# Seismic Assessment of Historical Masonry Buildings at Different Scale Levels: A Review
## 1 Introduction  
The conservation of historical masonry buildings has been widely debated, especially over the last half-century, thanks to their undeniable social and economic importance. On the one side, cultural heritage is necessary for preserving collective memory and identity [1]; on the other side, in places where tourism is the driving force of the economy, the loss of cultural heritage would strongly affect the quality of life of the local population [2]. The concept of conservation can be seen, in general terms, as the set of practices oriented to defend an asset for future generations, restoring from possible existing damages and preventing potential deficiencies and critical issues. It is widely known that unreinforced masonry structures are designed to withstand static gravitational loads but are otherwise generally vulnerable to even low-entity horizontal seismic actions, resulting in the arising of cracks and partial or global structural collapses. In this framework, accounting for the conservation needs, the structural analysis can be seen as a necessary tool for understanding the features characterising the buildings state of the art and for eventually planning retrofitting measures starting from detected deficiencies. According to [PERSON] [3], the structural analysis marks all the steps contributing to the effective conservation of historical buildings, starting with the diagnosis and leading to a reliable retrofit design. More than for ordinary buildings, in the case of historical constructions, the retrofit design needs to pursue the principle of minimum intervention, applying only those measures required for reducing risks for people, structures and artworks and avoiding what could unnecessarily affect the authenticity of the asset. The choice of a proper method for assessing the structural performance of an existing building acquires, in this sense, a primary role in preventing over or under-statement of the effective capacity towards static or dynamic/seismic actions, possibly leading to incorrect retrofit planning and resulting economic waste. In the last decades, the overwhelming improvement of information technologies (IT) has promoted the application of increasingly developed computer tools for the analysis of historical buildings. Complex nonlinear analyses are becoming ever more widespread, allowing numerical simulations that were unthinkable until a few years ago. Despite that, the analysis of the cultural heritage preserves some challenging features that cannot be overcome by simply increasing computer power: historical buildings are characterised by limited initial knowledge concerning geometry, structural features, construction systems, material characterisation, inner heterogeneity due to overlapped construction, etc., and these aspects cannot be automatically accounted for in numerical analyses. In the present paper, a review of the principal existing methodologies for the structural assessment of historical buildings is presented and discussed with a critical approach, trying to point out the main limitations and possibilities. The selected methodologies are presented by distinguishing the level of details (or, in other words, the'scale') adopted for the modelling of materials, elements and whole buildings. In this sense, 'large-scale approaches', as in the following, can be even mentioned as 'territorial approaches' and include methods for the territorial/urban scale evaluation of a large number of masonry buildings and are often connected to risk assessment;'small-scale approaches' are adopted, as guessable, for portions of the building, structural components and single buildings, in this last chance eventually including the case of aggregates, even if the matter is of high complexity.