The support stiffness of a ballast bed may be changed by modifying ballast grading and materials.
In this regard, the homogenization effect cannot be realized by changing the stiffness of a rail pad. Rail pads are relatively stiff to maintain the dynamic height difference between movable rail parts and the stock rail/wing rail. The elasticity of a fastening is determined mainly by the plate pad. After selection, the flexural stiffness is determined and cannot be changed during stiffness optimization. of the rail must be taken into consideration in selecting rail types. For this, the strength, service life, process, etc. Track integral stiffness is affected by flexural stiffness of the rail as well as the supporting stiffnesses of fillers, rail pad, plate pad, and bed. By this method, the effective damping (in the vertical mode) may range from 40 to 100 percent of critical damping, based on the effective mass and stiffness of the track without additional unsprung mass. Kurzweil has calculated the theoretical damping due to radiation of energy into a “halfspace” and has concluded that this form of energy loss is significantly greater than the damping due to the ballast/soil loss factor.
Tests performed by the AAR on clean ballast of good quality have indicated equivalent viscous damping factors of 15 to 25 percent of “critical damping”, based on the apparent natural frequency of the test sample. Qualitatively, the damping is hysteretic in nature and depends upon many factors: type and condition of the ballast, degree of compaction, amount of “fines” and moisture present, etc. We may assume the rail, probably the tie, contribute negligible damping to the structure, so that energy dissipation occurs solely in the ballast. (19) m b = 3.0 ( W tie / 2 g l t + ρ b ) / 2 βĭamping is perhaps even more difficult to define quantitatively.
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