Structural Analysis of Historic Masonry and Technical Guideline Application: The Case of the Insula del Centenario [IX, 8] in Pompeii

[5] The latter indication, about the average values of the mechanical parameters, it seems subsequently surpassed in section 4. 2, which states that The starting values of the mechanical properties, which may apply to the confidence factor will be defined as a function of the level of knowledge the mechanical properties of materials, with ranges shown in Tables C8A. 2. 1 C8A. 2. 2 and the Appendix to chapter C8 Circular and operating with a similar methodology. About the confidence factor, designing at level LV3 for the supposed new roofing structure of the main atrium, to maintain the value of Fc = 1. 35 and the mechanical characteristics described above which have been used, in various combinations when processed with the structural software for modeling of the walls of the main hall in the state as built and designed. The structural model Laser-scanning technology for a fundamental survey of the geometry of the main atrium and the neighboring interiors to provide a correct, three-dimensional reconstruction of the elevations.

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[18] We divided the structural model as follows: - model of the main atrium in its current condition, with an assessment of the tensile stress induced by its own weight and by an earthquake in both directions X and Y perpendicular to each other (with the X axis parallel to via di Nola); - model of the roofing structure: corrugated sheet roofing supported by tubular steel profiles, with uprights resting on perimeter, reinforced concrete stringcourses. The use of CorTen steel provides good durability and good matching of the colors and high mechanical performance. - model of the designed main atrium assessment of the tensile state from its own weight and from an earthquake in the aforementioned directions. Numerous sections were made on the point cloud data of the laser scanner survey to model the current geometry, and we reconstructed a three-dimensional model of the atrium of the Insula of the Centenary. We also made adequate models of previous restoration and salvage works, such as wooden or cement architraves and clay-cement roofing, as in the two oecii, strengthened during the project. In particular, we suggest the seriously damaged roof of the white oecus, which is currently under-pinned like so many others, be replaced with a mixture of wooden beams and planks and a concrete slab anchored to an existing, perimeter stringcourse (which will be replaced). To model the structure of the walls we used shell finite elements, automatically generated by the software. The hypothetical roofing, modeled very precisely within the point cloud data, will rest, where possible, on new stringcourses on top of the perimeter wall of the main atrium, after a reconstruction or replacement of a stretch of sacrificial masonry at obviously variable heights. The model employs shells finite element for masonry panels. The proposed roofing structure will be setting on a perimetral concrete curb (rebars in stainless steel) that will be realized on a new portion of masonry needed to regularize the higher part of the irregular masonry panels. Cloud of points will be fundamental in designing this last part, see Figure 1. From the analyses made on the model, it appears obvious how the tensile state, due only to its own weight, is not currently at a critical level, and how the increase in tensile stress, due to the new roofing, has no negative effect on the estimated torque capacity of the masonry of the main atrium. The checks carried out clearly show how the majority of the wall bays do not comply with the requisites set by the NTC.

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[4] .

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[5] for shear stress and combined compressive and bending stress tests. They also show the benefit of stiffening by the stringcourses, which redistribute tensile stress more uniformly and diminish the critical state of the perimeter walls of the atrium and the roofing structure. A further improvement is provided by the injection of binding mixtures. In addition, the horizontal action forces in the white oecus are more equally divided and behave more like a box action since the floor has been replaced. The proposed roofing rests on the perimeter walls of the atrium and becomes one with the existing structure. Even though, on the one hand, it leads to an increase in stresses, on the other, it enables a better distribution of the horizontal action forces, as a result of the perimeter stringcourses it rests on. Finally, even though we used extremely precautionary resistances for the masonry, we will have to closely ascertain the condition of each individual wall panel, with probable local reinforcement in addition to what is already envisaged for the external facings (including work to re-adhere the plaster) and for the inner nucleus. Fig. 1 – Principal structure of the proposed roofing structure illustrated over the laser scanner survey points cloud. Analysis of the stress state The results related to the actual situation and those obtained from the state of the project, with the proposed new roofing structure were compared. The stress states examined are related to: - FZZ, load per unit length, is the vertical load and the positive (concordant with the positive direction of the Z axis directed upward) indicates traction, the negative sign indicates compression; - MZZ, moment per unit length, is the bending of the wall panel to a load placed on the horizontal top edge and perpendicular to the wall panel. The compressive stresses in the state of the art, due to the own weight of the wall structures are congruent with simple calculation and vary from a few daN/cm2 up to peaks of about 120 daN/cm2. After the insertion of the new roofing structure we notice a little increase in compression, particularly in the areas of support pillars supporting the roof, and the tractions at the lintels below. The state of stress remains within a range acceptable for the masonry strength, varying from about 30 daN/cm2 to about 130 daN/cm2, with the values thus far from the limit fk prescribed by the standard. Moreover, after the intervention an increase of Mzz due to an increment of the static forces that are proportional to the seismic inertia forces induced by the action. Note how the presence of the roof leads to an increase in stress in the masonry Mzz arranged in north-south direction, particularly high in the walls white oecus (where it is planned to replace the brick- concrete slab with a combined cover in wood and concrete as described above). It was finally checked the verification of the masonry panels in accordance with the Italian Standards, in particular in the case of diagonal cracking, with only the effect of the new roofing structure and strengthening curbs plus the consolidation of the masonry with injections of mixtures ligands (see Figures 2 and 3, where red panels indicates the masonry panels where crisis occurs). Fig. 2 – Verification of masonry panel in the actual state. Fig. 3 – Verification in the state of project after the insertion of the new roofing structure Summary Considering the performance decay of the Insula materials, plaster and floors, (and also their decorations) the priority is the protection from run-off of rainwater, then the design of a new roofing structure is the key intervention in order to preserve the entire structure or at least the main entrance. The coverage was assumed acting on the perimeter walls of the atrium. Vertical loads were analyzed using the model adopted by checking the estimated strength capacity of the walls: the state of stress due to its own weight does not appear to be critical. The load increase due to the presence of the new roofing structure is negligible. This result confirms the expectations and allows considering the new coverage acceptable under self-weight. However, the computations performed highlight that, in the actual state using self-weight and seismic conditions, almost all of the masonry panels does not meet the verifications prescribed by the Italian Standards.

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[4] In the design phase, under static conditions, and especially under the seismic action, the increase in stress state due to the presence of the cover is substantial but, on the other hand, analyzing the results obtained from masonry walls, it is clear that the increase of stress is in large part, captured by the presence of the curbs, that spread tensions in the critical locations such as the walls of the atrium. Finally, a further improvement is provided by injections of fluid mortars. A considerable improvement is obtained near the white oecus, where the replacement of the slab floor allows to obtain a better distribution of horizontal actions due to the activation of the box-like behavior. The proposed roofing structure even if leads to an increase of stress, on the other hand, increase the performance of the whole structure by means of external curbs and local intervention on masonry panels at the surface level (even if concerns the plasters) that allows a better distribution of the horizontal actions. Given the needs of achieving an efficient new coverage of the Pompeii structures, consider the recent and unfortunately ongoing traumatic events (the collapse of portions of masonry panels), the construction of the illustrated roofing structure results an acceptable solution. The new roof will drastically slow the deterioration process that walls and decorations are experiencing mainly due by atmospheric agents, but also will strength the structure allowing a better distribution of the horizontal actions on the masonry, improving the structural response to seismic action. Acknowledgements The computing facilities were provided by the Laboratory of Computational Mechanics (LAMC), DICAM, University of Bologna. SismiCad11 software has been provided for research usage by Concrete Srl of Padua. Bibliography.

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[1] A. Custodi, L. Sciortino, G. Castellazzi, L. Govoni, M. Rivola, Rilievo, modellazione e analisi strutturale delle murature dell'Insula del Centenario a Pompei, in atti della giornata di studio: Rilievo, modellazione e restauro di murature antiche. Il caso dell'Insula del Centenario a Pompei, a cura di A. Custodi e L. Sciortino, Bologna, Facoltà di Ingegneria, 16 settembre 2005. Terni, Edizioni Thyrus, 37-57.

DOI: 10.4995/fortmed2020.2020.11343

Google Scholar

[2] A. Custodi, L. Sciortino, Survey, analysis and structural modelling of ancient masonry building: the case of the Insula del Centenario [ IX, 8]" at Pompeii, in atti del "Structural Analysis of Historical Construction (Set of 3 volumes): Possibilities of numerical and experimental techniques. V° International Conference on Structural Analysis of Historical Constructions, a cura di P.B. Lourenço, P. Roca, C. Modena, S. Agrawal (EDS), New Delhi, India, 6, 7 e 8 novembre 2006. New Delhi, Macmillan India Ltd., vol. 3, 1851 – 1858.

DOI: 10.1201/9781482288377

Google Scholar

[3] A. Custodi, L. Sciortino, Dal rilievo all'analisi strutturale. Consolidamento e restauro nell'Insula del Centenario (IX, 8) a Pompei, in atti del Convegno Internazionale Vesuviana. Archeologie a confronto, a cura di A. Coralini, Bologna, 14, 15 e 16 gennaio 2008. Bologna, Ante Quem soc. coop., 623 – 635.

DOI: 10.3764/ajaonline1153.pavel

Google Scholar

[4] Nuove Norme Tecniche per le Costruzioni, Decreto Ministero Infrastrutture del 14 gennaio 2008, pubblicato nel suppl. ord. n. 30 alla G.U. n° 29 del 4 febbraio (2008).

Google Scholar

[5] Istruzioni per l'applicazione delle Nuove norme tecniche per le costruzioni, di cui al DM 14/1/2008, Circolare 2/2/2009 n° 617 C.S. LL. PP., pubblicata nel suppl. ord. n. 27 alla G.U. n. 47 del 26/02/(2009).

Google Scholar

[6] Valutazione e riduzione del rischio sismico del patrimonio culturale con riferimento alle Norme tecniche per le costruzioni di cui al D.M. 14/01/2008, Direttiva del Presidente del Consiglio dei Ministri 9 febbraio 2011, pubblicata nel suppl. ord. n. 54 alla G.U. n. 47 del 26/02/(2011).

DOI: 10.3280/riv2018-071007

Google Scholar

[7] G. Castellazzi et al., A coupled multiphase model for hygrothermal analysis of masonry structures and prediction of stress induced by salt crystallization, Construction and Building Materials 41, 2013, 717-731.

DOI: 10.1016/j.conbuildmat.2012.12.045

Google Scholar

[8] C. Colla et al., Damp and salt rising in damaged masonry structures: Numerical modelling and NDT monitoring, RILEM Bookseries 6, 2012, 1151-1156.

DOI: 10.1007/978-94-007-0723-8_160

Google Scholar

[9] G. Castellazzi et al., Modelling of non-isothermal salt transport and crystallization in historic masonry, Proceedings MuRiCo4, Ravenna, 9-11 settembre (2014).

Google Scholar

[10] MBAC – Istituto Centrale per il Restauro, Le coperture delle aree archeologiche – Museo aperto, a cura di M. C. Laurenti, Gangemi Editore, Roma, (2006).

Google Scholar

[11] S. Ranellucci, Coperture archeologiche – Allestimenti protettivi sui siti archeologici, DEI – Tipografia del Genio Civile, Roma, (2009).

Google Scholar

[12] J. P. Adam, L'arte di costruire presso i Romani – Materiali e Tecniche, Longanesi & C, Milano, (1988).

Google Scholar

[13] S. Santoro (a c. ) - Pompei. Insula del Centenario (IX, 8) – I – Indagini diagnostiche, geofisiche e analisi archeometriche, Ante Quem, Bologna, 2007, p.317.

Google Scholar

[14] P. B. Lourenco – A matrix formulation for the elastoplastic homogenisation of layered materials – Mechanics of cohesive frictional materials, vol. 1 (1996) 273-294.

DOI: 10.1002/(sici)1099-1484(199607)1:3<273::aid-cfm14>3.0.co;2-t

Google Scholar

[15] H.O. Lamprecht, Opus caementicium: Bautechnik der Römer. Düsseldorf: Beton-Verlag, (1984).

Google Scholar

[16] A. Samuelli Ferretti, Rapporto sulle prove di laboratorio ed in situ effettuate sui componenti, in Materiali da costruzione e tecnologie costruttive del patrimonio archeologico e monumentale romano con particolare riferimento al tipo laziale ed all'opus latericium, Roma, (1996).

Google Scholar

[17] C. Giavarini et al.,. Mechanical Characteristics of Roman Opus Caementicium, in S. Kourkoulis (ed. ), Fracture and Failure of Natural Building Stones. Dordrecht: Springer, (2006).

Google Scholar

[18] A. Custodi, L. Sciortino, Il Rilievo Laser Scanning nell'insula del Centenario [IX, 8] a Pompei, in atti del V° Congresso Nazionale di Archeometria Scienza e Beni Culturali, a cura di A. Gueli, Siracusa, 26-29 febbraio 2008. Siracusa, Morrone Editore, 379-387.

Google Scholar

[19] G. Castellazzi, C. Gentilini, and L. Nobile, Seismic Vulnerability Assessment of a Historical Church: Limit Analysis and Nonlinear Finite Element Analysis Advances in Civil Engineering Volume 2013, Article ID 517454, 12 pages.

DOI: 10.1155/2013/517454

Google Scholar

[20] C. Gentilini, E. Franzoni, S. Bandini and L. Nobile, Effect of salt crystallisation on the shear behaviour of masonry walls: An experimental study, Construction and Building Materials, (37) 181-189 (2012).

DOI: 10.1016/j.conbuildmat.2012.07.086

Google Scholar