Patent Grant
10895042
This application claims priority to and benefit of U.S. Provisional Patent Application 62/483,812, filed Apr. 10, 2017, entitled “Concrete Crosstie for Interspersing with Wood Crossties,” which is hereby incorporated by reference for all purposes as if set forth herein in its entirety.
The present disclosure relates generally to crossties, and more specifically to a high strength, integrally pre-stressed monoblock concrete crosstie with optimal rail seat configuration for use with optimal rail fastening system configuration and in ballasted railway.
Crossties are used to support rails for rails ways, and have traditionally been made from wood or concrete.
A monoblock concrete crosstie for railway tracks that achieves a high performance in operation includes a steel structure that is formed from ultra-resistant high strength steel plates embedded in a concrete element and having pre-stressed cold rolled wires with ends that form button head knots which are anchored to the steel plates. The crosstie includes rail seats each with a convex channeled formation that are mateable with an extending member of a tie faceplate of a rail fastening system wherein the rail seat has a width less than the width of the faceplate, and a center of the face plate has a first distance from a center of the concrete element and a center of the rails seat has a second distance from the center of the concrete element, the first distance greater than the second distance.
Other system, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims.
Aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views, and in which:
In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals. The drawing figures might not be to scale and certain components can be shown in generalized or schematic form and identified by commercial designations in the interest of clarity and conciseness.
Due to the general trend of increasing axle loads of railroad cars, the increase in the operating speed of the trains, and the growth in cumulative gross tonnage, the need to improve existing concrete crossties (also known as ties or sleepers) for railroads has become an important priority for the railroad industry and the economic competitiveness of rail transportation. Increased performance and reduced life cycle costs of concrete ties are necessary for building durable, sustainable railways, as performance and load demands on the track increase.
The present disclosure relates to a pre-stressed concrete monoblock crosstie for ballasted railways that is able to withstand the mechanical stresses caused by the loads transmitted to it by railway traffic.
The crosstie has an optimized pre-stressed steel structure with a configuration that allows it to resist loads efficiently and sustainably. The steel structure, specifically the steel wires, can be subjected to a tensile force before the casting process. After casting and curing, the wires can be released from the tensioning mold so as to transfer a compression force to the concrete that forms the crosstie. This force produces a compressive stress that is transferred to the concrete monoblock crosstie and has the function of balancing out the tensile stress that the concrete crosstie will otherwise have to bear when a bending load is applied. When pre-stressed steel is used, the adherence of the steel to the concrete increases gradually from the ends of the element to the center to achieve a maximum adherence only after a certain distance, an effect known as transfer length. The crosstie has a steel structure such that maximum adherence along the entire length of the steel wires is achieved within a negligible transfer length. This steel structure interacts with the crosstie's concrete, which is made of only one piece of concrete that is cast and cured all at once with no construction joints, hence being a monoblock. Together, these features allow the element to function as a beam that is capable of supporting axial, bending and torsion loads, which provides many competitive advantages over other crossties, including disruptive attributes of maximum reliability and performance. The crosstie configuration at its upper surface complies with the international standards for railroad track design and can adapt to the specific needs of various rail fastening systems that may be composed of pieces embedded in the concrete and fixed components on the outside. The crosstie configuration and rail fastening system work synergistically to diffuse distribution of forces along the crosstie so as to reduce concentration of stresses and abrasion.
Crosstie 100 includes ends 1, which are faceted to optimize the use of material, facilitate de-molding and promote the lateral interlocking of crosstie with the ballast. The metal structure is completely contained within the element, and once the manufacturing process is complete, the tension bolts are removed and the lateral orifices resulting from the removal of the bolts may or may not be sealed with low shrinkage concrete. This design protects the steel from corrosion and oxidation. On the sides of the upper surface, rail seats 3 can have a trapezoidal shape with hourglass form or, i.e., an embedded channel 4 with a concave shape and chamfers 21 and 22 formed therein. The channel 4 allows for the reception of rail fastening system 110 that includes a base structure with a protruding element for mating the protruding element with rail seat 3, see
Rail fastening system 110 includes tie face plate 30, fastener 31, and a tie pad 32. The rail fastening system 110 can be used to clamp a rail 33 to fastening system 110 which in turn can be coupled with concrete crosstie 100, see
Along the lateral surfaces of the crosstie, central wedges 6 and end wedges 7 are incorporated into the design in order to ensure interlocking with the ballast. Although
It should be understood that these measurements can be considered examples of a certain embodiment and approximations.
Clamping anchor plates 14 are made of high strength steel and are placed at the ends of crosstie 100 to allow pre-stressed wire 15 to acquire the required compression in the concrete. The pre-stressed clamping plates are made of ultra-high strength steel having dimensions of 6 inches long, e.g., with a bend 16 at the top and bottom areas at an angle close to 0°. In other words, the clamping plates essentially form a U-shape. These plates have four round holes 17 of at least ⅓ inches in diameter and two piercings 18, which allow the passage of tensioning bolts of a minimum diameter of 11/16 inches. The pre-stressed wires 15 are formed of cold rolled steel with a diameter of at least ⅓ inches and the group is composed of at least eight wires. The dimensions of the clamping plates 14 and pre-stressed wires 15 in relation with the crosstie 100 can be:
It should be understood that these measurements can be considered examples of a certain embodiment and approximations. The pre-stressed wires are formed of cold rolled steel with a diameter of ¼ inches (range of variability± 3/32 inches) and the group is composed of at least eight wires. These wires are arranged longitudinally and if seen from a cross section they are placed on a grid of three vertical levels and has at least two wires per level. The pre-stressed steel is tensioned to at least 70% (seventy percent) of its capacity. To achieve the tie-up of the wire to the anchor plate, button head knots 19, which hold themselves to the circular perforations of the plate, are used. The function of the button head is to secure and support the forces exerted by the pre-stressed wires on the anchor plate. Button head knots 19 of the pre-stressed wires have a diameter of at least 40% (forty percent) wider than the wire itself. The two holes for the locking of the tensing bolts allow the clamping of the anchor plate to exert a tensile force to the wires pre-stressing them during the manufacturing process, this force is maintained until the concrete has cured and afterwards, the bolts are removed.
The threaded plates 14 can be “U” shaped, where the U channel extends towards the center of the tie in the direction of the tensioning cables. This allows the end plates to apply a better distribution of force as compared to other configurations of the end plate. The upper and lower “U” shaped cut-outs in the U-shaped end plates at the centerline of the end plate 14, as seen in section A-A, provide flexibility between the two halves of the end plate, and facilitate the distribution of forces when the wires 41 are placed under tension. A steel rod 42 can be inserted into the threaded center holes/spindle holes (which eliminate the need for a bolt or nut to secure the structure to the end plate) and attached to a tensioning apparatus 43. When tensioning apparatus 43 is used to apply a tension to the tensioning cables, the “U” shaped cut-outs allow the tensioning cables to be more evenly tensioned and increase the bending strength of the end plate. Concrete is then poured into the mold 44, and the crosstie 100 can set with the tensioning wires 41 under tension. The end plates 14 cannot exceed the compressive strength of the concrete, which is typically limited to 0.6 times the design or expected compressive failure strength of the concrete. The wires 41 are arranged longitudinally and tensioned to at least 70% of its capacity. To achieve the tie-up of the wire to the anchor plate 14, button head knots 19, which hold themselves to the circular perforations of the plate, are used. The function of the button head is to secure and support the forces exerted by the pre-stressed wires 15 on the anchor plate 14. Button head knots 19 of the pre-stressed wires 15 have a diameter of at least 40% (forty percent) wider than the wire itself. The crosstie 100 is made from high performance and air entrained concrete with a low w/c ratio. The crosstie has a field compressive strength of at least 10,000 psi and a 28 day compressive strength.
The disclosure thus provides 1) a steel structure composed of anchoring plates at the crosstie's ends and pre-stressed wires that run longitudinally from one end to the other, 2) the use of high performance steel and concrete and their design that form a monoblock crosstie element with high performance rail seats and rail fastening systems that can tolerate heavy loads, and 3) a faceted geometry that promotes crosstie-ballast interlocking and the elements stability. The steel structure includes a set of cold drawn steel pre-stressed wires organized in a reticular grid. The wires extend longitudinally along the crosstie and are fastened to each end of the crosstie with a number of anchoring plates made of high yield-strength steel of a minimum tensile strength of 110 kilo pounds per square inch (ksi) derived from the cold forming of hot rolled steel strips. The ends of the wires are topped with button head type knots to provide adequate interlock with the anchor plates.
The plates and the wires work together. The plates compress the concrete from end to end and the wires adhere to the concrete all along their length, the structure transfers all loads to the concrete along its entire length, which in turn allows the design of a shorter monoblock crosstie. The interaction of the steel structure and the high strength concrete allows the crosstie to function integrally improving its performance and lifespan.
The design load on each axle is 41 tons (US) or more and crosstie is 8 feet and 6 inches long or less. The geometry of crosstie 100 can meet the specifications required to fulfil its functions and meet the load and strength requirements. The geometric outline of the rail seats and face plates are designed according to the different needs of the crosstie, but its form remains aesthetically attractive and has a unique identity. The geometry also provides increased stability and interlocking with the ballast. The lateral wedges of which the crosstie is provided allow the ballast to find a place in these slots to prevent movement. The trapezoidal and concave shapes of the rail seats also play a role in unifying the ballast-crosstie system due to the fact that they limit the movement of the ballast and partially confine it to the center of the sides of the concrete crosstie. This configuration causes the ballast to remain in place and in turn the latter favors the crosstie by holding it in position. In the crosstie ends, a multifaceted form with additional wedges has been provided. The end designs allows the allocation of the ballast gravel in positions that maximize its efficiency to stabilize the element. Chamfers and fillets are added to crosstie 100, which, together with the general geometry, reduce the amount of angles that are greater than ninety degrees, to diminish chipping and cracks in the concrete. The element results in a robust monoblock concrete crosstie that works efficiently to allow the safe transit of trains.
By bringing together innovative features into the crosstie's design as its pre-stressed steel structure, high strength concrete and rail seat and rail system design, it can be said that the efficiency achieved in respect to its functionality and performance is unprecedented in the rail industry.
It should be emphasized that the above-described embodiments are merely examples of possible implementations. Many variations and modifications may be made to the above-described embodiments without departing from the principles of the present disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.
| Number | Name | Date | Kind |
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| 20190309483 | Romero | Oct 2019 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20190309483 A1 | Oct 2019 | US |
