1,721,038 research outputs found
Augustus Bridge in Narni (Italy): Seismic Vulnerability Assessment of the Still Standing Part, Possible Causes of Collapse, and Importance of the Roman Concrete Infill in the Seismic-Resistant Behavior
Full text link[EN] The final results of advanced FE analyses performed on a Roman arch bridge, namely the Augustus Bridge (Ponte di Augusto) in Narni, center Italy are presented. The bridge, one of the most impressive Roman artworks, has been injured by several traumatic events during the millennia, the result of which is its present ruined condition. The aims are manifold, starting from a better understanding of the causes at the base of the partial collapse occurred on the central pier, passing through a seismic assessment of the ruined still standing part and ending with a discussion on the role played by Roman concrete on the stability against horizontal actions. An advanced material model exhibiting damage, plastic deformation, and softening in both tension and compression is adopted for Roman concrete. Both the case of a foundation settlement of the central pier and the application of a seismic excitation are investigated, by means of nonlinear static and nonlinear dynamic analyses. Numerical simulations are carried out within the FE code ABAQUS by means of detailed 3D models, using historical documentation and previous results of the latest research carried out on materials, assuming realistic models on both the uniaxial stress-strain relationships under nonlinear load-unload conditions by using independent damage parameters in tension and compression, and the multiaxial behavior ruled by a regularized Drucker-Prager strength criterion. The methodological approach turns out to be potentially valid for all existing Roman bridges. Results highlight the vulnerability of the ruins, that the collapse of the central part was probably due to settlement of the central pier and that Roman concrete plays a crucial role in increasing the stability against earthquake actions.Bertolesi, E.; Milani, G.; Lopane, FD.; Acito, M. (2017). Augustus Bridge in Narni (Italy): Seismic Vulnerability Assessment of the Still Standing Part, Possible Causes of Collapse, and Importance of the Roman Concrete Infill in the Seismic-Resistant Behavior. International Journal of Architectural Heritage. 11(5):717-746. doi:10.1080/15583058.2017.1300712S71774611
Numerical insight on the interaction effects of a confined masonry tower
No full textThe present paper provides a numerical insight into the structural behavior of a confined masonry tower. The study is carried out in relation to the Gabbia Tower, the tallest historical masonry tower in the city of Mantua (northern Italy), which is surrounded by multistory masonry buildings on all its sides. Three 3D FE numerical models are critically compared to investigate the sensitivity of the structural behavior of the tower with respect to the adjacent buildings, both in the linear and non-linear fields. Firstly, the tower is studied as a fictitious building isolated from the context, then two different constraints are considered for modeling the interaction between tower and buildings. In the first case, linear elastic springs are inserted along the height of the tower; while the other one focuses on the effect provided by the adjacent buildings, whose walls are modeled as monolithic elements joined to the main body of the tower. The validation of the FE models is carried out in the linear field by comparing mode shapes and frequencies resulting from the numerical modal analysis with the available experimental data provided by the ambient vibration test conducted in 2012. The effect of the different constraints on the seismic response of the tower is then investigated by performing a set of non-linear dynamic analyses and considering the accelerograms recorded during the earthquake of May 29, 2012 by the fixed station located in Mantua as seismic input. Numerical results indicate the modeling of the surroundings as an essential step for a realistic analysis of confined towers. In particular, the simulations highlight advantages and limitations of the proposed modeling approaches of the constraints, both in the linear and non-linear fields
ANALISI DELLA SICUREZZA DI TRAVI IN CA SOGGETTE A D AZIONE DI ESPLOSIONE
No full textIl carico da esplosione presenta grandi incertezze per quanto riguarda la posizione, l’intensità e la possibilità di accadimento. Sommando a queste incertezze quelle relative ai materiali, alla geometria e i sovraccarichi, si rende necessario un’analisi statistica finalizzata ad una più realistica stima della risposta strutturale. L'articolo presenta i risultati ottenuti da una indagine parametrica sulla risposta di travi inflesse in calcestruzzo armato soggette a carichi di tipo esplosivo. Mediante analisi dinamica non lineare di un sistema equivalente ad un grado di libertà sono state esaminate le risposte probabilistiche, in termini di massimo spostamento e di fattore di duttilità, di elementi inflessi in c.a. a seguito di azioni esplosive
Semi-automatic calibration of numerical models for the seismic safety assessment of masonry towers embedded in building aggregates
No full textThe present work addresses the topic of automated calibration of numerical models starting from the experimental characterization of the structure's dynamic behaviour. The importance of the topic is well known in the literature, especially in cases where it is necessary to have at disposal validated numerical models, necessary for the correct evaluation of the safety of existing buildings. Generally, the calibration problem is developed with a manual approach (manual tuning), with a positive outcome whenever there is a good knowledge of the boundary and internal constraint conditions and the elastic mechanical properties of the construction's constituent materials. Conversely, the positive outcome is particularly difficult to achieve manually when there are non-homogeneous and/or complex structures, as in the cases of historic masonry structures, which are often the result of constructions carried out at different times, organized in aggregates whose interaction between the portions is not simple to understand. For this purpose, the present work, using commercial software and specially prepared routines, illustrates a semi-automatic procedure, which employs genetic algorithms, suitable for the optimized identification of the numerical model that best represents the structure's experimental dynamic behaviour. The procedure is presented with reference to two case studies: the Gabbia Tower historic masonry aggregate in Mantua and the bell tower of the Monastery of the Ursuline nuns in Capriolo, Brescia. In the first case, in addition to the experimental dynamic characterization, a good instrumental characterization of the tower's masonry mechanical properties is available. In the second case, alongside a good experimental dynamic characterization, only a qualitative estimate of the masonry mechanical properties, based on visual inspections, is available. The two case studies allow for testing the validity of the numerical models’ calibration procedure, necessary for their application in the field of safety checks. Finally, for the case studies analysed the work presents an assessment of seismic vulnerability starting from the models identified with the semi-automatic procedure. The seismic vulnerability assessment was obtained using non-linear static analysis following the N2 method
Interpretation of collapse modalities for a timber roof truss
No full textRoof structures in historical buildings are often based on complex timber trusses; this is typically the situation of theatre buildings, where a wide room is present and large spans have to be covered. Several studies have been done on such structural systems showing that, in the case of complex roof systems, connections between timber elements were conceived in the past mainly to resist vertical loads corresponding to symmetrical patterns, with no consideration of eccentric loads and horizontal forces. In the paper, this problem is investigated with reference to the specific case study offered by a theatre, where a queen post truss was adopted for the roof system and the sudden collapse of one truss has occurred. The theatre, which is located in northern Italy, was built at the beginning of the 19th century. Although some modifications were made through time, the roof structure has preserved the original configuration. A precise identification of the real structural conditions has been obtained on the basis of the results of laser scanning and photogrammetric surveys. On this basis, numerical models have been developed in order to analyse a variety of load scenarios compatible with the observed structural collapse, with the final purpose of highlighting possible deficiencies in the original structural configuration, in line with the collection of similar cases which are reported in the literature
'HYBRID' FULL MODELS FOR SEISMIC ASSESSMENT OF MASONRY AGGREGATES THROUGH PUSHOVER ANALYSIS
No full textMost of the historical city centres in Southern Europe are made up of masonry buildings clustered in aggregate, which are a result of the urban tissue transformation over time. Recent earthquakes have shown their high vulnerability because buildings were built without any anti-seismic criterion, relying on simple rules of thumbs. Since the seismic behaviour of masonry aggregates cannot be a priori predicted - because of complex geometries, presence of materials having different behaviours and interactions among adjacent buildings - accurate analyses, such as pushover analyses, shall be performed. Masonry aggregates are typically characterized by the presence of different structural typologies, thus pushover analyses are generally performed on partial models, representing significant portions of the whole aggregate. The critical point in this type of analysis is the identification of the minimum length of the portions of the neighbouring walls that actually contribute to the extra-redundancy of the structural system, which cannot be taken into account within partial models. Hence the idea to consider “hybrid” full models, in which the material behaviour is assumed non-linear only for the portion subject of investigation, while it is assumed linear elastic for the context. This contribution shows the results - part of a wider work - obtained by means of pushover analyses performed for the ex-monastery of Santa Maria della Pace in Piacenza, Italy, on full and partial models of the entire aggregate with different material modelling assumptions, and the model that best represents the actual behaviour of masonry aggregates is proposed
COMPARISON OF THE RECORDED SEISMIC SIGNALS FOR THE 2012 EMILIA AND 2016 CENTRAL ITALY SEISMIC SEQUENCES WITH THE DESIGN EARTHQUAKES BASED ON THE PSHA APPROACH
No full textThe recent seismic sequences occurred in 2012 in the Emilia region and in 2016 in Central Italy have confirmed the high level of vulnerability typical of masonry historical buildings and historical centres. Among these, the historical centre of Amatrice was razed to the ground and most of the historical buildings of municipalities in the epicentral area suffered partial or total collapse. Ground motion recordings highlighted a remarkable difference with the design earthquakes provided by the national seismic hazard map, which is based on the PSHA (Probabilistic Seismic Hazard Assessment) approach. Specifically, the response spectra of the signals recorded at Finale Emilia and Mirandola (2012) and at Norcia and Amatrice (2016) have been compared to the design spectra prescribed by the national building code; from comparison, the strong underestimation of the design spectral accelerations is evident, especially for the historic centre of Amatrice, due to the additional effect of local amplification. All recent Italian earthquakes (L'Aquila 2009, Emilia 2012, Central Italy 2016) and many others around the world, have shown that the PSHA approach does not provide reliable results in case of severe events. On the contrary, the technical literature shows that the NDSHA (Neo-Deterministic Seismic Hazard) approach generally provides reliable results. The need to update the seismic regulations, therefore, is clear in view of a preventive policy against the collapse of historic centres and monuments, based on the correct definition of seismic hazard levels. In the present contribution the analysis of the above seismic events is presented, being part of a wider analysis on the effects produced on the built heritage by seismic sequences
The 2016 Central Italy seismic sequence: linear and non-linear interpretation models for damage evolution in S. Agostino’s church in Amatrice
No full textAn extensive numerical investigation of the structural behavior of the masonry church of Sant’Agostino in Amatrice (Italy) during the 2016–2017 seismic sequence is presented. The seismic performance of the church is studied in relation to the most energetic shocks of the sequence, occurred on August 24th, 2016, and October 30th, 2016, whose seismic parameters (PGA, Trifunac duration, Arias intensity, destructiveness potential factor) are analyzed in detail. In particular, a comparison between ground motion data recorded by different stations is presented in order to evaluate the influence of local amplification effects on the structural behavior. To achieve this goal, the ground motion data recorded by the permanent accelerometric station (AMT) located in Amatrice on type B soil and belonging to the National Accelerometric Network (RAN) are firstly considered. Then, they are critically compared with those provided by an accelerometric station temporarily installed after the first main shock in the downtown area close to the church site, showing a clear amplification due to the site effects. The dynamic behavior of S. Agostino’s church is numerically investigated by carrying out a set of non-linear dynamic analyses on the 3D finite element model of the church developed in Abaqus CAE and considering as seismic input both the accelerograms recorded by the AMT fixed station and those including the local amplification effects. Non-linear properties of materials are taken into account by defining an elasto-plastic constitutive law with reasonable damage parameters in tension. Numerical results are evaluated in terms of displacement time-history of some relevant control points located on the masonry walls and maps of tensile damage cumulated at the end of the simulations. Numerical results are in good agreement with the evidence based behavior of the structure, thus validating numerical simulations as effective tools for seismic analysis of masonry buildings. Furthermore, a hypothetical strengthening intervention concerning the improvement in masonry mechanical properties is implemented in the model to investigate its positive role in preventing collapse. In the latter case, the approach provides useful hints in interpreting the behavior of the church under the application of repeated accelerograms
An evaluation of the soil-structure interaction in the non-linear dynamic analysis of masonry towers
No full textThe object of the paper is the influence the soil-structure interaction on the dynamical response of a masonry
tower, for which a high level of stress is involved already in the static field. The relevant deformations and
displacements at the base of the tower suggest that a significant volume of ground is engaged into the overall
dynamic response, both as a participating mass and as a potential carrier of energy dissipation. In order to
investigate this aspect and assess the sensitivity of the dynamic response of the soil-structure system to different
soil characteristics, the non linear dynamic response of a case study is analyzed, by including in the model a
significant volume of foundation soil and considering two different ground types. The numerical model is based
on a specific Rigid Body and Springs approach, able to model the significant inelastic aspects of the constitutive
behaviour and the meso-scale damage mechanisms with a moderate computational effort
On the characterization of materials and masonry walls of historical buildings: Use of optical system to obtain displacement maps in double-flat jack tests
Full text linkAmong the testing techniques aiming at the mechanical characterization of masonry, the double flat-jack testing method is widely adopted to identify the local value of significant parameters needed to perform structural analyses, such as elastic modulus, Poisson’s ratio and compressive strength. The experience gained from many applications has allowed not only to collect experimental data concerning different types of masonry, but also to highlight the difficulty in the interpretation of the results and the limitations of both single and double flat-jack tests. Although the accuracy of the flat-jack technique in detecting strength and deformability behavior of masonry is still debated in the technical literature and practical activities, changes in the testing procedure aiming at ascertaining the validity of the test results have not been formally defined yet. After a brief description of the standard test procedure and its uncertainties, the present paper proposes an upgrade of the test procedure for improving the level of reliability of the test results. In particular, an experimental case study related to a historical brick masonry building located in Italy is presented to point out the additional information necessary to validate the results of the testing process
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