|1.||Sliding joint system for railway tracks allowing a wide longitu¬ dinal excursion, particularly for suspension bridges, characterized in that it comprises, for each rail of the track, on one side a first fixed rail (1) having a tapered end, and on the other side a second rail (2), positioned next to the tapered surface of the first rail (1) and sliding along the same, while continuously extending beyond said tapered surface, obliquely to the track axis under an acute angle; guide means being also provided to ensure the deviation and the sliding of said second rail (2) in respect of the first rail (1).|
|2.||Sliding joint system for railway tracks as in claim 1), wherein said first rail (1) is tapered on the outwardly facing sides of the track and said second rail (2) extends beyond the tapered surface of the first rail (1), in an oblique direction outwardly of the track.|
|3.||Sliding joint system for railway tracks as in claim 1), wherein said guide means comprise at least a set of three main rollers (3, 4, 5), one roller (4) being positioned on one side of the second rail (2) and the other two rollers (3, 5) being positioned on the other side thereof, said rollers being meant to align the second rail (2) parallely to the main longitudinal axis of the track, in a position preceding the zone of outward deviation. 4) Sliding joint system for railway tracks as in claim 1) or 3), wherein said guide means also comprise a plurality of secondary guide rollers (6) with fixed vertical axes, positioned so as to face the tapered surface of the first rail (1). 5) Sliding joint system for railway tracks as in claim 1), 3) or 4), wherein said guide means comprise moreover pairs of guide rollers (7), positioned at regular intervals along a channel (8) provided on the deviated extension of the second rail (2), beyond its zone of contact with the first rail (1), said channel (8) being meant to guide and pro¬ tect said second rail (2).|
|4.||Sliding joint system for railway tracks as in claim 1), wherein said second rail (2) is formed with a flange of reduced width.|
|5.||Sliding joint system for railway tracks as in claim 6), wherein the width of the flange of the second rail (2) is preferably equal to the width of its head.|
The present invention concerns suspension bridges comprising an essentially flat main structure, or framework, the top surface of which forms the roadway for the transport means crossing the bridge, and a suspension system formed of catenary cables anchored to end piers of the bridge and of a plurality of vertical stays or hangers to suspend the bridge framework to the catenary cables.
As known, the longer the suspension bridge, the wider the longitu¬ dinal excursion it undergoes, mainly due to thermal expansions, live load variations on the bridge, and/or displacements caused by the action of the wind.
The invention thus relates, in particular, to a sliding joint system for railway tracks, allowing a wide longitudinal excursion - in theory, unlimited - of one track section in respect of the other.
The problem of longitudinal excursion essentially arises in corres¬ pondence of the end piers onto which are anchored the catenary cables to suspend the bridge, whereby sliding joints have to be provided in these areas.
For what concerns the sliding joints for roadways, there are already known to be systems allowing considerable excursions. These systems generally consist of parallel intersecting racks, which are considered to provide a satisfactory solution to the problem.
Whereas, for what concerns railways, the only known system allowing a certain reciprocal sliding between the rails - while still ensuring a constant support of the train wheels - consists in tapering the opposed ends of the two railroad sections and placing said tapered ends side by side; the discontinuousness between the two rails thus appears in the form of an oblique cut (instead of being perpendicular to the rail axis). The narrower the angle formed between the axis of said cut and the rail axis - i.e. the more marked the tapering - the wider the excursion
allowed by ' such a joint system. In any case, there are no joints of this type allowing an excursion of more than a few decimetres.
However, in suspension bridges with a very wide span, for instance over 1 Km, one should foresee excursions of the order of metres. In the bridge being planned for crossing the Straits of Messina - to which refe¬ rence is made in EP-A-0.233.528, filed by the same Applicant - having a span wider than 3 Km, the reckoned excursion is of ± 3.5 m in rest condi¬ tions, with no traffic on the bridge. But it is perfectly known that, in railway technique, there is no joint system allowing an excursion of 7 m.
The object of the present invention is to therefore propose a sli¬ ding joint system for railway tracks, allowing a wide longitudinal excur¬ sion - in theory unlimited, but anyhow sufficient to satisfy the require¬ ments of modern suspension bridges - while constantly ensuring a correct support and a precise guiding of the train wheels. Such a result is ob¬ tained due to the fact that said sliding joint system comprises, for each rail of the track, on one side a first fixed rail having a tapered end, and on the other side a second rail, positioned next to the tapered sur¬ face of the first rail and sliding along the same, while continuously extending beyond said tapered surface, obliquely to the track axis under an acute angle; guide means being also provided to ensure the deviation and the sliding of said second rail in respect of the first rail.
Further characteristics and advantages of the railway sliding joint according to the present invention will anyhow be more evident from the following detailed description of a preferred embodiment thereof, given by way of example and illustrated on the accompanying drawings, in which:
Figs. 1a and 1b are diagrammatic plan and, respectively, elevation views of the railway sliding joint system according to the invention in an intermediate position of excursion;
Figs. 2a and 2b are similar views in a final position of excursion;
Figs. 3 and 4 are diagrammatic section views along the line III-III and, respectively, IV-IV of fig. 1b;
Fig. 5 is a diagrammatic plan view, on an enlarged scale, of the
area comprising the sliding joint system according to the invention;
Figs. 6 to 11 are diagrammatic section views along the lines VI-VI to XI-XI of fig. 5.
As shown on the drawings, the railway sliding joint system accord¬ ing to the present invention comprises a so-called fixed track section 1-1 and a slidable track section 2-2. Figs. 1 and 2 show the section 1-1 as being integral with the embankment T, while the section 2-2 is inte¬ gral with the bridge part P-P1 which is slidable along the platforms B-B1 by way of the supports A-A1.
From the position shown in figs. 1, the bridge end P can move in the direction of arrow F - i.e. when subject to contraction - as far ' as the final position shown in figs. 2, with the support A sliding along platform B up to reaching its outermost end. At the same time the longi¬ tudinal beam P1, forming an extension of the bridge P, slides with its support A1 along ' platform B1. Whereas, when the bridge end P moves in a direction opposite to arrow F - i.e. while elongation takes place - the supports A-A1 move as far as the platform heads T1, T2.
Figs. 3 and 4 show the tip-shaped section of the longitudinal beam P1, which slides telescopically into a guide channel B2. The slidable rail 2 is fixed on the tip of the beam P1.
As shown more clearly in the plan view of fig. 5 and in the section views of figs. 6 to 11 (which refer to the rails 1-2 illustrated in the lower half of fig. 1a or 2a, but - by symmetry - also to the rails 1-2 illustrated in the top half of these figures), the sliding joint system of the present invention comprises, in a characteristic way:
- on one side, the fixed rail 1 which is beveled, i.e. comprises a very marked tapering which practically extends between a point just before the section line VIII-VIII (fig. 8 shows in fact where the bevel starts) and a point just before the section line X-X (fig. 10 shows in fact only the rail 2, as the tapered portion of the rail 1 has terminated);
- on the other side, the slidable rail 2, which is positioned next to the tapered portion of the rail 1, without being tapered itself (as clearly
shown in figs. 6 to 11), but rather bending and deviating outwardly of the track under an acute angle, guided along and sliding against the tapered surface of the rail 1.
Although the rail 1 has a stiffened structure (as shown in the sec¬ tions of figs. 6 to 10), it would not be sufficient to stand the pressure forces of the rail 2 due to its deflection. To endure this outward deflection, the rail 2 is thus constantly guided also:
- by a set of three main rollers 3, 4, 5, which are also meant to align the rail 2 parallely to the main longitudinal axis of the track, in a position preceding the zone of outward deviation;
- by a plurality of secondary guide rollers 6, positioned so as to face the tapered surface of the rail 1; and finally
- by pairs of guide rollers 7, positioned at regular intervals along a channel 8 meant to guide and protect the rail 2.
To be able to work correctly, the sliding joint system according to the invention must comprise a rail 2 apt to undergo the foreseen progres¬ sive deflections or straightenings, while keeping within the range of its elastic limits. In other words, it is evident from the above that the rail 2 - which undergoes a certain temporary deflection - should always be able to elastically recover its rectilinear configuration.
To favour said deflection, the rail 2 is preferably formed with a flange of reduced width, for instance the same width of the head (as clearly visible in figs. 6 to 10), so as to improve the deformation by lateral eLastic deflection, though allowing to keep the induced stresses within acceptable limits, also taking into account the fatigue strength.
Reverting briefly to figures 1 it can be noted that, in the inter¬ mediate position of fig. 1a, the rail 2 extends into the channel 8 till about half of its length; while in the final position of fig. 1b, the channel 8 is completely free in that the rail 2, together with the bridge P, is fully set back (maximum contraction of the bridge) whereby its end part finds itself in correspondence of the rollers 6. In a fully advanced position of the bridge (maximum elongation) - not shown in the drawings -
the rail 2 would occupy the whole channel 8.
It is anyhow understood that the invention is not limited to the particular embodiment described heretofore, which is only a non-limiting example of its scope, but that many other embodiments are possible - both for what concerns the positioning of the guide channel 8, which could be on the inner side of the track instead of being on its outer side, and above all for what concerns the guide means of the rail 2 - all these embodiments being within reach of a technician skilled in the art and thus falling within the protection field of the present invention.