Concrete rail tie

Details Concrete rail tie Concrete rail tie

2001-12-12

2003-08-12

Le, Mark T. (Department: 3617)

Railways: surface track

Rail seats

Cast

C238S083000, C238S264000, C238S287000

Reexamination Certificate

active

06604690

ABSTRACT:

TECHNICAL FIELD
This invention relates to a rail fastening assembly of the type where a rail is clamped to a concrete rail seat by elastic rail fasteners held in shoulders cast into the concrete tie and an elastomeric pad is used between the bottom of the rail and the concrete rail seat. An optional abrasion plate may be fitted between the bottom of the pad & the top of the rail seat. The present invention addresses the problem of wear on the concrete surface where the rails sit on the tie.
BACKGROUND
Concrete ties have been in use in some parts of the world for a long time but it is only since 1985 that they have been able to provide cost benefits for use in North America relative to wooden ties.
Some of the advantages of concrete ties over wooden ties in USA are:
1. Improves track stability
2. Lower track maintenance costs
3. Fewer derailments
4. In some cases higher axle loads & travel speed have been possible.
5. Overcomes the problems of finding environmentally safe methods of treating wood ties to prevent termite damage.
6. Releases a large amount of structural quality timber for more appropriate use.
7. Eliminates the difficulty of finding environmentally safe ways to dispose of used chemically treated wooden ties.
The usage of concrete ties in USA has progressively increased and the benefits listed above have been confirmed.
However in 1988 a previously unknown problem was found. Ties which had been in use for only 1 year in some heavy traffic locations began to show wear on the rail seat. The cement paste was being worn away leaving the stones in the concrete upstanding as a diamond in a ring is held by a clasp at the bottom. As time progressed it was found that as the cement paste continued to be eroded the stones finally came out & the process continued on the layer below. After a few years in some extreme locations the damage was so bad that the rails began to tilt outwards thereby increasing the distance between the rail heads and if allowed to continue would eventually lead to a derailment. In extreme cases the wear on the rail seat outer edge was 10 mm or more. One of first inventions aimed at solving the rail seat erosion problem was by Buekett U.S. Pat. No. 4,925,094 and he used a stainless steel plate cast into the surface of the rail seat and the plate had legs which extended into the concrete to secure it in the rail seat.
There are two problems with this approach apart from the high cost and these are caused by the very weak bond of concrete to steel and the difference in elasticity between steel & concrete. Most concrete ties are prestressed by steel tendons in the tie and when the stress is applied the tie shortens about 1.3 mm and at the end of the first year the steady compression stress causes the tie to creep and the length shortens approximately by an additional 1.5 mm to give a total shortening of about 2.8 mm. Since the modulus of elasticity of steel is about 6 times greater than for concrete there will be slight differential movement between the concrete close to the bottom of the plate and the steel plate itself and the weak bond between the bottom of the steel plate will be broken by the resulting shear forces.
Buekett overcame this problem by providing legs at the ends of the plate which are embedded in the concrete to give a mechanical connection to the concrete so that there is no structural need for a perfect cement paste bond. When the track loads are applied to the tie the rail seat area will flex slightly and the difference in elasticity will further increase the likelihood of a cement paste bond failure below the plate.
A solution to the problem was provided by U.S. Pat. No. 5,110,046 (Young) and this is still the main method in use for controlling the problem. Tie rail seats are protected by using a thin steel abrasion plate about 1 to 1.5 mm thick on top of a closed cell foam gasket & used ties are repaired by bonding the abrasion plate onto the rail seat with epoxy. When Young devised his first solution it was necessary to make the system work with existing rail seats & rail fastening systems which placed limits on what could be done. For example the original steel abrasion plates were 0.9 mm thick and they were subsequently increased to 1.4 mm but this is the limit that the rail fastenings can cope with since the plate lifts the rail above the originally intended position.
However although the method works time has shown that in some cases it will not last for the life of the tie & the rail seats will need to be repaired in track which is inconvenient and expensive.
At the time Young conceived the original invention he thought that that the wear mechanism driving the problem was caused by the movement of the elastomeric pad between the bottom of the rail and the surface of the concrete rail seat. When each loaded axle passes over the rail above the rail seat a load pulse is transmitted through the pad to the rail seat which causes the elastic pad to deflect vertically & due to the Poisson's ratio of the material it must also deflect horizontally and this horizontal rubbing action was thought to cause the problem in the presence of sand particles. This is described in U.S. Pat. No. 5,110,046.
A number of subsequent attempts to improve the inhibition of rail seat erosion relied on the same insights as Young and also utilised the thin plate solution.
U.S. Pat. No. 5,405,081 uses an impervious polymeric membrane between the rail pad and rail seat.
U.S. Pat. No. 6,045,052 uses an abrasion plate having a polymer coating on the bottom which is thicker around the edges than in the center in order to accommodate irregularities in the rail seat. This is intended to work by the thicker band around the periphery being subject to more pressure and thereby providing a water tight seal while the slight cavity in the central region gives room to accommodate irregularities.
This principle has been tested on rubber and polyurethane pads. A downward projecting band was used around the pad periphery on the bottom which acted as a seal. This worked initially but as the load pulses were applied the sealing band deflected according to Poisson's ratio as described by Young (U.S. Pat. No. 5,110,046) and a slight rubbing action occurred under the band which eventually caused one small part not to seal effectively and pumping started.
U.S. Pat. No. 5,549,245 Utilizes a metal plate with a rail pad bonded on the top side and the assembly is bonded to the rail seat by a methyacrylate ester adhesive. This adhesive bonds rapidly which is an advantage over epoxy resins and other adhesives. In addition this arrangement overcomes the problem of pumping and micro jetting so long as the bond remains effective. One major disadvantage of this system is that where there is heavy rail traffic and curves the pads need to be replaced periodically which is difficult because they are bonded to the tie. Another problem is that in some situations the bonds have been known to fail which may be the result of the rail seats being damp when the bonding was done. However in many locations particularly in the mountains the ties are frequently damp.
Another patent which addresses the use of rail plates with concrete ties is WO 01/36749 which discloses a plate having a central hole for insertion of a polyurethane buffering pad.
It is an object of this invention to provide a rail seat assembly for concrete ties which inhibits erosion of the ties for the useful life of the tie.
SUMMARY OF THE INVENTION
To this end the present invention provides a railroad tie and rail seat assembly for supporting a rail which includes
a) a concrete rail tie having at least one rail seat defined by a shallow recess
b) a rail plate seated over said recess so that the peripheral edges of the plate extend at least to the edges of said recess
c) polymeric adhesive within said recess to bond said plate to said tie
d) an optional rail pad on said plate adapted to lie beneath the rail flange.
This invention is predicated on the better understanding of the causes of rail seat erosion as set out below.
T

Affiliated with

Also associated with

Rating

Concrete rail tie does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Concrete rail tie, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Concrete rail tie will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3130196