Search

This paper describes the shaking table testing performed on the full-scale prototype of a device developed in the framework of the EC Collaborative Project SILER (Seismic-Initiated events risk mitigation in Lead-cooled Reactors) to protect the seismic gap in Generation IV LFRs (Lead-cooled Fast Reactors) provided with base isolation. The need of a seismic gap is due to the relative movement between the seismically isolated building and the adjacent ones, during earthquakes. In fact, collisions between the reactor building and the pit wall during beyond design seismic events can be avoided only by the presence of sufficient clearance between the two structures. The joint cover shall be waterproof, fireproof and resistant to impacts. The specimen was a 2.5 x 3.45 m full-scale prototype subjected to three seismic tests, sine and combined sine-sweep tests at the UTTMAT-QUAL laboratory of the ENEA Casaccia Research Center. Together with traditional accelerometers, a 3D motion capture system was used to measure triaxial absolute displacements with easy and fast test set-up, high accuracy and the possibility to link the 3D motion time histories with CAD drawings of the structure and validate the FE models in real time experimental data assimilation. © 2015, International Society for Structural Health Monitoring of Intelligent Infrastructure, ISHMII. All rights reserved.

The 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.

Large efforts are in progress in Italy and in particular, at ENEA (Italian Agency for New Technology, Energy and the Environment), for the development, validation and application of innovative anti-seismic techniques for civil and industrial structures. This paper very shortly summarizes the main activities which were performed so far by ENEA, in the framework of both national projects and projects funded by the European Commission.

A significant proportion of the built heritage in historic centres is constituted by rubble stone masonry structures. Collapses by leaf separation and disaggregation observed after earthquakes highlight their dramatic vulnerability, especially under out-of-plane loads. Nevertheless, their dynamic response still needs to be fully investigated and their capacity may be overestimated by assessment approaches based on rigid-body mechanics. Effective retrofitting solutions are also needed to protect human lives and safeguard the built heritage, while ensuring the conservation of its architectural value. This paper describes the design of a shake table investigation on stone masonry walls, whose materials and arrangement reproduce those surveyed in the villages of central Italy struck by the 2016-2017 earthquake sequence. The test setup was conceived to induce out-of-plane vertical bending under earthquake base motion and investigate the dynamic response of multi-leaf rubble stone masonry and the gain in seismic capacity that can be achieved with mortar-based composite reinforcements, designed to prevent the leaf separation and disaggregation of the wall without compromising its fair face.

The 2016-2017 Central Italy seismic sequence severely affected existing unreinforced-masonry constructions in four regions. Those in Latium region proved the most prone to fragmentation because of an unfortunate combination of undressed natural stone units and very low lime content in mortar. Within the framework of a research project funded by the regional government, shake table tests are planned to investigate masonry disintegration as well as possible intervention techniques, as described in a companion paper. All specimens will have natural stone units retrieved from the debris in Collespada, a settlement of the municipality of Accumoli, one of the most affected by the seismic sequence. To push further the representativeness of the specimens with respect to field conditions, wall geometry, masonry fabric and mortar recipe are carefully designed. The wall thickness will be approximately equal to 0.5 m, close to average thickness surveyed in the area. Following the survey of several vertical sections of actual masonry walls, the specimens will present unconnected external leaves with a limited nucleus. Based on tests on mortar sampled from collapsed buildings, mortars will be prepared by a part of natural lime every nine parts of sand. Shear tests on sampled mortar delivered apparent cohesion and friction coefficient that are used as preliminary values of a finite-discrete element model, which can account for masonry fragmentation in dynamic non-linear analyses. The numerical model was tested under the envisioned sequence of records, belonging to the Amatrice station and related to the East component, approximately fault normal, of the two main seismic events, 24 August and 30 October, 2016.

Masonry walls are particularly vulnerable against out-of-plane seismic actions. Steel tie-bars and crowing beams in reinforced masonry can prevent their overturning, but collapse may take place also by bending, leaf separation or disaggregation. Textile Reinforced Mortar (TRM) composites, comprising high strength fabrics and inorganic matrices, can be effectively applied to improve the seismic capacity of masonry load-bearing walls and infill panels. Nevertheless, a deeper knowledge on the dynamic response and ultimate capacity of retrofitted walls still needs to be gained before TRM systems can be confidently used in engineering practice. This work describes a shake table test carried out on two full-scale wall specimens, one made of regular tuff blocks and one of two leaves of rubble stones, subjected to seismic out-of-plane vertical bending. The walls were tested unreinforced, repaired and strengthened with TRMs and tested again. A unidirectional textile of ultra high tensile strength steel was used on the tuff wall, whereas a bidirectional basalt mesh was applied over the entire surface of the stone wall, with the addition of transversal steel connectors. The responses of the specimens before and after retrofitting are compared to show the improvement in terms of acceleration and displacement capacity entailed by TRM retrofitting and the modification of, deflection profiles, failure modes, damage development and dynamic properties. Test outcomes prove the effectiveness of TRM composites for the protection of existing masonry structures, including architectural heritage, in earthquake prone areas and provide information on the reliability of analytical predictions for seismic assessment.

A new methodology for digital image processing, namely the Motion Magnification (MM), allows to magnify small displacements of large structures. MM acts like a microscope for motion in video sequences, but affecting only some groups of pixels. The processed videos unveil motions hardly visible with the naked eye and allow a more effective frequency domain analysis. We applied the MM method to several historic structures, including a 1:10-scale mockup of Hagia Irene in Constantinople tested on shaking table, the so-called Temple of Minerva Medica in Rome and the Ponte delle Torri of Spoleto. MM algorithms parameters were calibrated by comparison with reference consolidated modal identification methods applied to conventional velocimeters data. Encouraging results were obtained in terms of vibration monitoring and modal analysis for dynamic identification of the studied structures, offering a low-cost, viable support to the standard vibration sensing equipment, such as contact velocimeters, laser vibrometers and others.

The 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.

A new methodology for digital image processing, namely the Motion Magnification, allows to magnify small displacements of large structures. Motion magnification acts like a microscope for motion in video sequences, but affecting only some groups of pixels. The processed videos unveil motions hardly visible with the naked eye. We apply the motion magnification to a scale mockup of the Hagia Irene church stressed by a shaking table, to the so-called Temple of Minerva Medica in Rome and to the Ponte delle Torri of Spoleto. Results are surprising, offering a low-cost, viable support to the standard equipment such as contact accelerometers, laser vibrometers, linear variable differential transformers.

Motion 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.

The application of 3D motion capture systems to shaking table testing provides a unique tool for recording relative displacements of a large number of measurement points of the tested structure. The analysis of 3D relative displacements during dynamic tests allows us to evaluate the structure deformations and to monitor the cracks formation and evolution. The present paper focuses on the processing and analysis of 3D motion capture data to extract accurate displacements between markers positioned on a full-scale model of a masonry cross vault representing a vault of the mosque of Dey, Algiers, tested at the ENEA Casaccia Research Centre. The management and processing of the data acquired through 67 markers located on the vault are described, showing the potentialities of the methodology. Moreover, the possible formulation of damage indices based on the structure deformations and cracks aperture detected from markers relative displacements (MRDs) was explored. In particular, cracks could be counted and classified as a function of the detected apertures, following damage thresholds indicated in the Italian regulations. Moreover, the failure mechanism could be easily visualized and analysed by monitoring the cumulative MRDs. In addition, in-plane and out-of-plane deformations of walls could be monitored during each seismic test, providing accurate information on the torsional and bending effects.

Large-scale seismic experimental facilities play a relevant role and provide essential contribution to the performance-based earthquake engineering. In such a context, recent advances in experimental data acquisition methodologies in large laboratories can open new perspective to the evaluation of structural performance of tested mockups under seismic load. In particular, the application of 3D motion capture systems to shaking table testing provides a unique tool for recording relative displacements of a large number of measurement points. The analysis of 3D relative displacements during dynamic tests allows to evaluate the structure deformations and to monitor the cracks formation and evolution, which can lead to the formulation of damage indices. Also, the failure mechanism could be easily visualized and analyzed by monitoring the cumulative relative displacements between markers. In addition, in-plane and out-of-plane deformations of walls could be monitored during each seismic test, providing accurate information on the torsional and bending effects. A case study is presented about a full-scale model of a masonry cross vault of the mosque of Dey, Algiers, tested at the ENEA Casaccia shaking table. The cross vault was subjected to a seismic sequence based on the 21-May-2003 earthquake recorded at Keddara station. The results obtained through the processing of the data from 67 markers located on the vault showed the potentialities of the methodology.

Unconventional computer vision and image processing techniques offer significant advantages for experimental applications to shaking table testing, as they allow the overcoming of most typical problems of traditional sensors, such as encumbrance, limitations in the number of devices, range restrictions and risk of damage of the instruments in case of specimen failure. In this study, a 3D motion optical system was applied to analyze shake table tests carried out, up to failure, on a natural-scale masonry structure retrofitted with steel reinforced grout (SRG). The system makes use of wireless passive spherical retro-reflecting markers positioned on several points of the specimen, whose spatial displacements are recorded by near-infrared digital cameras. Analyses in the time domain allowed the monitoring of the deformations of the wall and of crack development through a displacement data processing (DDP) procedure implemented ad hoc. Fundamental frequencies and modal shapes were calculated in the frequency domain through an integrated methodology of experimental/operational modal analysis (EMA/OMA) techniques with 3D finite element analysis (FEA). Meaningful information on the structural response (e.g., displacements, damage development, and dynamic properties) were obtained, profitably integrating the results from conventional measurements. Furthermore, the comparison between 3D motion system and traditional instruments (i.e., displacement transducers and accelerometers) permitted a mutual validation of both experimental data and measurement methods. © 2016 Techno-Press, Ltd.

Vibration monitoring of buildings in the urban environment is a relevant issue for health survey and early damaging detection in sustainable and enhanced resilient cities. To this end, we explore the potentialities of vibration monitoring by motion magnification analysis that acts like a microscope for motion in video sequences, but affecting only some groups of pixels. The magnified motion is a new discipline in the field of the analysis of mechanical structures and buildings. It was developed from the analysis of small motions in videos. The motion magnification uses the spatial resolution of the video camera to extract physical properties from images to make inferences about the dynamical behavior of the observed object. The methodology does not rely on optics, but on algorithms capable to amplify only the tiny changes in the video frames, while the large ones remain. 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 laser vibrometers. The extension of magnified motion to monitoring of buildings would provide many advantages: a clear, simple, immediate and intuitive diagnosis of the structure, flexibility, predictive potentialities, ease of use, low costs. But also some difficulties still do exist and are discussed. Here we give an introduction to the methodology and some case-studies, both in laboratory and in the real-world (see videos from the link): applications to the short-term urban resilience is straightforward. © Springer Nature Switzerland AG 2018.

In the present paper an integrated approach of a wide range of non-destructive tests (NDTs) was applied to study an archeological ruined building located in Rome, the so-called Temple of Minerva Medica. Applied NDTs focused on the monument properties and environmental conditions affecting its structural behavior (geometry, thermal and mechanical properties, microclimatic monitoring, ambient vibration response). Two surveys were performed in August and December 2016 combining 3D laser scanning, thermal infrared, air temperature and relative humidity acquisitions. In addition, high resolution digital images were acquired and processed by stereo-photogrammetry Structure from Motion (SfM) methodology, carried out for detailed reconstruction of the crack pattern of the monument. In order to obtain information on the integrity and consistency of the masonry, a sonic testing of each pillar was also performed. The integration of the above NDTs provided quite complete and comprehensive understanding of the structural behavior and state of the building, reducing the amount of invasive measurements further needed.

In the present study non-destructive testing (NDT) methods involving ultrasonic and sonic wave propagation in the solid matter were applied in order to detect and investigate the modifications induced by the seismic load on reinforced concrete (RC) buildings. In particular, the aim of this experimental work was to delineate a methodology for quick and easy application on-the-field to provide information on the state of health of a RC structure subjected to a seismic event by investigating the columns in lower stories, which are generally more safely reachable for inspection. The methodology was experimented through shaking table tests reproducing several earthquakes. Shaking table tests were performed at ENEA Casaccia Research Centre on a full-scale 2-storey RC frame building designed under the current Italian code (NTC2008). Among the considered NDT techniques, direct and indirect sonic methods, as well as partial and complete approaches for ultrasonic tomography application were explored. The above NDTs were applied to the specimen before and after the shaking table testing. Numerical simulations by finite element methods (FEMs) were also adopted for a better comprehension of the dynamic behaviour of the specimen and interpretation of the experimental results. Through the comparison with typical damage indicators formulated for RC buildings, derived from the modal parameters evolution and from the displacements of the structure during the seismic load, promising indications were obtained and the proposed NDT-based methodology was discussed. © 2018 Elsevier Ltd

We applied a new methodology, namely the motion magnification (MM), to the dynamic identification of historic constructions. MM acts like a microscope amplifying small motions in video sequences, therefore tiny motion patterns are made visible with the naked eye. This technique provides advantages of particular interest to the dynamic identification: no wires, no physical contact, simplicity and low costs. In this paper, we investigated the ambient vibration monitoring of historic structures in urban environments, which is a relevant issue for the health surveying and early damage detection, particularly for ancient buildings. We give an introduction to the MM methodology and describe its practical application to the frequency domain through two case-studies: the so-called Temple of Minerva Medica of Rome and the Ponte delle Torri of Spoleto. Since in the outdoor environment the MM is much more prone to noise because of the wind, shadows, atmospheric refraction, light reflection, distance from the object, weak vibration sources, the case study of the Ponte delle Torri represents a hard test-bed for MM. However, the MM estimates of the first modes showed a good agreement with the experimental data of contact velocimeters. © Published under licence by IOP Publishing Ltd.

The dynamic identification by ambient vibration data is widely used to supply information on the global health of structures through the investigation of changes in their modal parameters. It can be used even for verification of the state of damage of structures after hazardous threats, for example seismic activity. Therefore, it can play a crucial role to integrate and support conservation strategies for historic architectural assets. Sometimes, in historic constructions only a limited number of positions are accessible or usable to install sensors, and so modal analysis must be based on data from few measurement points. Moreover, they might not be the optimal positions for the studied structure, so the obtained results would need further verification. In such circumstances, the mutual validation between different modal analysis techniques can be useful to assess the reliability of results. In the present paper a case study of application to the so-called Temple of Minerva Medica, Rome, is described. Ambient vibration data were acquired in four rowing acquisition sessions carried out from July 2016 to July 2017, which is a timespan usable to assess the impact of the recent Central Italy seismic sequence. For problems related to the installation of the scaffolding only few points were available for instruments positioning. A variety of techniques were applied, including FRF, FDD, EFDD, SSI, HVSR and complex modal models. The variance of the modal parameters obtained by each different technique was utilized to provide indications on the reliability of the average values. © Published under licence by IOP Publishing Ltd.

Vibration 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.

Fibre Bragg Grating (FBG) sensors are increasingly being used on a wide range of civil, industrial and aerospace structures. The sensors are created inside optical fibres (usually standard telecommunication fibres); the optical fibres technology allows to install the sensors on structures working in harsh environments, since the materials are almost insensitive to corrosion, the monitoring system can be positioned far away from the sensors without sensible signal losses, and there is no risk of electric discharge. FBG sensors can be used to create strain gages, thermometers or accelerometers, depending on the coating on the grating, on the way the grating is fixed to the structure, and on the presence of a specifically designed interface that can act as a transducer. This paper describes a test of several different FBG sensors to monitor an high pressure pipe that feeds the hydraulic actuators of a 6 degrees-of-freedom shaking table at the ENEA Casaccia research centre. A bare FBG sensor and a copper coated FBG sensor have been glued on the pipe. A third sensor has been mounted on a special interface to amplify the vibrations; this last sensor can be placed on the steel pipe by a magnetic mounting system, that also allows the its removal. All the sensor are placed parallel to the axis of the pipe. The analysis of the data recorded when the shaking table is operated will allow to determine which kind of sensor is best suited for structural monitoring of high pressure pipelines. © 2017 SPIE.

The 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.

This study presents a first-level spatial assessment of the susceptibility to earthquake-induced landslides in the seismic area of the Agri Valley (Basilicata Region, southern Italy), which hosts the largest onshore oilfield and oil/gas extraction and pre-treatment plant in Europe and is the starting point of the 136-km-long pipeline that transports the plant’s products to the refinery located in Taranto, on the Ionian seacoast. Two methodologies derived from the ones proposed by Newmark (Geotechnique 15(2):139–159, 1965) and Rapolla et al. (Eng Geol 114:10–25, 2010, Nat Hazards 61:115–126, 2012. doi: 10.1007/s11069-011-9790-z ), based on different modelling approaches, were implemented using the available geographic information system tools, which allowed a very effective exploitation of the two models capability for regional zoning of the earthquake-induced landslide hazard. Subsequently, the results obtained from the two models were compared by both visual evaluation of thematic products and statistical correlation analysis of quantitative indices, such as the Safety Index based on the Newmark’s approach and the Susceptibility Index from Rapolla’s model. The comparison showed a general agreement in highlighting the most critical areas. However, some slight differences between the two models’ results were observed, especially where rock materials and steep slopes are prevailing.