Damage Assessment of Structures VII

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Authors: Daniele Zonta, Matteo Pozzi, Paolo Zanon
Abstract: This paper presents a damage detection procedure based on Bayesian analysis of data recorded by permanent monitoring systems as applied to condition assessment of Precast Reinforced Concrete (PRC) bridges. The concept is to assume a set of possible condition states of the structure, including an intact condition and various combinations of damage, such as failure of strands, cover spalling and cracking. Based on these states, a set of potential time response scenarios is evaluated first, each described by a vector of random parameters and by a theoretical model. Given the prior distribution of this vector, the method assigns posterior probability to each scenario as well as updated probability distributions to each parameter. The effectiveness of this method is illustrated as applied to a short span PRC bridge, which is currently in the design phase and will be instrumented with a number of fiber-optic long gauge-length strain sensors. A Finite Element Model is used to simulate the instantaneous and time-dependent behavior of the structure, while Monte Carlo simulations are performed to numerically evaluate the evidence functions necessary for implementation of the method. The ability of the method to recognize damage is discussed.
Authors: Nathanael C. Yoder, Timothy J. Johnson, Douglas E. Adams
Abstract: In current tire durability tests, technicians must stop tests periodically to inspect each tire, resulting in a time consuming, expensive, and relatively subjective process. Online tire monitoring would thus be a dramatic improvement over the current methodology. If such a system could be extended to on-line vehicle use, it could dramatically increase safety, reduce downtime, and lead to better fuel efficiency in commercial and passenger cars and trucks. A near real-time system to monitor the initiation of bead area damage in rolling tires was developed using vibration data collected from the wheel end spindle. To generate an accurate model of the forced response of the wheel end spindle, a tire on a fixed spindle was impacted with a modal punch while the tire was preloaded against a plate. The frequency response functions acquired from this system were then used to develop a rotating tire model consisting of time-delayed forcing functions applied to the tire patch at the rolling frequency; this model was used to assist in interpreting the results from the near real-time monitoring system. The near real-time continuous monitoring system has been deployed in a manufacturing test environment and utilizes frequency data from three mutually orthogonal acceleration measurements. These data are combined to create a highly sensitive composite index that identifies when the initiation of bead area damage has occurred.
Authors: Joseph Morlier, P. Salom, F. Bos
Abstract: This paper presents an introduction to structural damage assessment using image processing on real data (non ideal conditions). Our contribution is much more a groundwork than a classical experimental validation. After measuring the bridge dynamic parameter on a small resolution video, we conjointly present advantages and limitations of our method. Finally we introduce several “computer vision” based rules and focus on the technical ability to detect damage using camera and video motion estimation.
Authors: Zhen Xu, Qian Chen
Abstract: Cointegration testing method from economics area is introduced for condition monitoring and fault diagnosis for nonstationary engineering systems. The cointegration testing method seeks a a linear combination of a set of nonstationary stochastic variables, which describes long-run dynamic equilibrium relation of the nonstationary variables. This feature provides a possibility for researchers in engineering areas to utilize the cointegration testing method for nonstationary system monitoring and fault diagnosis. To verify the feasibility and performance of the cointegration testing method, an example based on a simulated nonstationary fluid catalytic cracking unit (FCCU) system is discussed. The results of the example show that the cointegration testing method has a potential in engineering system monitoring and fault diagnosis.
Authors: Joanna Grabowska, Magdalena Palacz, Marek Krawczuk, Wiesław M. Ostachowicz, Irina Trendafilova, Emil Manoach, Matthew P. Cartmell
Abstract: The main aspect of the paper is to give an answer to the question of what specific kind of defect has actually occurred in a structure and how to distinguish between different kinds of discontinuities. For this purpose composite rods and beams with fatigue cracks, step changes in cross-sectional area and small changes in material properties have been investigated. The objective of the work has been to propose a signal processing methodology based on wavelet transformation for identification of specific discontinuity. The identification of a fatigue crack from other discontinuities has been demonstrated. It has been also found that the proposed methodology might be useful for precise indication of the size of the identified fatigue damage.
Authors: C. Valente, Daniele Spina, S. Gabriele
Abstract: The paper presents the revised formulation of a signal processing methodology aimed at identifying the dynamics of buildings hit by earthquakes. The methodology is based on the Gabor joint time-frequency representation and allows to identify an evolutionary modal model whose time changes are used to evaluate the damage presence and severity. Dynamic tests are performed in advance to provide reference values and their confidence ranges used for the assessment of the results. The methodology has been extensively applied to the buildings belonging to the Italian national network of seismic structural monitoring. A sample application referred to a representative reinforced concrete buildings is shown.
Authors: Jerome Antoni, Roger Boustany
Abstract: Rolling-element bearing vibrations are random cyclostationary, that is they exhibit a cyclical behaviour of their statistical properties while the machine is operating. This property is so symptomatic when an incipient fault develops that it can be efficiently exploited for diagnostics. This paper gives a synthetic but comprehensive discussion about this issue. First, the cyclostationarity of bearing signals is proved from a simple phenomenological model. Once this property is established, the question is then addressed of which spectral quantity can adequately characterise such vibration signals. In this respect, the cyclic coherence - and its multi-dimensional extension in the case of multi-sensors measurements -- is shown to be twice optimal: first to evidence the presence of a fault in high levels of background noise, and second to return a relative measure of its severity. These advantages make it an appealing candidate to be used in adverse industrial environments. The use and interpretation of the proposed tool are then illustrated on actual industrial measurements, and a special attention is paid to describe the typical "cyclic spectral signatures" of inner race, outer race, and rolling-element faults.
Authors: Fu Cai Li, Lin Ye, Gui Cai Zhang, Guang Meng
Abstract: Impulse response provides important information about flaws in mechanical system. Deconvolution is one system identification technique for fault detection when signals captured from bearings with and without flaw are both available. However effects of measurement systems and noise are obstacles to the technique. In the present study, a model, namely autoregressive-moving average (ARMA), is used to estimate vibration pattern of rolling element bearings for fault detection. The frequently used ARMA estimator cannot characterize non-Gaussian noise completely. Aimed at circumventing the inefficiency of the second-order statistics-based ARMA estimator, higher-order statistics (HOS) was introduced to ARMA estimator, which eliminates the effect of noise greatly and, therefore, offers more accurate estimation of the system. Furthermore, bispectrums of the estimated HOS-based ARMA models were subsequently applied to get clearer information. Impulse responses of signals captured from the test bearings without and with flaws and their bispectra were compared for the purpose of fault detection. The results demonstrated the excellent capability of this method in vibration signal processing and fault detection.
Authors: Giovanni Damonte, Stefano Podestà, Giuseppe Riotto, Sergio Lagomarsino, Georges Magonette, Francesco Marazzi
Abstract: Monitoring represents one solution for the safeguard of historical buildings. The need for a non-destructive and comprehensive monitoring methodology suggests using related to Structural Health Monitoring. This paper is intended to present the outcomes of an experimental campaign on a masonry triumphal arch representing a real scale model of a church part, which was built outside ELSA laboratory at the Joint Research Centre of European Commission. This study aims to evaluate the damage pattern of the structure through simplified dynamic methods producing a quick evaluation of structural safety, easy to use on real cases. As in traditional monitoring, both the instrumentation precision and the measurement variability due to the different testing condition (e.g. ambient conditions) have to be considered. The related effects on the structural dynamic behaviour were analysed and evaluated in order to distinguish an effective change in the “structural health” (a real damage) from an alteration caused by external conditions (a “false positive”). Once studied such effects, settlements were induced to one column base through an “ad hoc” device. Varying the settlement width, three damage levels were obtained in the structure. For each state the structural dynamic properties and their variation were evaluated. Sensitivity of dynamic behaviour to structural damage and to its changes was analysed comparing the results for each level.
Authors: Elena Candigliota, Alain Le Maoult
Abstract: Tests on shaking table have been carried out on a 3D full scale infilled r.c. frame specimen (55 tons). These tests have been performed by the EMSI Laboratory of C.E.A. Saclay (France) together with a research team of the Universities of Chieti-Pescara (Italy), Roma Tre (Italy) and Patras (Greece). These tests are included in Ecoleader European research program. Many characterization tests of infill components (mortar and bricks) have been performed in the SCAM Laboratory of the University of Chieti-Pescara while tests on masonry walls were made in the laboratory of University of Rome 3. The structure represents the first floor of a two floors frame structure previously tested. The mockup is a full-scale one storey rc infilled frame with four columns, 3 meters high, with about 4 meters side square floor and infilled with double bricks wall. The main aim is to get information about the behavior of real structures. The instrumentation with about one hundred channels was set up to measure the rc frame response and the different behavior of the double walls during the tests. First, monodirectional and bidirectional tests at low seismic intensity (0.10 g and 0.15 g PGA levels) have been performed on the bare frame in order to characterize its structural characteristics and to check the design provisions. Then, the bare frame has been infilled and other tests have carried out at increasing seismic intensity in order to define its serviceability and ultimate limit states. Monodirectional and bidirectional tests up to 0.45 g PGA level were carried out. The last sequence included a monodirectional test on the infilled frame with only two walls. The high seismic input (0.55 g PGA level) was parallel to the direction of the walls. In this paper, research program and some main test results are presented.

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