Structural health monitoring of historical buildings in Italy: applications and uncertainty overview

Structural Health Monitoring (SHM) is currently more and more considered (and applied) in It- aly for the study of Cultural Heritage (CH) buildings, as a key activity to increase the knowledge on their structural behavior and to have a deeper insight on their actual conditions, reducing uncertainties connected to material properties and structural capacity. In recent years the research group at the University of Padua, in collaboration with public administrations, has installed several SHM systems on heritage structures: two case studies are presented and discussed within this paper. The Arena of Verona and the Cathedral of Conegliano are excellent examples of ongoing monitoring activities, performed through static and dynamic approaches. In parallel to the application of innovative monitoring techniques, statistical models and data processing proce- dures have been developed and applied in order to eliminate uncertainties and exploit monitoring results for an effective assessment and protection of historical constructions

Uncertainty quantification in structural health monitoring: applications on cultural heritage buildings

In the last decades the need for an effective seismic protection and vulnerability reduction of cultural heritage buildings and sites determined a growing interest in structural health monitoring (SHM) as a knowledge-based assessment tool to quantify and reduce uncertainties regarding their structural performance. Monitoring can be successfully implemented in some cases as an alternative to interventions or to control the medium- and long-term effectiveness of already applied strengthening solutions. The research group at the University of Padua, in collaboration with public administrations, has recently installed several SHM systems on heritage structures. The paper reports the application of monitoring strategies implemented to avoid (or at least minimize) the execution of strengthening interventions/repairs and control the response as long as a clear worsening or damaging process is detected. Two emblematic case studies are presented and discussed: the Roman Amphitheatre (Arena) of Verona and the Conegliano Cathedral. Both are excellent examples of on-going monitoring activities, performed through static and dynamic approaches in combination with automated procedures to extract mean- ingful structural features from collected data. In parallel to the application of innovative monitoring techniques, statistical models and data processing algorithms have been developed and applied in order to reduce uncertainties and exploit monitoring results for an effective assessment and protection of historical constructions. Processing software for SHM was implemented to perform the continuous real time treatment of static data and the identification of modal parameters based on the structural response to ambient vibrations. Statistical models were also developed to filter out the environmental effects and thermal cycles from the extracted features

Experimental Investigations and Seismic Assessment of a Historical Stone Minaret in Mostar

Minarets, tall structures, connected or not to the mosque attract attention due to their specific architectural features. Vulnerability to seismic damage has been witnessed throughout history on tall and slender structures after earthquake ground motions. In that respect, it is of the utmost importance to investigate the dynamic characteristics and resilience of historical stone minarets. This paper aims to provide the results of an on-site dynamic investigation of a stone minaret in Mostar and deliver its seismic assessment. The minaret is part of the Tabačica mosque built at the turn of the 16th and 17th century in the City of Mostar, Bosnia and Herzegovina. The on-site investigation comprised dynamic identification of the minaret by ambient vibration testing and qualitative estimation of the masonry wall by sonic pulse velocity testing. Besides the modal analysis a time-history analysis was performed by using the Applied Element Method (AEM), considered an appropriate tool for assessing the behavior of historic masonry structures. A good match is found between the first natural frequency obtained by the on-site investigation and the modal analysis which is a solid basis for further seismic assessment of the minaret as a slender tower-like structure. The concentration of stresses is observed at the transition zones

Dynamic Identification & Monitoring of the churches of St. Biagio and St. Giuseppe in l\u2019Aquila

In the framework of a wide investigation campaign carried out by the authors - together with the Polytechnic of Milan - in the churches of St. Biagio d\u2019Amiterno and St. Giuseppe dei Minimi, severely struck by the 6th of April 2009 earthquake, dynamic investigation (Operational Modal Analysis) and structural monitoring were employed in order to obtain a first snapshot of the dynamic characteristics of the aggregate buildings \u2013 also for model calibration purposes \u2013 and to control their dynamic features with the passing of time. The st. Biagio church\u2019s main damage was the collapse of the tympanum on top of the facade; other damages involved part of the central nave timber vault, the shallow domes of the lateral naves and some cracking of the pillars and of the apses. The rest of the structures showed an overall satisfying seismic performance. The oratory of St. Giuseppe dei Minimi reported higher \u2013 however localized - damage: the fa\ue7ade was subjected to a significant overturning mechanism towards the outside, as indicated by the wide cracks on the two side walls, close to the corners. Few other damage mechanisms were detected, such as shear damage in the fa\ue7ade and in the back wall of the apse. The complex is currently undergoing structural interventions, namely repair and seismic improvement, to correct their deficient - however globally satisfying - seismic performance. The paper reports the outcomes of the ambient dynamic identification of the two churches (spring-fall 2010) and of some portions of the surrounding aggregate buildings, which showed - according to their different structural configuration - a marked different dynamic behavior, as well as the results of the first months of the structural static and dynamic monitoring (installed in Dec 2010), consisting of 6 accelerometers, 8 displacement transducers and two temperature and relative humidity sensors

SHM for historical buildings: preventive and post-earthquake controls

Structural health monitoring (SHM) is being more and more applied in the study of cultural heritage (CH) buildings, as a key activity to increase the knowledge on their structural behavior and to have a deeper insight on their conditions. This knowledge allows to carry out with more confidence (and only if necessary) possible strengthening interventions, but also to prevent the execution of intrusive repair works, if they are not justified by an experimentally demonstrated worsening of the structural conditions. The use of monitoring systems applied under ordinary conditions and installed on CH structures allows to: (i) validate the functioning of the adopted structural models; (ii) identify the ongoing damaging processes; (iii) validate the effectiveness of the strengthening interventions. In case of a seismic event, SHM can furthermore prove its usefulness in order (i) to quantitatively evaluate the progression of the assessed damage pattern, (ii) to design effective and urgent interventions if an unsafe displacement patterns is recorded, (iii) to define an early warning procedure for the safety of the workers employed in the strengthening interventions. Monitoring can also be effective when implemented on seriously damaged buildings, if the time schedule for the interventions is difficult to be a priori planned. In this framework, the authors (University of Padova, Italy) in collaboration with the officer of the Cultural Heritage Authority, the university of Nagoya (Japan), the National Institute of the Conservation and Restoration (ISCR) designed and installed SHM systems on six representative and emblematic CH buildings in L\u2019Aquila after the devastating earthquake occurred on the 6th of April 2009 in the Abruzzi Region. The selected case studies SHM systems \u2013 presented in the paper \u2013 will allow to confirm the effectiveness of the use of structural monitoring during and after the emergency activities in case of a seismic event

The dynamic behaviour of the mammoth in the Spanish fortress, L’Aquila, Italy

The fossil remains of a “Mammuthus Meridionalis” were found the 25th of march 1954 in a lime quarry close to the city of L’Aquila. The Mammoth skeleton was soon “reconstructed” on a forged iron frame, and it was located in one of the main halls of the Spanish fortress in L’Aquila. A comprehensive restoration was recently completed (2013-2015), also considering the study of the adequacy of the supporting frame, which demonstrated to survive the relevant 2009 l’Aquila earthquake. After a laser-scanner survey, allowing to build a very detailed Finite Element model, Operational Modal Analysis was employed in order to obtain the dynamic identification of the structure. Results of the experimental activities explained the capacity of the structure to bear the 2009 main shock, since the natural frequencies demonstrated to be quite reduced. The structure acted as a “natural” seismic device, avoiding to reach its Ultimate Limit State however paying the toll of relevant displacements. The seismic motion caused several cracks at the edge of the bones, indicating the non-fulfilment of the ALS (damage Limit State of Artistic contents). A proposal for seismic isolation and redesign of the supporting frame was then discussed. The paper illustrates the scientific activities assisting the restoration intervention, entailing a multidisciplinary approach, in the fields of restoration, palaeontology and seismic engineering

Emergency actions for the preservation of cultural heritage buildings after the L\u2019Aquila earthquake

The earthquake occurred on the 6th of April 2009 in the Abruzzo Region of Italy seriously hit the Cultural Heritage (C.H.) patrimony with major destructive effects on L\u2019Aquila, a city of 70,000 inhabitants with the size and the historical and strategic importance of the region\u2019s capital. The toll in terms of structural damages was enormous, also considered that a vast amount of buildings were made of poorly arranged masonry composed by round pebbles, with mortar of scarce mechanical characteristics

The Spanish Fortress in l\u2019Aquila: emergency actions, investigations and monitoring

The earthquake occurred on the 6th of April 2009 in the Abruzzo Region of Italy seriously hit the Cultural Heritage (C.H.) patrimony with major destructive effects on l\u2019Aquila, a city of 70,000 inhabitants with the size and the historical and strategic importance of the capital of the Region. The emergency activities to protect the C.H. have been developed following two parallel levels: (i) damage survey and (ii) design and implementation of temporary safety measures. The organization of emergency actions was managed by a centralized structure, the so-called Function 15 \u201cProtection of Cultural Heritage\u201d directed by a Special Commissioner. The structure coordinated the on-site surveys of protected buildings and the design and implementation of temporary safety measures. Several Italian Universities during and after these first emergency actions were invited by the Commissioner to work on selected Case Histories: the aim was on the one hand to provide a first interpretation of the observed damages and on the other hand to define some guidelines for a higher level of investigation. In this paper the case study of the Spanish Fortress in L\u2019Aquila supervised by the authors is reported with the description of the earthquake damages and the emergency intervention derived from the \u201cPalaces template\u201d [Ref. 1]. The emergency interventions were carried out in order to avoid progressive damages due to the following several aftershocks. The authors decided together with the officers of MiBAC (Ministry of C.H.) in L\u2019Aquila to proceed with further on site investigations and monitoring. A series of non destructive and minor destructive testing were performed in the Spanish Fortress by the research groups of the Politecnico of Milan and the University of Padova in order to characterize and evaluate quantitatively and qualitatively the state of damage of the masonry structures (walls and pillars) and to identify the structural response of the most damaged wings of the building. The experimental campaigns included: (i) sonic pulse velocity tests, radar tests and thermography, (ii) single and double flat jack tests, (iii) dynamic identification tests. The ND tests were mainly aimed at defining the state of damage of the heavy pillars and of the transversal bearing walls on the ground floor and at designing the most effective strengthening interventions. Furthermore a permanent static and dynamic monitoring system was installed by the ISCR (Rome) and the University of Padova respectively in order to control the dynamic characteristics of the fortress, constantly verify the damage pattern of the structure and provide a step-by-step monitoring procedure during each phase of restoration

Structural Health Monitoring of historical buildings: preventive and post-earthquake controls

Structural health monitoring (SHM) has been recently more and more exploited in the study of cultural heritage (CH) buildings, as a key activity to increase the knowledge on their structural behavior and to have a deeper insight on their conditions. This knowledge allows to carry out with more confidence and only if necessary a strengthening intervention, but also to prevent the execution of intrusive repair works, if they are not justified by an experimentally demonstrated worsening of the structural conditions. The use of monitoring systems applied under ordinary conditions and installed on CH structures allows to: (i) validate the functioning of the adopted structural models; (ii) identify the ongoing damaging processes; (iii) validate the effectiveness of the strengthening interventions. The effectiveness of this approach is demonstrated by the installation of SHM systems on four important monuments in northern Italy (Verona Arena and the stone tomb of \u201cCansignorio della Scala\u201d in Verona, the \u201cBertoliana\u201d library in Vicenza and the church of S. Sofia in Padova) and on the Qutb Minar in New Delhi. In case of a seismic event, SHM can furthermore prove its usefulness in order to: (i) evaluate quantitatively the progression of the damage pattern, (ii) design effective and urgent interventions if an unsafe displacement patterns is recorded; (iii) define an early warning procedure for the safety of the workers employed in the strengthening interventions. Monitoring can also be effective when implemented on seriously damaged buildings, if the time schedule for the interventions is difficult to be a priori planned. A low cost diffused monitoring system permits to proceed more urgently on selected cases, if a worsening of their structural conditions is noted, or to postpone the interventions in a successive phase, if the assessed damage pattern maintains an acceptable stability. In this framework, the authors and the university of Padova in collaboration with the officer of the Cultural Heritage Authority, the university of Nagoya (Japan), the National Institute of the Conservation and Restoration (ISCR) and the Veneto region designed and installed SHM systems on six representative and emblematic CH buildings in l\u2019Aquila after the devastating earthquake occurred on the 6th of April 2009 in the Abruzzo Region. The selected case studies (S. Agostino church, S. Biagio church and S.Giuseppe oratory, S. Marco church, Civic Tower and Spanish Fortress) give the possibility to validate the use of monitoring during and after the emergency activities in case of a seismic event