Track Design Handbook for Light Rail Transit, Second Edition (2012) / Chapter Skim
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From page 271... ...
5-i Chapter 5 -- Track Components and Materials Table of Contents 5.1 INTRODUCTION 5-1 5.2 RAILS 5-1 5.2.1 Introduction 5-1 5.2.1.1 Types of Rail for Light Rail Transit 5-1 5.2.1.2 Rail Lengths 5-1 5.2.1.3 Joining Rails 5-2 5.2.1.4 Rail in Curves 5-2 5.2.1.5 Rail Handling 5-2 5.2.1.6 Rail/Wheel Interface Issues 5-2 5.2.2 Tee Rail 5-3 5.2.2.1 Rail Section -- 115 RE 5-3 5.2.2.2 Rail Strength and Metallurgy 5-5 5.2.2.3 Rail Straightness 5-6 5.2.2.4 Rail Running Surface Finish 5-6 5.2.2.5 Precurving of Tee Rail 5-7 5.2.2.6 Procurement of Tee Rail 5-8 5.2.3 Groove Rail 5-9 5.2.3.1 Advantages of Groove Rail for Embedded Track 5-9 5.2.3.2 Available Groove Rail Sections 5-9 5.2.3.3 Groove Rail Head Profile Compatibility with Tee Rails 5-11 5.2.3.4 Groove Rail Strength and Chemistry 5-16 5.2.3.5 Precurving of Groove Rail 5-18 5.2.3.6 Procurement of Groove Rail 5-18 5.2.3.7 Block Rail 5-19 5.2.4 Rail Wear 5-20 5.2.5 Wear-Resistant Rail 5-21 5.3 RESTRAINING RAIL DESIGNS FOR GUARDED TRACK 5-22 5.3.1 Groove Guard Rail for Embedded Track 5-22 5.3.1.1 North American Girder Guard Rail -- Background 5-22 5.3.1.2 Restraining Rail Issues with CEN Groove Rails 5-23 5.3.1.3 The Possibility of a New North American Groove Rail 5-23 5.3.1.4 Alternatives to Groove Rail for Guarded Embedded Track 5-24 5.3.2 Restraining Rail Options for Use with Tee Rail Construction 5-25 5.3.2.1 Vertically Mounted Restraining Rails 5-25 5.3.2.2 Horizontally Mounted Restraining Rails 5-27 5.3.2.3 Strap Guard Rail 5-27 5.3.2.4 33C1 Restraining Rail 5-30 5.3.3 Restraining Rail Recommendations 5-32 5.3.4 Restraining Rail Thermal Expansion and Contraction 5-33 5.3.5 Restraining Rail Restrictions 5-33
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From page 272... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-ii 5.4 RAIL FASTENINGS AND FASTENERS 5-34 5.4.1 Definitions 5-34 5.4.2 An Introduction to Common Designs 5-34 5.4.3 Insulated Fastenings and Fasteners 5-35 5.4.3.1 Isolation at the Rail Base 5-36 5.4.3.2 Isolation at the Fastener Base 5-36 5.4.4 Elastic Rail Clips 5-36 5.4.5 Fastenings for Timber and Concrete Cross Ties for Ballasted Track 5-38 5.4.6 Fasteners for Direct Fixation Track 5-40 5.4.6.1 Fastener Design Consideration 5-40 5.4.6.1.1 Vertical Static Stiffness 5-41 5.4.6.1.2 Ratio of Dynamic to Static Stiffness (Vertical) 5-41 5.4.6.1.3 Lateral Restraint 5-41 5.4.6.1.4 Lateral Stiffness at the Rail Head 5-42 5.4.6.2 Shims beneath Direct Fixation Rail Fasteners 5-42 5.4.7 Fasteners and Fastenings for Embedded Track 5-43 5.5 CROSS TIES AND SWITCH TIES 5-45 5.5.1 Timber Cross Ties 5-45 5.5.2 Concrete Cross Ties 5-47 5.5.2.1 Concrete Cross Tie Design 5-48 5.5.2.2 Concrete Cross Tie Testing 5-48 5.5.3 Switch Ties -- Timber and Concrete 5-48 5.5.3.1 Timber Switch Ties 5-48 5.5.3.2 Concrete Switch Ties 5-49 5.6 JOINING RAIL 5-50 5.6.1 Welded Joints 5-51 5.6.1.1 Electric Pressure Flash Butt Weld 5-52 5.6.1.2 Exothermic ("Thermite")
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From page 273... ...
Track Components and Materials iii-5 56-5 noitarugifnoC larutcurtS 2.01.5 5.10.3 Rail Expansion Joint Track Details 5-65 5.10.3.1 Rail Expansion Joints for Open Trackforms 5-65 5.10.3.2 Rail Expansion Joints for Embedded Track 5-66 5.10.4 Rail Anchorages 5-67 5.11 END-OF-TRACK BUMPERS AND BUFFERS 5-68 5.11.1 Warning Signs/Signals 5-69 5.11.2 Fixed Non-Energy-Absorbing Devices 5-69 5.11.3 Fixed Energy-Absorbing Devices 5-70 5.11.3.1 Non-Resetting Fixed Devices 5-71 5.11.3.2 Resetting Fixed Devices 5-71 5.11.4 Friction (or Sliding) End Stops 5-71 5.12 REFERENCES 5-72 List of Figures 4-5Figure 5.2.1 115 RE tee rail with 8-inch crown radius Figure 5.2.2 CEN 51R1 and 59R2 groove rail sections 5-12 Figure 5.2.3 CEN 53R1 and 60R2 groove rail sections 5-13 Figure 5.2.4 CEN 62R1 and 67R1 groove rail sections 5-14 Figure 5.2.5 CEN 56R1 groove rail and 76C1 construction rail sections 5-15 Figure 5.2.6 LK1 block rail section 5-19 Figure 5.3.1 Typical restraining (guard)
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From page 274... ...
5-1 CHAPTER 5 -- TRACK COMPONENTS AND MATERIALS 5.1 INTRODUCTION The track components that form the track structure generally include steel rails, a rail fastening system, and an underlying structure that provides overall stability and strength. The most familiar form of trackwork is ballasted track, where cross ties embedded in ballast rock provide the last function.
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From page 275... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-2 favorable conditions for delivery and handling of such lengths prevail, rail transit projects could consider procuring such longer rail sections. 5.2.1.3 Joining Rails Bolted rail joints between contiguous rails have always been the weak link in the track.
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From page 276... ...
Track Components and Materials 5-3 Vehicle operational and ride performance is highly dependent on the primary and secondary suspension systems that allow the vehicle to traverse the track system and negotiate track curves. The manner in which the wheels and axles are incorporated into the vehicle truck, together with the wheel and rail profiles, control how well the vehicle truck steers in curves and at what speed truck hunting will commence on tangent track.
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From page 277... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-4 Figure 5.2.1 115 RE tee rail with 8-inch crown radius
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From page 278... ...
Track Components and Materials 5-5 The "115" and the "RE" in the rail section identification 115 RE mean the following: • 115 is the mass (weight) in pounds per one yard length.
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From page 279... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-6 A general guideline for transit installations is the use of clean rail steel with a hardness not less than • 300–320 BHN (standard rail) in tangent tracks, except at station stops (and similar locations of heavy traction or braking)
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From page 280... ...
Track Components and Materials 5-7 stresses between the rail and the wheels. However, under transit wheel loadings, mill scale on the running surfaces of the rail will not wear away as quickly and can cause several problems: • It can interfere with the reliable shunting of low-voltage signal circuits.
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From page 281... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-8 • High-Strength Rail − Precurve rail horizontally for curve radii below 400 feet (120 meters)
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From page 282... ...
Track Components and Materials 5-9 be thought through before finalizing the rail procurement methodology and specifications. See Chapter 13 for additional considerations about procurement of rail and other track materials.
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From page 283... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-10 lists and illustrates the groove rail profiles available and stipulates requirements for their manufacture. There are about a dozen groove rail sections still being manufactured, most of which have been adopted as standard sections under the European Norms.
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From page 284... ...
Track Components and Materials 5-11 extensively machining the groove to increase the gauge corner radius and widen the flangeway. • Section 62R1 (formerly NP4aS)
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From page 285... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-12 Figure 5.2.2 CEN 51R1 and 59R2 groove rail sections
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From page 286... ...
Track Components and Materials 5-13 Figure 5.2.3 CEN 53R1 and 60R2 groove rail sections
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From page 287... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-14 Figure 5.2.4 CEN 62R1 and 67R1 groove rail sections
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From page 288... ...
Track Components and Materials 5-15 Figure 5.2.5 CEN 56R1 groove rail and 76C1 construction rail sections
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From page 289... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-16 Until 2009, the 115 RE rail section, which was first rolled shortly after World War II, included a 10inch (254-millimeter) crown head radius.
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From page 290... ...
Track Components and Materials 71-5 Table 5.2.1 Chemical composition of CEN groove rail steel CEN Steel Designation Percent by Mass of Liquid Steel H, max in PPM Tensile Strength, MPa, min Running Surface Hardness, HBW C Si Mn P (max)
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From page 291... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-18 European rail manufacturer has developed a proprietary head hardening process for groove rail. Their rail is categorized as Head Special Hardened (HSH)
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From page 292... ...
Track Components and Materials 5-19 delivery to the project. It should be very clear that acceptance and payment for the rail is conditional on meeting the stated requirements.
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From page 293... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-20 • Fabrication of temporary tracks, particularly temporary crossover tracks that sit on top of existing embedded trackwork. • Construction of modular embedded tracks using precast concrete panels.
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From page 294... ...
Track Components and Materials 5-21 stiffness against rotation of the vehicle truck. The latter increases the force against the rail, increasing friction and wear, and concurrently reduces the speed of the vehicle.
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From page 295... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-22 Such post-manufacturing treatments are now seldom used as more wear-resistant grades of groove rail are now readily available directly from the rail mills. 5.3 RESTRAINING RAIL DESIGNS FOR GUARDED TRACK Guarded track in light rail transit design, as described in Chapter 4, Article 4.3, can reduce outer rail gauge face wear on sharp curves by restricting movement of the wheels toward the outer rail.
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From page 296... ...
Track Components and Materials 5-23 worn to meet quality requirements. For various reasons, the product line was not sufficiently profitable to justify the investment in new rolls, so production ceased.
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From page 297... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-24 • What should the new section look like? • Where can it be rolled?
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From page 298... ...
Track Components and Materials 5-25 • Strap guard rail, bolted to 115 RE tee running rail, as described in Article 5.3.2.3 of this chapter. 5.3.2 Restraining Rail Options for Use with Tee Rail Construction When groove rail is not used, but a restraining rail is desired, tracks with sharp curves have been equipped with various designs to provide the required restraint.
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From page 299... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-26 Figure 5.3.1 Typical restraining (guard) rail arrangements For curves with radii greater than 300 feet [91 meters]
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From page 300... ...
Track Components and Materials 5-27 On timber cross ties, the combined running rail/restraining rail assembly will usually be installed on a common extended rail fastener or tie plate unlike those used under single running rails. Restraining rail installed on concrete cross ties will require a special restraining rail cross tie with a wider shoulder mounting.
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From page 301... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-28 Figure 5.3.2 Strap guard rail The strap guard section was developed for the Pittsburgh light rail transit system in the early 1980s based on similar sections that were rolled for use with ASCE tee rails in the early 20th century. Pittsburgh is the still the largest user of strap guard, using it in all trackforms, and considering nothing else for restraining rail.
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From page 302... ...
Track Components and Materials 5-29 • When considering rail breaks in areas of strap guarded rail, the strap guard rail actually provides some minimal security against both a wide gap and rail end mismatch since its shape effectively places a joint bar across the rail break. On the other hand, the resulting electrical continuity would mask a running rail break from the signal system by providing an alternate path for signal current around the rail break.
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From page 303... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-30 only one rolling mill in Europe. When restructuring of the European steel industry resulted in the closure of that specific rail mill, GGR-118 suddenly became unavailable.
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From page 304... ...
Track Components and Materials 5-31 The major advantage of using the 33C1 section as a restraining rail is the capability of independent mounting from the running rail, as shown in Figure 5.3.1. In addition, the 33C1 section's independent bracket mounting assembly eliminates very nearly all of the negative issues related to field drilling of the running rails to match the restraining rail hole pattern and placement of fasteners and cross ties.
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From page 305... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-32 Special four-bolt joint bar assemblies and insulated joint assemblies are used to join lengths of 33C1 rail. These joints are preferably located between supporting brackets so as to avoid the need for a special bracket.
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From page 306... ...
Track Components and Materials 5-33 • Embedded Track -- there are three options, listed below in order of preference. In all cases, the assembly should be insulated from the embedding pavement structure unless it is contained within an insulated bathtub.
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From page 307... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-34 5.4 RAIL FASTENINGS AND FASTENERS Perhaps the most important elements of the track assembly are the devices that hold the rails to proper alignment and gauge. These items are called rail fasteners and fastenings.
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From page 308... ...
Track Components and Materials 5-35 assemblies can incorporate electrical isolation measures either at the base of rail or between the plate and the cross tie. Modifications of this rail fastener assembly are sometimes used on concrete cross ties within special trackwork.
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From page 309... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-36 typically elastic rail clips, although rigid clips held in place by a bolt assembly have been used. The anchorage assembly typically consists of two or more bolts that pass through the fastener body and are then threaded into female anchor inserts embedded in the underlying track slab or plinth.
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From page 310... ...
The s the fin stress to the atomi embri subwa icing p The w no op with s within comp teel in elastic ished clip. ed when ins base of rail.
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From page 311... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-38 extracted from the rail fastener shoulders because exfoliated rust had filled the small void space around the shank of the rail clips, trapping them in place. Because of such problems, it is strongly recommended that if spring clips are proposed for use in such a hostile environment, consideration should be given to specifying that the clips have a robust and proven protective coating.
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From page 312... ...
Track Components and Materials 5-39 (Photo courtesy of Bay Area Rapid Transit) Figure 5.4.3 Threadless plate fastenings on concrete switch ties The elastomer pad in direct fixation rail fasteners has been manufactured from natural rubber, synthetic elastomers, and polyurethane products.
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From page 313... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-40 fastener's anchor inserts. Shimming of the fastener requires only removing the anchor bolts and lifting the rail and fastener body a small amount more than the desired shim thickness.
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From page 314... ...
Track Components and Materials 5-41 5.4.6.1.1 Vertical Static Stiffness Vertical static stiffness is often called spring rate, and represents the slope of the load versus deflection over a prescribed range of 1,000 to 12,000 pounds (5,000 to 55,000 N)
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From page 315... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-42 fasteners use an upsweep curved bottom plate design to restrain or act as the limiting flange. The guiding design principle is to provide a three degree-of-freedom isolator.
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From page 316... ...
Track Components and Materials 5-43 experience has shown that slotted shims can shift out of position during service, and they are therefore not recommended. Shims are typically provided in a variety of thicknesses, and the contractor will stack shims of one or more thicknesses to achieve the requisite shimmed height.
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From page 317... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-44 for installation, and the jacking screws on the end of the leveling beam. (The track has not yet been elevated to final grade in this view.)
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From page 318... ...
Track Components and Materials 5-45 circumstances, the use of plastic rail clips can reasonably be considered. However, should the embedment material be of a nature to not securely restrain the booted rail (as in the case of turf track)
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From page 319... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-46 by their botanical name. The use of a common name can result in obtaining an inferior material.
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From page 320... ...
Track Components and Materials 5-47 are used in a curbed ballast section such as that shown in Chapter 4, Figure 4.5.5, it may not be possible to change out individual defective ties, particularly if the track center dimension is less than about 13 feet [4.0 meters]
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From page 321... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-48 provide better panel stability. Extra long cross ties can also be considered for transition zones between ballasted track and stiffer trackforms, as shown in Chapter 4, Figure 4.4.1.
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From page 322... ...
Track Components and Materials 5-49 reducing the projection of the switch machine above top-of-rail elevation. This low profile is generally necessary only on heavy rail transit systems where additional clearance is desired because of the third rail shoes on the transit vehicle.
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From page 323... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-50 Concrete switch ties for light rail transit use should be approximately 10 inches [255 millimeters] wide at the top of the tie, 11 ¼ inches [285 millimeters]
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From page 324... ...
Track Components and Materials 5-51 − Thermite (kit) weld Other types of welded joints (e.g., gas pressure welding and cast welds)
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From page 325... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-52 Rail welding in North America is generally accomplished using either the electric pressure flash butt weld or the thermite weld method. 5.6.1.1 Electric Pressure Flash Butt Weld Most rail strings are welded together by the electric pressure welding process (commonly called "flash butt welding")
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From page 326... ...
Track Components and Materials 5-53 CWR strings might be both very short and fabricated in a variety of lengths to suit the field conditions. During the electric flash butt welding process, heat-affected zones (HAZ)
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From page 327... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-54 Prefabricated CWR rail strings are generally joined or welded together by the thermite weld process; however, many transit agencies, whenever practical, require use of a portable electric flash butt welder to join rail strings in order to eliminate thermite welds. For additional information on electric flash butt and thermite welding during construction refer to Chapter 13.
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From page 328... ...
Track Components and Materials 5-55 These are the only insulated joints that are practical for field assembly under adverse weather conditions and in locations, such as crossing diamonds, where correct assembly of a glued insulated joint with the pot life of the adhesive would be problematic at best. 5.6.2.2 Glued Bolted Insulated Rail Joints Glued insulated joints, sometimes known as "bonded" insulated joints, are similar to non-glued joints, except that the joint bars are shaped to fit the rail fishing to allow the bars to be glued to the web of the rail.
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From page 329... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-56 When non-insulated bolted joints of any design are used in electrified rail transit tracks, it is necessary to bridge them with an electrical cable so that signal and traction power currents can pass through. For additional information on electrical bonding for signal and traction power, refer to Chapters 10 and 11.
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From page 330... ...
Track Components and Materials 5-57 Photo courtesy of Voest Alpine Figure 5.6.1 Machined central block for compromise rail Light rail transit vehicles often exceed 100,000 pounds [45,500 kilograms] , placing increased importance on the track structure, particularly the ballast quality and quantity.
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From page 331... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-58 • With Timber Cross Ties − Granite and traprock, as noted above for concrete cross ties. − Quartzite: granoblastic metamorphic rock consisting of quartz and formed by recrystallization of sandstone or chert by metamorphism.
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From page 332... ...
Track Components and Materials 5-59 5.7.1.3 Testing Ballast Materials Ballast material should be tested for quality through a series of tests undertaken by a certified testing laboratory. The tests should include the following: • ASTM C88: Soundness of Aggregates by Use of Sodium Sulfate (NaSO4)
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From page 333... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-60 Table 5.7.2 lists the recommended limiting values for the ballast material tests. The ballast guidelines for timber and concrete cross tie applications are based on experiences with concrete cross tie ballasted track.
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From page 334... ...
Track Components and Materials 5-61 5.7.2 Subballast Materials Subballast is a granular base material placed and compacted over the top of the entire embankment or roadbed to prevent penetration of the ballast into the subgrade. Common subballast materials include crushed stone, natural or crushed gravel and sands, or a mixture of these materials.
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From page 335... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-62 modified to adapt to the track crosslevel and to intercept and channel roadway surface drainage away from the track. It generally is not recommended to construct crossings using asphalt except in instances where the roadway traffic is extremely light.
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From page 336... ...
Track Components and Materials 5-63 Design of the track and civil engineering elements of highway/railway crossings must be carefully coordinated with the designers of the LRT signal systems and crossing warning systems. See Chapter 10, Article 10.2.10, for additional information.
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From page 337... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-64 exposed to the intrusion of heavily loaded cars, multiple car trains, track conditions that permit the intruding cars to gain momentum in advance of the derail, and tight curvature on the siding track. The switch point derail provides the greatest insurance that all wheels of the intruding vehicle will be derailed and deflected away from the main track.
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From page 338... ...
Track Components and Materials 5-65 5.10.2 Structural Configuration Bridge trackwork that includes rail expansion joints still needs to have the rail anchored at some location. In those high-restraint areas, a conventional direct fixation fastener is utilized, and the structure is designed to accept the thermal stress loads generated by movement of the structure.
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From page 339... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-66 Figure 5.10.1 Double-ended sliding rail expansion joint As a guideline, rail expansion joints in ballasted track or direct fixation track are only recommended for long bridges or aerial structures. They are also needed at the fixed span approach to a movable bridge.
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From page 340... ...
Track Components and Materials 5-67 superstructure from stray current corrosion by limiting the amount of traction power return current carried by the rails on the bridge. While embedded track can be used on an aerial structure, the complications cited above mean that it will require frequent inspection and maintenance.
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From page 341... ...
Track Design Handbook for Light Rail Transit, Second Edition 5-68 5.11 END-OF-TRACK BUMPERS AND BUFFERS As important as the tangent and curved track is throughout the transit system, the end of track cannot be overlooked. Bumping posts, friction buffers, and hydraulic buffers are therefore used to prevent an out-of-control vehicle from overrunning the end of the track.
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From page 342... ...
Track Components and Materials 5-69 All end-of-track devices take up a certain amount of track length. In particular, sliding friction buffers require a significant length of track beyond the striking face.
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From page 343... ...
Track Design Handbook for Light Rail Transit, Second Edition 07-5 5.11.3 Fixed Energy-Absorbing Devices The end stop is the point of impact, the location where kinetic energy has to be dissipated. The kinetic energy is determined considering the mass or weight of the vehicle or vehicles (train)
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From page 344... ...
5.11.3 Non-r stops moun inevita cushio rebuil of-trac 5.11.3 Reset hydra energ forces magn the en the sh 5.11.4 Frictio end o surfac .1 Non-Res esetting fixed . These dev ds are effecti ble.
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From page 345... ...
Track Design Handbook for Light Rail Transit, Second Edition 27-5 Friction end stops consist of two types: • Units that are clamped to the rail. • Units that are mounted on skids that slide with the weight of the vehicle upon them, dissipating the energy between the skids and the concrete base of track structure.
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