Operational modal analysis for the characterization of ancient water towers in Pompeii

In the framework of an investigation campaign carried out in June 2015 by the authors on four ancient water towers (10\u201320 BC) in the archaeological site of Pompeii, modal analysis and output-only identification techniques were employed to extract the dynamic properties in order to assess structural vulnerabilities and support numerical model updating. The four investigated towers (selected among the fourteen present within the archaeological site) are free-standing structures at least 6 m tall, belonging to the Castellum Aquae, i.e. the ancient aqueducts system of the city. During the Roman Age, until the destruction of Pompeii due to the volcanic eruption in 79 AD, water towers provided fresh water to houses, palaces and villas. This particular type of structures are classified as no. 1, 2, 3 and 4 by archaeological literature: no. 1 and 4 are made of soft stone masonry (tuff, limestone), while no. 2 and 3 are composed by brickwork masonry. The paper reports the outcomes of ambient vibration tests performed on four towers in terms of extracted modal parameters using various operational modal analysis techniques. Obtained data are then used to study numerically the soil-structure interaction problem and implement model updating procedures

Protection of cultural heritage buildings and artistic assets from seismic hazard: A hierarchical approach

The occurrence of natural disasters such as earthquakes represent a worldwide challenge in the conservation of cultural heritage (CH), which suffer from damage due to high vulnerability conditions. Therefore, the protection of CH from seismic hazard is of paramount importance. Damage and vulnerability assessment of CH and artistic assets play a key role in the identification of conservation strategies. Effective strategies require the stabilization of severely damaged buildings and the preventive improvement of constructions structural response to seismic actions. Although the operation of emergency inspections is meant to classify buildings on the basis of buildings residual seismic capacity, investment decisions in restoration and conservation strategies of such vulnerable structures must take into consideration tangible and intangible values of both building structures and artistic goods as well as must combine objectives of verifying structural safety standards and preserving cultural heritage significance. Damage and vulnerability assessment depend on different criteria, which, on the one hand, are related to buildings structural characteristics, materials, and geometrical properties. On the other hand, to the peculiarities and uniqueness of artworks and artistic goods present on structural elements. In this paper, an AHP (absolute) model is proposed to rank multi-criteria prioritization of protection and restoration interventions on a set of 15 churches, which were damaged by earthquakes, occurring in Italy in the last decades. In detail, in order to structure the decision problem, identify key factors, and define the hierarchy, we conducted an extensive literature review and interviewed a pool of experts. Focus groups were organized to develop the set of criteria and sub-criteria and validate the hierarchy by dynamic discussion

Calibration of the dynamic behaviour of incomplete structures in archeological sites: The case of Villa Diomede portico in Pompeii

This paper reports the research activities carried out on Villa Diomede in Pompeii, built during the "Pre-Roman period" (i.e. the 3rd century BC) and discovered between 1771 and 1774 during the archaeological excavations. It is one of the greatest private buildings of Pompeii and it is located on the western corner of the modern archeological site. Three levels compose the building: the ground floor, the lower quadriportico with a square plan and a series of colonnades on the four sides around the inner garden and the cryptoportico. Villa Diomede was damaged by the strong earthquake occurred in AD 63 that caused the collapse of the western pillars of the quadriportico and later damaged after the big eruption of Vesuvius in AD 79. In June 2015 a series of nondestructive tests (NDT) were carried out by the authors in order to obtain information on the state of conservation of the building and to assess its structural behavior. Direct and tomographic sonic pulse velocity tests, ground penetrating radar, endoscopies and operational modal analysis were performed on the remaining structural elements on the two levels of the Villa. The present paper reports the main outcomes and findings of ambient vibration tests implemented to extract the modal parameters in terms of eigenfrequencies, mode shapes and damping ratios. Operational modal analysis and output-only identification techniques were applied to single stone pillars of the quadriportico structure and then to the entire square colonnade of Villa Diomede. Results are then used to study the soil-structure interaction at a local level and extend the gained information for the numerical calibration of the whole structure. Thanks to this methodology a detailed model updating procedure of the quadriportico was performed to develop reliable numerical models for the implementation of advance structural and seismic analysis of this "incomplete" archaeological structure

Correlation of vulnerability and damage between artistic assets and structural elements: The DataBAES archive for the conservation planning of CH masonry buildings in seismic areas

Historical buildings in seismic hazard-prone regions need specific measures in safety protection, largely due to the presence of artistic assets and/or decorations, both movable (e.g., statues, pinnacles, etc.) and unmovable (e.g., frescoes, valuable plasters or wall paintings, mosaics, and stuccoes). A correlation of damage between structural systems and artworks is fundamental for defining limit states, which can identify the proper conditions for interventions. Nevertheless, several vulnerability aspects can be identified before a seismic event occurs, the study of which can provide the basic dataset for setting up preventive measures in conservation programs. In this paper, the vulnerability and damage conditions related to structural elements (SE) and unmovable artistic assets (AA) belonging to historical masonry buildings are analysed. Optimized survey forms for the onsite detection of either intrinsic (e.g., compositional) defects or deterioration phenomena for both materials and structure are proposed, and results are provided in a web data system (called DataBAES). This enables us to compare the current levels of vulnerability and damage of AA and SE on a scale of five increasing grades. This procedure has been validated on a series of buildings struck by earthquakes in Italy and can be used for correlations of the seismic behaviour of SE and AA in predictive analyses

Lidar data analyses for assessing the conservation status of the so-called baths-church in hierapolis of phrygia (TR)

The LiDAR technology has aroused considerable interest in the field of structural study of historical buildings, aimed at the structural assessment in the presence of different states of stresses and at the evaluation of the health status. The interest is due mostly by the ability of generating models of the built structures being able to predetermine different levels of schematization, two-dimensional and three-dimensional, in order to be able to perform evaluation processes assigning simplified geometric contents that correspond to the physical reality of the artefacts. This paper intends to report some results of these experiences applied in archaeological domain, to the so-called Baths-Church at Hierapolis in Phrygia (Pamukkale, TR). In particular, the generation of accurate models from dense clouds and their reduction to models with simplified geometries too, is explored, with the further aim of testing automated strategies for features detection and editing process that leads to appropriate models for visual and analytical structural assessment. The accuracy and density parameters of the LiDAR clouds will be analysed to derive orthophotos and continuous mesh models, both to obtain the best results from the application of research algorithms such as region growing to detect blocks, and to allow visual analysis on digital models and not on site. The ability to determine with high accuracy both the size and the anomalies of the wall systems (out of plumb and other rotation or local mechanisms of collapse), together with the possibility of identifying the lay of the individual drywall blocks and also the signs of cracks and collapses, allow deriving suitable models both for FE (Finite Elements) analysis and DE (Discrete Elements) analysis, as well as analytical ones

2016 Central Italy Earthquakes: comparison between GPS signals and low-cost distributed MEMS arrays

Abstract. Modern seismic ground-motion sensors have reached an excellent performance quality in terms of dynamic range and bandwidth resolution. The weakest point in the recording of seismic events remains spatial sampling and spatial resolution, due to the limited number of installed sensors. A significant improvement in spatial resolution can be achieved by the use of non-conventional motion sensors, such as low-cost distributed sensors arrays or positioning systems, capable of increasing the density of classical seismic recording networks. In this perspective, we adopted micro-electro mechanical system (MEMS) sensors to integrate the use of standard accelerometers for moderate-to-strong seismic events. In addition, we analyse high-rate distributed positioning system data that also record soil motion. In this paper, we present data from the 2016 Central Italy earthquakes as recorded by a spatially dense prototype MEMS array installed in the proximity of the epicentral area, and we compare the results to the signal of local 1s GPS stations. We discuss advantages and limitations of this joint approach, reaching the conclusion that such low-cost sensors and the use of high rate GPS signal could be an effective choice for integrate the spatial density of stations providing strong-motion parameters

Damage survey of a historic town and comparison with past events after the 2016 central Italy earthquake

Central Italy is an active seismic area and many earthquakes struck the historic centre of Campi Alto di Norcia (Perugia) since its foundation in the 13th Cent. Nevertheless, every time, Campi has been restored without losing its identity, until the shocks occurred in 2016 caused the definitive collapse of a large part of it. Residential buildings have been restored introducing modern techniques and materials, as injections, jacketing and substitution of structural parts, which showed, already in the 1997 Umbria-Marche earthquake, their inefficiency and incompatibility with historic masonry. Therefore, today we can observe again the effects of the recent interventions and evaluate them on large scale. A first damage evolution is here reported, by mapping the damage levels to evaluate the causes of such a severe scenario. Surveys and studies after the 1997 earthquake provided the first correlation between structural interventions and damage, but major efforts were put in the definition of collapse mechanisms and in tools which could apply the new approach. Other earthquakes (L’Aquila 2009, Emilia 2012) confirmed the aetiology of certain seismic damages to specific interventions, but only qualitative relations were established. In addition, a description of seismic effects interpreted also as a result of specific interventions is still missing, especially on quantitative basis. The paper presents a systematic damage survey supported by a GIS system and a specific form, both aimed at defining, if possible, a relation between the damage on each intervention and the damage of a building as a whole

LIDAR DATA ANALYSES FOR ASSESSING THE CONSERVATION STATUS OF THE SO-CALLED BATHS-CHURCH IN HIERAPOLIS OF PHRYGIA (TR)

The LiDAR technology has aroused considerable interest in the field of structural study of historical buildings, aimed at the structural assessment in the presence of different states of stresses and at the evaluation of the health status.The interest is due mostly by the ability of generating models of the built structures being able to predetermine different levels of schematization, two-dimensional and three-dimensional, in order to be able to perform evaluation processes assigning simplified geometric contents that correspond to the physical reality of the artefacts.This paper intends to report some results of these experiences applied in archaeological domain, to the so-called Baths-Church at Hierapolis in Phrygia (Pamukkale, TR). In particular, the generation of accurate models from dense clouds and their reduction to models with simplified geometries too, is explored, with the further aim of testing automated strategies for features detection and editing process that leads to appropriate models for visual and analytical structural assessment. The accuracy and density parameters of the LiDAR clouds will be analysed to derive orthophotos and continuous mesh models, both to obtain the best results from the application of research algorithms such as region growing to detect blocks, and to allow visual analysis on digital models and not on site.The ability to determine with high accuracy both the size and the anomalies of the wall systems (out of plumb and other rotation or local mechanisms of collapse), together with the possibility of identifying the lay of the individual drywall blocks and also the signs of cracks and collapses, allow deriving suitable models both for FE (Finite Elements) analysis and DE (Discrete Elements) analysis, as well as analytical ones.</p

Mortar-based systems for externally bonded strengthening of masonry

Mortar-based composite materials appear particularly promising for use as externally bonded reinforcement (EBR) systems for masonry structures. Nevertheless, their mechanical performance, which may significantly differ from that of Fibre Reinforced Polymers, is still far from being fully investigated. Furthermore, standardized and reliable testing procedures have not been defined yet. The present paper provides an insight on experimental-related issues arising from campaigns on mortar-based EBRs carried out by laboratories in Italy, Portugal and Spain. The performance of three reinforcement systems made out of steel, carbon and basalt textiles embedded in inorganic matrices has been investigated by means of uniaxial tensile coupon testing and bond tests on brick and stone substrates. The experimental results contribute to the existing knowledge regarding the structural behaviour of mortar-based EBRs against tension and shear bond stress, and to the development of reliable test procedures aiming at their homogenization/standardization