Zbornik radova Koridor 10 - Kirilo SaviÄ

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3rd International Scientific and Professional Conference CORRIDOR 10 - a sustainable way of integrations Ballastless tracks with continually elastically supported rails have relatively less noise emission compared to tracks with discretely elastically supported rails. Ballast spreading over the ballastless track, implantation of prefabricated noise absorption elements (Figure 8) or grass cladding is applied in addition to standard noise protection measures (Figure 9). FIG. 8. Ballast spreading over the asphalt slab (middle) and built-in noise-absorbing elements (right) in the track type FFBS ATS SATO (left) on the railway between stations Mannheim and Karlsruhe in 1996 (Mailänder Ingenieur Consult, 1996) FIG. 9. Track type "Rasengleis" for long-distance traffic on the test section between stations Mannheim and Karlsruhe before (left) and after installation of noise protection elements (right) (Mailänder Ingenieur Consult, 1996) 5. WHEEL/RAIL NOISE CONTROL MEASURES By analyzing equation (1) for calculating noise level according to (Die Deutsche Bundesbahn, 2006), it can be concluded that wheel/rail noise control must include strategy and measures in design and maintenance of both vehicles and track, as well as measures in the organization of transport. L mE 0.1(51 DFz DD D1 DV ) 10 lg 10 DFb DBr DBue DRa (1) where: 51 dB is the basic value of noise emission level, DFz is the influence of vehicle type, DD is the influence of brake type, D1 is the influence of vehicle length, DV is the influence of vehicle speed, D Fb is the influence of track type and state, D Br is the influence of bridges, D Bue is the influence of level crossings, and D Ra is the influence of track curvature. Belgrade, 2012 259
3rd International Scientific and Professional Conference CORRIDOR 10 - a sustainable way of integrations 5.1 Maintenance of the upper part of the rail head Corrugation of the upper part of the rail head is the common cause of the roughness of the rail head running surface (Figure 10). The phenomenon is observed as a periodical sequence of bright ridges and dark hollows on the running surface (International Union of Railways, 2002). Constructive measures for corrugation reduction are continual rail support or decrease of space between discrete rail supports (space between sleepers 60 cm, which increases rail bending stiffness) and decrease of direct fastening system stiffness (recommended value of static stiffness of rail pads is up to 200 kN/cm). Experience showed that corrugation doesn’t occur in the case of continually supported rails, or it occurs with time delay with respect to discretely supported rails. FIG. 10. Rail head slip waves - code number 2202 (photos taken on the New Belgrade – Zemun section, 28 July 2004) To eliminate rail head corrugation, grinding is applied (International Union of Railways, 2007). Today, grinding (along with lubrication of outer rail in curve) is a part of the routine rail-care. Timely grinding of surface roughness prevents its further development. The grinding effect is not permanent. After some time, corrugation reoccurs. It is considered that the noise decrease potential, based on the rail-care, is from 15 to 20 dB(A) with respect to the track condition without rail-care (Schöch, 2008). The objective of grinding strategy is rail life extension, reduction of total track and vehicle maintenance costs, and reduction of railway traffic vibration and noise level. Preventive, corrective and cyclic activities make the grinding strategy. Preventive activities are undertaken before the defects are noted in the zones where their occurrence is empirically expected. Preventive grinding is applied after laying new rails on the track before acceptance of works. If the rail has to be replaced on the existing track, new rails can be grinded right away or a few weeks after the assembly. The target of corrective grinding is re-establishing regular longitudinal rail profile by removing corrugation. Different railway managements set different limit values of corrugation depth for application of corrective grinding. In spite of diversity of corrugation grinding strategies, it is generally accepted in Europe that removing corrugation is essential and worthwhile. Depending on the depth of the rail head damage, material is removed from the surface of the head in order to allow the wheels to roll on the undamaged steel surface. By removing the material by grinding, rail cross profile has to be maintained, so that the wheel/rail contact stresses are maintained within acceptable limits and a stable ride quality is provided. Sometimes corrugation appears combined with squats (Figure 11, right) mainly on straight lines and curves of radius R ≥ 3000 m with high shear stresses, especially zones where accelerations and breaking occurs (Schöch, 2008). If the defect is noticed in the initial stadium, it can be removed by grinding and thus the rail replacement can be deferred. Only in some cases welding can repair this defect. Rail replacement most frequently solves the problem, though. Belgrade, 2012 260
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Zbornik radova Koridor 10 - Kirilo SaviÄ