SCIENZA E BENI CULTURALI XXXI. 2015 METALLI IN ARCHITETTURA Conoscenza, Conservazione, Innovazione Atti del convegno di studi Bressanone 30 giugno – 3 luglio 2015 Edizioni Arcadia Ricerche ISBN 978-88-95409-19-1 Questo volume presenta gli atti del Convegno Scienza e Beni Culturali "Metalli in architettura. Conoscenza, Conservazione, Innovazione " svoltosi dal 30 giugno al 3 luglio 2015 presso la sede estiva Università studi di Padova a Bressanone. Tutti i diritti riservati 2015, EDIZIONE ARCADIA RICERCHE Srl Parco Scientifico Tecnologico di Venezia Via delle Industrie 25/11 – Marghera Venezia Tel.:041-5093048 E-mail: arcadia@vegapark.ve.it www.arcadiaricerche.eu È vietata la riproduzione, anche parziale o ad uso interno o didattico, con qualsiasi mezzo, non autorizzata. Le riproduzioni a uso differente da quello personale potranno avvenire, per un numero di pagine non superiore al 15% del presente volume, solo a seguito di specifica autorizzazione rilasciata dall'editore. SCIENZA E BENI CULTURALI XXXI. 2015 METALLI IN ARCHITETTURA Conoscenza, Conservazione, Innovazione Atti del convegno di studi Bressanone 30 giugno – 3 luglio 2015 a cura di Guido Biscontin e Guido Driussi Organizzazione: Associazione Scienza e Beni Culturali; Università degli Studi di Padova, Dipartimento di Scienze Chimiche; Università Ca’ Foscari di Venezia, Dipartimento di Scienze Ambientali, Informatica e Statistica; Università degli Studi di Genova, Dipartimento di Scienze per l'Architettura e Scuola di Specializzazione in Beni Architettonici e del Paesaggio; Politecnico di Milano, Dipartimento di Architettura, Ingegneria delle Costruzioni e Ambiente Costruito. Enti Patrocinatori: MiBACT Ministero dei beni e delle attività culturali e del turismo; Consiglio Nazionale delle Ricerche; Società Chimica Italiana – divisione di Chimica dell’Ambiente e i Beni Culturali, Provincia Autonoma di Bolzano – Alto Adige; Associazione degli Amici Università di Padova Con la collaborazione di: Provincia Autonoma di Bolzano - Alto Adige, Amministrazione Comunale di Bressanone, Azienda di Cura e Soggiorno di Bressanone, Arcadia Ricerche S.r.l., Associazione degli Amici Università di Padova, Colorificio San Marco S.p.A, Domodry S.r.l, Secco Sistemi S.p.A. ORGANIZING COMMITTEE Andrea Alberti Salvatore Alberti Lorenzo Appolonia Paolo Bensi Renzo Bertoncello Guido Biscontin Antonietta Boninu Roberto Bugini Emanuela Carpani Renata Codello Stefano della Torre Carla Di Francesco Guido Driussi Fabio Fratini Prisca Giovannini Giuseppe Longega Alessandra Marino Ruggero Martines Antonia Moropoulou Stefano Musso Roberto Parenti Anna Patera Serena Pesenti Daniela Pinna Antonio Rava Antonia Pasqua Recchia Maria Pietrogiovanna Lucia Saccani Francesco Trovò Elisabetta Zendri SCIENTIFIC COMMITTEE Andrea Alberti Salvatore Alberti Lorenzo Appolonia Amedeo Bellini Renzo Bertoncello Guido Biscontin Caterina Bon Valsassina Antonietta Boninu Roberto Bugini Agostino Bureca Renata Codello Paola Raffaella David José Delgado Rodrigues Stefano Della Torre Carla Di Francesco Guido Driussi Fabio Fratini Prisca Giovannini Stefano Gizzi Giuseppe Longega Alessandra Marino Ruggero Martines Antonia Moropoulou Stefano Musso Giorgio Palandri Roberto Parenti Anna Patera Serena Pesenti Daniela Pinna Antonia Pasqua Recchia Maria Pietrogiovanna Antonio Rava Luca Rinaldi Lucia Saccani Antonio Sgamellotti Francesco Trovò Elisabetta Zendri INDICE E.Vio pag. Il rivestimento plumbeo delle cupole della Basilica di San Marco in Venezia. 1 D. Pittaluga, A. Canziani, E. Giordano, D. Patelli, G. Stagno Catene e muratura: un binomio ricorrente nella tradizione Seicentesca genovese. Il caso del quartiere Galata nel porto di Genova. 9 M. Bellanova, A. Baggioli, B. Rivolta, R. Felicetti, A. Cornaggia Metallurgical and mechanical characterization of the historical tie-rod of Duomo di Milano. 23 C. Gardella, D. Pittaluga, N. Campana, E. Vajda Miniere e cave della Liguria di Levante, conoscenza antica degli antichi giacimenti e valorizzazione culturale 35 E. Zamperini Per una storia degli elementi metallici nella costruzione e nel consolidamento delle capriate lignee. 45 R. Vecchiattini, C. Calderini, P. Piccardo Catene metalliche negli edifici storici in muratura. Primi risultati di una ricerca in corso. 63 F. Amendolagine, L. Petriccione, R. Portolan La cupola della rotonda del Palladio, problematiche di restauro degli elementi ferrosi a supporto statico delle statue a sbalzo e/o delle presenze ferrose strutturali all’interno delle masse plastiche. 75 B. Vinardi La conservazione dell’identità di manufatti in ferro del XIX Secolo in due esempi in Torino. 85 A. Alberti, A.M. Basso Bert, A. Moretti, M. Nascig L’uso del metallo nel restauro e miglioramento sismico della Basilica di S. Andrea a Mantova. 97 E. Bernardi, S. Raffo, C. Chiavari, C. Martini, L. Nobili, M. C. Bignozzi, I. Vassura Cor-ten in marine atmosphere: the influence of the environment on corrosion. pag. 113 G. Favaretto, C. Mariotti, A. Ugolini, A. Zampini Quando la materia inganna il tempo. Il Cor-ten nel progetto sulla preesistenza. M.G. Ercolino Forme antiche, nuovi materiali: reintegrare con l’acciaio Corten. 123 R. Picone, A. Spinosa, L. Veronese Il restauro delle leghe metalliche nell'era della loro riproducibilità. La cassa armonica nella villa Reale di Napoli. 149 M. Biasio, L. Comino M. Pedroni Il mausoleo Fracchia a Bargone. Conoscenza e conservazione di un rivestimento in lastre di alluminio.” 161 L. Scappin La ‘collaborazione invisibile’ in strutture archeologiche: pietra e metallo negli interventi di consolidamento tra gli anni Cinquanta e Settanta del Novecento. 173 F. Gotta Materiali metallici e architettura antica: da presidio statico a struttura protettiva. 185 E. Sorbo I metalli nel progetto di restauro. Dal restauro archeologico ad un metodo archeologico per il restauro. 205 L. Del Core, V. Santoro Titanium fastening systems monuments stone integration. 219 in the 135 archaeological B.G. Marino Pierre armée e problemi conservativi. Sull’uso del ferro nell’architettura dell’Ottocento Francese tra ambizioni tecniche e questioni di ‘ordonnance’ .” 231 B. Salvadori, E. Cantisani, T. Bruni, A. Cagnini, M. Galeotti, pag. S. Porcinai, A. Santagostino Barbone, C. Bonzanigo Approccio multi-analitico per la caratterizzazione di patinature artistiche su opere in bronzo di epoca contemporanea. 241 M. Matteini Interventi di conservazione dei bronzi in ambiente urbano. Tecniche innovative di inibizione della corrosione. 253 R. Bertoncello, D. Quinziato, C. Bortolussi Deposizione di film a base di silice per la protezione di superfici bronzee. 265 E. Joseph, P. Junier, M. Albini, P. Letardi, E. Domon Beuret, L. Brambilla, L. Mathys, C. Cevey, R. Bertholon Biologically induced patina for metal built Heritage. 273 L. Jurina, M. Giglio, S. Bonfigliuoli Sviluppi nella sperimentazione armato”. 283 della tecnica dell’“arco E. Petrucci, F. di Lorenzo Metal tie-rods and anchor plates in old buildings: structural elements with high aesthetic impact. 293 F. Zaccheo, L. Jurina La tecnica della “torre nella torre”: due casi a Pavia. 305 V. Bernardini I serramenti metallici nell’architettura moderna in Italia del periodo 1930-40: problemi di conservazione e di restauro. 315 G. Fatta, C. Vinci Armature e complementi in ferro nelle cuspidi maiolicate dei campanili in Sicilia. 327 S. Agnoletti, A. Cagnini, E.Della Schiava, M. Galeotti, M. D. Mazzoni, S. Porcinai, F. Tattini Il parco museo Quinto Martini. 339 SCIENZA E BENI CULTURALI XXXI.2015 METAL TIE-RODS AND ANCHOR PLATES IN OLD BUILDINGS: STRUCTURAL ELEMENTS WITH HIGH AESTHETIC IMPACT Enrica Petrucci1, Francesco Di Lorenzo2 1 Università di Camerino, Scuola di Architettura e Design “E.Vittoria”, Viale della Rimembranza – Ascoli Piceno, enrica.petrucci@unicam.it 2 PHD, Università di Chieti-Pescara, Facoltà di Architettura ABSTRACT Throughout history metal tie-rods and anchor plates have been installed to deal with structural problems, reinforce the masonry structure, and absorb the outward pressure. In the 13th–16th centuries, arches, vaults and domes were made by inserting metal or wooden reinforcement elements during the construction or the restoration phase. Many writers recommended their use in various guises to raise walls and construct vaults. The effectiveness of these elements was questioned by some authors because they felt that the tie-rods lose their effectiveness over time. Despite the discussion surrounding the efficacy and aesthetics of tie-rods, since the 15th century, coinciding with an improvement in the quality of iron, they have been used as common engineering practice. The tie-rods were then blocked with anchor plates or wall washers. In some cases the anchor plate was also in the shape of a slab. The anchor bar or slab put the tie-rod in traction and distributed the force exerted on the masonry over a greater area. In many countries, especially during the 18th and 19th centuries, the preference was to confer a particular aesthetic value on anchor plates with ornamentation, using the most suitable design for their neat entry on the façade. The tie-rods were studied with a more correct, scientific method. More recently, this has become a favoured method for seismic safety improvements with the activation and development of local mechanisms, and they represent one of the most commonly used devices in restoration. The technical solutions are varied, in fact, from more traditional metal tie-rods with simple bar anchors to solutions that look for special aesthetic effects in the realization of the head plate. In a review of the solutions analyzed, the case history is particularly extensive, and it induces a reflection on their indiscriminate use in restoration, studying the most effective and most aesthetically pleasant systems. Keywords: reinforcement, aesthetic impact, ties, anchor plate 294 SCIENZA E BENI CULTURALI XXXI.2015 1.1 The use of tie-rods throughout history Observing the buildings in most historical centres in Italy, many metal elements can easily be seen sticking out of the masonry in more or less evident ways and with various shapes and sizes. These visible ends of the so-called tie-rods have the form of a metal plate or bar and are generically called “anchor plates”. Such devices represent one of the oldest ways of reinforcing a structure, and they are still very much used today due to their simplicity and considerable low cost in retrofitting. The use of tie-rods is a construction practice that is widely documented in ancient architecture, both in Republican and Imperial Rome1. With the Romans’ very advanced design, which was characterized by a notable tendency towards innovation, the use of iron tie-rods took advantage of a material’s resistance to traction to reduce the size of imposts, lighten the load resting on the free architraves, limit the effect of possible differential instabilities, and guarantee the stability of complex, jointed systems, especially in connection with destructive events2. From the medieval era on, the use of tie-rods, encircling ties, clamps, and other metal coupling elements became widespread as favoured methods of absorbing thrusts and improving faulty joints or restoring those that were completely nonexistent. Important examples can be found in numerous historical monuments, where the choice of metal components, both in later consolidation interventions and in the actual construction of the structure, frequently characterized historical building. Structural stability was entrusted to the imposts, which needed a sufficiently large area; however, the shoulders were often too narrow and not capable of supporting the horizontal pressure of the arch. Therefore, starting in the 13th-14th centuries, arches, vaults, and cupolas were built by inserting wooden or metal tie-rods directly in the construction phase. These were capable of counteracting the outward pressure of the vaulted structure, in particular in the case of segmental arches and masonry with an insufficient crosssection. Dimensioning the metal tie-rods was linked to simple principles that can be understood within the so-called “trade standards”, and by implicitly considering the possibility of an intervention even after the retrofit is finished in order to guarantee the structure’s safety over time3. If we analyse the anchoring elements such as bars, plates, or other various shapes, the desire was to ensure the device’s effectiveness through simple technical solutions that could be adapted to both small and large buildings without further analysing the aesthetic/figural aspects of how they were inserted on the façade. The use of iron elements for structural reinforcement became common practice in Genoa starting with an ordinance in 1545 that had two aims: to avoid the use of external buttresses to support the masonry but at the same time to avoid structural failure caused by the horizontal thrust of the arches, vaults, and ceilings. Tie-rods were generally made of wrought iron and were composed of two elements: the SCIENZA E BENI CULTURALI XXXI.2015 295 rods, which were square or circular in cross-section, and the anchor plates, which the tie-rods were attached to4. The restraining elements -simple bar anchors in an older phase-had to be situated at an angle with respect to the horizontal; such rotation, which varied from 45° to 60°, was studied to confer the most structural functionality of the element in relation to the stonework. In some regions, such as Lombardy, the preference was to situate the bar vertically in order to prevent visual disturbance of the façade, which was generally organized in horizontal planes marked with stringcourses. Fig.1. Assisi, Superposition of different anchor plates corresponding to different restorations. The poor evaluation of elements composing the façade is evident Fig.2. Mantova, Church of S. Maria degli Angeli. Anchor plate in ribbed iron for a double tie-rod dating to the early 1970s. It appears to consider the aesthetic aspects 1.2. References to treatises and manuals Many writers have considered the use of iron tie-rods to be one of the most common reinforcement systems for dilapidated buildings. Since they are so widespread in construction, it is not surprising that their use has been the object of a wide debate on the convenience of leaving the elements in view, sometimes provoking negative interference with compositional aspects of the façades. Among the most distinguished voices, Alberti, Francesco di Giorgio Martini, Serlio, and Tibaldi stand out. Alberti writes that segmental arches require “metal tie-rods secured to the two sides of the wall”5, while Pellegrino Tibaldi states that “in every way a vault is made, it is necessary to make the pillars or columns straight using large iron anchors in the walls, so they do not fall under their own weight due to said iron anchors, which sometimes go in the circle of the vault; and this dark iron anchor is alive and visible and also dead, which is not seen” 6. In fact, in many cases, instead of the visible intrados tie-rods, which he calls “alive” anchors, for aesthetic reasons and to prevent the visibility of protective devices extraneous to the masonry, invisible tie-rods, so-called extrados or “dead” anchors 296 SCIENZA E BENI CULTURALI XXXI.2015 were preferred, encompassed by the stonework of the vault and therefore situated “within the mass of the vault and the floor, which hides them, making them unapparent”7. The effectiveness of the tie-rods was discussed by Giacomo Barozzi da Vignola, who writes, “I do not accept that using iron anchors is good; so that well-designed buildings can support themselves and not be attached with ‘strings’, and massive where one can freely choose to best apply them”8. Teofilo Gallacini was of the same mind; in his Treatise on errors in architecture, he stated the need to not build “sides that are too weak, especially when multiple floors are needed, which, due to the small arch and great weight, have the force to push the walls in a way that the iron rods are not enough to keep them fixed, and narrow so they don’t fall, and massive if there is nothing to flank them. But against their force no other resistance can be made than the mass of the wall; while it is a grave error to trust the rods”9. Among the writers who mark the step from Classicism to the technical writing of the 19th century, Milizia is favourable to the use of tie-rods in consolidation works10, as were Cavalieri San Bertolo and Rondelet, who contributed to spreading knowledge in the use of these elements11. Fig.3. The use of tie-rods to prevent walls from spreading. (Rondelet J. B., Trattato teorico e pratico dell’arte di edificare [Theoretical and Practical Treatise on the Art of Building], 1831, L. VII Ironworks, Sect. I - Use of iron in buildings, Ch. I - On chains, tie-rods, and brackets, Tav. CXLVIII) At the end of the 19th century, Giovanni Curioni contributed to the latest knowledge, stating that “in modern civil construction, the enormous thick walls generally seen in ancient buildings are no longer admissible, and thinner, lighter forms have taken the place of massive, heavy ones”. For this reason he suggests the use of different materials and technology, including tie-rods, which can effectively contribute to the overall stability of the building12. Many theses in favour of or SCIENZA E BENI CULTURALI XXXI.2015 297 against the use of tie-rods in new or dilapidated buildings are dictated by the desire not to alter the aesthetics of the building by exposing elements that could be seen as unpleasant, especially near particular architectural elements. Such a need led some authors to prefer camouflaged solutions. Opinions have therefore always been particularly diverse regarding the correct use of tie-rods. One architect from Bologna in the late Baroque era, Carlo Francesco Dotti, published a brief treatise in 1730 to demonstrate the uselessness of bracket tie-rods, which were much used in that region and in a large part of 17th-century Italian architecture. Dotti rejects the use of such systems as completely inadequate for counteracting the thrust of the vaults, preferring instead the traditional horizontal tie-rod placed at the intrados of the arch13. Fig.4. Extrados tie-rods. (Valadier G., L’architettura pratica [Practical Architecture], 1831, tav.CCLXVI) Fig.5 . Metal extrados tie-rods with brackets and tie-rods positioned near the keystone. (Cattaneo L., L’arte muratoria [The Art of Masonry], 1889, tavv. 23 -25) In manuals from the beginning of the 1900s, we see more technical description in the use of metal rods. Cristoforo Russo advises, for example, the use of “long, large anchors, and thus the best are double-T beams reinforced with iron plates located among the wings”. The use of paired rods is also suggested when vaulted environments are very wide, with the consequence of having considerably long (greater than 4 m) horizontal plates14. Some years later, the argument was dealt with systematically by Sisto Mastrodicasa. He evaluated the effects of metal rods used in various ways and highlighted the positive and negative aspects, supporting theoretical considerations with formulas and calculations. Attention was primarily 298 SCIENZA E BENI CULTURALI XXXI.2015 directed at building techniques, but aesthetic aspects were also considered “so that the insertion of anchors would not damage the appearance of the façade”15. Fig.6. Bar anchors. (Mastrodicasa S., Dissesti statici delle strutture edilizie [Static instabilities in Buildings], 1993, p. 371) Fig.7. Circular anchor plate. (Mastrodicasa S., Dissesti statici delle strutture edilizie [Static instabilities in Buildings], 1993, p. 971) 1.3 The influence of anchors in the aesthetics of the façade In the practice of structural improvements, and especially as a result of the seismic events that have characterized the Italian territory in the last fifty years, the use of metal tie-rods has become consistently widespread16. This use seems to be perfectly in line with the basic theoretical principles of restoration, among which are reversibility, compatibility, and distinguishability. The insertion of rods is the minimum intervention that can be adopted to reinforce a building with structural problems17. This spread is therefore linked to some basic principles, including allowing the maximum durability of authentic material, limiting changes to what is strictly necessary, and realising recognizable, reversible interventions in order to control them and possibly remove them in time. The spread of metal tie-rods and their indepth analysis in structural terms as reinforcement implemented after a retrofit has not corresponded to a timely definition of the negative effects on building façades and therefore to the limits within which they should be used. Such elements, beyond their merely structural purpose, can sometimes have particular shapes in order to provide them with an effect that is best in harmony with the aesthetic appearance of the façade. In many European nations, tie-rods were already in use starting from the medieval period. Buildings using short wall anchors are found in Europe before the 17th century, but the phenomenon increased over the course of the 19th century to give the façades a new figurative message18. The styles of anchor plate include earthquake washer, triangular washer, S-iron, and T-head. They are easy to find in cities with substantial legacies of 18th- and 19th-century brick construction, such as New York, Philadelphia, St. Louis, and Charleston, South Carolina, and in older earthquake-prone cities such as San Francisco. SCIENZA E BENI CULTURALI XXXI.2015 299 Fig.8. Types of anchors from New York and Pennsylvania (Sonn Albert H., Early American Wrought Iron, New York, 1928) Fig. 9. Drawing of a wall-anchor from Vergelegen, in South Africa (James Walton J., Some South African decorative wall-anchors, “Restorica”, 21, 1987, p. 7) Fig.10. Wall anchors in Palatine Chapel of Aachen Fig.11. Wall anchors in Stockholm In Italy, the use of metal reinforcement and decorative anchors was not so widespread. More frequently simple bar anchors are seen, used either singly or in pairs, and only in rare cases do the elements have more complex shapes, as the fruit of a construction need united with a search for shape. In the latter, a binary situation was created. On the one hand, there is therapeutic excess in structural reinforcement with the multiplication of restraining elements, which is also related to the formulation of various community regulations19. On the other hand, there is a need to provide the elements with an aesthetic/figurative value, with results whose effectiveness is sometimes doubtful. 300 SCIENZA E BENI CULTURALI XXXI.2015 Fig.12. Building regulations for the City of Vertova (BG). Directions for the architectural qualification of buildings, Tav. IX. Types of metal tie-rods and anchors, February 2013. 1. Simple bar and wedge; 2. Separated double bar (grommet); 3. Pin (contrast wedge); 4. Nailed and bolted bar; 5. Ribbed plate; 6. Separated double bar and bolt (threaded bar, blocking bolt). Fig.13. Example of therapeutic excess in structural reinforcement with tie-rods. Fig.14. The façade of Bonaparte Palace in Ascoli Piceno. The flower-shaped anchors were inserted, in contract with its style/shape characteristics. Conclusions When inserting metal tie-rods in a restoration to improve seismic resilience, it is necessary to look for the right balance, which can only grow out of a careful study of the ancient building. If it is true that the intrusion of anchors is now minimal, in that they have now become part of historical memory and are also commonly accepted on significantly valuable façades, it is likewise necessary that particular attention be paid to simplifying their form and position, avoiding decorative elements or other architectural elements that characterize the composition of the façade. In sum, we can therefore affirm that the position of a tie-rod is also an act that becomes a careful critical choice. SCIENZA E BENI CULTURALI XXXI.2015 301 NOTES 1 The first examples of tie-rods that can be documented reliably date from the Augustan Age in connection with a focused political euergetism to create important monuments. Cf. Amici C.M., L’ uso del ferro nelle strutture romane [The Use of Iron in Roman Structures], in “Materiali e Strutture”, 2-3, 1997, p. 85-95. The tendency towards design innovation typical of Roman architecture is exemplified by the use of resistent systems based on metal tie-rods. The chronological period of reference goes from the first century BCE to the third century CE. 2 In the Dizionario universale d'architettura e dizionario vitruviano, accuratamente ordinati da Baldassarrre Orsini [Universal Dictionary of Architecture and Vitruvian Dictionary, Carefully Ordered by Baldassarre Orsini], Perugia, 1801, vol. I, p. 80, at the entry for enchain (incatenare), it says “Architects use it to mean putting chains [tie-rods] in buildings. 3 Until the beginning of the 1900s, the trade standards, which exhausted a good part of the technical information, were still in force, while training held a close, necessary connection with the “materiality” of making it concrete. Cf. Margani G., Costruzione e recupero. Regola dell’arte e principi di consolidamento [Construction and Recovery. Trade Standards and Reinforcement Principles], Il Lunario, Enna, 2009, p. 25-26. 4 Cf. De Cesaris F., Sui dispositivi di contenimento delle spinte [Devices to Control Thrusts], in Carbonara G. (Ed.), Trattato di restauro architettonico [Treatise on Architectural Restoration], UTET, Turin, 1996, vol. 2, p. 100-103. According to the author, metal tie-rods were sized and distributed according to the entire mass of interest and the possibility of redistributing the forces induced by the tie-rod over the masonry. At the end of the last century, the simple restraining bars were replaced with reinforced plates, and more recently with scraps of I-bars, C-beams, or other metal profiles. 5 Alberti L. B., L’architettura (De re aedificatoria) [Architecture], Orlandi G. and Portoghesi P. (Eds.), Il Polifilo, Milan 1966, p. 124-125. 6 Tibaldi P., L’architettura [Architecture], G.Panizza (Ed.), Il Polifilo, Milan, 1990, p. 90. See also, Della Torre S., Schofield R., Pellegrino Tibaldi architetto e il S.Fedele di Milano: invenzione e costruzione di una chiesa esemplare [Pellegrino Tibaldi, Architect, and San Fidele of Milan: Invention and Construction of an Exemplary Church], Nodo Libri, Como, 1994. 7 Francesco di Giorgio Martini. Trattati di architettura, ingegneria e arte militare [Treatises on Architecture, Engineering, and the Military Arts], Corrado Maltese (Ed.), Il Polifilo, Milan, 1967, p. 92. 8 Ticozzi S. (Ed.), Giacomo Barozzi da Vignola. Raccolta delle lettere sulla pittura, scultura ed architettura [Giacomo Barozzi da Vignola. Collection of Letters on Painting, Sculpture, and Architecture], Giovanni Silvestri, Milan, 1822, vol. I, p. 499. See also Varagnoli C., Teoria e empiria dal Settecento all’Ottocento [Theory and Empiricism in the Eighteenth and Nineteenth Centuries], in Aa.Vv., Trattato sul consolidamento [Treatise on Consolidation], Mancosu, Rome, 2003, section A, p. 100-119. Reference is made to the various positions of the writers with respect to Vignola, who states that supporting the buildings with “strings” is not effective. 9 Gallaccini T., Trattato sopra gli errori degli architetti [Treatise on Architect Errors], Gregg International Publishers Limited, Westmead 1970, p. 50-52. 10 Milizia F., Principj di architettura civile [Principles of Civil Architecture], Remondini, Bassano, (1781), 3rd ed, 1813, vol. 3, p. 56-58. 11 See Corradi M., Ars o τεχνωµ: considerazioni critiche sulle tecniche di consolidamento tradizionali dell’architettura storica e monumentale [Ars o τεχνωµ: Critical Considerations on the Techniques of Traditional Consolidation in Historical and Monumental Architecture], in Proceedings from the Tercer Congreso Nacional de Historia de la Construcción, Seville 26-28 October 2000, vol. I, p. 239254; Fatta G., Sui tiranti metali nell’edilizia storica [On Metal Tie-Rods in Historical Construction], in Fumo M. (Ed.), II recupero degli edifici antichi. Manualistica e nuove tecnologie [The Recovery of 302 SCIENZA E BENI CULTURALI XXXI.2015 Ancient Buildings. Manuals and New Technologies], Proceedings from the Convegno Internazionale, Naples 29-30 October 1993. Clean, Naples, 1994, vol. I, p. 568-569. 12 Curioni G., L’arte di fabbricare [The Art of Building], Negro, Turin, 1868, p. 91-92. 13 Dotti C.F. Esame sopra la forza delle catene a braga con che si dimostrano le bragature essere inutili per reggere l’urto degli Archi e Volte [Examination of the force of braga tie-rods, which demonstrates that bragature are useless for supporting the force of arches and vaults], Stamperia S.Tommaso d’Aquino, Bologna, 1730. Valadier takes up the theme of tie-rods hidden in the vault intrados, confirming that “this sort of tie-rod reinforces little or not at all and yields to the pressure of the vault”. Valadier G., L’architettura pratica dettata nella scuola e cattedra dell’insigne accademia di S. Luca (1831) [Practical Architecture Dictated in the School of the Renowned Academy of San Luca (1831)], Ediltografica, Rome, 1992, p. 76-92. 14 Russo C., Le lesioni dei fabbricati (sintomi, cause, effetti, rimedi) [Building Damage (Symptoms, Causes, Effects, Remedies)], UTET, Turin, 1930, vol. I, Studio teorico - pratico, p. 343-350. 15 Mastrodicasa S., Dissesti statici delle strutture edilizie [Static Instabilities in Buildings], Hoepli, Milan, 1993; in particular Ch. XXV, Tiranti metallici [Metal tie-rods], p. 369-394. In relation to the bar anchors, advice is given to restrict the length to avoid the “overly onerous use of iron and damage to the aesthetics”. 16 Cf. Linee Guida per la valutazione e riduzione del rischio sismico del patrimonio culturale [Guidelines to Evaluate and Reduce Seismic Risks of the Cultural Heritage], Gangemi, Rome, 2006; in particular, section 6.3.2 Interventi volti a ridurre le carenze dei collegamenti [Interventions to Reduce Connection Deficiencies], p. 39. 17 Fiorani D., Posterità e minimo intervento [Posterity and Mimimum Intervention], in Aa.Vv., Il minimo intervento nel restauro [Minimum Intervention in Restoration], Proceedings from the Convegno, Siena 18-19 June 2004, Nardini, Florence, 2004, p. 17-25. According to the author, “reasoning on the principle of minimum intervention means, most of all, situating oneself within a specific vision of restoration and then identifying the nature within the limits that define the concept of ‘minimum’ in the context of the intervention”. 18 For a broad illustration of the use of anchors in various contexts, both European and abroad, see http://www.zen156113.zen.co.uk/index.html, in which P. Ruth Alcock Reynolds investigates the theme with a thesis presented in June 2008 entitled Transmission and Recall: the use of short wall anchors in the wide world. 19 Norms regarding the positioning of metal tie-rods are established by general regulations that define the “architectural qualification of buildings” and describe in a more or less detailed way the technical means of insertion and the formal qualities. SCIENZA E BENI CULTURALI XXXI.2015 303