Structural Framework Evolution from the Seventeenth to the Twentieth Century in the Genoa Republic’s Shipyard.

Architectural Archaeology Investigates the Layers of the Structure

Chiara Calderini, Andrea Canziani, Sergio Lagomarsino and Daniela Pittaluga INTRODUCTION This paper describes the role of architectural archaeology studies in the restoration design and yard of the Galata Quarter, the new site of the “Sea and Seafaring Museum” in Genoa. It analyses how the structural frame of the building evolved because of important transformations that occurred between the eighteenth and twentieth century to the original structure of the seventeenth. The archaeological analysis of the elevated building revealed the original seventeenth century structure of the shipyard, called “Arcate Nuove” (i.e. New Arcades), as it was described in ancient documents. The pillar and arch structure was completely hidden by later parts of the building and it was presumed completely lost. There are 45 pillars (70 x 150 cm wide, 8 metres tall) in marly limestone blocks, in 5 rows of 9 pillars each. Each pillar is connected to the next by a 4-metre wide brick arch, and to the facing one by a wider 9-metre one. The structure is similar to other shipyards from the same period. This structure was absorbed in the second half of the eighteenth century by a continuous one: stone and brick walls with barrel vaults in stone splinters; giving rise to four levels of large galleries, more than 50 metres long with large stone vaults, 9 metres wide. Archaeological investigation revealed the building transformations, through a rigorous survey of the structure and scientific analysis (mensio-chronology, walling techniques, dendrology, dendrochronology, mortar mineralogy and petrography). Precise interpretative hypotheses were made, by intuition, on structural systems over the centuries; however, these hypotheses were later supported by the results of a structural model of the building. This model has been used to study chronological variations of tensions and deformations in wall structure, analysing the interaction between new and pre-existing structures, considering both construction and demolition phases (that are sometimes critical). Interaction between architectural archaeology and structure modelling disciplines was very productive: indeed the historical analysis provided both geometrical data (structure and layout evolution over time) and constructive information (phases and techniques of construction and demolition). A finite-element structural model was devised, that included a non-linear constitutive model and the possibility of activating/deactivating the elements by mass and stiffness variations. Static analyses were performed to evaluate the structure’s behaviour. Knowledge of building phase and evolution

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over the centuries allowed us to evaluate the structural role of each element and the overall safety margins. HISTORIOGRAPHAL NOTES First period: building the Arcate Nuove between 1600 and 1616 At the end of sixteenth century the Genoese Republic was expanding its maritime power. The existing shipyard buildings, on the Prè shore, were a simple sequence of stone pillars, sheltered by a reef, supporting arches covered by slated roofs (“abayini”). Under these arches the galleys were built, repaired and armed (Doria 1988, pp.75-76). Because of the very bad condition of the shipyard arcades, in 1590 a commission for the reorganisation of the Arsenal area was appointed and on 10th September 1599 a plan for new building-slips was proposed by Giovanni Battista D'Oria, Gerolamo Assereto, Stefano Giustiniani and Giovanni Battista Senarega. The idea was to build a platform next to the west Darsena wall, sheltered by a new reef that has to be built in continuation of the existing Darsena one:

Vi si edificasse quel numero di portici che fosse possibile, ognuno de'quali portici fosse per lo meno capace d'un corpo ossia scafo di galera; calcolandosi che potevano riuscire cinquanta portici, tra quali cinque capaci di ricevere una galeassa per ognuno di essi. Che la fabbrica di detti portici si facesse in maniera che riguardassero da ponente a levante, ed ogni filza di essi portici fosse capace di cinque corpi di galere e vi fossero dieci filze, ognuna delle quali andasse a varare nella Darsena. Che a tale effetto si gettasse in terra la muraglia dividente il Darsenale dalla Darsena, ed in luogo di essa vi si facesse una muraglia matta per chiudere l'ultimo portico di ognuna delle filze essendo essa più facile a rovinarsi e poi rifarsi in caso di varamento. (New arches, as large as a galley, have to be built. The number has to be not less than fifty, five of them have to be as wide as a big galley. Ten lines of arcades have to be built and their orientation has to be from east to west to permit the galleys’ launching in the Darsena. The wall towards the Darsena has to be demolished and in its place has to be built a false wall to close the last arch of each arcade, easy to demolish and to rebuild in case of launching)

(from the project report, in Podestà 1913, p.276) On 21st January 1600 the Republic decided on a reduced version of the plan: just eight arcades that form the new Arsenal shipyards, with the name of Arcate Nuove. Designed as a sequence of pillars connected by brick arches covered by wooden roofs, they imitated the building typologies of other contemporary shipyards. In 1607 the Authority for the Arsenal governance (“Magistrato dell'Arsenale”) was established but the building was not yet finished. Building costs are revealed in

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documents up to 1635 (Genoa State Archive, Senato, Sala Gallo, p.566, bilanci del Magistrato dell'Arsenale 1628-1635, quoted in Repertorio, p.68). Gerolamo Bordoni in his Civitas Janue, (attr., oil on canvas, Pallavicini Collection) painted the Arcate Nuove in 1616 as a sequence of eight lines of arcades, each made up of seven arches. In the extremely detailed lithography La famosissima e nobilissima città di Genova (copper engraving, B.N.P. Collection) in 1637 Alessandro Baratta represented the new and old shipyards as structures of pillars and arches (fig.1). The new shipyards were soon used for other functions: in 1618 bonded warehouses occupied the two southern arcades near the sea (Podestà 1913, p.282). Over the years walls and wooden floors were built between the pillars (see also Michele Codeviola's water-colour plans of the eighteenth century). During the seventeenth century the Arsenal had a very important part to play in making up the Genoese navy: 28 hulls between 1629 and 1648, 43 launchings between 1640 and 1662, 11 galleys were launched between 1658 and 1664, a dozen between 1710 and 1719 (Gatti 1999, p.159-160 and Genoa State Archive, Cancellieri di San Giorgio, A. Correggia, Secretorum, anni 1660-1664, quoted in Repertorio, p.68). The main function of the shipyard was maintained at least until the first decade of the eighteenth century and this can be seen in the documents for Genoese and foreign orders. The number of skilled workers in the Arsenal is increasing until the second half of the eighteenth century (mid 1600s: 60-66 carpenters; second half 1700s: 30-70 carpenters and 50 caulkers; second half 1800s: 100-115 caulkers. Doria 1988, p.160).

Figure 1. La famosissima e nobilissima città di Genova, Alessandro Baratta,

1637, copper engraving, B.N.P. Collection.

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As early as 1664 the Arsenal Authority had had to cope with a decrease in foreign orders (Gatti 1999, p.159-160). The crisis of the galleys’ military power was revealed. Moreover the role of the Genoese Republic on the international scene was reducing. It is possible to see the consequences after the French shelling in 1684: a large part of the navy was demobilized and several arcades remained empty (the Republican Navy in 1684 is made up of only six galleys. Giacchero 1979, p.569). On 12th August 1738 the Arsenal Authority was suppressed because of some defective hulls and lack of foreign orders (Genoa State Archive, Arc. Seg., prepositionum, p.1056, quoted in Repertorio, p.75). Second period: building the vaults and the large roof between in the second half of eighteenth century The progressive demobilizing of the navy and the new needs of the shipyards from the beginning of the eighteenth century (Gatti, 1999, p.35) require a large transformation of the Arsenal structures. Between 1738 and 1797 the seventeenth century pillar structure of the northern five arcades is completely hidden by a continuous structure, formed by thick walls dominated by barrel vaults. The space under the arcades is divided into two storeys and the wide transversal arches are demolished because their intrados level is lower than the new vaults. Only the first northern arcade is not divided in two, maintaining the function of shipyard and slipway for the more important galleys, called Captain Galley (“Galea Capitana”). A new storey is added over all five northern arcades and the sequence of five roofs, covering each arcade, is replaced by a new large saddle roof, orientated east-west, with a wooden structure and slate covering (fig.2). At the fall of the Genoese Republic in 1797 the “Arcate Nuove” maintained the function of warehouses and workshops. Nothing happened during the age of the Ligurian Republic until in September 1797 the “Darsena” was given to the War Authority (Municipio 1910, p.44).

Figure 2. 1810. The “Arcate Nuove” in the survey published in: Mémoire sur les divers Ètablissements de la Marine Impériale au Port de Gênes avec un préambule historique sur l'origine et la fondation de cette Ville et

de son Port.

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With the annexation to the Napoleonic Empire several plans were made to reorganize the harbour. Among them one involves the Arsenal. A detailed description of existing and foreseen functions is to be found in the surveys of an anonymous French engineer, made between 1807 and 1810 and published 30th March 1810 under the title of Mémoire sur les divers Ètablissements de la Marine Impériale au Port de Gênes avec un préambule historique sur l'origine et la fondation de cette Ville et de son Port.

The third western wet basin has a surface of 5 950 square metres, but the sounding-depth is almost completely full of rubbish. It was there that the galleys and other ships were built, under several arcades built for that purpose: it was possible to build five of them at the same time. The galleys that were built under the northern arcades [the old ones] were launched under the opening expressly opened under the large arch or bridge. The ones built under the western arcade [the “Arcate Nuove”] were launched in the second basin; under these same arcades it was possible to build several schooners at the same time.

Memoire 1810, p.30-31 The proposals of the Napoleonic engineer were realized before 1815: the third western wet basin was filled; a new slipway was made to beach ships on the site of the Captain Galley arcade (see also Genio Civile 1892, p.9); the third storey of the “Arcate Nuove”, which had not been used up until then, was converted into a warehouse and was connected to the lower storey with a wooden stair; wide windows open on the northern and southern walls to give light to this level (fig. 3).

Figure 3. 1885. The “Arcate Nuove” covered by the large saddle roof, whit the wide windows opened on the northern wall before 1815 and, in foreground, the sequence of the roofs of the old shipyards.

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Third period: demolishing the Captain Galley arcade and building the buttresses and the flat roof in 1890 In 1815 with the Restoration the Arsenal was placed under the control of the Sardinian Navy. The workshops were renewed and enlarged. In 1851 Cavour proposed moving the Arsenal to La Spezia, as part of a large plan that included the transfer of all the Darsena area to the Municipality and its transformation into commercial docks. This one, like other projects of the Civil Engineers, was not carried out (Municipio 1910, p.59). In 1870 the Sardinian Government finally transfered the Darsena area to the Municipality to finance the La Spezia Arsenal (Municipio 1910, p.62). In 1889 a general plan was approved to settle the area (Approved by the Municipal Council eighteenth and 21st February 1889 for more than six million Lire) (fig.4). The plan was part of the settlement of the harbour connected with the Duke of Galliera’s legacy. The works on the Darsena began in 1890 and were modified by the Council several times between 1891 and 1894 (Municipio 1910, p.68). Metelino, Caffa, Tabarca and Cembalo Districts were finished before 1895, the Scio District was finished before 1898. The “Arcate Nuove”, from 1897 called Galata District, remained almost the same, with its structure made of four large galleries, more than fifty metres long and nine metres wide, enclosed by thick walls and stone vaults repeated over four storeys. Instead the Captain Galley arcade was demolished and replaced by a sequence of powerful buttresses. The plan was modified by the insertion of two large granite stairways and a central corridor. The large slate saddle roof was replaced by a flat roof, also used as storage space (Municipio 1910, p.72), and the last storey was covered by iron beams with bricks vaults. Many iron chains were inserted to increase the capacity of each single storey that reaches 2 000 Kg per square metre for the first floor, 1 600 Kg for the second, 1 200 Kg for the third and 1 000 Kg for the terrace (Municipio 1910, p.87). The Galata District was equipped with three electric elevators in 1910 (Municipio 1910, p. 89). The Galata was used as bonded warehouses for the Municipality whose coat-of-arms was painted on the facade, under the new small clock tower. Fourth period: building concrete terraces in 1923 By 1910 the necessity for more storage space led to the idea of replacing the metallic sheds towards the Darsena with others “in reinforced concrete and flat roof doubling the potential and making it possible to move the goods from the ships directly onto the terrace of the new sheds with cranes and from here to the bonded warehouses” (Municipio 1910, p.105). In 1923 the Garbarino and Sciaccaluga builders cast a new reinforced concrete front, made up of terraces and two elevator towers that created the image of the Galata from then to the end of the twentieth century (Nove 1987, p. 72).

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Figure 4. 1896. The general plan approved in 1889 to settle the Darsena area THE ARCHAEOLOGY IN THE YARD PHASE: THE UNDERSTANDING OF THE STRUCTURES In the period between 2002 and 2004, when the restoration yard was active, new archaeological notes and findings were collected during a study campaign on this arsenal. The transversal arches These large round arches (“a tutto sesto”) are about 75 cm thick and have a 9.20-metre span. They are primarily made of bricks, with a weaving of six-brick thickness: every two or three brick rows there is a stone row. The bricks are mostly “ferrioli”, i.e. hard baked, resistant bricks, usually applied to the more stressed structures (arches, vaults, pillars etc.). It is good quality material, with no usage of broken or splintered or re-utilized bricks. Near the chains there are carefully installed, stone elements. The connecting mortar is of very good quality: the binder consists of pure aerial mortar, the sand comes from the beach of Sampierdarena (a few miles away), the “clasti” / matrix ratio is low (low percentage of sand granules compared to the quantity of binder), the “clasti” are precisely selected for similar dimensions. This mortar is very tenacious, evidently superior to all other samples taken from the transformation units (e.g. vaults, partitions, etc.). The bonding is precise. The bricks are primarily positioned “head on” (small side in sight), while “fascia” positioning (long side in sight) is used in the lower part of the arch. The surface shows a light

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whitewashing; it is hard to say whether this is an original treatment or whether it is due to more recent transformations. The structural materials don't show particular degradation: no degraded joints, no broken up mortar, and the bricks are perfectly conserved. A possible explanation for this is that the structure remained buried inside the masonry for a long time and therefore it was not exposed to atmospheric agents. From the structural point of view, some evident cracks appear in the region between the chain and the middle part of the arch. The chains of the transversal arches, set to the height of the backs (“reni”) of the arch, are in forged iron. They have a round section, 5 cm in diameter. The stratigraphical analysis shows that they were already put in place in the original construction; stones are inserted above or below the chain itself. The stratigraphical analysis of the arches in relationship to the adjoining masonries is complex. The longitudinal masonry (e.g. stratigraphic units u.s. 108, 109 and 182) is certainly later, because they lean against the arches. The pluggings (e.g. u.s. 116, 137) are obviously more recent. The stratigraphical relation between the arch extrados and the adjoining masonry (e.g. u.s. 115 and 113) is more difficult to define. Very little of this interface is visible now; in some cases it shows a perfect adherence between the masonry and the underlying arch (e.g. u.s. 115 and the arch u.s. 114), suggesting a contemporaneity of the two structures; elsewhere (e.g. u.s. 113 with the arch u.s. 110) there are more evident signs of break-up between the different stratigraphical unities. However, a contemporaneity is hypothesised between the arch and the masonry over it; this implies that a crowning masonry above the transversal arches supported the roof from the first phase of the arsenal. The longitudinal arches Longitudinal round arches (“a tutto sesto”), with the same binding patterns as the transversal ones, connect the arcades in the east / west direction with a span of 4.50 m in between. The keystone (“chiave”) portion is primarily in bricks, from the spring to the backs there is a prevalence of marly limestone splinters. The spring quota is the same as the transversal arches. Material quality is the same as in the transversal arches: “ferrioli” bricks, mortar with very good resistance, blocks and splinters of marly limestone. Only the front part of the arch is visible, it has a thickness of three bricks; the remaining part is still inserted in the masonry. During the restoration, in some sample areas, the surface of these hidden parts were unveiled, but they didn’t reveal the whole masonry section; hence the real thickness of those arches remains unknown. In a niche on the first floor a chain is still visible, located at the back of the longitudinal arch and a part of the arch itself. The arch thickness may be evaluated as about 40 cm. The longitudinal arches, therefore, would be a little thinner than the whole pillar. The arches are filled in with more recent walls; interlocking is rare. The analysis of the walls, that stand over the extrados of the arches, is quite complex from the

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stratigraphical point of view. There seems to be some continuity between the extrados of the arch and the masonry above it; such an interruption is clearly related to different materials (bricks for the arch, stone and brick masonry above); in both parts the mortar was made with sand from Sampierdarena beach, but this aspect cannot help in dating them (this sand from Sampierdarena had been used in Genoa from the beginning of the seventeenth century up to the beginning of the nineteenth century, i.e. the whole period when those transformations occurred). If the masonry above the arches were same age of the arches themselves, a coherence should be recognised between arch and masonry and in their thickness, while both of them should be slightly thicker than the filling below (this difference in thickness should be compensated for by plaster). The masonry, where it was not subject to following transformations, shows an alignment and a great continuity with the arch next to the extrados in the area between the spring and the backs. In current visibility conditions it is not possible to know whether this masonry continues up to the arch keystone (“chiave”). In conclusion, the longitudinal arches are made to join together by pieces of wall; currently there is no archaeological proof to demonstrate that these walls were a basis for the roof above. An answer to this question would help to understand what the first roof of the arsenal was. The longitudinal chains are in forged iron; they have the same 5 cm diameter as the transversal ones, they are in the same position at the level of the backs. A few of them were cut to open passage-ways, while the others were inserted in the masonry and still come to the surface in the open niches (south and north walls of first floor stores). The pillars in marly limestone The pillars are about 8 metres high, with dimensions of 140-150 cm in the east-west direction and 75 cm in the north-south direction; terminal pillars are longer, between 180 and 210 cm. They were built of marly limestone square blocks and interconnected to each other with great care. There are up to three ashlars (90 x 50 cm) on each row, alternated with other smaller rows. Those blocks are very precise in height. The weaving has staggered joints; at regular intervals there is a single block as wide as the whole pillar thickness. Where longitudinal and transversal arches connect to each other, the structure of the pillars changes: here splinters of marly limestone and some blocks of the same material are used. The ashlars were shaped “a punta grossa”, with a rough trimming near the edges. The limestone shows good quality, in most of the blocks it is free from calcite hair or other irregularities. Horizontal joints are regular, between 1 cm and 1.5 cm thick. Vertical joints are slightly less precise, about 1 cm thick. The bonding technique is “alla moderna”, stone blocks are sparingly interleaved with splinters of stone and bricks pieces.

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Both from the structural and from the materials points of view there is no apparent degradation. At foundation level the pillars might have a slightly larger section (as was drawn from data collected in a 2002 excavation campaign) (fig. 5).

Figure 5. Pillars and arches visible on the south wall of the northern arcade MODELLING THE STRUCTURAL VARIATIONS OF MASONRY CONSTRUCTIONS The structural behaviour of a historical masonry construction depends not only on the actual state of the structure (geometry, construction details, mechanical properties of materials, loads), but also on its history. In fact, the succession of building works, on the one hand, and the occurrence of both natural and anthropical events, on the other, bring about a progressive modification of the structure over time. In particular, earthquakes or winds may produce damage (cracks, partial collapses); structural repairs or structural variations associated with use (construction of new elements, partial demolitions, permanent load variations) may cause further damage and, in general, changes in the global stress states. For these reasons, the identification of the actual structural behaviour of a historical construction should be based on the description of its entire life, from the beginnings (construction), through its successive damage and variations, until the present.

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The knowledge of structural history is, indeed, a fundamental tool for structural analyses. Thus close cooperation between historians/archaeologists and structural engineers is essential in the conservation of cultural heritage. The description of structural changes of masonry constructions requires adequate methodological choices and specific numerical tools. In general, the following three observations should be considered:

• the effect of structural changes should be considered at the scale of the building; in fact, even if localised, such changes may influence the entire structure or a large part of it; in any case, it is difficult to identify the region of the structure where their influence is meaningful;

• the chronological variation of the stress field and the presence of damage processes requires the performing of evolutive analyses, able to describe the non-linear behaviour of a step-by-step changing structure; the description of the structural changes requires the capability to model structures changing in terms of geometry and loads.

Finite element modelling has been recognised as a suitable tool for chronological structural analyses. On the one hand, it allows a full-scale modelling approach; on the other, it allows one to perform evolutive analyses considering a finite number of progressively different geometrical configurations of the structure. Chronological analysis of the structure In this paper, a finite-element model of the Arsenal of Genoa is presented. The structure has been modelled in order to consider the entire set of structural variations identified from the historical analysis. The masonry structure has been modelled by means of 4-node shell elements with transverse shear strain capability. Such elements have a number of integration points through the thickness. This feature enables one to describe the behaviour of walls by mean of series of layers subjected to in-plane mechanisms; thus, a description of their out-of-plane behaviour can be obtained (Calderini and Lagomarsino 2004). In order to describe the geometrical changes of structure, the birth and death option has been employed. Such an option, furnished by the finite element code used (ANSYS 8.0), allows one to activate/deactivate sets of elements and nodes. A deactivated element remains in the model but contributes a near-zero stiffness value to the overall matrix and contributes nothing to the overall mass matrix. Given a set of activated elements, an evolutive analysis is performed; the stress/strain field obtained (and, in the case of non-linear constitutive loads, the entire set of state variables) is saved. In the following analysis, it can be reloaded, considering a new set of activated elements.

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The constitutive model employed in analyses can be either linear elastic or non-linear. In this paper, a non-linear constitutive model has been adopted (Calderini and Lagomarsino 2005). The constitutive equations, in plane stress, are based on the homogenisation theory and consider the non-linear stress-strain relationship in terms of mean stress and mean strain. Different in-plane damage mechanisms, involving both mortar and blocks, are considered. The damage process is governed by evolution laws based on an energetic approach derived from Fracture Mechanics and on a non-associated Coulomb friction law. Based on a micromechanical approach, the model is capable of describing the effect of the interlocking between blocks (related to the masonry pattern) on the behaviour of the material. Such a feature appears to be useful in the study of structural variations because, frequently, the introduction of new structural elements posed ancient builders the problem of connections between pre-existing and new masonries. Wood and iron elements have been modelled by means of elastic beams. The geometry of the model is based on an accurate geometrical survey, avoiding any simplification or regularisation. As a consequence, the structures are modelled considering all their irregularities, deriving both from building procedures and from deformations. On the basis of the information provided in the paragraph “Historiography notes” three main building periods have been considered (see table 1):

• Period 1 – The original construction. The structure is made up of a set of longitudinal and transversal arches. Iron tie-rods connect the transversal arches. The arches are regularised on top by mean of masonry walls, supporting the wooden structures of the roof. The geometry of the transversal arches, not longer existing, have been identified on the basis of archaeological studies, such as illustrated in the paragraph “Transversal arches”. The inclination of the masonry tympani supporting the root has been supposed on the basis of the observation of similar contemporary structures. Masonry walls closing the openings between the arches have not been modelled, because it is documented that such walls were temporary non structural elements.

Table 1. The finite element model, with the sequence of the building phases.

Original construction – Phase 1 Phase 2 - 1

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Phase 2 – 2 Phase 2 – 3

Phase 2 – 4 Phase 2 – 5

Phase 3 – 1 Phase 3 – 2

• Period 2 - Structural variations of late large saddle roof (phase 2.5). • Period 3 – Structural variations of late counterbalance the thrusts deriving from the

adjacent vaults, a set of buttresses is built (phase 3.2). Besides the three main chronological phases described above, asymmetrical parts (fig.6-a and fig.6-b).

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a) b)

Figure 6. Particular of the mesh, with the introduction of an opening in the masonry walls. The fundamental mechanical parameters adopted in the model are summarised in table 2, where �t is the tensile strength and �c is the compressive strength of masonry, and where � = b/h (b and h being the standard length and height of blocks, respectively) describes the interlocking. Unfortunately, experimental tests on the constituent materials have not been performed.

Table 2. Mechanical parameters adopted in the model.

Material �

(Kg/m3)

E

(MPa)

� �t

(MPa)

�c

(MPa)

�

Masonry made up of large stone blocks, constituting the original pillars of the structure.

2400 3500 0.2 0.2 8.0 5.0

Brick masonry constituting the original longitudinal and transversal arches.

1800 2000 0.2 0.4 5.0 3.0

Stone masonry constituting vaults. 2000 2000 0.2 0.2 5.0 3.0

Rubbed stone masonry employed in the structural variations of the eighteenth century (phase 2).

1800 1800 0.2 0.1 4.0 2.0

Rubbed stone masonry employed in the structural variations of the nineteenth century (phase 3).

1600 1800 0.2 0.1 4.0 2.0

The only known parameter is the elastic modulus of the masonry employed in the eighteenth century (E = 1900 MPa). For this reason, it is worth noting that the employed parameters are purely indicative. It should be considered that the objective of the study is not a description of the local stress states of the structure, but a description of its global behaviour. For wood and iron structures

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the following conventional parameters have been adopted: for wood � = 700 Kg/m3 and E = 11000 MPa, for iron �= 7500 Kg/m3 and E= 190000 Mpa. Results and conclusions The numerical analyses have been performed by considering only gravity loads. Non-linear analyses highlighted that the masonry structure is not affected by any consistent damage. Such an observation is confirmed by the accurate damage survey of the building, carried out in 2003. In order to show the necessity of considering the succession of the building phases, two different typologies of analyses are presented. In one case (Type A), the three main building phases are considered and the analysis is performed in three successive steps. In the other (Type B), the building is considered in its present configuration, without considering its chronological variations; the analysis is performed in one step.

Phase 1

Phase 2

Phase 3

-1.5 -1.0 -0.5 -0.1 +0.1 0.0 MPa

Figure 7. Stresses normal to mortar bed joints in the middle longitudinal wall (Type A analysis).

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-1.5 -1.0 -0.5 -0.1 +0.1 0.0 MPa

Figure 8. Stresses normal to mortar bed joints in the middle longitudinal wall (Type B analysis).

Figure 7, concerning Type A, shows the stress pattern in the local reference system of the masonry. The stress component normal to the masonry mortar bed joints is represented. The middle longitudinal wall of the building is considered. It can be observed that in the first phase, the pillars are subjected to low compressive stresses (-1.0 ÷ -0.5 MPa); longitudinal arches are all subjected to compressive stresses, except for the crowns of the two lateral ones devoid of symmetrical thrusts. In phase 2, its the increase of the compressive stresses on pillars can be observed (-1.5 ÷ -1.0 Mpa). Longitudinal arches are all compressed. In phase 3, the stress field doesn’t change significantly; thus, loads associated to the old saddle roof are comparable to the ones of the new iron-masonry roof. Moreover, it can be noticed that the opening introduced slightly modifies the stress field in the central arch.

Typ A analysis Type B analysis

Figure 9. Stress state in the buttresses obtained with the two considered types of analysis.

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Figure 8 shows the stress pattern of the same wall, obtained with a Type B analysis. By comparing such a stress pattern with the one represented in figure 7, phase 3, the difference between the two types of analyses can be illustrated. In the multi-step analysis (Type A), the compressive stresses are concentrated in the original pillars and longitudinal arches. The single-step analysis (Type B) shows a more homogeneous stress pattern; the slight stress concentration on the pillars is associated with their higher mechanical stiffness. The buttresses built onto the northern façade in the third phase (replacing the original Captain Gallery arcade) are now considered. In figure 9, stresses normal to the mortar bed joints are shown. The results of the two types of analysis are represented. Also in this case, the difference between the two stress fields is evident. In Type A (top) the compressive stresses in the buttresses are low and uniformly distributed. They derive mainly from the dead weight of the elements. The slight bending effect (higher compressions on the external corners of the butresses) derives mainly from the deformation of the internal vaults associated with the increasing of loads in phase 3. In Type B (bottom) an evident bending behaviour of the buttresses can be observed; in fact, by performing a single-step analysis, the deformations of vaults are integrally transferred to the buttresses.

The study of Arsenal of Genoa highlights the importance of technological surveys and historical notes in the performing of structural analyses. The presence of the pillars (unknown until 2003) modifies the behaviour of the masonry structure, as a consequence of its internal dishomogeneity. Moreover, the actual stress field has been influenced by structural and loads variations. Without in-depth knowledge of the structure (based on both historical and archaeological information) and specific analysis methods, the actual stress state of the structure could not have been described.

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