Railway Track Stiffness: Dynamic Measurements and Evaluation for Efficient Maintenance

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George Rangel
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Railway Track Stiffness: Dynamic Measurements and Evaluation for Efficient Maintenance

Mensagem por George Rangel » 21 Out 2014, 19:31

Autor: Eric Berggren (Berggren E.)

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Instituição: Royal Institute of Technology (KTH)
Departamento: Aeronautical and Vehicle Engineering
Cidade: Stockholm
Ano: 2009
Berggren - 2009.pdf
Abstract:
Railway track stiffness (vertical track load divided by track deflection) is a basic parameter of track design which influences the bearing capacity, the dynamic behaviour of passing vehicles and, in particular, track geometry quality and the life of track components. Track stiffness is a broad topic and in this thesis some aspects are treated comprehensively. In the introduction part of the thesis, track stiffness and track stiffness measurements are put in their proper context of track maintenance and condition assessment. The first aspect is measurement of track stiffness. During the course of this project, Banverket has developed a new device for measurement of dynamic track stiffness called RSMV (Rolling Stiffness Measurement Vehicle). The RSMV is capable of exciting the track dynamically through two oscillating masses above one wheelset. The dynamic stiffness is a complex-valued quantity where magnitude is the direct relation between applied load and deflection (kN/mm) and phase is a measure of deflection-delay by comparison with force. The phase has partial relationship with damping properties and ground vibration. The RSMV repeatability is convincing and both overall measurements at higher speeds (up to 50 km/h) and detailed investigations (below 10 km/h) can be performed. The measurement system development is described in Paper A and B. The second aspect is evaluation of track stiffness measurements along the track from a track engineering perspective. Actual values of stiffness as well as variations along the track are important, but cannot always answer maintenance and design related questions alone. In Paper D track stiffness is studied in combination with measurements of track geometry quality (longitudinal level) and ground penetrating radar (GPR). The different measurements are complementary and a more reliable condition assessment is possible by the combined analysis. The relation between soft soils and dynamic track stiffness measurements is studied in Paper C. Soft soils are easily found and quantified by stiffness measurements, in particular if the soft layer is in the upper part of the substructure. There are also possibilities to directly relate substructure properties to track stiffness measurements. Environmental vibrations are often related to soft soils and partly covered in Paper C. One explanation of the excitation mechanism of train induced environmental vibrations is short waved irregular support conditions. This is described in Paper E, where track stiffness was evinced to have normal variations of 2 – 10 % between adjacent sleepers and variations up to 30 % were found. An indicative way of finding irregular support conditions is by means of filtering longitudinal level, which is also described in the paper. Train-track interaction simulation is used in Paper H to study track stiffness influence on track performance. Various parameters of track performance are considered, e.g. rail sectional moment, rail displacement, forces at wheel-rail interface and on sleepers, and vehicle accelerations. Determining optimal track stiffness from an engineering perspective is an important task as it impacts all listed parameters. The third aspect, efficient maintenance, is only partially covered. As track stiffness relates to other condition data when studied from a maintenance perspective, vertical geometrical defects (longitudinal level and corrugation/roughness) are studied in paper F. The general magnitude dependency of wavelength is revealed and ways of handling this in condition assessment are proposed. Also a methodology for automated analysis of a large set of condition data is proposed in Paper G. A case study where dynamic track stiffness, longitudinal level and ground penetrating radar are considered manifests the importance of track stiffness measurements, particularly for soil/embankment related issues.

Keywords: Railway track stiffness, maintenance, soil dynamics, measurement, simulation,
vibration
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