Assessment of the track condition using the Gray Relational Analysis method

The execution of current research on recording the acceleration caused by tram vibrations in operating conditions, using on-board diagnostics systems and wireless data transmission, enables the track condition assessment based on the vehicle dynamic response analysis [5 ÷ 7]. This issue is very important from the infrastructure maintenance point of view, as it allows for an ongoing assessment of its technical condition in normal operating conditions. Such systems are particularly suitable for rail networks where driving conditions are constant, reproducible and without significant interference or changes in driving behavior [e.g. 1; 3; 12]. In urban conditions, this is not a trivial task, as it results from the substantial spread of data received even from the same vehicle type and the same measuring section. This is due to the fact that the vehicle is moving at different speeds within the same track, variable load (number of passengers), driving behavior of the motorists (rapid or gentle acceleration and deceleration), weather conditions, traffic at different hours and days, technical condition of the vehicle, etc. The measurement uncertainty of the monitoring system itself should also be taken into account. All of these factors make it difficult to estimate the track condition for light rail vehicles using the acceleration level measured in the vehicle. In order to eliminate some of the above mentioned factors and to propose a methodology for evaluating the track condition, it was decided to, at the first stage, select the data from different track sections (in different parts of the city) of one type, i.e. with 60R2 tram rail, excluding areas using a classic railway track (mainly 49E1). In addition, it was decided to include the tram speed recordings for a given track, forming a certain profile characteristic for a particular track condition (the relation between the effective acceleration values and the tram speed). For each passing, the maximum speed was taken into account, assuming that the information about the technical condition of the track will be most visible for such driving speed. Another factor, whose impact was eliminated, was the technical condition of the vehicle itself. The data considered were from a new vehicle, but this does not limit the application of the proposed methodology. In practice, it is always possible to eliminate this factor by installing a vibration measurement system on a new or renovated vehicle. The presented analysis used data collected from more than two months of operation of a modern low-floor tram in normal passenger traffic. The information on the vibration acceleration value determined from a 1 second time window in the range of 0 to 100 Hz, recorded on the vehicle body located above the first bogie. Thus this is in a way a measure of travel comfort (there are currently no official legal acts in this field dedicated to light rail vehicles such as a tram). The effective value of vibration acceleration was selected after a comparative analysis of various statistical measures [7]. Evaluation of the track sections actual technical condition was determined on the basis of independent information obtained from maintenance services, assisted by independent measurements of track geometry. Finally, the data presented in Table 1 and presented in Figure 1 were taken into account. The proposed grading scale of the track technical condition assessment is deliberately coincidental with that adopted in MPK Poznan (local tramway operator). TABASZEWSKI M, FIRLIK B. Assessment of the track condition using the Gray Relational Analysis method. Eksploatacja i Niezawodnosc – Maintenance and Reliability 2018; 20 (1): 147–152, http://dx.doi.org/10.17531/ein.2018.1.19.