Pomiary sztywności toru tramwajowego metodą wizyjną Tram track stiffness measurement based on the vision method

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(1)PRACE NAUKOWE POLITECHNIKI WARSZAWSKIEJ z. 124. Transport. 2019.

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(3) Warsaw University of Technology, Faculty of Transport. Bartosz Firlik Poznan University of Technology, Faculty of Transport Engineering. TRAM TRACK STIFFNESS MEASUREMENT BASED ON THE VISION METHOD Manuscript delivered, June 2019. Abstract: One of the main parameters characterizing properties of railway track is vertical stiffness. Provision of its appropriate value is crucial from the point of view of dynamic interactions occurring in a wheel-rail contact, what in turn translates into vehicle running behaviour and safety, passenger comfort, as well as further degradation of track condition. Track stiffness measurement is a cumbersome process requiring expensive equipment and can be carried out only if the line is closed. The following research is intended to estimate tram track vertical stiffness by means of vision method which can be performed during regular tram operation. Track deflections of tram line in the city of Poznan were carried out using high-speed camera and further used for vertical stiffness estimation. Keywords: tram track, vertical stiffness, high speed camera. 1. INTRODUCTION Provision of an appropriate stiffness and damping of rail track is crucial from the point of view of dynamic interactions occurring in a wheel-rail contact. The substantial deviations of track vertical stiffness relative to the nominal one and variations of its value along the track cause additional dynamic interactions in a wheel-rail system [1, 3]. From the vehicle point of view these extra dynamic loads lead to reducing of running safety and comfort level. Variations of the wheel-rail contact forces due to different track stiffness give rise to the phenomenon of track settlement and vibration propagation caused by repeating loads [2]. Hence stiffness can be treated as an additional track diagnostic indicator, along with track geometrical parameters, in the entire track condition assessment process. Total stiffness k experienced by a moving vehicle is combination of stiffness of the individual track elements. It depends on bending stiffness EJ, as well as type and condition of: rail fastening, sleeper,.

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(5) >9(+ , Bartosz Firlik. ballast, subgrade, subsoil. Methods of track stiffness measurement methods are categorized by Wang et al. in two groups: standstill and continuous methods [7]. In the standstill methods stiffness is measured in a selected point of track, and the typical methods falling into this category are: hydraulic jackloading, impact hammer, FWD – falling weight deflectometer, TLV – track loading vehicle. General idea of continuous methods is to measure stiffness on long-distance selected track sections with use of rail vehicles equipped with instrumented vehicles. Both types of methods require expensive equipment and closing the railway lines or performing measurements in limited time window due to transport operation. Despite high

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(16) & &y a highspeed camera. This uncommon method is also used in the following study which aim was to determine tram track stiffness. One of the most significant advantages of the method is relatively low cost compared with conventional railway methods using specialized equipment, which is not usually possessed by tram track operators, as well as lack of necessity of closing the line or performing measurements at night. The measurements were taken on

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(23) – the tram and infrastructure operator in Poznan uses several types of rail vehicles in exploitation. The vehicles represent different technological state, starting from design solutions from 1960s years and ending with the low-floor trams as of XXI century. The tram infrastructure in Poznan is extensive and includes 21 lines. The system consists of 18 daily lines, 2 night lines and one tourist line which are opened from May to October, operated by historical vehicles. Infrastructure consist of normal gauge track (1435 mm) of total length of tracks is ca. 200 km. Depending on track location, there are rails of the following types: railroad type rails S49, tram type rails: 180S, Ri60N, Ri60, block-type rails LK-1. Track stiffness measurements with use of high-speed camera, which can be classified as standstill ones, were taken in the selected location: ,

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(33) Tram track stiffness measurement based on the vision method. 47. Location #3: Warszawska street – behind the Termy Maltanskie tram stop, in direction to Warsaw. In each of the mentioned locations, the measurements were taken in the one, randomly selected point on a rail, above sleeper. An important factor influencing the measurement results is method for supporting the rails as well as the condition of the track bed at the point of measurement. The locations were chosen taking into account track condition and frequency of tram running. An example of tram passage and measurement in localization#1 is shown in figure 1.. ¯GG9

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(37) ! – location #1. Contrary to location #1 and #2, the tested section of track infrastructure at location #2 consists of wooden sleepers. It should be noted also that this section of the tram infrastructure is also equipped with reinforced concrete sleepers. However, the measurements were taken on wooden sleepers. The rails are attached to the wooden sleepers with screw-type Skl-12 fasteners. Q

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(43) #¯ Tram line. Fastening of rails to the prestressed concrete sleepers is carried out by means of spring clips of SB-3 type.. 3. CONDITIONS OF RECORDING AND IMAGE ANALYSIS In order to record track deflection, a high-speed camera Phantom V310 was used. The camera recording parameters were the same in all locations, namely: picture resolution: 800x600, recording time: 3.47 s. The volume of the recorded films for the above settings was about 10 GB per movie. During the measurements, in which the distance between the camera and the track was %

(44) ! G * wska str.), the lens used for recording was Nikon AF NIKKOR 50 mm 1: 1.4 D. However, since the distance from camera to the track was grat-.

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(53) ((( lens: Nikon AF NIKKOR 80-200 mm 1: 2.8 D. Track deflection was analyzed in TEMA Motion software by tracking vertical displacements of the marker attached to rail head. Markers were placed on the outer side of a rail web (below rail head) at location #1 and #2 whereas on the rail head at location #3. In the case of visual measurements of track deflection its accuracy depends mainly on the following factors: determination of the reference length for the image scaling, location of the recorded point. TEMA Motion software sets the default distance in pixels. However, it is possible to scale the image so that distances are given in typical units, e.g. millimeters. For this purpose, it is necessary to determine reference distance in the software basing on two selected points. In this study scaling was performed on the basis of the point located in the center of the marker (at the interface of contrasting quadrants) and the top point located on the common line of two quadrants edge (the line extending from the center of the marker). The nominal height of the half-square is 25 mm (fig. 2), however, as a result of cutting the marker from the paper block, and taking into account the limited accuracy in indicating the point in the program, this distance has been reduced by 1 mm. After scaling one pixel corresponded to the length of approximately 0.6 – 0.87 mm.. Fig. 2. Contrasting marker applied to rails. The equivalent static stiffness k of the rail vertical support can be, in the simplest terms, estimate as a rate of change of the vertical force F on a wheel relative to changes of the vertical displacement y of the center of the track marker: =. . (1). The values appearing in the formula are indicated in the diagram in fig. 3.. Fig. 3. Diagram of the wheel-rail system with the designation of the estimated stiffness.

(54) Tram track stiffness measurement based on the vision method. 49. To estimate stiffness k displacement of the marker center was read in the software for the time step when the wheel center was in line with the center of the marker. This time step corresponds approximately to the maximum deflection of the rail what is shown in figure 4.. Fig. 4. Position of the center of the wheel above the center of the marker. Displacement values of the marker center were filtered by a 5th order Butterworth filter. Due to the unknown dynamic loads F of a tram wheels on a rails it was assumed that this interaction is quasistatic, since velocity of the trams was low (in close vicinity of tram stops). Hence, static load of one tram wheelset was substituted for F in equation (1). Simultaneously with pictures recording, the number of passengers travelling by tram was counted. One passenger mass of 70 kg was adopted according to PN-EN 15663 [5].. 4. EXPERIMENTAL RESULTS AND STIFFNESS ANALYSIS Each of the measurement is characterized by different load applied to the rails, since the lines are operated by various tram types whose load per wheel depends on their nominal mass and number of passengers travelling during the measurement. All the types of tram models taking part in the experiment are listed with their nominal masses in table 1. Tab. 1 Tram types and their nominal masses Tram Tram mass [kg] Bogie mass [kg] Mass per wheel [kg] Konstal 105N 16 500 8 250 2 063 Tramino 42 500 14 167 3 542 Combino 32 380 10 793 2 698 Tatra 32 850 10 950 2 738 Moderus Beta 40 650 10 163 2 541 Moderus Alfa 18 500 9 250 2 313.

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(56) >9(+ , Bartosz Firlik. The sample results of track deflection analysis of one tram passage at location #1 are presented in figure 5. The X marker refers to time step at which wheel center was in line with marker’s center, what in turn correspond to the greatest deflection of each wheel. Deflections were caused by a three-bogie tram Solaris Tramino.. Fig. 5. Track deflection at location #1 – passage no. 8, tram Solaris Tramino. The values of tram static loads, deflections and calculated stiffness are presented in tab. 2. As the result in table 2 have shown, the estimation of actual mass of has a considerable impact on the estimated stiffness value what is reflected in discrepancy reaching up to 12.3% between the lowest and the highest estimated value from one measurement. The greatest discrepancy calculated in location #1 was 21.8%. Tab. 2 Results of the measurement at location #1, passage no. 8, tram: Solaris Tramino Wheel Load/wheel [N] Deflection [mm] Stiffness [MN/m] Bogie #1 – 1st wheel 0.65 56.2 36 461 Bogie #1 – 2nd wheel 0.69 52.7 Bogie #2 – 1st wheel 0.65 57.4 37 233 Bogie #2 – 2nd wheel 0.67 55.3 st Bogie #3 – 1 wheel 0.61 60.1 36 890 Bogie #3 – 2nd wheel 0.62 59.5. Comparison of calculated stiffness values is presented in fig. 6. These values vary in each location depending on tram model (load per wheel). Triangle pictogram informs about mean stiffness value for each tram whereas values below and above triangle stand for lower and upper quartile respectively. Discrepancies between lower and upper quartile are also an effect of unequal number of measurements taken for different tram models and total number of measurements in each location which were: for location #1 – 13 measurements, location #2 – 16, and for location #3 – 8 measurements..

(57) Tram track stiffness measurement based on the vision method. 51. Fig. 6. Calculated stiffness regarding tram model and location. Despite substantial differences of stiffness obtained for different tram models, all of the stiffness values for each wheel of every tram model (from one location) were taken further to calculate global (mean) stiffness and standard deviation for the measurement points which are depicted in tab. 3. Track supported on wooden sleepers (location #2) is characterized by the lowest stiffness value. Although concrete sleepers are placed in location #1 and #3, stiffness in the latter one is higher, what in this case indicate prestressed concrete technology. Tab. 3 Stiffness statistical parameters Location Mean stiffness [MN/m] Standard dev. [MN/m] Loc. #1 41.2 8.7 Loc. #2 16.1 2.8 Loc. #3 64.0 16.0. 5. CONCLUSIONS The study presented herein concerns track stiffness estimation method based on vision measurement with use of high-speed camera. The main advantage of such the approach is possibility of taking measurements during normal operation of vehicles. The presented results of measurements and analyzes for each location refer only to one, randomly selected measuring point. However, the method itself has limited accuracy what is indicated by substantial standard deviation values of track stiffness (location #1 and #3) and it varies with tram models. Another issue having effect on the measurement results is estimation of.

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(59) >9(+ , Bartosz Firlik. the current load of tram (passenger location and mass). Normative passenger mass value has been assumed, however. Basing on the analyzed deflections from all locations, it can be concluded that uncertainty of the visual measurement should not exceed 0.2 mm. This value corresponds to the amplitude fluctuations of zero level – a state at which vehicle did not cause track deflection and markers should not physically move. Nevertheless, such the movement was recorded which was caused by tracking algorithm in the software. However, uncertainty of this algorithm has not been explicitly revealed by software’s developer. A high-speed camera measurement of track deflection can be useful for approximate estimation of track stiffness and thus track condition. Since it is a contactless method, there is no risk of track damaging. Moreover, this method can be classified as a standstill with track load occurring in normal operation.. References 1. Berggren, E.: Railway track stiffness dynamic measurements and evaluation for efficient maintenance,. Doctoral thesis, KTH, Sweden, 2009. 2. Dahlberg T.: Railway track settlements – a literature review, Report for the EU project SUPERTRACK,. 2004. 3. Dahlberg T.: Railway Track Stiffness Variations – Consequences and Countermeasures, International. Journal of Civil Engineerng, Vol. 8, No. 1, 2010, 1–12. 4.

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(66) (. Transport, Vol. 22, No. 2, 2010, 153–162. 5. PN-EN 15663+A1:2019-02 Railway applications – Definition of vehicle reference masses. 6. Vorster J., Gräbe H.: Axle load and track deflection on a heavy haul line, Civil Engineering, May 2010,. 44–49. 7. Wang P., Wang L., Chen R., Xu J., Xu J., Gao M.: Overview and outlook on railway track stiffness. measurement, Journal of Modern Transportation, Vol. 24, No. 2, 2016, 89–102.. '1!32"3+'841"'6"!+!)'+./'."'7;+123); Streszczenie: q % %

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