The Cloister of Michelangelo was erected in the XVI century inside the ruins of the Diocletian Baths in Rome together with the church of Santa Maria degli Angeli, which re-uses some of the great halls of the central body of the baths. In 1890, the cloister of Michel-angelo, the minor Ludovisi’s cloister, and some of the great halls became the seat of the Museo Nazionale Romano, which nowadays hosts offices and exhibition space. It has a 360 meters perimeter and covers an area of 10,000 square meters.
Numerous restorations and structural interventions have been done in the cloister to rehabilitate and maintain severely deteriorated areas of the complex since the first years of the XX century.
As for timber roofs, the object of this paper, a number of interventions have been made throughout the years to replace, reinforce, or adapt the various elements. Although the original timber structure exact age is uncertain, it can be assumed that it dates back to 1910.
The office roof area is free from previous structural maintenance. In the museum, in the 1980s, interventions were carried out with braces and steel jacketing.
Recently, from 2014 to 2016, some bays of the roof were substituted with new chestnut wood elements; the initial on-site inspections for the first intervention were conducted in 2014 and were helpful in determining the general situation, the pre-existing conditions, and which beams had already been reinforced or replaced. As a result, some statistics have been conjectured due to the inability to conduct precise surveys.
The wooden supporting beams of seven spans were replaced in the west corner with the addition of new braced steel elements. No previous interventions were found.
After this first phase, also in the same period, it was continued with a first stretch of the NE wing of nine spans, extended subsequently. Given the general conditions, with insufficient sections and altered poorly monitored and maintained, it was decided to extend the same intervention by an additional eight spans.
5.2. HBIM Modeling and Values
A structural HBIM model was built, shown in
Figure 9 and
Figure 10, through the Autodesk Revit software, [
52], as this methodology employed the seven dimensions of modeling (3D, cost, time, management, and sustainability) and allowed us to create a summary schedule that could be used to find the values needed to compare alternatives.
Once the necessary data were obtained, it was possible to develop a structural construction model.
Then, the families of the elements were designed. Families with shared parameters were chosen to use so that it was possible to easily create the required schedule. After completing this first operation, the different interventions were modelled and placed. Each element was built according to UNI 11337 [
53].
The Level of Details (LOD) geometry was equal to F and G depending on the elements since the degradation state was only partially done. Only the structure below the roof turned out to be an LOD D.
The alternatives to be analyzed, to find out the most sustainable intervention according to various aspects, were, therefore, the four presented: the complete replacement of the wooden element and the stiffening through the creation of steel bracing and a C-shaped beam connecting the bays inserted in the wall and used as a support to the bracing plate; the creation of a steel jacket with L-shaped profiles combined with each other and joined by support connectors; the use of a support beam with double steel L-profile to support the existing with the addition of braces in steel; and the use of only braces in steel, but always with C-beam inserted inside the wall.
The indices to be evaluated according to the decision tree are shown in
Figure 11, where there are three fundamental Requirements for the assessment of sustainability (R
1 Environmental, R
2 Economic, R
3 Social), with the addition of a Requirement slightly investigated in the literature, R
4 Cultural/Structural. The addition of a combined Requirement was useful to define those parameters of cultural evaluation that also refer to structural functions but were typical of the theory of restoration for the approach to the historical heritage. In addition, the presence of codes or existing legislation was useful to evaluate the possibility of performing the interventions in a correct way.
The schedules were then extracted through HBIM modeling, which led to the construction of the following
Table 3, with the indices and values for each alternative.
Emissions (I
1): The emissions in this analysis were related to the production and transport of the two main materials, chestnut wood and steel. To accomplish this, a task was considered, according to the standards ISO 14040 and ISO14044 [
54,
55], for the first four phases of the environmental product declaration (EPD). Then, the first four steps, Raw Materials, Transport, Manufacturing, and Transport, were analyzed. In essence, emissions were then counted “from cradle to gate”, that is, from extraction to distribution locally.
The transport from the headquarters to the construction-site must be added, which was counted in the document produced by the company. This transfer is regulated at the European level by the Association des Constructeurs Européens d’Automobiles (ACEA), which, since 2019, has been committed to the development of guidelines and software that can help such counting. VECTO [
56] is an application that has already become mandatory for certain categories of heavy vehicles in 2019. This program provides the decision-maker with an absolute CO
2 emission value in grams in terms of the distance travelled in grams of emissions per kilometer and the load transported in grams per ton kilometer. The selected category falls into category 4 (truck carrying 16 tons or more), one of the first to be standardized along with categories 5, 9, and 10. Moreover, the category 4 with the acronym RD (Regional Delivery) must be identified, as it previewed mostly transportation from Tuscany to Lazio. The emission average, therefore, refers to a value of 198.1 [g/tkm]. The importance of this last added phase is because the heavy goods transport sector, within the transport sector (22.3% of total greenhouse gas emissions) covers 25% and 6% globally. Given the importance of these transports, the companies closest to the site have been chosen, which have made the EPD public and searchable for the necessary products.
Once the companies were identified through the quantities (in m, m3, and kg as needed), the steel emissions were calculated, equal to 1033.10 [kgCO2eq] per unit declared (tons) and wood, equal to 646 [kgCO2eq] per cubic meter. It should be remembered that the extraction in the 4 phases is certainly considered the most relevant for emissions, which, for example, covers 71% for steel. The second, third, and fourth intervention (A2-A3-A4) also includes emissions due to the journey from the laboratory to the construction site.
Consumption (I2-I3): As for material consumption, these are expressed in kg and are obtained from HBIM modeling, which guarantees a higher accuracy in the counting of the elements used. Having the volume, inserted as a shared parameter within the created families, the weight density was inserted through the modification of the properties of the material.
Waste (I4): Waste is expressed in m3 and is given by the material that has been substituted by the addition of the elements provided by the EPDs, divided into hazardous, non-hazardous, and radioactive waste. They were included because they are rarely taken into account, and, especially for large construction sites, they are a fundamental element to be considered. For the second, third, and fourth intervention (A2, A3, A4), NDT waste was considered. In fact, some test apparatuses can deteriorate and require a replacement to maintain the reliability of the results.
Costs (I
5): The cost of interventions was considered using the “Prezziario (price list) della Regione Lazio per Opere Edili e Costi della sicurezza” [
57]. The costs of the material, the workmanship, and the safety of the construction-site were added. The costs of the second, third, and fourth intervention (A
2, A
3, A
4) included the laboratory cost NDT investigations and technical staff. The list of prices for the first processing included the items of disassembly and reconstruction of the roof, so the price was higher than the other alternatives, where, instead, the incidence of the cost was mainly given by the metal profiles that were inserted and calculated per kg. The safety costs for the A
1, A
3, and A
4 were roughly the same; they differed from A
2 for the safety of welding work involving special equipment, such as shielding and masks.
Worker safety (I6): The probability–damage matrix was used to verify the safety rate. This compares the probability of damage occurring to several activities and the damage they would cause. The values obtained are then multiplied by factors of reduction, based on training and information of workers. The risks considered in this case related to the work at the height and the possibility of inhaling dust (a factor that also weighed heavily in the calculation of safety costs).
Need for skilled workers (I7): This index, like the following, was expressed with a binary code identified with 0 as absence or difficulty in finding and 1 as present or easy. An intermediate value was added to indicate difficulties, but not impossibilities, in order to have an alternative value. The need to find skilled workers is essential for restoration work that is difficult to achieve without the appropriate knowledge, skills, and know-how. The total renovation of a roof is certainly less complex than welding on site in a crawl space. These are all elements to consider, albeit with lower weights.
Closure (I8): The closure is considered relevant in an area used as offices or museum, creating problems related to staff and visitors.
Reversibility (I9): Reversibility and compatibility are the fundamental characteristics to be taken into account for a restoration of structures. As it is made of wood and steel elements, the second has always occurred, so it considered only the first. Reversibility provides a fundamental requirement for modern restorations, as it allows them to take a step back if deemed necessary. Moreover, the total substitution, insofar as is necessary in very serious cases, represents a loss in terms of material, historical value, and constructive tradition.
Future inspections (I
10): This field has been added based on the authors’ experience, as often, during on-site inspections, conducting non-destructive monitoring, and diagnostics investigations, it is impossible to see the structural elements or their defects. The use of fire retardant covering paints, for example, leads to problems related to the poor visibility of surface defects, not allowing the inspection of nodes, lesions, or biotic attacks, making it impossible to do a visual inspection introduced by the technical norm UNI 11119:2004 [
58]. The same goes for steel claddings that allow even less visibility for monitoring. Awareness of the state of the conservation is a fundamental requirement to be considered.
Codes and regulations (I
11): The presence of legislation is a fundamental element for the preparation of a restoration intervention through structural design. If there is no performance or prescriptive regulation, it is more complex to manage the design or maintenance of an intervention. Even the mere presence of guidelines is considered relevant. Substitution intervention (A
1) is nationally regulated by NTC2018, but there are also guidelines proposed by the Tuscany region that, for example, describe the fundamental characteristics of the material together with details of technology necessary for proper use. There is also a specific chapter on regulatory references; these guidelines provide design principles with indispensable tools for effective and safe design [
59]. As for the other interventions, the cladding (A
2) can be made either in r.c. or in steel. Made of steel, they are poorly described by the Standard for the beams, but they are mainly used for reinforcements of structures in elevation. In Chapter C8.7.4.2.2, entitled “Steel cladding”, it addresses the issue mainly by pointing out the increase in the shear strength of the pillars [
60]. In addition, the third intervention (A
3) concerning the reinforcement beam has no normative references.
Other inventions (A
4), on the other hand, which have been amply regulated, concern the applications of steel bracing. First, the elements (bracing for structural consolidation) must be manufactured in accordance with the UNI EN 1090-1 [
61] standard and must bear the CE marking, as required by the standard. This intervention is described in chapter C8.4.1 of the Circular 2019, where it is reported that “The restoration or reinforcement of existing links between individual components or between parts of them or the creation of new connections (for example between walls, between walls and beams or floors, including through the introduction of chains/tie rods, nails between wooden elements of a roof or a slab, between prefabricated components) fall into this category”.