**1. Introduction**

Masonry buildings in historic city centres are recognised as being structures that are prone to damage from earthquakes due to vulnerabilities associated with their architectural type (e.g., church, palace, tower) as well as specific constructional aspects (e.g., the quality of materials, construction details, connections) and current state conditions (e.g., decay, previous interventions). The concurrence of these factors can cause severe damage scenarios and losses of cultural heritage (CH) assets even under medium-intensity earthquakes, as demonstrated by several episodes of seismic activity in Italy in recent decades (e.g., 1997 Umbria-Marche, 2009 L'Aquila, 2016 Central Italy earthquakes) [1,2].

A post-earthquake emergency in historical city centres often requires the implementation of safety measures for unmovable artistic assets, i.e., those which are integral to damaged structural components. This is the case with the frescoes, decorated plasters, mural paintings, mosaics and stuccoes, which are supported by vaults, columns, ceilings, or walls of a historical building [3,4]. This phase involves both structural engineers and experts on the preservation of CH assets, who usually can make decisions based on the compliance with safety conditions according to their specific knowledge (i.e., on the

artistic asset or the structure) and suggest appropriate actions if necessary. Nevertheless, due to the close interconnection between the artwork and its structural support, the evaluation of the current conditions of the former heavily depends on the latter, whose worsened conditions can jeopardise the safety of the whole building.

As an example, a typical severe and, unfortunately, common condition is that of a fresco borne by a wall that has no constraints (e.g., ties, effective connections with adjacent walls and the floor/roof) to counteract overturning under seismic loads, or has low masonry quality (e.g., multi-leaf rubble section). The fresco is in the highest risk condition, because the structural element (the wall to which the fresco is connected) behaves according to the weakest and most brittle mechanism (i.e., out-of-plane collapse) (Figure 1a). On the contrary, in a building where the activation of overall behaviour is provided by more earthquake-resistant conditions, limited structural damage is expected (e.g., in-plane shear cracking in a wall), although it can provide severe patterns, which could affect the fresco integrity (Figure 1b).

**Figure 1.** Examples of damage of artworks due to out-of-plane (**a**) and in-plane (**b**) mechanisms for frescoes and stuccoes.

Studies on the correlation of damage between artistic assets (AA) and structural elements (SE) are very limited in literature, especially if related to historic/traditional materials (e.g., plasters). Calderini et al. [5] examined the mechanical interaction between stone masonry panels and covering plasters simulating frescoes by either diagonal compression or shear tests, integrated by non-destructive techniques (NDT, e.g., infrared thermography and ground-penetrating radar). The study highlighted the damage propagation from the wall to the plaster and contributed to the definition of the limit states of plaster regarding the condition of the SE. Valluzzi et al. [6] measured the overall interaction between a fresco and its supporting wall under laboratory compression tests. Various plasters (in terms of composition and finishing quality) applied to the surfaces of a rubble stone masonry panel were taken into consideration, and laser scanning and infrared thermography were also applied to monitor the damage progression during loading. The test caused surface detachments and spalling, which was limited in the plaster that complied with better application criteria. Both studies highlighted the high fragility of plasters in terms of either in-plane or out-of-plane behaviour. More contributions in literature concern the application of NDT for the evaluation of the conservation conditions of CH assets [7–10], or are mainly focused on modern render products, both in terms of the theoretic approach of elasticity applied to multi-layer systems [11] and of the effect of weathering on durability [12,13]. A significant contribution aimed at supporting the design of strengthening interventions for the preservation of architectural buildings comes from comprehensive EU research, e.g., PERPETUATE [14,15] and NIKER [16] projects. The former included the study of buildings with the contained artworks, and the latter provided guidelines for strengthening actions in the form of a structured web catalogue [17]. Recent developments in web-based tools [18] also provide decision-making processes in assessing failure modes through the observation of post-earthquake scenarios.

Nevertheless, at present, while the knowledge of the mechanical behaviour of structural components has been clarified by several studies and has been supported by reliable evaluation procedures (for both damage and vulnerability aspects), there are not yet any prediction tools encompassing the vulnerability of artworks. In particular, the parameters affecting the combined behaviour between AA and SE need to be identified, and their mutual influence must be properly quantified to optimise integrated and all-encompassing solutions for historic buildings in seismic zones.

Therefore, there is a need for a comprehensive procedure, to use contextually among different areas of expertise, which can encompass both specific aspects related to single issues of both AA and SE and to combine their evaluations. With this aim in mind, an extensive interdisciplinary research was carried out between the University of Padova and the Venetian Cluster. The research focused on the proposal of an integrated approach that was able to take into consideration architectural (for structural elements) and compositional (for artistic assets) details, as well as the critical aspects related to execution or deterioration/damage conditions. This information was structured in a web database (called DataBAES) so that both aspects of vulnerability and damage in a building may be correlated between artworks and their specific supporting structural components.

The procedure provides a multilevel approach through two survey forms, which are to be used for basic (level I form) or deeper (level II one) onsite visual inspections. The level I form provides the correlation of damage between AA and SE, whereas at level II, both the correlation of damage and vulnerability are proposed. Level II corresponds to an in-depth autopsic analysis to understand the state of conservation of the artworks and the bearing structure, as well as to the possibility of carrying out further studies (e.g., in terms of the quality and quantity of present salts, biological attacks, as well as the presence of '*bottaccioli*' or '*calcinaroli*'). Of course, particularly at level II, ND procedures (e.g., the above-mentioned georadar, infrared thermography, and laser scanning) can be used to help in the identification of the aspects and parameters (in relation to both materials and structure) needed in the following phases of investigation, according to a more detailed knowledge plan.

The applicability of levels I or II might correspond to different conditions, respectively, e.g., (i) the surveying of emergency conditions for preliminary and quick evaluations just after the earthquake occurrence, or (ii) as a predictive tool, focused on collecting data before an event on each possible mechanism of the various SE and related AA. The results are correlated in terms of five degrees of vulnerability/damage (increasing from the lowest to the highest) to provide prioritisation in the possible interventions for the building. Furthermore, according to information collected on various buildings in a certain area through DataBAES, prioritisation evaluations can be extended on a wider scale to integrate possible conservation plans.

The basic reference for the new procedure consists of the survey forms currently applied in Italy, specifically to churches (form A-DC) [19], palaces (form B-DP) [20], and artistic assets (form C-BM) [21] in the emergency post-earthquake phases, as well as the recommendation/classification charts available for evaluating surface decay [22,23] and structural damage (EMS-98, European Macro Seismic Scale) [24].

The procedure was applied to case studies in various conditions for its validation. At present, the archive includes about 100 case studies (i.e., evaluated AA) belonging to about 30 historic masonry buildings. Results are provided in either quick or more extended charts/summaries, including main pictures and descriptions, which can be easily exported in common formats (e.g., pdf documents) for further elaborations.

### **2. The DataBAES Archive**

'DataBAES' is a web archive created within the framework of the Italian project ProVaCi ('Technologies for the Seismic Protection and Valorisation of Cultural Heritage', 2011–2015 [25]) aimed at promoting multi-disciplinary actions for the seismic protection and valorisation of cultural heritage, this term meaning an integrated and broad extent of assets. The tool correlates the vulnerability and damage aspects between artistic assets and their supporting architectural components for a given

historical building that is either exposed to seismic risk or has already been damaged by an earthquake. The acronym BAES stands for the Italian words 'Beni Artistici' (BA) and 'Elementi Strutturali' (ES), i.e., 'artistic assets' and 'structural elements', respectively.

DataBAES was developed in PHP and JavaScript with a MySQL DBMS backend. Its content is available at https://databaes.dicea.unipd.it/ [26] to registered users. Registration is free of charge and is open to students, scientists, and researchers who deal with historical and cultural heritage preservation.

The archive structure is based on survey forms representing two levels of investigation for historical and cultural heritage assets, i.e., the "Evaluation and correlation of damage of unmovable artistic assets and structural elements" and "Evaluation and correlation of damage and vulnerability of unmovable artistic assets and structural elements", respectively. These new forms are included in the Supplementary Materials of this paper. Each form refers to a specific building. Each building contains one or more case studies, each of which are defined by the following four components: the artistic asset, its supporting structural component, a possible failure mechanism for the structural element, and its localisation within the building. Artistic assets are defined by a sequence of capital letters (i.e., A ... Z, ... ), whereas structural elements are defined by integers (1 ... N), so that each case study is identified by a letter-number label (i.e., A1, B2, C3, ... ). In case of two artworks borne by the same macro-element (e.g., a fresco in a stucco frame against a wall), the two AA will be connected to the same SE by using, as an example, A1 and B1 (for the fresco and the stucco, respectively).

The forms are composed of the following four sections: (1) general information on the building and identification of the significant case studies (AA related to SE); (2) a survey of the damage and vulnerability of the architectural components; (3) a survey of the damage and vulnerability of the artworks; (4) a schematic of the concise judgment of the damage and vulnerability for the list of case studies in the building in question. Sections 1 and 4, being the introductory and the conclusive parts, respectively, have a grey background. This distinguishes them from the two central sections, which can be replicated for the number of case studies identified in the same building.

The options for items that relate to damage and vulnerability aspects are square or round check boxes, which correspond to multiple or single choice, respectively. Detailed degrees of vulnerability and damage are inserted by users, while the average levels are automatically calculated by the system according to given algorithms and/or evaluation scales.

As a result, a table with an overview of the correlation of vulnerability and damage between AA and SE is generated for each building; a scale of colours of five degrees, from green to red, indicates the increasing condition (of damage and vulnerability), so that the most critical artistic assets can be identified and prioritisation measures may be applied if necessary. Levels equal to or greater than three indicate that an emergency threshold has been passed for specific actions to apply to AA and/or SE. Figure 2 shows the process flow diagram of the archive.

**Figure 2.** Overview of DataBAES' functioning.
