Determination of Vertical Alignment of Track using Accelerometer Readings

IMechE Stephenson Conference for Railways: Research for Railways, 21 - 23 April, 2015Railway 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.European Commission - Seventh Framework Programme (FP7

Finite element modelling of the Loopline Bridge and model validation using ground-based radar interferometry

The 2022 Civil Engineering Research in Ireland (CERI) and Irish Transportation Research Network (ITRN) Conference, Dublin, Ireland, 25-26th August 2022This research investigates the procedure of using ground-based radar interferometry to develop and validate a finite element model of the Loopline Bridge in Dublin, Ireland. A description of the bridge is outlined and a three-dimensional finite element model was developed using RFEM, a commercial software package. The modelling approach was first validated against known theoretical solutions. The bridge model was then verified with section property calculations, experimental studies in the literature and deflection tests. The dynamic deflection at midspan of the Loopline Bridge was measured for two train crossing events using ground-based radar interferometry. A single train crossing event showed the deflection of the loaded side of the span with respect to the unloaded side. Additionally, a dual train crossing event demonstrated the twist in the deck from the train loads travelling in opposite directions on separate sides of the bridge. The same loading conditions were simulated in the finite element model and the resulting deflections were extracted. A comparison between both sets of deflection data was carried out and their correlation validated that the model accurately captures the behaviour of the real Loopline Bridge structure for both train loading scenarios

Determination of railway track longitudinal profile using measured inertial response of an in-service railway vehicle

The use of sensors fixed to in-service trains has the potential to provide real-time track condition monitoring to inform maintenance planning. An Irish Rail intercity train was instrumented for a period of 1 month so that a numerical method developed to find track longitudinal profile from measured vehicle inertial responses could be experimentally tested. A bogie-mounted accelerometer and gyrometer measured vertical acceleration and angular velocity as the train made regular service operations between Dublin and Belfast on the island of Ireland. Cross entropy optimisation is used to find a track longitudinal profile that generates a numerical inertial response that best fits the measured response. Tolerance limits are used to inject variance where required to ensure a good match between measured and modelled signals. A section of track with known track settlement history is selected as a case study. A level survey was undertaken during the measurement campaign to characterise the longitudinal profile through the test section. Bandpass filters are used to compare inferred profiles and the surveyed profile. Good agreement is found between the two profiles although improvements in accuracy and reproducibility are required before conformance with current standards is achieved

Calculation of the Dynamic Allowance for Railway Bridges from Direct Measurement

Railways 2016: The Third International Conference on Railway Technology: Research, Development and Maintenance, Sardinia, Italy, 5-8 April 2016In 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

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.European Commission - Seventh Framework Programme (FP7

Drive-by structural health monitoring of railway bridges using train mounted accelerometers

5th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Crete Island, Greece, 25 - 27 May, 2015Bridge 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.European Commission - Seventh Framework Programme (FP7

Aplasia cutis congenita in dizygotic twin infants

Aplasia cutis congenita (ACC) is a rare heterogenous group of disorders characterized by the absence of a portion of skin in a localized or widespread area at birth. 1 ACC is often sporadic but familial cases have been reported. 1,2 We report a case of a dichorionic diamniotic (DCDA) twin pregnancy in which both the male and female twins had matching areas of aplasia cutis on their scalps