Now showing 1 - 10 of 26
  • Publication
    On the estimation of bridge mode shapes from drive-by measurements
    This paper summarizes the latest approaches proposed on indirect bridge monitoring and provides recommendations for future development. The possibility of the estimation of bridge mode shapes from indirect measurements, is investigated. The Hilbert transform is applied to the responses measured from two following axles to extract the amplitudes of the signals. The global bridge mode shapes are constructed by applying a rescaling process to the local mode shapes obtained from the amplitudes. The performance of the proposed method is demonstrated using a numerical case study.
  • Publication
    Cross entropy weight minimization of a compressive strut
    (Research Publishing Services, 2016-05-19) ; ;
    In this study, a population-based optimization algorithm is used to minimize the weight of a compressive strut. A geometrically nonlinear analysis is carried out to get an accurate measure of the structure's true capacity, allowing for individual member and overall structure (and sub-structure) buckling. To overcome the computational challenge of nonlinear analysis, the study uses a simple definition of the onset of instability and hence the number of iterations is cut to a minimum.
  • Publication
    Identification of bridge mode shapes using a passing vehicle
    (International Society for Structural Health Monitoring of Intelligent Infrastructure, 2015-07-03) ;
    This paper describes the Short Time Frequency Domain Decomposition (STFDD) method for identification of bridge mode shapes using the responses measured in a passing vehicle. Several segments are defined on a bridge and a truck-trailers system is employed to measure the signals. Subtraction of the responses measured from following axles on the truck-trailers is used to remove the effect of road profile. The sensitivity of the STFDD method to sampling time interval and vehicle velocity is investigated using numerical studies. It is shown that selecting an optimum time interval may improve the accuracy of the results obtained. Furthermore, keeping vehicle speed below 4 m/s provides enough data for successful identification of bridge mode shapes.
  • Publication
    Estimation of traffic load effects on Forth Road Bridge using camera measurements
    This paper explores the possibility of using a camera and image analysis to extract congested traffic data. A video system was installed on the Forth Road Bridge. The system captured traffic video data at a rate of 1 frame per second for approximately five months. Simple image processing methods, e.g. adaptive thresholding and morphological reconstruction, are used to automatically analyse the images extracted from the videos. The body shapes of the vehicles are accurately extracted. Identified vehicles are framed within rectangles and the rectangle’s dimensions are used to approximate the length of the vehicles. The study confirms that the image data can be used efficiently to measure the lengths of the vehicles. The vehicle lengths can be ultimately used for the estimation of site specific characteristic maximum traffic load effects.
  • Publication
    Investigating the Contact-Point Response for Drive-By Damage Detection in Bridges
    Bridges are critical elements in any road or rail transport network and ensuring their safety is paramount. Recent years have seen significant research efforts to develop cost-effective techniques for bridge monitoring on a large scale. Drive-by bridge inspection techniques, whereby sensors inside a vehicle are used to monitor bridge condition, are at the focus of much of this work. This paper develops a relationship between the measured response in a vehicle and the contact-point response between the wheel and the surface of a bridge using a quarter-car representation of the vehicle. Numerical simulations are carried out to examine the feasibility of using the contact-point response as an indicator of damage. A number of passages of the quarter-car vehicle model traversing a Finite Element representation of a bridge are simulated and the contact-point response is evaluated for each passage. Varying levels of damage are simulated in the bridge to assess whether the presence of damage can be detected by the contact-point response. Results show that the method is very effective at identifying the bridge frequencies and can also detect changes in bridge frequency with increasing damage levels. A major advantage of using the contact-point response as a damage indicator lies in its ability to detect bridge frequencies without being influenced by the vibrational frequencies of the vehicle itself. The contact-point response shows promise for implementation into drive-by bridge inspection regimes, however further work is required to investigate the feasibility of the approach at higher vehicle speeds.
  • Publication
    Acceleration-based Bridge Scour Monitoring
    This paper comes from a research project focused on the safety assessment of bridges using camera-based technologies. The project is developing methods that transform measured sensor signals and video images into a form that is highly damage-sensitive for bridge safety assessment. It will advance sensor-based structural health monitoring with computer-vision and accelerometer-based techniques, leading to practical applications for bridge damage detection. Many sensor types have been used in test installations, with varying degrees of success. Strain gauges and transducers are well established technologies and sufficiently accurate sensors are available at a reasonable cost. However, strain transducers can only detect damage if it occurs close to the point of measurement and are completely insensitive to scour-induced settlement. Deflection at any point on a bridge is a function of support conditions and the flexural stiffness at all points. As such, it has the potential to provide an indication of damage at any point. Deflection can be difficult to measure and some of the partners in this project are working to develop image analysis techniques to improve the accuracy of camera-based deflection measurement systems. Doppler laser vibrometers measure the derivative of deflection with respect to time, i.e., velocity, but they are expensive and it is impractical to deploy large numbers on smaller bridges. Acceleration is the 2nd derivative of deflection so it is, in theory at least, sensitive to scour damage. Furthermore, accelerometers are widely available and can provide accurate measurements at a reasonable cost. This paper reports on the use of acceleration measurements for bridge scour monitoring. Traffic induced acceleration on a bridge is the result of a range of excitations. The signal is influenced by a number of vehicle-related factors such as speed, inter-axle spacing and tyre and suspension properties. In this project, the portion of the acceleration signal in the region of the bridge first natural frequency is filtered from the raw input in order to amplify the portion of the signal most likely to be influenced by bridge damage. Vehicle/bridge dynamic interaction simulations are used to show the nature of the response, before and after filtering. It is shown that the filtered signal is considerably more sensitive to bridge damage than the original raw signal and has good potential for bridge health monitoring.
  • Publication
    Application of output-only modal method in monitoring of bridges using an instrumented vehicle
    In this paper, application of a well-known output-only modal analysis method called Frequency Domain Decomposition (FDD) method in monitoring of bridge frequency is presented. The obtained modal data can be used efficiently for bridge health monitoring. Three measurement strategies are suggested to collect the acceleration responses from vehicle axle for FDD method in a numerical study. It is shown that using multi vehicles leads to better results in compare to using one vehicle. The efficient effect of ambient excitation to all sides of the bridge is also discussed. In addition, application of FDD method in the case of closeness of vehicle frequency to bridge frequency is investigated. Finally, it is discussed that the FDD method can be an efficient alternative to FFT analysis which is common for analysing the vehicle measurement passing over the bridge.
  • Publication
    Railway track monitoring using drive-by measurements
    This paper presents the possibility of detecting considerable changes in track stiffness using the measurements from a laser vibrometer installed on a passing train. A numerical model of a two-dimensional train-track system is implemented in Matlab using the finite element method. The loss of stiffness in the track is modeled by reducing the stiffness of the sub-ballast layer of the track at specified points. The instantaneous velocity of the rail under the train is measured using four laser vibrometers mounted on the train. The simulations show that a change in the sub ballast stiffness of the track can be detected and located from the drive-by measurements.
  • Publication
    On the use of a passing vehicle for the estimation of bridge mode shapes
    This paper presents a novel algorithm for the estimation of bridge mode shapes using the response measured on a passing vehicle. A truck-trailer system is assumed, equipped with an external excitation at a frequency close to one of the bridge natural frequencies. The excitation makes the bridge response dominant at its natural frequency. The acceleration responses are measured on two following axles of the vehicle. It is shown that the amplitude of the signal includes the operational deflected shape data which can be used to estimate the bridge mode shapes. The energy of the responses measured on two following axles is obtained using the Hilbert Huang Transform. It is shown that the bridge mode shape can be estimated with high resolution and accuracy using a rescaling process. The presence of road roughness introduces additional contributions to the response measured on the vehicle, in addition to the bridge response. The concept of subtraction of the responses measured from two identical axles is used to remove the effect of road roughness.
      648Scopus© Citations 101
  • Publication
    Rigid body stiffness matrix for identification of inertia properties from output-only data
    Identification of inertia properties (mass, location of the center of mass and inertia tensor) is essential for designing of engineering structures. Using modal testing is a possibility for estimation of the inertia properties in which they can be identified using the orthogonality property of mass-normalized rigid body mode shapes. However, identification of rigid body mode shapes using modal testing is not always possible, because it is not possible to excite the structure at all degrees of freedom. In this paper, output-only modal analysis in which the structure can be excited in different directions is used to identify the rigid body modes of the structure. It is shown that all of the rigid body modes of the structure can be extracted using the data extracted from output-only modal analysis. As the obtained rigid body mode shapes from output-only modal analysis are not scaled, a new method is proposed for scaling them using rigid body stiffness matrix. The inertia properties of the structure are obtained from the scaled mode shapes. The accuracy of the proposed method is studied using a numerical case study of a steel structure as well as an experimental case study of a steel frame.
      875Scopus© Citations 4