Keywords: historical centres, building aggregates, L'Aquila earthquake, vulnerability analysis, masonry strengthening.

In this paper the seismic behaviour of the historical centre of Poggio Picenze (L'Aquila, Italy) has been investigated and discussed in detail by performing comprehensive and large scale in-situ surveys. During these survey activities, two main seismic vulnerabilities were detected: lack of maintenance and structural alterations of roofs. These alterations to geometric layout and materials also included the absence of transverse connection elements (headers) and a lack of contact with the stones of the masonry walls. These seismic deficiencies were detected in a typical hillside building aggregate analysed as a case study, they producing both in-plane and out-of-plane collapse mechanisms [1]. In particular, the absence of roof-top masonry wall connections produced the overturning of masonry panel portions, whereas the lack of headers within the masonry thickness provoked the disaggregation of the external layer of the masonry wall, which was not able to exhibit a monolithic behaviour.

Subsequently, a new seismic vulnerability and damage assessment procedure for large scale structures was applied to the investigated historical centre [2]. The results achieved in terms of damage prediction were compared with real detected damage. In this case, a third degree polynomial relationship between the vulnerability index and the mean damage grade was derived for each of the two different historic centre zones, namely the west area and the castle zone, characterised by different seismic intensities. The comparison between the results showed that the proposed procedure does not provide an estimate of the seismic behaviour of building aggregates on the safe side. This result could be caused by coupling near-fault conditions with the site effects induced by the complex geological structures of Poggio Picenze, which further contributed to the increase in the complexity of the built-up earthquake ground motion effects. The analysis of additional Abruzzo historic centres affected by the 2009 earthquake, as well as the careful evaluation of site effects, represent the future developments of the study which will have as its ultimate goal the definition of a seismic damage - vulnerability law taking into account the actual seismic hazard of the site investigated.

Finally, because the local and large scale analyses performed showed the very bad seismic performance of masonry walls studied, a strengthening strategy has been implemented. It is based on the use of both connections between masonry layers and stone wedge elements. These interventions are used to guarantee both vertical and horizontal mechanical interlocks of masonry according to the "rules of art", which have not been generally fulfilled in the Abruzzo constructive practice for masonry walls. Therefore, an experimental test on a masonry panel strengthened with the above interventions, namely headers plus stone wedge elements, was carried out. The achieved results showed a substantial seismic performance increase of the tested reinforced panel, able to both behave as a rigid block and attain a strength level four times larger than the unreinforced panel.

1

R. Fonti, A. Formisano, F.M. Mazzolani, "The historic built-up of Poggio Picenze: the case study of a hillside aggregate", Proc. of the 14th Italian Conference on Earthquake Engineering ANIDIS 2011, Bari, September 18-22, 2011. (in Italian)

2

A. Formisano, G. Florio, R. Landolfo, F.M. Mazzolani, "Numerical Calibration of a Simplified Procedure for the Seismic Behaviour Assessment of Masonry Building Aggregates", in B.H.V. Topping, Y. Tsompanakis, (Editors), "Proceedings of the Thirteenth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 172, 2011. doi:10.4203/ccp.96.172

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