Railways: surface track – Roadbed – Street crossing
Reexamination Certificate
2000-05-23
2002-07-09
Le, Mark T. (Department: 3617)
Railways: surface track
Roadbed
Street crossing
Reexamination Certificate
active
06415988
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to rail track surface structures and more particularly to a new and improved rail track surface structure employing resilient closure inserts between each side of the rails and adjacent road surfaces.
In rail track construction, it is frequently necessary to align the rail head with adjacent road surfaces. In heavy weight railway trackage, this occurs at level crossings, where vehicular roadways intersect railway trackage, and in light rail trackage in urban areas where street surfaces are aligned with rail head levels to facilitate pedestrian and vehicular movement.
Rails employed in both railway and light rail urban transport include a base, a vertical web, and a head portion; each pair of rails forming a track having inner sides designated “gauge” sides, facing each other, and outer sides designated “field” sides.
Rail design conventionally employed in railway trackage uses a T-rail section, generally symmetrical in cross-section, in which the flange of the railway wheel laterally engages the gauge side of the head portion of the rail, with no underlying engagement of the flange. However, for light rail transportation such as in typical urban light rail transportation systems, a girder-rail section is being increasingly employed, in which a flangeway is formed integrally in a gauge side lateral extension of the head of the rail, to accommodate the downwardly depending flange of the railcar wheel, the upstanding leg of the rail head so defining the flangeway then engaging the road surface between the rails to accommodate vehicular and pedestrian traffic.
It is with each of these rail designs that the present invention is concerned, as will be apparent as this disclosure proceeds.
Considerable effort and ingenuity has heretofore been displayed to improve rail track surface structures to reduce maintenance at the interface between rail and adjacent road surface.
Degradation of the structure results from water and solid particulate foreign matter (“detritus”) intrusion adjacent the rails, which passes downwardly to the rail bed, causing deterioration of the structure and frequent maintenance.
A further problem resulting from unwanted water intrusion into the rail bed results from the breakdown in the electrical insulation normally existing between the metal rail and the ground. In this regard, the rails are frequently employed as conductors of low-voltage currents used in signalling, or in applications of light rail transport in which the locomotive is electrically powered, the rail functioning as a conductor in the power circuit. Negative consequences result in stray currents escaping from the metal into surrounding structures or the ground, when water is permitted to intrude into the rail bed. The problem of water intrusion into the rail bed is further aggravated when dissolved road salts, entrained in the surface water, reach the metal in the rail bed, resulting in costly corrosion.
Conventionally, rail track surface structures have employed resilient electrically non-conductive inserts adapted for insertion in the space defined on both gauge and field sides of the rail members between the rails and the adjacent road surfaces, the purpose of which has been to attempt to seal the adjacent rail members from water and detritus while permitting the use of conventional asphalt materials between and against adjacent rails, on the gauge sides and field sides thereof, respectively. Typical of such level crossing inserts are those shown in U.S. Pat. No. 4,461,421 to Maass; U.S. Pat. No. 4,899,933 to Martin and U.S. Pat. No. 3,469,783 to Uralli, each of which discloses a railway crossing insert of resilient material, resting on the base of the rail, cooperating with the rail on the one side, and interfacing with the adjacent road surface on the other side.
Much of the sealing problem is occasioned by the necessary provision for accommodation of downward flexing of the rail and track bed consequent on the passage of heavy rail loadings from rail traffic. Such deflections are unavoidable and normally are of the order of several millimeters, which movement is largely manifest at the interface between the insert and the adjacent road surface, the insert itself moving with the rail. This rail and insert movement, however, is attendant with negative consequences, due to spalling, crumbling and cracking of the asphalt material on the adjacent road surface where it interfaces with the insert, requiring maintenance and restoration of the road surface.
Other problems in rail track surface structure insert design arise due to the necessity of providing sufficient support to the insert to stand up under automobile and truck traffic passing over the road level railway, causing such seals to break down.
It will be understood by those familiar with modern track construction, and particularly with light urban transit track, that tracks are frequently laid on a rail bed comprising steel track plates laid on concrete slabs, with electrical insulation between the base of the rail and the track plate; heavy rubber extrusions are usual for such purpose.
In such rail bed construction, known as “Direct Fixation”, the track plates are secured to the concrete slab by electrically insulated hold-down bolts set in the concrete slab; rail clips of the Pandrol (trademark) or similar type, flexibly secure the rail to the track plates underlying the electrical insulation, under downward spring biasing.
Further attention to insert design has been directed to modification of the bottom surface of the insert in order to accommodate such flexible rail clips used to secure the rail to the underlying track plates. Typical of such designs are those shown in U.S. Pat. No. 4,606,498 to Grant and U.S. Pat. No. 4,899,933 to Martin, each of which discloses means of relieving the undersurface of the insert adjacent the rail clips, thereby to form a chamber in order to accommodate the rail clips.
It will be recognized that the rail space between the rail members and the adjacent road surface will, in cross-section, be generally that of a truncated pyramid, having stepped sides, so dictated by the practical considerations of minimizing the width of the rail space at its top surface where exposure to surface traffic occurs, and increasing the width of the rail space at its bottom surface to accommodate the width of the rail base and rail securing clips. This generally truncated pyramidal cross-sectional shape dictates the design of the track surface structure insert assembly.
It is the object of the present invention to address and overcome each of these problems by providing a rail track surface structure for use in Direct Fixation track construction comprising insert members which adapt to both T-rail and girder rails, and accommodate vertical flexing of the rail relative to the adjacent road surface without resulting degradation of the adjacent road surface, while continuing to seal against the intrusion of water and solid detritus into the rail bed.
SUMMARY OF THE INVENTION
Accordingly, the present invention comprises a rail track surface structure insert assembly comprising electrically non-conductive and flexible sealing assemblies for insertion in each of the gauge side and field side of the rail. In a first preferred embodiment, each insert assembly comprises a longitudinally extending first rail insert member sealingly registering with and contoured to fit against the head, web and base of the rail on each of its field side and gauge side; a longitudinally extending second offset insert member operatively interfacing with each of the first rail insert members at a generally vertical slippage plane formed therewith, while sealingly registering and interfacing with the adjacent road surface; and longitudinally extending support means cooperating with and supporting the second offset insert member and registering at its bottom surface with the underlying rail bed.
Each first rail insert member is extruded or moulded to a cross-sectional profile having a rail-engaging surface
Le Mark T.
Martin John Kesner
LandOfFree
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