Computational Methods for Identification of Vibrating Structures (original) (raw)
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System identification of suspension bridge from ambient vibration response
Engineering Structures, 2008
The paper addresses and evaluates the application of system identification to a suspension bridge using ambient vibration response. Toobtain dynamic characteristics of the bridge, two output-only time-domain system identification methods are employed namely, the RandomDecrement Method combined with the Ibrahim Time Domain (ITD) method and the Natural Excitation Technique (NExT) combined with theEigensystem Realization Algorithm (ERA). Accuracy and efficiency of both methods are investigated, and compared with the results from a FiniteElement Model. The results of system identification demonstrate that using both methods, ambient vibration measurement can provide reliableinformation on dynamic characteristics of the bridge. The NExT-ERA technique, however, is more practical and efficient especially when appliedto voluminous data from multi-channel measurement. The results from three days of measurements indicate the wind-velocity dependency of natural frequency and damping ratio particularly for low-order modes. The sources of these dependencies appear to be the effect of aerodynamicforces alongside the girder, and friction force from the bearing near the towers.
Computer-Aided Civil and Infrastructure Engineering, 2008
In this paper, wind-induced vibration response of Vincent Thomas Bridge, a suspension bridge located in San Pedro near Los Angeles, California, is simulated using a detailed three-dimensional finite element model of the bridge and a state-of-the-art stochastic wind excitation model. Based on the simulated wind-induced vibration data, the modal parameters (natural frequencies, damping ratios, and mode shapes) of the bridge are identified using the data-driven stochastic subspace identification method. The identified modal parameters are verified by the computed eigenproperties of the bridge model. Finally, effects of measurement noise on the system identification results are studied by adding zero-mean Gaussian white noise processes to the simulated response data. Statistical properties of the identified modal parameters are investigated under increasing level of measurement noise. The framework presented in this paper will allow to investigate the effects of various realistic damage scenarios in long-span cable-supported (suspension and cable-stayed) bridges on changes in modal identification results. Such studies are required in order to develop robust and reliable vibration-based structural health monitoring methods for this type of bridges, which is a long-term research objective of the authors.
System Identification from Ambient Vibration Measurements on a Bridge
Journal of Sound and Vibration, 1997
The cross-correlation function between two response measurements made on an ambiently excited structure is shown to have the same form as the system's impulse response function. Therefore, standard time domain curve-fitting procedures, which are typically applied to impulse response functions, can now be applied to the cross-correlation functions to estimate the resonant frequencies and modal damping of the structure. This derivation is based on the assumption that the ambient vibration source is a white noise random process. Curve-fitting cross-correlation functions to obtain modal properties offers advantages over standard procedures that identify resonant frequencies from peaks in the power spectrum and damping from the width of the power spectrum. The primary advantage is the ability to identify closely spaced modes and their associated damping. The resonant frequencies of a highway bridge that were identified by curve-fitting the cross-correlation functions, using traffic excitation as the ambient vibration source, are compared to modal properties identified by standard forced vibration testing methods. Results of this comparison showed a maximum discrepancy of 3·63 percent. Similar comparisons for the average modal damping values identified by the two methods showed a 9·82 percent difference. This experimental verification implies that the proposed method of analyzing ambient vibration data can be used to accurately assess the dynamic properties of structures in a non-intrusive manner. 7 1997 Academic Press Limited
Data processing in subspace identification and modal parameter identification of an arch bridge
Mechanical Systems and Signal Processing, 2007
A data-processing method concerning subspace identification is presented to improve the identification of modal parameters from measured response data only. The identification procedure of this method consists of two phases, first estimating frequencies and damping ratios and then extracting mode shapes. Elements of Hankel matrices are specially rearranged to enhance the identifiability of weak characteristics and the robustness to noise contamination. Furthermore, an alternative stabilisation diagram in combination with component energy index is adopted to effectively separate spurious and physical modes. On the basis of identified frequencies, mode shapes are extracted from the signals obtained by filtering measured data with a series of band-pass filters. The proposed method was tested with a concrete-filled steel tubular arch bridge, which was subjected to ambient excitation. Gabor representation was also employed to process measured signals before conducting parameter identification. Identified results show that the proposed method can give a reliable separation of spurious and physical modes as well as accurate estimates of weak modes only from response signals. r
Modal identification of bridge systems using state-space methods
Structural Control and Health Monitoring, 2005
Arrays of large numbers of sensors and accompanying complex system identification (SI) methods have been recently used in engineering applications on structures ranging from complex real space trusses to simple experimental beams. However, practical application to strong motion data recorded on large civil engineering systems is limited. In this study, state-space identification methods are used for modal identification from earthquake records with further investigation into the effectiveness of the methods from the viewpoint of sensor layout configuration. The study presented in this paper adopts a deterministic approach, which is complemented with statistical evaluation in another paper. The used SI methods include eigen realization, system realization with information matrix and subspace methods. The application of the methods on instrumented bridge systems in California is included and the performance of these methods is compared in terms of success and feasibility. Subsequently, viability of the methods on arrays of different numbers of sensors on the bridge systems is investigated. This is motivated by the fact that sensor arrays with wireless communication may be conveniently installed on civil engineering structures in the future. Computational costs and limits of applicability are examined using simulated ground motion analysis with detailed finite element models for a bridge system after validation using recorded data from real ground shaking. Moreover, the effect of the configuration of the sensor arrays is considered, accounting for different noise levels in the data to reflect more realistic situations.
System Identification of a Base-Isolated Bridge Using Ambient Vibration Data
Sciarapotamo Bridge located in Reggio Calabria Province, Italy has been recently retrofitted by replacing the deteriorated concrete bridge deck with composite concrete-steel deck, and isolating the deck with eight high damping rubber (HDR) and four multi-directional sliding bearings. Full-scale ambient vibration dynamic commissioning tests were performed on the bridge in June 2012 just before the bridge has become fully operational. The dynamic response of the bridge was recorded using an array of 4 uni-axial and 4 tri-axial force-balanced accelerometers placed along the entire length of the bridge. Different output-only system identification methods are used to identify the modal parameters of the bridge including: (1) Multiple Reference Natural Excitation Technique in conjunction with Eigensystem Realization Algorithm (MNExT-ERA), (2) Enhanced Frequency Domain Decomposition (EFDD). In this study, modal parameter estimation results obtained using different system identification met...
System Identification of Alfred Zampa Memorial Bridge Using Dynamic Field Test Data
Journal of Structural Engineering, 2009
The Alfred Zampa Memorial Bridge (AZMB), a newly built long-span suspension bridge, is located 32km northeast of San Francisco on interstate Highway I-80. A set of dynamic field tests were conducted on the AZMB in November 2003, just before the bridge opening to traffic. These tests provided a unique opportunity to identify the modal properties of the bridge in its as-built condition with no previous traffic loads or seismic excitation. A benchmark study on modal identification of the AZMB is performed using three different state-of-the-art system identification algorithms based on ambient as well as forced vibration measurements. These system identification methods consist of: (1) the multiple-reference natural excitation technique combined with the eigensystem realization algorithm, (2) the data-driven stochastic subspace identification method, and (3) the enhanced frequency domain decomposition method. Overall, the modal parameters identified using these system identification methods are found to be in very good agreement for each type of tests (ambient and forced vibration tests). For most vibration modes, the natural frequencies and mode shapes identified using the two different types of test data also match very well. However, the modal damping ratios identified from forced vibration test data are in general higher than those estimated from ambient vibration data. The identified natural frequencies and -2-mode shapes are finally compared with their analytical counterparts from a three-dimensional finite element model of the AZMB. The modal properties of the AZMB presented in this paper can be used as baseline in future health monitoring studies of this bridge.
2009
In this paper, wind-induced vibration response of Vincent Thomas Bridge, a suspension bridge located in San Pedro near Los Angeles, California, is simulated using a detailed three-dimensional finite element model of the bridge and a state-of-the-art stochastic wind excitation model. Based on the simulated windinduced vibration data, the modal parameters (natural frequencies, damping ratios, and mode shapes) of the bridge are identified using the data-driven stochastic subspace identification method. The identified modal parameters are verified by the computed eigenproperties of the bridge model. Finally, effects of measurement noise on the system identification results are studied by adding zero-mean Gaussian white noise processes to the simulated response data. Statistical properties of the identified modal parameters are investigated under increasing level of measurement noise. The framework presented in this paper will allow to investigate the effects of various realistic damage ...
Automated modal identification in operational conditions and its application to bridges
Engineering Structures, 2013
The increasing diffusion of long term dynamic monitoring systems for structural condition assessment is currently driving a strong interest towards automated procedures of output-only modal identification. Different approaches have been recently developed in the literature for this purpose, often based on Stochastic Subspace Identification (SSI) methods. Such procedures usually rely on heuristic decisional criteria, hence demanding for independent checks with validation purposes.
STRUCTURAL IDENTIFICATION OF BRIDGES BASED ON AMBIENT VIBRATION MEASUREMENTS
First European …, 2006
The evaluation of the actual dynamic characteristics of civil engineering structures through measurements of their response to various excitations has been attracting an increasing research effort worldwide in the past years. A methodology for the assessment of the modal characteristics of bridges is proposed, based on recordings of their dynamic response to ambient excitations. Additionally, a finite element model updating methodology is developed as a useful tool for monitoring the condition and assessing the integrity of instrumented bridges. The proposed procedures are applied for the case of two bridges on Egnatia Motorway in northern Greece, whose response to traffic excitations has been systematically monitored with special accelerometer arrays. The integration of the proposed methodologies in a bridge monitoring system, can provide to the managing authorities of Highways a useful tool for the assessment of the structural condition of the bridges under their surveillance.