.
The second objective of the intervention is to rebuild the wall to include the brick foundation and add up to an additional 1m height to the adobe wall. The transept longitudinal walls are reinforced with a horizontal geomesh, placed every 4 adobe courses over the entire height of the brick plinth.
The roof framing system consists of a series of quincha barrel vaults over the central nave, transept, and altar. Quincha domes cover the side aisles and the central part of the transept.
The lunette beam caused the collapse of the central vault. The proposed retrofitting measure consists of replacing the original lunette beam with a new termite-resistant beam. The connection between the new lunette beam and the wooden transverse arch (fajon arch) is ensured by a stainless-steel connector.
The principle of the retrofitting intervention for the transept dome is its complete reconstruction, keeping the original wooden beams, which will be restored. The dome is composed of 36 wooden trusses fixed in a base ring, and joined to a wooden compression ring of 1.20m in diameter.