1,721,014 research outputs found
Historic masonry monitoring by motion magnification analysis
No full textVibration monitoring of historic structures in urban environment is a relevant issue for health survey and early damaging detection in sustainable and enhanced resilient cities. This study explores the potentialities of vibration monitoring by Motion Magnification Analysis. Motion magnification acts like a microscope for motion in video sequences, but affecting only some groups of pixels. The motion magnification uses the spatial resolution of the video-camera to extract physical properties from images to make inferences about the dynamical behaviour of the object, e.g. to visualize at least the first mode shape, no matter its dimensions, since any point on the surface of the object can be considered a virtual sensor. Recently, a number of experiments conducted on simple geometries like rods and other small objects, as well as on bridges, showed the reliability of this methodology compared to accelerometers and lasers. Researchers have been also very interested in assessing the method’s feasibility, since conventional devices are surely more precise, but more expensive and much less practical. In this paper, we give an introduction to MMA and describe its application to the analysis of two full-scale historic masonry walls tested on shaking tables. This is an interesting point, because the size of tested walls is larger than usual small experimental set-ups implemented in MMA testbed until now. Results showed that MMA allowed a visual identification of fractures in advance. Moreover, we performed some conventional calculation for modal analysis of the walls, such as FRF and PSD, on MMA output data. Though the used equipment (camera, tripod and lighting) was of low quality, in order to test the methodology in an unfavourable environment with very high data noise, the estimate of the first modal frequency showed a good agreement with modal analysis by a more conventional optical system used as reference. © 2017 WIT Press
Finite element validation using displacement data from shake table tests within a virtual laboratory
No full textThe present paper shows an interactive and iterative methodology for the validation of finite element models with experimental data acquired during shaking table tests using a three-dimensional motion capture system. Such a system can detect the complete motion of up to hundreds of retro-reflective markers placed on the tested structure. The markers trajectories, reconstructed by spatial triangulation of camera rays, are processed with a dedicated displacement data processing (DDP) procedure to extract motion parameters. In the followed methodology a preliminary finite element analysis (FEA) is performed to identify the critical points of the model. Then such a FEA is integrated with the displacement data processed by DDP, focusing on the points where the strain energy concentration is most dangerous and allowing the numerical model validation. The displacements of selected markers are imposed at the corresponding nodes of the finite element model, while the displacements of the remaining nodes of the finite element analysis are compared with the corresponding markers on the real structure. In order to calibrate the model during the experimental investigation, the finite element model is updated at each step of the test sequence exploiting the hardware resources available in CRESCO, the ENEA HPC system. © Civil-Comp Press, 2014
Health assessment and ambient vibration testing of the “Ponte delle Torri” of Spoleto during the 2016–2017 Central Italy seismic sequence
No full textThe Ponte delle Torri is a large medieval masonry bridge, one of the main architectural heritage of Spoleto, Italy. The location of the bridge is less than 50 km from the main epicenters of the recent Central Italy earthquakes (Mw > 5.0) that occurred between August 2016 and February 2017. In addition, some minor quakes of the sequence (Mw between 3.0 and 4.0) occurred within 10 km from the bridge, causing some damages and fear among the population around Spoleto. In this context, the present paper aims at contributing to understand the effects on the structural health of the bridge by analyzing the ambient vibration data acquired before, during and after the seismic sequence, as changes in the dynamic behavior of the structure might indicate the evolution of the state of damage of the monument. In particular, vibration data were processed by modal analysis techniques for mutual validation of the extracted modal parameters. Environmental and vibration data were simultaneously acquired to take into account the seasonal effects on the dynamic behavior. Through a preliminary finite-element model (FEM) the modal shapes were obtained to choose the positions where to locate the sensors for the vibration spot acquisition session of June 2015. The same positions were acquired in October 2016 and at the end of May 2017. Subsequently, a more detailed FEM was produced based on a 3D reconstruction by structure-from-motion stereo-photogrammetry technique with high-resolution photos from unmanned aerial vehicle of the bridge. The model was validated through comparison with the damage pattern experienced by the bridge and then used for assessing the seismic safety by means of both, nonlinear dynamic and static push-over analyses. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature
3D photogrammetric reconstruction by drone scanning for FE analysis and crack pattern mapping of the "bridge of the Towers", Spoleto
No full textTechnological advances in the digital camera industry and computing resources make the use of photogrammetry a very fast, low-cost, contactless and non-destructive technique. It can represent a good alternative to obtain 3D information for monitoring and conservation of cultural heritage assets, especially where it is not possible to use 3D laser scanners and also in situations where areas to be inspected are not easily accessible [1]. Resolution generally depends on the number of images, their quality and the level of overlap between them, as well as hardware and software capabilities. Starting from 2D aerial or terrestrial photographic images, photogrammetry allows to reconstruct a 3D model in the form of a "point cloud" and also to derive accurate 3D measurements of large architectural elements. This paper is about stereo-photogrammetric scanning by drone performed by MENCI software s.r.l. aimed at the definition of the state of conservation of the "Bridge of the Towers" in Spoleto and its long term preservation without building scaffoldings. It was performed within the RoMA (Resilience enhancement of a Metropolitan Area) project, through an agreement between the "Italian National Agency for New Technologies, Energy and Sustainable Economic Development" (ENEA) and the "Italian Ministry of Cultural Heritage and Activities" (MIBACT). Photogrammetric scanning and FE modelling were applied within the project together with many other monitoring techniques in order to assess the bridge cracks pattern and its structural health by a multidisciplinary approach that allows their mutual validation [2]. As one of the most important problems in the use of photogrammetric 3D reconstruction is the considerable demand in terms of hardware and software resources for images processing and data storage, thanks to the HPC (High Performance Computing) resources provided by the CRESCO infrastructure (Research Computational Centre on Complex Systems), it was possible to analyse and process a large amount of high-resolution photos in order to detect the crack pattern and to assess the actual damage state to be monitored over time [3]. © 2017 Trans Tech Publications
Shaking table tests of an arch-pillars system and design of strengthening by the use of tie-rods
No full textIn arches and vaults, tie-rods play a decisive role in counterbalancing horizontal thrusts produced by both permanent and seismic loadings. In this paper, the effectiveness of flexible tie-rods to improve the seismic response of arch-pillars system is assessed by means of shaking table tests and simple analytical models, developed in the framework of displacement-based design. The reduced scale model, made of rigid blocks with dry joints, has been tested without tie-rod and considering different configurations of strengthening. Both experimental and theoretical results have proved the importance, in particular for this kind of flexible masonry structure, of improving displacement capacity rather then strength, because in this latter case other brittle mechanisms could be activated. The paper shows the possibility of describing the dynamic seismic response of rocking masonry structures, characterized by complex mechanisms made of many blocks and hinges, by an equivalent nonlinear SDOF system
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Modal identification from motion magnification of ancient monuments supported by blind source separation algorithms
No full textMotion Magnification (MM) is an emerging video processing methodology that acts like a microscope for motion in digital videos. Hardly visible motions are magnified leaving unchanged the general topology of the image. Therefore, the micro-displacements produced by vibrations can be amplified greatly and made available to the standard frequency domain analysis. The MM was recently successfully explored as a viable method to perform modal identification, at least in laboratory. In outdoor environment ambient vibration acquisitions are unavoidably affected by significant noise disturbing the modes identification. However, the first three or four modes, which are usually the most relevant to the dynamic behaviour of most structures, can be identified with little supervision, possibly reducing the calculation requirements as much as possible. All these tasks may be accomplished using MM together with the Blind Source Separation (BSS) algorithm. BSS allows the separation of mixed signals without previously known information about the mixture. MM provides the data while the BSS improves the identification of the modes by separating their contribution within the mixed noisy signals. A case-study is proposed to explore the application of the methodology to large ancient masonry structures, which represent very challenging objects for their structural complexities and heterogeneities. In particular, the studied structure was represented by an ancient bridge, the Ponte delle Torri, Spoleto. Due to the outdoor environmental difficulties, to the state of damage of the bridge and to the high level of noise in the video footages, this case-study has to be considered a very demanding one, nevertheless the modes were identified with good approximation in comparison to the results by Operational Modal Analysis (OMA) techniques, applied to ambient vibration data from seismographs equipped with accurate triaxial velocimeters
Estimating the epidemic growth dynamics within the first week
No full textInformation about the early growth of infectious outbreaks is indispensable to estimate the epidemic spreading. A large number of mathematical tools have been developed to this end, facing as much large number of different dynamic evolutions, ranging from sub-linear to super-exponential growth. Of course, the crucial point is that we do not have enough data during the initial outbreak phase to make reliable inferences. Here we propose a straightforward methodology to estimate the epidemic growth dynamic from the cumulative infected data of just a week, provided a surveillance system is available over the whole territory. The methodology, based on the Newcomb-Benford Law, is applied to the Italian covid 19 case-study. Results show that it is possible to discriminate the epidemic dynamics using the first seven data points collected in fifty Italian cities. Moreover, the most probable approximating function of the growth within a six-week epidemic scenario is identified
Urban transport vibrations and cultural heritage sites in Rome: The cases of the temple of Minerva Medica and of the Catacomb of Priscilla
No full textThe coexistence of modern transport systems with the presence of cultural heritage sites in urban environments is a very crucial issue in sustainable city planning. In particular, in the historic centre of cities with plenty of scattered archaeological sites, such as Rome, urban traffic vibrations must be monitored to assure the conservation of ancient monuments. In fact, cultural heritage sites may suffer from traffic vibration impact in terms of aesthetical damages even in cases in which the structural health is not compromised. In such context, the present paper focuses on the impact of traffic vibrations induced on two monuments studied within the CO.B.RA. project (aiming at developing advanced technologies and methods for the conservation of cultural heritage). The so-called Temple of Minerva Medica and the Catacomb of Priscilla are exposed to different types of traffic vibration sources and are characterized by different structural conditions. Besides the ambient vibration monitoring, several non-destructive tests (NDTs) and noncontact investigations were conducted at the two sites in order to study the state of damage and the structural conditions of the two monuments. In particular, the ambient vibration monitoring gave remarkably different outcomes in these two cases and provided objective data for interesting observations on the sustainability of tramways, railways and road traffic near such diverse archaeological assets. © 2017 WIT Press
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