Finite element micro-modelling for the characterization of inclined head joints archaeological masonry: the case of Villa Diomede in Pompeii

Villa Diomede is a great roman building located on the western corner of the modern archaeological site of Pompeii, built during III century BC and discovered between 1771 and 1774 during archaeological excavations. The system is composed by three levels: the road level, the garden level, which hosts the portico structure, and the underground level. The building includes diverse types of masonry with a wide range of unit shapes, dimensions and materials (i.e. tuff, limestone, volcanic stone, clay brick etc.). Besides, an unconventional tuff masonry type was observed on some structures of the garden; it reveals inclined head joints, whose structural function is still unknown. The paper reports the numerical micro-modeling of this particular texture of masonry, where the constitutive materials (tuff units and mortar) are discretized. The main goal of the work is the assessment of inclined masonry joints as an aseismic detail compared with widespread traditional tuff running bond masonry. Micro models of masonry wallettes were created assigning a non-linear constitutive behavior, i.e. total strain crack model (with a parabolic behavior in compression and an exponential softening behavior in tension, whereas damage due to tensile cracking was modeled adopting a rotating crack model). Moreover, brittle 2D interfaces were modeled between mortar and units at inclined joints surfaces. The paper focuses on numerical prediction of compressive response of masonry models subjected to uniaxial compressive tests.Postprint (published version

Seismic analysis of masonry structures applying and comparing different numerical approaches: finite element and macro-element methods

Building rehabilitation is increasingly important in the construction sector, both to improve functional aspects and for conservation of architectural heritage. Masonry structures are a large portion of the existing building stock and have proven to be vulnerable to seismic loads. Indeed, in earthquake-prone areas, buildings safety and conservation rely on the assessment of its seismic vulnerability. Different numerical modelling approaches have been proposed for seismic analysis of masonry structures, but the criteria for their use need to be better defined. This work aims at comparing different numerical approaches for seismic analysis in order to establish suitable application criteria. Two modelling methods, i.e. a finite element macro-model in DIANA software and a discrete macro-element method in 3DMacro software, are compared in predicting the damage pattern and the stiffness and strength evolution of masonry buildings under incremental static loading. Pushover analyses are performed on a building complex of the University of Padova. Geometrical data were available from a previous survey, but the masonry mechanical characteristics were unknown. So, a comprehensive estimation of the material properties within the range of values recommended in the literature and design codes is performed. Parametric analysis is then carried out to evaluate the influence of given parameters, such as mesh resolution and masonry tensile and shear strengths, on the global response of the models. A good agreement has been found with respect to the crack patterns and base shear capacity obtained from the two modelling approaches. The advantages and limitations in using each of them are identified

A Detrimental Feedback Loop: Deleveraging and Adverse Selection

Market distress can be the catalyst of a deleveraging wave, as in the 2007/08 financial crisis. This paper demonstrates how market distress and deleveraging can fuel each other in the presence of adverse selection problems in asset markets. At the core of the detrimental feedback loop is agents' desire to reduce their reliance on distressed asset markets by decreasing their leverage which in turn amplifies the adverse selection problem in asset markets. In the extreme case, this leads to a market breakdown. I find that adverse selection creates both an "ex-ante" inefficiency because it distorts agents' long-term leverage choices and an "interim" inefficiency because it distorts agents' short-term liquidity management. I derive important implications for central bank policy

Integrated Methodologies Based on Structural Health Monitoring for the Protection of Cutural Heritage Buildings

In the last decades the need for an effective seismic protection and vulnerability reduction of strategic structures and particularly the architectural heritage determined a growing interest in Structural Health Monitoring (SHM) as a measure of passive mitigation of earthquake effects. The object of monitoring is to identify, locate and classify type and severity of damages induced by external actions or degradation phenomena and to assess their effects on the structural performance. In this way it is possible to take appropriate measures to reduce the danger of collapse and, when necessary, perform strengthening interventions to improve the structural and seismic capacity. Motivated by the above reasons, this thesis aims at providing a contribution to the development of techniques and integrated methodologies, based on SHM, for the assessment and protection of Cultural Heritage (CH) buildings and monuments. Firstly, after a detailed state of the art review on specific topics related to SHM of civil engineering structures, a new methodology for the implementation of monitoring techniques on historic masonry structures is proposed. Selected case studies, equipped with distributed sensors and acquisition systems, allowed the definition and successive validation of SHM as a knowledge-based assessment tool, implemented to evaluate intervention needs, following an incremental approach during their execution, and to control the damage states of buildings in a post-seismic scenario. In order to maximize the benefits of SHM and optimize the entire process, dedicated software for static monitoring and automated algorithms for modal parameters identification have been developed, able to provide almost real time information on the health state of the monitored structure. Finally integrated procedures based on robust statistical and numerical models have been implemented to interpret and exploit SHM outputs to assess the structural conditions of the investigated CH buildings

Knowledge-based data warehouse of interventions for the protection of masonry historical heritage

The great social, cultural and economic losses caused by seismic events on the cultural heritage assets have stimulated, in the last decades, a great research effort in the development of new integrated knowledge-based approaches and tools for their protection from earthquake-induced risk. Great amounts of data have been collected and several databases developed so far to gather information about peculiar aspects on the seismic behaviour of masonry historical buildings. The detail level of such databases is usually influ- enced by the required survey or intervention, with a generalised lack of information on the fundamental pa- rameters that affect the seismic response, i.e. boundary conditions, used materials, types of connections and constraints, etc. A global systematization is required, to take advantage from the considerable and precious amount of available data, linking all information on the basis of the relation between construction typologies and elements and failure mechanisms, including also survey and monitoring procedures and tools available in literature. A new web-based data warehouse was developed within the FP7 European research project NIKER (2010-2012) “New Integrated Knowledge-based approaches to the protection of Cultural Heritage from Earthquake-induced Risk”) to collect, systematize and analyse available data. This tool is able to link con- struction typologies and structural elements with collapse mechanisms into a matrix of interventions where end-users can easily select optimum solutions for the seismic improvement and assess the effectiveness, on the basis of pre- and post-intervention parameters. The interactive and dynamic functionalities, together with the capacity of cross-correlation of information at different knowledge levels and the sharing philosophy of a web-based system, make the data warehouse a powerful tool for a new innovative, integrated and knowledge based approach to the protection of cultural heritage, useful both to professionals and researchers

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

Dynamic behavior of a two-storey cross laminated timber mockup

Timber constructions have gained an increasing attention in the last years, due to the limited installation time and the reduced expertise in manpower required, since panels assemblage is mainly based on dry mounting techniques. Among these, Cross Laminated Timber (CLT) products are extensively used in constructions, as they allow to overcome the main weaknesses of hardwood artifacts. Moreover, CLT components are also being tested within the restoration and re-use of existing buildings. Since these timber products are relatively new in the construction market, experimental data and site investigations are still limited and some aspects still unknown. Among the many, dynamic characterization of CLT structures, and related model updating, is rare in literature. In such a context, an experimental campaign aimed at assessing the linear dynamic behavior of CLT structures was carried out. A building-scale specimen (mockup) was constructed; it was made of C24 CLT walls and diaphragms (floor and roof) with 10- and 14-cm thick panels, respectively, connected through steel brackets and screws. The mockup was investigated via dynamic identification tests, by implementing 12 piezoelectric accelerometers, i.e., 4 on the first floor and 8 on the roof. The experimental characterization was aimed at: (i) assessing the structural dynamic behavior and identifying the role of structural details on it; (ii) evaluating the experimental stiffness, compared to analytical predictions. At last, a finite element (FE) model was implemented and updated based on the experimental outcomes

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