Abstract: A full-scale 7-story reinforced concrete building slice was tested on the unidirectional University of California–San Diego Network for Earthquake Engineering Simulation (UCSD-NEES) shake table dur...

Abstract: This paper presents the earthquake response of a historical masonry minaret after a finite element model updating was undertaken using the information from full scale ambient vibration testing. The Iskenderpasa historical masonry minaret dating back to the 16th century with a height of 21m located in the city center of Trabzon, Turkey is selected as an application. Analytical modal analysis is performed on the 3D finite element model of the minaret considering field survey and engineering judgments to obtain the analytical frequencies and mode shapes. The field ambient vibration tests on the minaret under natural excitations such as wind loading and human movement are conducted. The Peak Picking and the Stochastic Subspace Identification techniques are used to extract the modal parameters from the ambient vibration test. A good correlation was found among the modal parameters identified from the two techniques. The finite element model of the minaret is updated to minimize the differences between analytically and experimentally estimated modal properties by changing some uncertain modeling parameters such as material properties and boundary conditions. The analytical model of the minaret after finite element model updating is analyzed using the 1992 Erzincan earthquake record, which occurred near the area, to determine the earthquake behavior of the minaret. At the end of the study, maximum differences in the natural frequencies are reduced on average from 27% to 5% and a good agreement is found between analytical and experimental natural frequencies and mode shapes by model updating. Also, it is seen from the earthquake analysis that the displacements increase along the height of the minaret and the maximum and minimum principal stresses occur at the region of the transition segment and the cylindrical body.

Abstract: This paper addresses the temperature-induced variations of measured modal frequencies of steel box girder for a suspension bridge using long-tem monitoring data. The output-only modal frequency identification of the bridge is effectively carried out using the Iterative Windowed Curve-fitting Method (IWCM) in the frequency-domain. The daily and seasonal correlations of frequency-temperature are investigated in detail and the analysis results reveal that: (i) the identified modal frequencies using IWCM provide an effective indication for changes of the bridge due to the ambient temperature variations; (ii) temperature is the critical source causing modal variability, and there is an overall decrease in modal frequency with temperature for all the identified modes; (iii) the random variations in measured modal frequencies mainly arise from the identification algorithm due to the nonstationary loadings, which can be effectively eliminated using multi-sample averaging technique; (iv) the daily averaged modal frequencies of vibration modes have remarkable seasonal correlations with the daily averaged temperature and the seasonal correlation models of frequency-temperature are suitable for structural damage warning if future seasonal correlation models deviate from these normal models.

Abstract: This paper presents the finite element calibration of Berke Arch Dam by using Operational Modal Testing. Achievement of this purpose involves structural vibration characteristics of Berke Arch Dam using analytical and Operational Modal Analyses. Therefore, the study has two parts — analytical and experimental. In the analytical part of the study, the authors developed a 3D finite element model of Berke Arch Dam-reservoir-foundation system using ANSYS software, and analytically determined vibration characteristics such as natural frequencies and mode shapes. In the experimental part of the study, sensitive accelerometers were placed to several points of Berke Arch Dam, and ambient vibration tests were conducted over four days to obtain dynamic characteristics. The Enhanced Frequency Domain Decomposition technique is used to estimate natural frequencies, mode shapes and damping ratios of the Berke Arch Dam experimentally. Results showed that there were some differences between analytical and experimental na...

Abstract: This is a review paper on mathematical modeling of actively controlled piezo smart structures. Paper has four sections to discuss the techniques to: (i) write the equations of motion (ii) implement sensor-actuator design (iii) model real life environmental effects and, (iv) control structural vibrations. In section (i), methods of writing equations of motion using equilibrium relations, Hamilton`s principle, finite element technique and modal testing are discussed. In section (ii), self-sensing actuators, extension-bending actuators, shear actuators and modal sensors/actuators are discussed. In section (iii), modeling of thermal, hygro and other non-linear effects is discussed. Finally in section (iv), various vibration control techniques and useful software are mentioned. This review has two objectives: (i) practicing engineers can pick the most suitable philosophy for their end application and, (ii) researchers can come to know how the field has evolved, how it can be extended to real life structures and what the potential gaps in the literature are.

Abstract: New modern bridges and older structures exposed to accelerated deterioration need permanent condition monitoring. The major tools used in bridge condition evaluation are based on the results of the experimental modal analysis of bridge structures. This paper focuses on the methodology of Forced Vibration Tests performed by means of mechanical exciters. A comprehensive testing system called MANABRIS, developed at Wroclaw University of Technology, is presented. The system is equipped with a rotational eccentric mass exciter and dedicated software for programming and controlling the tests and for acquiring and processing measurement data. The results of a Forced Vibration Test carried out on a typical railway bridge are compared with the results of a conventional modal test of the structure excited by trains. The precision of the considered testing techniques is evaluated and the range of their effective application is proposed.

Abstract: This paper presents the dynamic characterization of a CX-100 wind turbine blade using modal testing Obtaining a thorough dynamic characterization of turbine blades is important because they are complex structures, making them very difficult to accurately model without supplementing with experimental data The results of this dynamic characterization can be used to validate a numerical model and understand the effect of structural damage on the performance of the blades Also covered is an exploration into Structural Health Monitoring (SHM) techniques employed on the blade surface to detect changes in the blade dynamic properties SHM design parameters such as traveling distance of the wave were examined Results obtained during modal and SHM testing will provide a baseline for future work in blade damage detection and mitigation

Abstract: Research highlights? Two novel methods for identification of mass-damping-stiffness of shear buildings. ? In the first method, modal properties are estimated from forced vibration responses. ? In the second method, a direct strategy of structural identification is developed. ? The noise effects may partially be eliminated by using high-order FIR filters. In this research, two novel methods for simultaneous identification of mass-damping-stiffness of shear buildings are proposed. The first method presents a procedure to estimate the natural frequencies, modal damping ratios, and modal shapes of shear buildings from their forced vibration responses. To estimate the coefficient matrices of a state-space model, an auto-regressive exogenous excitation (ARX) model cooperating with a neural network concept is employed. The modal parameters of the structure are then evaluated from the eigenparameters of the coefficient matrix of the model. Finally, modal parameters are used to identify the physical/structural (i.e., mass, damping, and stiffness) matrices of the structure. In the second method, a direct strategy of physical/structural identification is developed from the dynamic responses of the structure without any eigenvalue analysis or optimization processes that are usually necessary in inverse problems. This method modifies the governing equations of motion based on relative responses of consecutive stories such that the new set of equations can be implemented in a cluster of artificial neural networks. The number of neural networks is equal to the number of degree-of-freedom of the structure. It is shown the noise effects may partially be eliminated by using high-order finite impulse response (FIR) filters in both methods. Finally, the feasibility and accuracy of the presented model updating methods are examined through numerical studies on multistory shear buildings using the simulated records with various noise levels. The excellent agreement of the obtained results with those of the finite element models shows the feasibility of the proposed methods.

Abstract: Machine tool vibrations have great impact on machining process. In this paper the dynamic behavior and modal parameters of milling machine is presented. For this purpose, the CAD model of the milling machine structure is provided in CATIA and then Natural frequencies and mode shapes of the machine tool structure are carried out through FEM modal analysis under ANSYS Workbench. The model is evaluated and corrected with experimental results by modal testing on FP4M milling machine. Finally, the natural frequencies and mode shapes obtained by both experimental and FEM modal analysis are compared. The results of two methods are in widely agreement.

Abstract: Our paper deals with a non-probabilistic computational approach for mechanical systems with structural uncertainties. Uncertainties are considered as bounded possible values – intervals. The main goal is to propose algorithms for modal and spectral interval computations on FE models. An application of the chosen approaches is presented, i.e. the first one a simple combination of only inf-values or only sup-values; the second one presents full combination of all inf-sup values; the third one uses the optimization process as a tool for finding out a inf-sup solution and last one is Monte Carlo technique as a comparison tool.

Abstract: The presence of damping, gyroscopic behavior, and gearing complicates traditional vibration analysis. This paper presents a methodology for conducting modal reduction on a geared rotor dynamic system under the influences of general damping and gyroscopic effects. Based on the first-order, state-space methodology, a coordinate transformation is presented for diagonalizing the state equations of motion for each substructure in the system. A modal synthesis procedure assembles the system equations from the individual substructures. The substructures are coupled via gear-mesh interactions. Using this technique, the size and complexity of a model can be reduced without incurring significant loss of accuracy. The reduced model allows for traditional methods of system analysis to include eigen-solution analysis, and frequency response. Validation occurs through application to a simple geared system widely discussed in the literature. The results of the modal reduction match closely with the full finite element m...

Abstract: The dominant and persistent trend with wind turbine technology, particularly in the past three decades, has been growth in the length of the blades. In order to investigate design choices which reduce blade weight, Sandia Labs initiated a study, which is near completion, to evaluate innovative concepts for large blades. The innovations include strategic use of carbon fiber in the spar caps, bend-twist coupling in the composite layup, and thick, flatback airfoils. Several large blades were designed and then built at a down-scaled 9-meter length. Each blade design has undergone a full series of structural tests including modal tests, static tests, and fatigue tests. The modal tests performed for evaluation of these blades is the focus of this paper. Major findings from these tests are summarized, and they include: (1) techniques for experimental quantification of uncertainty in the modal parameters, (2) insight into model calibration using both static load-deflection data and the modal parameters, (3) novel test techniques for reducing the uncertainty in the root boundary condition, and (4) the development of validated structural models. This paper will provide a summary of blade modal testing and structural model validation, and will emphasize recent validation tests using a seismic-mass-on-airbags boundary condition.

Abstract: This paper describes the modal testing and in situ vibration monitoring of a high profile UK stadium during 2004 and 2005, including multiple concerts and sports events. The paper explains how current design guides pertaining to crowd dynamic loading of grandstands can be practically implemented using experimental modal data or finite element (FE) models. Three major pieces of guidance are considered: Canadian, ISO, and UK. Particular attention is given to new UK Recommendations as they are a major diversion from other methods and have yet to be robustly verified against real events on full-scale structures. This paper is therefore a unique verification exercise for all three guidelines because it makes use of rare combined in situ video and structural vibration response data pertinent to crowd dynamic loading of grandstands. Canadian guidance is found to predict the order of magnitude of responses well but lacks reliable precision, whilst the UK Recommendations are found to be very good at recreating res...

Abstract: One of the key factors in designing a motor built-in high speed spindle is to assemble the motor rotor and shaft by means of hot-fit. Presented in this paper is a study of the influence of a hot-fit rotor on the local stiffness of the hollow shaft. Dynamic analyses of the rotor-hollow shaft assembly using contact elements are conducted. The normal contact stress state between the rotor and the hollow shaft is obtained through the use of contact elements with friction effects included. The normal contact stress, considered as the pr-stress between the rotor and the hollow shaft, is then adopted for subsequent modal analyses. In this study, the modal analysis results are verified by a modal testing experiment. The percent errors of the first natural frequency and the second natural frequency are down to about 0.58% and 0.79%, respectively.

Abstract: The dynamic stability under the passage of a moving train has become one of the most important issues in railway bridge designs. A precise application of the dynamic properties of a structure will lead to a precise description of the dynamic behavior of a structure under moving train loads. A railway bridge is completed with a track structure, which is composed of rail, sleeper and track (concrete or ballast). A track structure can change the modal properties of the railway bridge, through the contribution of stiffness as well as mass effects. Consequently, the critical speed of the train that gives rise to the resonance behavior should be also changed, with or without the track. In the present study, a twin I-shaped steel composite girder bridge was fabricated as a test specimen, and modal testing was carried out with the installation of non-ballast, ballast track and concrete track. Modal tests were performed with hydraulic dynamic actuators. The natural frequencies, damping ratios and dynamic responses of each type of track structure were observed, along with the variation of magnitudes, frequencies and amplitudes of dynamic loading. From the results, the effects of a track structure on the railway bridge can be evaluated.

Abstract: The modal analysis of piping system in air conditioner (AC) outdoor unit is essential to investigate the vibration properties of the system. In view of the growing significance of numerical finite element (FE) model for vibration behaviour prediction, the AC piping elastic end support characterization has been explored. The axial and radial stiffness variables (k a , k r1, k r2) of the compressor-piping mounting are obtained and represented by dynamic stiffness of compressor grommet. They are obtained from dynamic load deflection test based on compressor operating condition such as excitation frequency and amplitude. The unknown stiffness variables of the other tube end (chassis-piping mounting) are determined by parameter fine tuning. An experimental modal analysis using impact hammer test has also been employed to determine the vibration properties such as natural frequencies, mode shapes and damping ratio of the piping structures. The modal parameters acquisition using SCADAS mobile acquisition system and LMS Impact Testing software is compared with the corresponding simulated modal properties using Abaqus. Most of the simulated natural frequencies achieve good correlation with the measured frequencies and it is reasonably a good prediction model to predict vibration behaviour of AC piping structures.