Acoustic and dynamic characteristics of a complex urban turnout using fibre-reinforced foamed urethane (FFU) bearers

Transcription

1 Massachusetts Institute of Technology From the SelectedWorks of Sakdirat Kaewunruen September 11, 13 Acoustic and dynamic characteristics of a complex urban turnout using fibrereinforced foamed urethane (FFU) bearers Sakdirat Kaewunruen Available at:

2 Acoustic and dynamic characteristics of a complex urban turnout using fibrereinforced foamed urethane (FFU) bearers S Kaewunruen RailCorp Track Engineering, Level 13, 477 Pitt St, Sydney NSW 00, Australia Tel: , Fax: , sak.kaewunruen@railcorp.nsw.gov.au Summary A special track system used to divert a train to other directions or other tracks is generally called railway turnout. A traditional turnout system includes rails, switches, crossings (special track components), steel plates, fasteners, screw spikes, timber bearers, ballast and formation. The wheel rail contact over the crossing transfer zone has a diplike shape and can often cause detrimental impact loads on the railway track and its components. The large impact also emits disturbing noises (either impact or groundborne noise) to railway neighbors. In a brownfield railway track where an existing aged infrastructure requires renewal or maintenance, some physical constraints and construction complexities may dominate the choice of track forms or certain components. With the difficulty to seek for highquality timbers, a methodology to replace aged timber bearers in harsh dynamic environments is to adopt a suitable material that could mimic responses and characteristics of timber in both static and dynamic situations. A critical review has suggested a field trial of an alternative material called Fibrereinforced foamed urethane (FFU) because of its comparable characteristics to timber, highimpact attenuation, high damping property, and longer service life. After the review of laboratory testings, a field trial of the FFU material has been implemented at an urban turnout junction in RailCorp s suburban rail network. The effectiveness of such method has then been evaluated using integrated numerical simulations, axle box acceleration and ride quality data obtained from the calibrated track inspection vehicle AK Car, and operational passby measurements of noise and vibration. The field trial demonstrates that using the FFU bearers in an urban turnout is effective in retaining the level of impact vibration and passenger ride comfort. It is also found that FFU material responds to operational actions in a similar manner as timber. The material can well suppress the highfrequency impact vibration at the crossings. However, it is important to note that, in addition to lateral stability consideration, the vertical stiffness transition along the track is recommended in order to mitigate the damages onto track components due to rigid body modes of track vibration.

3 2 1 Introduction Railway turnout is a special track system used to divert a train from a particular direction or a particular track onto other directions or other tracks. A turnout is the structural grillage system that consists of steel rails, points (or called switches ), crossings (special track components, also known as frog ), steel plates, rubber pads, biscuits, fasteners, screw spikes, beam bearers (either timber or concrete), ballast and formation, as shown in Fig. 1 [1]. Currently, the procurement for highquality long timber bearers used in complex turnout systems has been very difficult for construction and renewal processes in Australia. Many problems with long timber turnout bearers (>4m.) also include localised weakness, large deformation, warping or unstable dimensions that can easily cause obstructions during the turnout assembly resulting in a poor geometry of new turnouts. Then, the wheel/rail interaction (see Fig. 2) over such poor shortpitch irregularity induces impact force and vibration that exacerbates the condition and undermines the service life of turnout components and the integrity of turnout system as a whole [1]. Points Closure Rails Check Rail Check Rail Crossing Fig. 1. Typical turnout geometry Nose Wing rail Fig. 2 Transfer zone at crossing where a conical wheel traversing a vcrossing (white paint showing the contact band) and running over a dip angle inducing impact force []

4 The difficulty to seek for highquality timbers has led to two possible alternatives in practice: first, to use the concrete long bearers with splice plates; second, to use the alternative material (i.e. Fibrereinforced Foamed Urethane or socalled FFU; composite materials, plastic rubber materials, etc.) with the similar characteristics as a timber. A critical review has suggested a field trial of FFU material because of its highimpact attenuation, high damping property, high UV resistance, and long service life. As a result, the complex turnout junction with aged timber bearers at Hornsby NSW Australia has been renewed in 10 using FFU material. There were five stages of construction: note that the first turnout was in October 10 and the double slips were in late June 11. Also, due to the light weight of FFU bearers, a special arrangement was designed to maintain lateral stability to the turnouts [6]. 3 Table 1 Basic properties of FFU material in comparison with timber bearers [6] Properties Timber Birch FFU bearers [] bearers 1 bearers 2 New After 10 years After 1 years After 30 years Service life (years) Density (kg/m 3 ) Bending strength (MPa) > 70 Vertical compression strength (MPa) > 40 Shear strength (MPa) > 7 Elastic modulus 16, (MPa) > 6000 Fatigue flexural strength 0,000 cycles at 40 MPa 0,000 cycles at 40 MPa 1 million cycles at 94 MPa Hardness (MPa) Water absorption (mg/cm 2 ) < Impact bending strength C Destructive voltage (kv) dry (>,000) wet (>,000) Insulation resistance (Ω) dry (> 1.0x10 4 ) wet (> 1.0x10 4 ) Dog spike pullout strength (kn) > 1 Screw spike pullout strength (kn) > 30 <1 < >2 22 >2 24 >2 23 > x x x x x x x10 4.9x x10.9x x Timber bearer properties are derived from AS17 Strength Group 2 [6] 2 Birch timber bearer properties are derived from the technical datasheet [6]

5 This paper focuses on the acoustic and dynamic performance of the alternative FFU material as a likeforlike replacement of timber bearers. This study involves the inspection, traintrack interaction, sound pressure and vibration measurements of the double slips, and benchmarking with other available field data [6]. 2 Fibrereinforced Foamed Urethane (FFU) Bearers FFU bearers are made of continuous glass fibre reinforced rigid polyurethane foam. The foam contains advantages over plastic and wood, e.g. durability and corrosion resistance, electrical insulation, heat resistance, lightweight and strength, and good fabrication/assembly/coating. The high damping characteristic of FFU bearers would be beneficial to the impact and vibration absorption in turnout crossings and supporting components. Fundamental engineering properties of the FFU material are tabulated in Table 1 [, ]. In the field installation, FFU bearers with the cross section of 20mmx10mm have been utilised throughout. 3 Trial Site Because of the complexity of the junction, a set of urban turnouts has been chosen for this trial. The trial site is at Hornsby, New South Wales. The junction comprises of three set of turnouts, two sets of single slips and a set of double slips. In this study, the double slips as shown in Fig. 3 were chosen for acoustic and vibration measurements. 4 Fig. 3 Double Slips (21/22) at Hornsby NSW 4 Acoustic and Vibration Measurements 4.1 Field condition Fig. 4 shows a test site at Hornsby (Northern line of RailCorp network). The diamond crossings and heel joints create additional impacts. The track configuration consists of 60kg rails, fastening system (eclip type), steel plates (no rubber pads), FFU bearers, ballast bed and formation. The track supports mixed traffic (passenger and freight trains). The operational speeds are 60 km/h

6 for freight trains and 0 km/h for passenger trains, although almost all the electric passenger trains stop at Hornsby station. The axle load of freights could be up to 2t axle load. 4.2 Instrumentation Accelerometers were installed at the rail web, base plates and bearers at kcrossing and at the interface between FFU bearers and concrete sleepers as shown in Fig.. High speed camera was used to read the dynamic displacement of the turnout. A sound level meter was installed at 7.m from the nearest kcrossing of the diamond. Train speed radar was installed at a nearby OWH mast. Fig. 4 Test Site Fig. Instrumentation Results and discussions In total, 26 operational passbys had been recorded at a sampling rate of 10 khz. Table 2 shows the list of the representative vibration measurements from the passbys, which comprehensively spread over all train travelling directions. Table 2. Measurement list of train passbys (selected) File No Measured Train speed (km/h) (empty) Type of rolling stocks Direction Maximum overall noise level (7.m) dba 0 Maximum dynamic rail displacement at kcrossing (mm) 6 (X main) (X main) (X main) ( main) Freight ( main) (Down shore) ( main) Down

7 The maximum dynamic rail displacements at kcrossing were observed at about 46mm. The impact noise levels were found to be peaked up to 91 db(a) for a very short duration. Fig. 6 shows the vibration characteristics of the double slips at kcrossing and at the interface between FFU bearers and concrete sleepers. 6 a) at kcrossing b) at interface between FFU bearers and concrete sleepers Fig. 6 Frequency analysis (No 11 X Main)

8 The vibration characteristics of the double slips show the large amplitude of vibrations at the kcrossing and it has been damped out considerably by the FFU bearers. Note that the steel crossing is mounted directly onto steel plates on the bearers. In addition, the rigid body motion is the key contributor to the damage of turnouttrack substructure at the interface. Fig. 7 shows slightly increased vertical train body vibration over the doubleslips section and Fig. shows the benchmarking with other field measurements. The results confirm that relatively the dynamic characteristics of FFU bearers are equivalent to timber bearers [9]. 7 Vertical ride quality, RMS (mg) Undulation due to unsettlement of brand new turnout Distance (KM:m) Fig. 7 Ride comfort Before: After: Average Peak Vibration, g Hornsby V (FFU) Flemington V1 (timber) Bondi V (concrete slab) Glenfield Swing nose (concrete) Linear (Hornsby V (FFU)) y = 2.293x R 2 = Average train speed, km/h y = 0.461x R 2 = y = x R 2 = 0.19 P1 Vibration, g 1 P2 Vibration, g 6 10 Hornsby V (FFU) Flemington V1 (timber) Bondi V (concrete slab) Glenfield Swing nose (concrete) Linear (Hornsby V (FFU)) 4 2 Hornsby V (FFU) Flemington V1 (timber) Bondi V (concrete slab) Glenfield Swing nose (concrete) Linear (Hornsby V (FFU)) Average train speed, km/h Average train speed, km/h Fig. Vibration data benchmarking (top: overall; bottom left: P1; and bottom right: P2)

9 6 Conclusions Based on the condition inspection and vibration measurements, it is found that FFU material has equivalent acoustic and dynamic performance relatively to timber bearers while lasting longer. Also, FFU bearers perform well in P1 region but not very well in P2 band. This is because the impact excitation in P1/P2 frequency band could excite the resonant behaviour of FFU bearers. However, FFU bearers exhibit relatively remarkable vibration suppression characteristics in comparison with crossings. High damping characteristics of FFU material were demonstrated in the frequency analyses. It is important to note that the stiffness transition at the interface between FFU and concrete sleepers must be established to suppress rigid body vibration damaging substructure components. Acknowledgement The author is grateful to RailCorp for the permission to publish this paper. The author would also like to sincerely thank Australian Federal Government for the Endeavour Executive Award, which has provided him the financial support for this conference attendance and the professional development at Charmers Railway Mechanics Centre (CHARMEC), Massachusetts Institute of Technology (MIT), and Harvard University. References [1] Andersson, C., Dahlberg, T.: Wheel/rail impacts at a railway turnout crossing, Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. 212F, (03). [2] Remennikov, A.M., Kaewunruen, S.: A review of loading conditions for railway track structures due to train and track vertical interaction, Structural Control and Health Monitoring. 1(2), 7234 (07). [3] Kaewunruen, S., Remennikov, A.M.: Dynamic flexural influence on a railway concrete sleeper in track system due to a single wheel impact, Eng Failure Analysis. 16(3), 70712, (09). [4] Kaewunruen, S.: Effectiveness of using elastomeric pads to mitigate impact vibration at an urban turnout crossing, in Maeda et al. (Eds.) Noise and Vibration Mitigation for Rail Transportation Systems, Springer, 3736 (12). [] Kaewunruen, S (09) Review of alternative fibrereinforced foamed urethane (FFU) material for timberreplacement turnout bearers, Technical Report TR162, RailCorp Track Engineering, Sydney NSW, 14p (11). [6] Kaewunruen, S. Insitu performance of alternative fibrereinforced foamed urethane (FFU) material for timberreplacement turnout bearers, Technical Report TR1, RailCorp Track Engineering, Sydney NSW, 6p (11). [7] Kaewunruen, S. Vertical and lateral stability performance of alternative fibrereinforced foamed urethane (FFU) material for timberreplacement turnout bearers, Technical Report TR197, RailCorp Track Engineering, Sydney NSW, 40p (12). [] Sekisui Co.: Engineering Properties of FFU materials, Tokyo Japan, (12). [9] RailCorp Rolling Stock Engineering: Minimum Operating Standards for Rolling Stock, Sydney, Australia, (12).