Now showing 1 - 10 of 21
  • 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.
      339
  • Publication
    Sensitivity of SHM Sensors to Bridge Stiffness
    Bridges play an important role in transport infrastructure and it is necessary to frequently monitor them. Current vibration-based bridge monitoring methods in which bridges are instrumented using several sensors are sometimes not sensitive enough. For this reason, an assessment of sensitivity of sensors to damage is necessary. In this paper a sensitivity analysis to bridge flexural stiffness (EI) is performed. A discussion between the use of strain or deflections is provided. A relation between deflection and stiffness can be set by theorem of virtual work, expressing the problem as a matrix product. Sensitivity is obtained by deriving the deflection respect to the reciprocal of the stiffness at every analysed location of the bridge. It is found that a good match between the deflection and the bridge stiffness profile can be obtained using noise-free measurements. The accuracy of sensors is evaluated numerically in presence of damage and measurement noise. Field measurements in the United States are also described to identify the potential issues in real conditions.
      176
  • Publication
    On the use of a passing vehicle for bridge health monitoring
    The large number of short-span and medium-span bridges in transportation systems makes it hard to instrument all of them for direct inspection. This issue has resulted in an increased interest in indirect monitoring of these bridges, i.e., monitoring using sensors in a vehicle passing overhead. With indirect monitoring, no sensors or data acquisition system needs to be installed on the bridge. This paper explains the theoretical background of indirect bridge monitoring and reviews the most important advances that have been made recently. Finally there is discussion and recommendations on the most important challenges that remain.
      306
  • Publication
    Application of Laser Measurement to the Drive-by Inspection of Bridges
    (National Technical University of Athens (NTUA), 2015-05-27) ;
    This paper introduces the application of laser vibrometer measurements to the drive-by inspection of bridges. Drive-by methods usually process the acceleration response measured from an accelerometer installed on a vehicle passing over a bridge. In this paper, two laser vibrometers and two accelerometers are installed on the vehicle to measure a rela-tive velocity between the bridge and vehicle and the vehicle acceleration. The vehicle velocity is removed from the relative velocity by subtracting the time integration of the vehicle accel-eration. It is shown by subtracting two following bridge spatial velocities at moving coordi-nates, that the spatial velocity of the road roughness can be removed. As a result, the bridge velocity at the moving coordinate is obtained. By applying the FFT to the bridge velocity, the fundamental frequency of the bridge is visible in the spectrum.
      493
  • 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.
      599
  • 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.
      241
  • 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.
      128
  • 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.
      261
  • Publication
    Bridge Scour Detection using Vehicle Acceleration Measurements
    Bridge scour is a serious issue concerning bridge condition and can have adverse consequences if undetected. It is the most common cause of bridge collapse today. One method of assessing the issue is through the use of visual inspections but this has drawback in that often an underwater inspection may have to be carried out. This makes it an expensive solution. Human objectivity leads to inconsistencies in the approach also and this is an issue. A sensor-based approach is a suitable alternative due to these reasons. The use of vehicle acceleration measurements to detect scour is analysed in this paper. The continuous wavelet transform is used to decompose the accelerations into time and frequency information. It is found that the location of the pier under which the scour is present can be identified using this method.
      130
  • Publication
    Application of empirical mode decomposition to drive-by bridge damage detection
    A new method is proposed in this paper for bridge damage detection using the response measured in a passing vehicle. It is shown theoretically that such a response includes three main components; vehicle frequency, bridge natural frequency and a vehicle speed pseudo-frequency component. The Empirical Mode Decomposition (EMD) method is used to decompose the signal into its main components. A damage detection method is proposed using the Intrinsic Mode Functions (IMFs) corresponding to the vehicle speed component of the response measured on the passing vehicle. Numerical case studies using Finite Element modelling of Vehicle Bridge Interaction are used to show the performance of the proposed method. It is demonstrated that it can successfully localise the damage location in the absence of road profile. A difference in the acceleration signals of healthy and corresponding damaged structures is used to identify the damage location in the presence of a road profile. The performance of the method for changes in the transverse position of the vehicle on the bridge is also studied.
    Scopus© Citations 127  743