CE 515 Railroad Engineering Track Source: Armstrong Ch 3, AREMA Ch. 3, REES Module 2 “Transportation exists to conquer space and time -”

Track Structure Basics Responsible for supporting load from locomotives and train cars Transforms loads applied by the wheel to a moderate pressure that the foundation can maintain without failure Responsible for guiding locomotive and train car movement Typical parts of structure: Wheel Rail Tie plates or other fastening system Ties Ballast Sub-ballast Sub-grade

Loading of the Track Structure Types and Sources of Load Application: Vertical Loads Weight of vehicle Additional loads accompanying motion of vehicle Longitudinal Loads Mechanical forces from train actions Changes in temperature Lateral Loads Flanging of locomotive or train car against rail around curves Side-to-side movement of train at high speeds Sources of Loads Figure 3-7 Armstrong, pg 28

Load Distribution Analysis/Behavior Figure 3-6, Armstrong, pg 27 Load distribution through structure Structure typically must support a 36,000# (from REES module) load from each wheel “typical 4-axle rail car” Load transfer path Wheel Rail Tie plates/other fastener system Ties Ballast Sub-ballast Sub-grade

The Rail Most expensive, valuable part of structure Key Functions Transfer weight from wheels to ties Provide smooth running surface Guide wheel flanges From wood to high strength “T” Necessity for evolution Today’s rail accommodates up to 1 billion gross tons of traffic daily Figure 3-8, Armstrong, pg 30

The Rail, cont’d How is rail identified? Can’t last forever.. Weight 90 – 141 lbs/yd AREMA, AAR (ARA), ASCE set code standards Size Base (5.5” – 6”) Height (6” – 8”) Can’t last forever.. Rail wear, corrugation, fatigue and other defects history.howstuffworks.com

Rail Joints Rail manufactured in sections Typical Joints Joints bolted together What’s that racket? Typical Joints Standard Compromise Insulated “Rock and Roll IS noise pollution” For rail reference.findtarget.com Continuous-Welded Rail Welding can be applied in plant or field Electric butt and thermite welding Eliminates joints and maintenance costs However, is not free to expand or contract… acwr.com

CWR Disadvantages “Sun Kinks” or Rail buckling (above) telegraph.co.uk “Sun Kinks” or Rail buckling (above) CWR application limited to narrow temp. range Pull-aparts – caused by excessive tensile stresses Less of a problem than buckling (don’t cause derailments) Both taken into consideration

Ties Key Functions From Stone to Wood Today typically made from Timber Transmits loads from the rails to ballast section Provide resiliency and absorption of impact loads Maintain gage From Stone to Wood Today typically made from Timber Concrete Steel Composites

Crosstie Options Timber (hardwood, softwood) Concrete Pressure treated with creosote to extend its life “Nailable” Sufficient resiliency to cushion impact of wheels on rail Reduces forces from load applied on track Concrete Weighs 3 to 4 times as much as timber (600-800# vs 200#) However, more stable system Better for severe service High speed passenger Heavy tonnage haul lines For use on slow, heavy tonnage large curves Good for parts of world that are low in timber supply Requires more complex fastening system waterquality.montana.edu lbfoster.com

Crosstie Options, cont’d Steel Require less ballast Plant operations Beneficial in tunnels with limited headway clearance Not widely popular Problems with shunting of signal current flow to ground Fatigue cracking Composites Extensive research to create new ties Rubber, plastic, polymers Mostly research based, some used in light tonnage rail Not much known on benefits/ disadvantages yet narstco.com rti-railroad-tie.com

Complete the System Final resistance measures to defer lateral and longitudinal loads Tie Plates Provide smooth, uniform bearing surface between rail and tie Helps in maintaining gage Not always used Single vs. double-shoulder plates Rail Anchors Control “rail creep” Connected directly between rail base and tie Fasteners Reduce movement between tie plate and tie Prevents plate cutting into the tie Spikes Maintain gage between running rails Secure rail to tie ossloh-track-material.com commons.wikimedia.org

Complete the System, cont’d Elastic Fastener System vs. Cut-Spike Systems Elastic fastener system Same system used on concrete crossties Alternative to cut-spike Been adapted for use on timber crosstie track Stronger track structure Eliminates need for rail anchors Eliminates “spike killing” on wood ties Good for areas where rail is changed out repeatedly - curves

Ballast Substructure What about Ballast? Just any Crushed Rock? Layer of crushed rock under ties Anchors ties and provides stability Distributes reduced loads to sub-grade Provides immediate drainage to structure Allows for easy maintenance Provides essential elasticity and resilience to structure Just any Crushed Rock? No, tougher and harder rock is necessary Eliminates possible shattering under loading conditions Durable and resistant to abrasion and weathering Low first cost Typically – granite (preferable), limestone, blast furnace slag Is a Sub-Ballast always needed? No, only if poor sub-grade exists Sub-ballast will be layer of smaller sized rock Use of geotextile fabric between layers of ballast used to spread load out more and maintain clean ballast Especially in use where extreme loading conditions exist

Ballast Substructure, cont’d Basic Ballast/Sub-ballast dimensions (below) Effects of Unclean and Inefficient Ballast Fouled ballast will freeze in winter Higher stresses in rail and tie system once thawed in spring Cause rapid deterioration of track geometry Need to be maintained and/or replaced throughout life Ballast Cleaner in Action Ballast Cleaner at Work

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