Structural Analysis of Historical Constructions - Modena, Lourenço & Roca (eds) © 2005 Taylor & Francis Group, London, ISBN 04 1536 379 9 Vulnerability study in seismic areas: the role of on-site and archives investigation A. Anzani, A. Baila, D. Penazzi & L. Binda Department ofStructural Engineering, Po/itecnico di Milano, Milano, lta/y A8STRACT: The seismic response of old stone masonry buildings in Western Liguria is approached by a multi-disciplinary view. The historical centres of Bajardo, Taggia and Bussana and others, still display signs of damage due to XIX century earthquakes, to which the problems of lack of maintenance and, in many cases, of abandon have overlapped. A method for evaluating their seismic vulnerability is proposed after: (i) a direct survey ofthe buildings (based on a stratigraphical survey and on a survey ofthe crack patterns and ofthe wall sections), Oi) the collection ofindirect information from documentary sources, (iii) the collection ofdata recorded through in-si tu non destructive or low destructive mechanical testing and laboratory investigation aiming at the chemical, physical and mechanical characterization ofmasonry components. The ro le ofhistorical analysis will be shown as a basic source of knowledge of the structures for the subsequent assessment of seismic vulnerability. INTRODUCTlON masonry morphologies and the need of improving the retrofitting techniques applied after the previ­ Most of the historic centres in Italy are characterised ous earthquake of 1979 was evident. The problem by the presence not only of monumental buildings of repairing and retrofitting should be approached like churches and palaces, but also by a complex in a multidisciplinary way, that is, considering dif­ built environment made of simple houses which itself ferent complementary aspects of the problem such constitutes an important part of the cultural heritage. as: historical evolution ofthe building, geometry and This so called "minor" architecture, often poorly con­ crack pattern, material characteristics, technology of structed, is mainly composed of stonework buildings construction, possible fai lure mechanisms, etc (Binda with timber roofs and floors. In spite of the use et aI., 1999), (Penazzi et aI., 2000). To this respect, the of apparently similar material and construction tech­ participation of architects/"conservators", historians, niques, building characteristics vary according to their structural engineers is also important. A compari­ typology - from isolated to arrayed buildings - and to son and a correlation between all the collected data their location - from flat to steep mountain sites. This will allow a more robust interpretation of the struc­ variety is directly connected to the orographical pro­ tural response according to the examined masonry and file ofthe site and also to the common seismic history. building typology. This in order to support techniques Urban structures, like those described, have been fre­ for evaluating the seismic vulnerability and to define quently abandoned and not maintained, therefore they reliable retrofitting procedures of stone-masonry are particularly vulnerable to earthquakes. In many buildings. other cases, retrofitting and repair techniques have The paper describes the application of a multi­ been systematically applied according to the Italian disciplinary procedure, addressed to an articulated seismic Code, but mostly without any investigation of knowledge of three historical centres of the Western the characteristics ofmaterials and structures. The fail ­ Liguria built in stonework masonry, with special atten­ ure of some of these interventions has been basically tion to the contribution of the historic survey into due to the lack of knowledge and inadequate skills in the understanding of the seismic vulnerability (8inda the application. et aI. , 2003a). Aim of the research is the suggestion After the most recent earthquakes, the need of some guidelines for the investigation procedure of adjusting the adopted structural models to the that may orient the interventions on historic buildings typical behaviour of some building typologies and toward the objective of safety and compatibility. 1051 2 STUDY OF THE HISTORIC SOURCES of the Clavesana Marquis first and of the Genovese Republic later. The different phases of expansion co[­ A fundamental analysis for studying an urban centre is responded to the construction of new fortified rings, lhe historical survey. This is articulated into a twofold as historically documented (Fig. 3). research line: on the one hand the cataloguing and The medieval historic centre ofBajardo is laying at the analysis of the data collected through documen­ 900 m above the sea. Feud of the Ventimiglia Earls, tary sources (indirect sources); on the other hand the the village was occupied in 1259 by the Genoese and direct and criticai observation of the evolution of the remained under their domination until the birth of village and of the manufacts that it is made of. This the Ligure Republic . The upper part of the village, compared study is fundamental especially when the nearby the church and the Castle, was abandoned after research objects are minor centres, mainly made of the earthquake of 1887. Therefore, the inhabited part rural architecture, like in the case ofTaggia, Bajardo expanded toward the valley (Fig. 4). and Bussana. In fact, in these cases the documen­ At present, the ancient part of the village consists tary and historical sources (indirect) are generally not of vaulted passages and radial paths, whereas many enough to allow the complete reconstruction of the medieval ruins still remain. evolution ofthe centre. Therefore, it is necessary that the historical information coming from the paper doc­ uments are confirmed in situ and accompanied by the direct analysis of the centre so to define a complete know1edge. Direct analysis is based on lhe observation of the characteristics ofthe centre, giving information about the historical-constructive evolution ofthe manufacts, their dating and their constructive techniques. Indirect sources include archives and bibliographic information, collected for reconstructing the evolution of the centre, its building and transformation phases and its load history as a history of the earthquakes occurred in the past. Of great relevance are also the iconographic aspects "" L t (views, ancient documents) giving information on the historical housing, allowing the evaluation ofthe trans­ Figure 2. Taggia: evolution of the historical defence walls. formations of a territory and the comparison with its present configuration (Figs. 1 and 4). Taggia was founded in 641 after raids by the Saracens had made the previous settlement on the coast unsafe (Costa Balenae). The inhabitants built the new centre within the Aulella valley, constituting a medieval fortified village with a castle "Castrum Tabia". The history of the village is connected to the long Benedictine colonization, lasted until the coming Figure 3. Bajardo, evolution of the ancient centre. Figure l. Taggia in XIll century (pri vate archive). Figure 4. Old Bussana in a view or 1770. 1052 Bussana is built on 10p of a hill dominating the Riviera since 951 until 1890 had been subjected to a Armea valley. The first paper referring to Bussana series of heavy and destructive earthquakes. is a document of 979 indicating that its territory Taggia, Baj ardo and Bussana registered four rele­ was a property of the Bishop of Genova, Teodolfo. vant events: 1818, 1831 , 1854 and 1887, as reported Later, his authority was substituted by that ofthe Ven­ by the R. D. of 26th June 1887 n. 106, Province timiglia Earls, Lords ofthe territory placed west ofthe of Porto Maurizio, Lis! 0/ most/y damaged centres Armea River. They were responsible of the construc­ (Figs. 5-7). Since 1831 only, detailed and precise tion of a castle, dominating the area of the successive descriptions of earthquakes and their consequences Bussana (fig. 4). After the earthquake of 1887, a new are available. centre was built, whereas the old village was aban­ doned without any institutional declaration about the property of the ruins. Since the fifties of the XX 4 DIRECT SURVEY century, the area was occupied by a community of artists who autonomously carried out repair and con­ Direct sources, which are the sole available when his­ solidation interventions without any official project, toric documents have been lost, include various meth­ and organized artistic performances, attracting a new ods for approaching the knowledge ofthe building, of diffused attention to the centre. its chronological phases, construction techniques and materiaIs. In particular they are: a) geometrical sur­ vey; b) photographic survey; c) typological analysis of 3 CHRONOLOGY OF SEISMIC EVENTS the buildings; d) stratigraphic survey, when possible, for gaining chronological information and the building The approach to the vulnerability study of historical centres implies the acquisition of data about the geo­ morphology ofthe site, the chronology and "history" of seismic events. When it is known, the seismic his­ tory ofthe centre and the single building is particularly relevant with respect to the safety aspects and to the intervention implications. This data series contributes to define, on a probabilistic base, the seismic risk which characterises the area under study. The western Figure 6. Ruins of the sacristy and annexed buildings. (Historie picture, Municipality of Bajardo) a) a) b) b) Figure