Damage Assessment of Structures VII

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Authors: Julia Armesto, Pedro Arias, Celestino Ordóñez, Henrique Lorenzo, Natalia Caparrini
Abstract: The measurement and monitoring of structural damages in masonry monuments is an important task in the field of conservation and restoration of architectonic heritage. Traditional surveying devices provide punctual measurements of the damage size and usually are contactdemanding, being an important limitation since risky systems are needed when structural problems appear in no accessible locations. In this field close-range Photogrammetry depict a valuable option. In this paper the dimensional analysis and temporal monitoring of crack is accomplished. Accurate 3D clouds of points defining the crack boundary are obtained in different dates. A quantification of the crack size in each date is obtained by shape parameters. This procedure allows detecting any displacement in ashlars and obtaining a feasible knowledge of the crack growth even when no fixed references are available to align 3D models obtained in different times.
Authors: Oliver R. de Lautour, Piotr Omenzetter
Abstract: Time series based Structural Health Monitoring (SHM) methods are being increasingly explored. In this study, Autoregressive (AR) models were used to fit the acceleration time histories of a 3-storey laboratory structure under excitation by earthquake records in several damaged and undamaged states. The coefficients of the AR models were used as inputs into an Artificial Neural Network (ANN) and the ANN was trained to relate the AR coefficients to the damage at each storey. The results showed that proposed method was able to detect, locate and quantify the damage in the structure with a very high accuracy.
Authors: David A. Clifton, Peter R. Bannister, Lionel Tarassenko
Abstract: A novelty detection approach to condition monitoring of aerospace gas-turbine engines is presented, providing a consistent framework for on- and off-line analysis, each with differing typical implementation constraints. On-line techniques are introduced for observing abnormality in engine behaviour during aircraft flights, and are shown to provide early warning of engine events in real-time. Off-line techniques within the same analysis framework are shown to allow the tracking of single engines and fleets of engines from ground-based monitoring stations on a flight-by-flight basis. Results are validated by comparison to conventional techniques, in application to aerospace engines and other industrial high-integrity systems.
Authors: Igor Bovio, Leonardo Lecce
Abstract: The purpose of the paper is to present an innovative application within the Non Destructive Testing field based upon vibration measurements developed by the authors, and already tested for analysing damage of many structural elements. After having tested this application on different test articles in laboratory condition, experimental tests have been executed, in collaboration with the ATR company, on a turboprop ATR-72 aircraft, in order to validate the technique on a real aeronautical structure. The monitoring system have operated an off-line check on the structure, during the aircraft ground operations, as if it were a normal maintenance procedure. The results are reported in the paper. This proposed new method is based upon the acquisition and comparison of the Frequency Response Functions (FRFs) of the monitored structure before and after damage occurs. Structural damage modify the dynamic behaviour of a structure affecting its mass, stiffness and damping, and consequently the FRFs of a damaged structure, when compared with the FRFs of its sound configuration, making the identification, localization and quantification of damage possible. The activities presented in the paper focus mainly on a new FRFs processing technique based upon the determination of a representative “Damage Index” for identifying and analysing damage. Furthermore, a dedicated neural network algorithm has been elaborated to develop an automatic system which recognises positive samples, “healthy” states of the analysed structure, discarding negative ones, “damaged or perturbed” states of the analysed structure. From an architectural standpoint, piezoceramic patches have been used as both actuators and sensors.
Authors: Marco Allara, Stefano Zucca, Muzio M. Gola
Abstract: Stresses due to resonant vibrations induce fatigue damage in turbomachinery blades jeopardizing their structural integrity. Damping plays a fundamental role in passive control of resonant stresses. In the present work the effect of ‘crowning’ of dovetail joints on blade-root friction damping is for the first time investigated. In detail, the damping of a simplified blade is measured under varying centrifugal load for two different joint geometries: a customary dovetail attachment and a ‘crowned’ one. A theoretical model is developed to quantify the damping generated at the contact surfaces. Experimental results and analytical predictions are compared.
Authors: Kai Xiong, Dong Xiang Jiang, Yong Shan Ding, Kai Li
Abstract: RBF neural network and support vector machine (SVM), two Artificial Intelligent (AI) methods, have been extensively applied on machinery fault diagnosis. Aero-engine, as one kind of rotating machine with complex structure and high rotating speed, has complicated vibration faults. As one kind of AI methods, RBF neural network has the advantages of fast learning, high accuracy and strong self-adapting ability. Support vector machine, another AI method, only needs a small quantity of fault data samples to train the classifier and does not need to extract signal features. In this paper, the applications of two AI methods on aero-engine vibration fault diagnosis are introduced. Firstly, the principles and algorithm of both two methods are presented. Secondly the fundamentals of two-shaft aero-engine vibration fault diagnosis are described and gotten the standard fault samples (training samples) and simulation samples (testing samples). Third, two AI methods are applied to the vibration fault diagnosis and obtained the diagnostic results. Finally, the advantages and disadvantages of the two methods are compared such as the computing speed, accuracy of diagnosis and complexity of algorithm, and given a suggestion of selecting the diagnostic methods.
Authors: Rosario Ceravolo, Giacomo V. Demarie, Silvano Erlicher
Abstract: This paper presents a technique for identification of non-linear hysteretic systems subjected to non-stationary loading. In the numerical simulations, a Bouc-Wen model was chosen for its ability to represent the properties of a wide class of real hysteretic systems. The parameters of the model are computed instantaneously by approximating the internal restoring force surface through an “ad hoc” polynomial basis. Instantaneous estimates result from time-varying spectra of the response signals. A numerical application of interest to earthquake engineering is finally reported.
Authors: Robert Jankowski
Abstract: The reports after earthquakes indicate that earthquake-induced pounding between insufficiently separated structures, or their parts, may cause substantial damage or even lead to structural collapse. One of the most spectacular example of pounding-involved destruction resulted from interactions between the Olive View Hospital main building and one of its independently standing stairway towers during the San Fernando earthquake of 1971. The aim of the present paper is to assess the range and intensity of damage caused by collisions between these reinforced concrete structures based on the results of a detailed 3D non-linear FEM analysis of poundinginvolved response. In the study, reinforced concrete has been modelled as layered material with rebar elements embedded into concrete. The non-linear material behaviour, including stiffness degradation of concrete due to damage under cyclic loading, has been incorporated in the numerical model. The results of the study show that pounding may lead to the significant increase of the range and intensity of damage at the base of the stairway tower, as a lighter structure, as well as may cause substantial damage at the points of contact. On the other hand, the intensity of damage induced in the heavier main building has been found to be nearly unaffected by structural interactions.
Authors: Raffaele Landolfo, G. Di Lorenzo, M.R. Guerrieri, O. Mammana, F. Portioli
Abstract: This paper is concerned with the results of the vulnerability assessment of the iron roofing structures of the Umberto I Gallery in Naples. The study is performed considering both the damage caused by corrosive phenomena and the seismic risk. In particular, the evaluation of the seismic performance has been carried out by developing a three-dimensional finite element model of the structure and calculating the thickness loss due to corrosion on the basis of suitable damage curves.
Authors: Gianfranco de Matteis, I. Langone, Fabio Colanzi, Federico M. Mazzolani
Abstract: This paper focuses on the dynamic behaviour of the Fossanova cathedral (Latina, ITALY), which represents a magnificent example of pre-Gothic style church, whose structural typology is largely present in the Mediterranean area, especially in many Countries characterised by a High-Medium seismic hazard. In particular, within the European research project PROHITECH, aiming at investigating the seismic vulnerability of such a structural typology, experimental and numerical analyses have been carried out. Firstly, detailed investigations have been devoted to the identification of the geometry of the main constructional parts as well as of the mechanical features of the constituting materials of the cathedral. Then, both Ambient Vibration Tests (AVT) and Numerical Modal Identification analyses by Finite Element Method (FEM) have been applied, allowing the detection of the main dynamic features. Finally, a refined FEM model reproducing the dynamic behaviour of the cathedral by using scaled physical quantities according to the Buckingham theorem has been developed. In fact, the present study has to be intended as a preliminary activity devoted to se up a shaking table test on a reduced scale physical model of Fossanova cathedral, which will be shortly carried out at the IZIIS laboratory (Skopje, Macedonia).

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