Design of restoration and structural consolidation works on the monumental complex of San Lorenzo fuori le mura in Aversa (CE)

The Abbey of San Lorenzo is located in Aversa, in the province of Caserta. The complex is called “Ad Septimum” because it is located seven miles from the city of Capua, on the ancient Via Consolare Campana road. The Abbey has an almost rectangular layout and is divided into three naves, marked by pillars connected by round arches.  The building, presumably constructed between 1000 and 1030, has undergone several modifications over the centuries.

 

Brief historical overview

The monastery of St. Lawrence in Aversa was probably founded in 998, before the city was founded (1022) and the county of Aversa was created (1030) by Rainulfo Drengot. It was located on the border between the Byzantine Duchy of Naples and the Lombard Principality of Capua, near other historical settlements, such as Septimum, along the consular road and the Via Campana.

In the 15th century, the monastery went through a period of decline due to the management of commendatory abbots who were not very interested in monastic life (1339-1513) and the earthquake of 1456, which caused the collapse of the Romanesque cloister and the transept of the basilica.

The year 1513 marked the beginning of a spiritual, cultural, and architectural renewal, with the aggregation to the Cassinese Congregation. During this period, the two main cloisters were built and the convent spaces were redistributed: the large cloister housed the three-nave basilica, the Renaissance choir, the chapels, the chapter house, the archive, the library, the refectory, the kitchen, the storerooms, the dormitories, and the abbot’s apartment; around the small cloister was the guest quarters for welcoming visitors.

The construction and renovation of the buildings lasted until 1627, while the pictorial decoration, altars, and furnishings were completed by 1728, giving the monastery the appearance it still has today.

At the end of the 18th century, the monastery began its final decline due to conflicts with the Bishop’s Curia and economic difficulties, and it was suppressed in 1807. Subsequently, the complex housed various institutions, including a college for noble girls, a military orphanage, and artistic and technical institutes.

Today, most of the complex is home to the Faculty of Architecture of the Second University of Naples, while the small cloister is part of the Basilica of St. Lawrence, recently restored and returned to the city after decades of neglect.

 

Historical critical analysis

Knowledge of a building’s history is essential both for assessing its current safety and for defining the interventions required and predicting their effectiveness. Historical analysis must be aimed at understanding the construction events, instability, degradation phenomena, stresses suffered by the building and, particularly frequent in masonry constructions, the transformations made by man that may have produced changes in the original static structure. In this sense, historical investigation becomes critical investigation and a source par excellence of documentation and knowledge aimed at interpreting structural behaviour. The analysis begins with gathering all available documents on the origins of the building, such as design drawings and reports from the initial construction and any subsequent work, existing drawings and surveys, and any test reports. It covers:

– the period of construction;

– the techniques, construction rules, and, if available, technical standards in force at the time of construction;

– the original form and subsequent modifications;

– the damage suffered and changes in the surrounding conditions;

– deformations, instability, and cracks, with indications, where possible, of their evolution over time;

– previous consolidation work;

– the urban and historical aspects that have regulated the development of the building complex of which the building is part.

The Abbey of San Lorenzo has undergone a complex evolution over time, a summary of which is provided below.

 

Description of the Church and the current situation

The church dates back to 1090, when Pope Urban II donated it to the monastery of San Lorenzo and Abbot Guarino, marking the start of the first phase of construction. The original building had an elongated presbytery, a choir with large arches on pillars and twin columns, and yellow tuff columns with white stone capitals in the remaining part. The façade had a pronaos, a rose window, decorations with hanging arches, bronze portals, and a mosaic floor.

The earthquake of 1456 destroyed most of the structure, including the bell tower and apses, and the church remained abandoned until the 16th century, when it was restored in Baroque style with Renaissance elements of Tuscan influence. During this period, two cloisters, the new bell tower, the sacristy, and the side chapels with valuable paintings were built. Parts of the ancient furnishings and mosaics were reused in new locations.

After Napoleon’s suppression, the church suffered further damage, including the collapse of the upper part of the façade. It remained in ruins until its restoration in 1979, which restored it to its current appearance.

Today, it has a sober façade with three portals; the central one, decorated with fluted Corinthian columns and sculptures of symbolic animals, is surmounted by a double tympanum and a 17th-century fresco depicting episodes from the life of St. Benedict. The side portals, in Renaissance marble, replace the original ones by Berardus.

The interior of the church has three naves, divided by pillars joined by round arches and marked by twin pilasters with composite capitals. In the upper part there were windows and frescoes depicting the life of St. Benedict, which have now disappeared. Stucco decorations, with capitals and volutes, enrich the vaults and chapels, many of which are currently empty or undergoing restoration.

From the 16th century onwards, the church possessed a considerable artistic heritage. Among the works mentioned were a painting from the school of Marco Pino da Siena depicting St. Peter freed by the angel, a Supper from the school of Lanfranco, a Nativity in the style of Caravaggio, and a panel of St. Mauro by Cavalier d’Arpino. The vault of the apse still features tempera paintings by Nicola Malinconico, depicting episodes from the life of St. Lawrence and Benedictine scenes, framed by decorative friezes. The apse area also preserves a majolica floor from 1695 and a polychrome marble altar from 1725 with paintings by Simonelli. The artistic furnishings included four paintings by Sebastiano Conca, now preserved, together with other sacred furnishings, at the Superintendency of Caserta and the Abbey of Montecassino. The side altars were particularly valuable. The one in the right aisle, dated 1788, has a marble frontal with plant motifs and a green breccia shield, while an identical altar, once in the left aisle, has been transferred to the church of Sant’Eufemia in Carinaro. The high altar, dating back to the late 15th century, is made of limestone with a frontal in medieval marble tiles. In the 18th century, it was enlarged with Baroque elements such as pilasters and volutes. The side altars, dating back to 1730 and made of local limestone, have phytomorphic rosette decorations and stone balustrades, which contrast with the sobriety of the main structures.

The Abbey, in its current state, presented a reasonable state of conservation of the main façade and the central and side naves, with no particular signs of instability and/or cracking. In the apse area, plaster was found to be detaching or completely detached and floors were partially raised. In addition, there were widespread signs of damp and rising damp in this area, with deterioration of the reinforcement in the reinforced concrete elements and widespread cracking. The roof of the Abbey was in fairly good condition overall, and no particular signs of subsidence or instability were found in the external areas at ground level.

 

Criteria underlying structural interventions

Consolidation work on historic buildings must follow the Guidelines for the assessment and reduction of seismic risk to cultural heritage, in line with the Technical Standards for Construction (Circular No. 26/2010 – MiC General Secretariat). These Guidelines provide for interventions aimed at local improvement, repairs, or limited works, avoiding significant changes to the existing structural behavior. The objective is to minimize intervention, sometimes accepting a higher level of seismic risk than ordinary buildings in order to preserve historical integrity.

Assessing the seismic safety of historic buildings is complex due to their variety of types, historical transformations, and state of conservation, which make it difficult to apply the same procedures used for modern buildings. It is necessary to calculate the seismic actions for each limit state, both before and after the intervention, using reliable models.

The operating procedure first involves assessing the seismic safety index in its current state, also considering qualitative vulnerabilities that are difficult to quantify, followed by estimating the index that can be achieved with interventions compatible with heritage protection: if the index is equal to or greater than 1, the intervention is sufficient; if it is lower, less invasive choices may be justified with qualitative assessments translated into quantitative terms.

The following actions are necessary for the design of the interventions:

– acquire detailed knowledge of the structure, its elements, and the behavior manifested by the damage present;

– adopt mechanical models consistent with the characteristics of the building and choose appropriate analysis methods;

– define a reference seismic safety level based on the use of the building;

– assess the nominal life in its current state and hypothesize its life after the intervention;

– design interventions compatible with conservation, ensuring durability, ductility, and compatibility of the new elements with the original ones.

Historical knowledge of the building is essential: the analysis must include construction events, instability, degradation phenomena, stresses suffered, and transformations that may have modified the original static structure. Studies on similar buildings complete the assessment, providing information on pathologies or construction deficiencies typical of the type and era.

 

Structural project

The structural project aimed to consolidate the structural elements of the Abbey so as not to alter the original layout of the masonry and finishes, by restoring the damaged structural elements. All the planned interventions can be carried out using minimally invasive technologies and methodologies that are compatible with conservation criteria and are also reversible. This refers to specific consolidation and restoration measures that fall within the scope of paragraph 8.4.1 “Repair or Local Intervention” of NTC2018. Measures of this type concern individual parts and/or elements of the structure. They do not significantly change the overall behaviour of the building and are aimed at achieving one or more of the following objectives:

– restore the initial characteristics of damaged elements or parts to their pre-damage configuration;

– improve the strength and/or ductility characteristics of elements or parts, even if undamaged;

– prevent local collapse mechanisms;

– modify an element or a limited portion of the structure.

For such interventions, the regulations stipulate that the design and safety assessment must refer only to the parts and/or elements concerned, documenting the structural deficiencies found and demonstrating that, compared to the configuration prior to the damage, deterioration, or alteration, no substantial changes are made to the behavior of the other parts and the structure as a whole, and that the interventions do not entail a reduction in the pre-existing safety levels.

Specifically, the project included the following interventions:

1. arch chaining

Chains made of Dywidag Φ26 bars were installed on the arches of the side aisles, at the level of the horizontal plane, in order to reduce the horizontal thrust of the arches.

A preliminary phase was planned for the execution of the works to secure the areas involved using wooden and metal props, bandages, hoops, and arches, in order to counteract the mechanisms of wall overturning. For interventions of this type, before installing the chain, it is necessary to clean the hole by removing dust and debris. Once the work phases have been completed, low-pressure injection of Mapei Antique F21 mortar is carried out.

2. regeneration of masonry with hydraulic lime mortar injections

The project involved the consolidation of masonry structures through hydraulic mortar injections, with the aim of restoring the integrity of the facings and regenerating the mortar joints. According to Circular 7/2019 (point C8.5.3.1), the use of binding mixtures serves to improve the mechanical characteristics of the masonry, paying particular attention to the chemical-physical and mechanical compatibility of the mixture with the existing material. The intervention does not involve changes to the structural balance or alterations to the external appearance of the building, but aims to improve the cohesion and overall strength of the masonry.

The planned work is as follows:

– Drilling holes in the masonry with a drill to insert the injection tubes, after thoroughly cleaning the holes.

– Preparing the mortar for injection (e.g., Mapei Antique F21), mixing it until it reaches a very fluid consistency.

– Injection of the grout at low pressure (less than 1 atm), proceeding from the bottom upwards to ensure complete saturation of the wall. The operation is complete when the mixture comes out of the adjacent or upper tubes, indicating that internal saturation has been achieved.

3. cracked frame reinforcement

The project involves filling the cracks using hydraulic lime mortar reinforced with short glass fibers added to the mixture.

The following work is planned to carry out the project:

– Removal of a 40 cm strip straddling the crack;

– Scraping of the joints between the disintegrated blocks or those that allow the grout to escape;

– Cleaning and dusting of the inside and outside of the cracks with alternating jets of water and compressed air until completely clean.

– Sealing of the crack with hydraulic lime mortar (such as Mapewall Intonaca & Rinforza);

– Restoration of the plaster.

4. masonry construction using stitching and unstitching techniques

The project involved stitching and unstitching, followed by the re-grouting of degraded joints. Stitching and unstitching is a traditional technique that involves restoring the continuity of the wall by removing damaged or degraded stone elements and creating a new wall texture with new elements, without compromising the static function of the masonry during the application process. In particular, work will be carried out where there are no frescoes.

The execution phases involve, after appropriate shoring, the recovery of material to be used that is similar in shape and size to that already existing on site, thus avoiding the phenomenon of detachment due to any discontinuity in the texture. Operationally, the following steps are planned:

– Scraping and cleaning the edges of the affected area in the wall, identifying and delimiting the area where work will begin and the direction in which it will proceed;

– Dismantling of the masonry in the affected area, attempting to remove each individual element, taking care not to break or damage it, leaving a jagged edge to allow for subsequent bonding between the existing and new parts. Where possible, the work will be carried out only on the surface of the facing without affecting the core;

– Preparation of surfaces by cleaning with low-pressure water and insertion of new elements;

– For mechanically weaker areas, the supports will be consolidated with a consolidant such as Mapei Consolidante 8020;

– Application with a trowel of Mape-Antique Allettamento mortar.

 

Reference standards

[1] D.M. 17 gennaio 2018 “Aggiornamento delle «Norme tecniche per le costruzioni»;

[2] Circolare 21 gennaio 2019, n. 7 C.S.LL.PP. Istruzioni per l’applicazione dell’«Aggiornamento delle “Norme tecniche per le costruzioni”» di cui al decreto ministeriale 17 gennaio 2018;

[3] Circolare n. 26/2010 – Segretariato Generale MiC – Linee Guida per la valutazione e riduzione del rischio sismico del patrimonio culturale allineate alle nuove Norme tecniche per le costruzioni.

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