Now showing 1 - 6 of 6
  • Publication
    Determination of longitudinal profile of railway track using vehicle-based inertial readings
    The longitudinal profile of a railway track excites a dynamic response in a train which can potentially be used to determine that profile. A method is proposed in this paper for the determination of the longitudinal profile through an analysis of bogie vertical accelerations and angular velocities resulting from the train/track dynamic interaction. The Cross Entropy optimisation technique is applied to determine the railway track profile elevations that generate a vehicle response which best fits the measured dynamic response of a railway carriage bogie. Numerical validation of the concept is achieved by using a 2-dimensional quarter-car dynamic model, representing a railway carriage and bogie, traversing an infinitely stiff profile. The concept is further tested by the introduction of a 2-dimensional car dynamic vehicle model and a 3 layer track model to infer the track profile in the longitudinal direction. Both interaction models are implemented in Matlab. Various grades of track irregularity are generated which excite the vehicle inducing a dynamic response. Ten vertical elevations are found at a time which give a least squares fit of theoretical to measured accelerations and angular velocity. In each time step, half of these elevations are retained and a new optimisation is used to determine the next ten elevations along the length of the track. The optimised elevations are collated to determine the overall longitudinal profile over a finite length of railway track.
    Scopus© Citations 28  1225
  • Publication
    Calculation of the Dynamic Allowance for Railway Bridges from Direct Measurement
    In a traditional deterministic assessment, a dynamic amplification factor (DAF) is applied to the static loading in order to account for dynamics. The codified DAF values are appropriately conservative in order to consider the wide range of structures and load effects to which they are applied. In the current analysis, a site specific assessment dynamic ratio (ADR) is calculated from direct measurement on an 80 year old steel truss Railway Bridge. The ADR is defined as the ratio of characteristic total stress to the characteristic static stress. The application of ADR is a relatively new concept which has rarely been considered for railway bridges. An assessment performed on the bridge in question showed a decrease in the dynamic allowance when considering the site specific ADR, corresponding to a 26% decrease in calculated stress. The measurements available were also used to derive a robust stochastic model for dynamic allowance which considered the correlation between DAF and stress level. The developed model was applied to a probabilistic assessment and resulted in a 9% increase in reliability.
      444
  • Publication
    Determination of Vertical Alignment of Track using Accelerometer Readings
    Railway track vertical alignment is an important indicator of serviceability condition. Through comparisons with past history, track alignment also informs maintenance planning. The vertical alignment of a railway track excites a dynamic response in a train which can potentially be used to determine that alignment. A method is proposed in this paper for the detection of the alignment through an analysis of vehicle accelerations resulting from the train/track dynamic interaction. The Cross Entropy optimisation technique is applied to determine the railway track profile heights that best fit the measured accelerations at and above a railway carriage bogie. Such an approach, using relatively low-cost accelerometers fixed to trains in regular service, would provide inexpensive daily 'drive-by' track monitoring to complement and compare data collected by the Track Recording Vehicle (TRV). The use of a TRV is the current preferred method used to determine railway track profiles using laser based methods. Numerical validation of the concept is achieved by using a 2-dimensional quarter-car dynamic model for the railway carriage and bogie to infer the track profiles in the longitudinal direction. The interaction model is implemented in MATLAB. The track is modelled as an infinitely stiff beam featuring various grades of rail irregularity which excite the vehicle inducing a dynamic response. Ten vertical elevations are found at a time which give a least squares fit of theoretical to measured accelerations. In each time step, half of these elevations are retained and a new optimisation is used to determine the next ten elevations along the length of the track. The optimised displacements are collated to determine the overall rail track profile over a finite length of railway track. This paper reports the results of the numerical simulations and the plans that are underway to further develop the model and test the concept in field trials.
      580
  • Publication
    Drive-by structural health monitoring of railway bridges using train mounted accelerometers
    Bridge damage can be detected by observing changes in its spectral properties. In its infancy, bridge health monitoring involved monitoring physical properties via direct instrumentation, i.e. sensors attached to the bridge. In recent years many authors have investigated the ability of indirect methods to assess the structural health of bridges, i.e. the vehicles traversing the bridges are fitted with sensors. This has the potential of reducing monitoring costs as the vehicle may be used to monitor many bridges on the network. Most of the investigation in this relatively new field of study has been on road bridges and road vehicles. A method is proposed in this paper for the detection of the bridge damage through an analysis of vehicle accelerations resulting from the train/track/bridge dynamic interaction. In a train/track/bridge interaction there are additional complications which do not exist on road bridges. The signal generated by the train as it traverses the bridge is normally short in duration. Studies on railway bridges are complicated by the addition of rails, sleepers and sometimes ballast between the tracks and the bridge deck. However, the weight of the train relative to the bridge is considerably larger than previous studies using road vehicles and this will excite the bridge to a higher degree. Numerical validation of the drive-by concept is achieved by using a 2-dimensional dynamic vehicle model with 10 degrees of freedom. The finite element interaction model is implemented in MATLAB. The track is modelled as a continuous beam, supported at 0.545m centres on three layers of springs and masses representing sleepers, and ballast lying on a simply supported bridge beam. This paper reports the results of the numerical simulations and the plans that are underway to test the concept in field trials.
      745
  • Publication
    Drive-by inference of railway track longitudinal profile using accelerometer readings taken by in-service vehicles
    (Civil Engineering Research Association of Ireland, 2016-08-30) ; ; ;
    Accurate knowledge of the longitudinal profile of railway track is essential to support maintenance planning by track asset managers. The dynamic response of a train is largely dependent on the longitudinal profile of the railway track it crosses. This dynamic response can potentially be used to determine that profile. Cross Entropy optimisation is used to infer railway track longitudinal profile elevations through analysis of measured vehicle bogie accelerations with added uncertainty in vehicle and track properties. A numerical analysis is presented in this paper using a 2 dimensional half car vehicle and a finite element 3-layer track model implemented in Matlab. A population of track longitudinal profiles is generated through a random mechanism. A vehicle track interaction with randomly generated uncertainty in vehicle and track properties is carried out for each longitudinal profile in the population. The bogie acceleration signal produced for each profile is compared to the measured signal. The best fitting bogie accelerations are used to gather an elite set of rail longitudinal profiles. This elite set is used to generate an improved population of estimates for the next iteration. Once a convergence criterion is met the profile generating an acceleration signal that best fits the measured bogie acceleration signal is kept as the inferred longitudinal rail profile. This paper reports the results of the numerical simulations.
      135
  • Publication
    Drive-by detection of railway track stiffness variation using in-service vehicles
    Railway track stiffness is an important track property which can help with the identification of maintenance related problems. Railway track stiffness can currently be measured using stationary equipment or specialised low-speed vehicles. The concept of using trains in regular service to measure track stiffness, has the potential to provide inexpensive daily 'drive-by' track monitoring to complement data collected by less-frequent monitoring techniques. A method is proposed in this paper for the detection of track stiffness variation through an analysis of vehicle accelerations resulting from the vehicle-track dynamic interaction (VTI). The Cross Entropy optimisation technique is applied to determine the track stiffness profile that generates a vehicle response that best fits the measured vertical accelerations of a railway carriage bogie. Numerical validation of the concept is achieved by using a 2-dimensional half-bogie dynamic model, representing a railway vehicle, to infer a global track stiffness profile along a track. The Track Stiffness Measurement Algorithm (TSMA) is implemented in Matlab. This paper reports the results of the numerical simulations. The proposed method gives good estimates of the track stiffness. To the authors' knowledge this is the first time an optimisation technique has been applied to the determination of railway track stiffness.
    Scopus© Citations 45  723