Ivan Roselli

Shaking table tests of an arch-pillars system and design of strengthening by the use of tie-rods

In 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.

Analysis of 3D Motion Data from Shaking Table Tests on a Scaled Model of Hagia Irene, Istanbul

The present paper focuses on the use of a 3D motion capture system for the dynamic identification and the damage monitoring of a 1:10 scaled mock-up (representing the large historic masonry structure of Hagia Irene, Istanbul) tested on shaking table at the ENEA Casaccia Research Center located near Rome, Italy. The dynamic identification of the structure during the shaking table tests was obtained by several techniques of Experimental Modal Analysis (EMA), such as FRF, FDD and EFDD. To such purpose Displacement Data Processing (DDP) of a large number of markers of the 3DVision (the passive 3D motion capture system installed at the ENEA laboratory) was performed. Markers were located on the tested mock-up accordingly to the indications of preliminary FEM analysis and modal shapes. Also conventional accelerometers were placed on the physical model and used as reference for the analysis of 3DVision data. In addition, the analysis of Markers Relative Displacements (MRDs) was useful to detect the occurrence and development of fractures during the tests, contributing to assessing the actual progress of the structural damage. The results from EMA techniques and MRDs analysis of 3DVision data are illustrated, showing the potentialities of this monitoring system in integrating the two complementary approaches.

Mapping the earthquake-induced landslide hazard around the main oil pipeline network of the Agri Valley (Basilicata, southern Italy) by means of two GIS-based modelling approaches

Abstract 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.

Displacement Based Approach for a Robust Operational Modal Analysis

Robust estimation of the dynamic modal parameters of structures during shaking table experiments is done by means of efficient time domain data-driven Crystal Clear Stochastic Subspace Identification (CC-SSI) of vibration data recorded by a new, innovative, high resolution 3-D optical movement detection and analysis tool tracking the dynamic displacement of several selected points of the structures during the dynamic tests of natural (earthquake) and artificial (mechanical) induced vibrations. The measure of the displacements is a crucial task for the numerical and experimental studies in structural dynamics, especially within the displacement based approach in seismic design and calculations. The innovative monitoring technique measures 3 axial absolute displacements with easy and fast test setup, high accuracy and the possibility to link the 3D-motion time histories of the tracked markers with CAD drawings of the structure and validate the FE models in real time experimental data assimilation.

3D motion capture application to seismic tests at ENEA Casaccia research center: 3Dvision system and DySCo virtual lab

In the last 4 years, a high-resolution 3D motion capture system named 3DVision was installed at ENEA Casaccia as integration to more conventional instrumentation for measuring motion parameters during seismic tests, such as accelerometers, LVDTs, wire transducers and laser displacement sensors. In the present paper, some examples are illustrated to show the ENEA experiences with this relatively new technique in comparison to the other consolidated measurement systems. 3DVision is described in terms of flexibility and accuracy and specific potentialities are stressed. The main peculiarities of the 3DVision system derive from its capability of monitoring in real-time the absolute 3D position of more than a hundred measurement points without locating any active sensor or cable on the studied structure and on the shaking table, but only by means of cheap passive markers. Consequently, any risk of instrumentation damage in case of destructive tests is intrinsically avoided and the acquisition of hundreds of channels is guaranteed. Within the DySCo virtual lab, the 3DVision friendly graphical interface for real-time monitoring and its synchronous overlay function between markers wireframe and tests movies revealed particularly effective for remote sharing of the experimental campaigns with research partners via the internet. Also a remarkable contribution is given by the possibility of integrating and comparing experimental data with FE results at the same positions, calibrating FEM boundary conditions (materials properties, model constraints, loads etc.) in order to improve the simulation significance and reliability for similar cases. Through the DySCO web portal such numerical simulations and computations can be carried out exploiting the software and hardware resources available in the ENEA-GRID.

Quasi real-time FEM calibration by 3D displacement measurements of large shaking table tests using HPC resources

Abstract The present paper concerns the implementation of a methodology aiming to achieve a quasi real-time calibration of Finite Element Models (FEMs) of large structural mock-ups during shaking table tests. The damage achieved after each test step is commonly evaluated by visual inspection, since running large numerical analyses or processing the experimental data for damage estimation with common computing resources is very time-consuming and in case of a prolonged stand-by the shaking tables oil temperature stability can be put at risk. On the other hand, the specimen damage level can be monitored through the modal parameters estimated using Finite Element Analyses (FEAs), but FEMs require to be calibrated to provide accountable results. In the proposed approach the FEM calibration was carried out using 3D motion data of a large number of passive markers. They were acquired and processed by a dedicated Displacement Data Processing (DDP) procedure combining the Savitzky-Golay filtering for data noise reduction and the convolution derivation approach for the extraction of the motion parameters. To obtain results in reasonable time between test steps (a few minutes) the methodology exploits the hardware and software resources available on the ENEA High-Performance Computing (HPC) system. Also, the proposed approach allowed to integrate within a single web interface the possibility to share the seismic experiments in real time, while providing updated FEM calibration at each step of the test sequence during the experimental session.

Mutual validation between different modal analysis techniques for dynamic identification of the so-called Temple of Minerva Medica, Rome

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.

Motion Magnification for Urban Buildings.

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.

PROCESSING OF 3D OPTICAL MOTION DATA OF SHAKING TABLE TESTS: FILTERING OPTIMIZATION AND MODAL ANALYSIS

The use of 3D optical motion data for structural dynamics is both promising and challenging. Further developments for on-the-filed applications are still needed, but, at the present stage, such techniques are already feasible for laboratory dynamic tests. A measurement system of this kind was installed for the first time for shaking table testing at the ENEA Casaccia Research Center. This 3D motion capture system is capable of acquiring the positions of more than a hundred passive markers with a constellation of 10 near-infrared cameras. In particular, this paper focuses on filtering and processing the markers displacements. A methodology is proposed for optimizing the displacement data processing to obtain an estimation of markers accelerations. Such methodology implies the optimal choice of the Savitzky-Golay-filter parameters for the implementation of a filtered numerical derivative of displacement data. The optimal parameters are calculated minimizing the error in the estimation of the peak acceleration of a reference marker compared to a conventional accelerometer located at the same measurement point. The accuracy of markers accelerations was estimated in the range of 0.01-0.02 g, which is appropriate for providing interesting indications for studied structures subjected to most shaking table testing. For example, markers displacements data and related estimated accelerations can be combined to obtain the hysteretic behavior of the structure or of portions of it. Markers data were also used for Experimental and Operational Modal Analysis (EMA/OMA) in order to extract the modal parameters and to calibrate/validate the Finite Element Models (FEM) of the structure. In particular, the combined used of OMA by markers data and numerical modal analysis by FEM permits to compare the resulting modal shapes for a more precise dynamic identification. An example of practical application is illustrated on a shaking table experimentation conducted on a twostory tuff-masonry prototype, which reproduces a typical ancient buildings of Central Italy. 4174 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 4174-4183

Numerical analysis of a MDOF structure protected with TMD techniques

In the present paper a complete numerical study of a 1:5 scaled four-storey steel-frame structure with the application of Tuned Mass Dampers (TMD) is reported. In particular, Passive Tuned Mass Dampers (PTMD), Semi-Active Tuned Mass Dampers (SATMD), and Hybrid Tuned Mass Dampers (HTMD) were considered and compared. The initial aim of this work was to define a Simplified Equivalent Model to be conveniently utilized for simulations instead of a realistic Prototype Numerical Model in order to estimate the designing parameters of the devices with good approximation and sensible time calculation saving. Subsequently, the feasibility, the reliability and the effectiveness of the considered seismic control techniques were also assessed. The results of the numerical analysis showed how the use of a simplified model allows to estimate the designing parameters with accuracy. More importantly, the numerical results showed to what extent the several TMD techniques revealed to be effective for the seismic response reduction.Copyright