Marialuisa Mongelli

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.

Structural Health Monitoring of Pipelines for Environment Pollution Mitigation

Oil and gas infrastructures may be exposed to landslides, earthquakes, corrosion and fatigue, and to damage from thefts or vandalism, leading to leakage and failure with serious economic and ecologic consequences. For this reason, an increasing interest in applied research on monitoring and protecting pipelines (for fuel, oil and natural gas transportation) arises. Aimed at the mitigation of catastrophic effects of human and natural damage, the present paper proposes a smart real-time Structural Health Monitoring (SHM) system capable to control structural integrity continuously, focusing on the issue of spillage for thefts of fuels which are not detectable, in real-time, by the existing monitoring systems.The system consists of a smart-pipeline containing a health monitoring integrated measurement chain, i.e. an enhanced Fiber Bragg Gratings-based fiber optics neural network on the pipes, for displacement and acceleration monitoring (gathering many other different measurements such as: ground motion, permanent ground displacement, pipeline temperature, pipeline deformation, leakage, etc.).Specifically, the ability to measure these characteristics at hundreds of points along a single fiber and the great accuracy of each point of measure, are particularly interesting for the monitoring of structures such as pipelines in order to detect hazardous and unauthorized intrusion and damage.Copyright

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.

Test of FBG sensors for monitoring high pressure pipes

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.

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.

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