Proceedings of JRC2006Joint Rail Conference

April 4-6, 2006, Atlanta, GA, USA

JRC2006-94050

UNDERSTANDING THE BENEFITS OF LONG TRAVEL CONSTANT CONTACT SIDE BEARINGS

Darrell llerTransportation Technology Center, Inc.

ABSTRACTIn 2001, a comprehensive test program was conducted underthe AAR strategic research initiatives program by theTransportation Technology Center, Inc. (TTCI), Pueblo,Colorado, to determine the best types of constant contact sidebearings (CCSBs) for use in 10 different North Americanfreight cars. Test results indicated that long travel (LT) CCSBdesigns generally provided the best overall performance, whichlead to an industry wide rule change. By using LT-CCSB, railoperations can be improved by maintaining better verticalwheel loads, providing high-speed stability, and providing morepredictable truck turning forces. With a better understanding ofboth CCSB performance and the needs of the rail industry, anupdated specification M-948 (AAR's Manual of Standards andRecommended Practices) [Ref. 1] was researched and revisedin 2005.

This paper documents the evolution of LT-CCSB researchand the industry's implementation efforts since testing began in2001. The testing and modeling that was performed in 2001concentrated on car types that had a history of unpredictableperformance. Well-maintained cars were selected to highlightthe characteristics of long, short, tall, and torsional stiffness thateach plays a part in the vehicles ability to reliably negotiate therailroad. Of the 10 cars, four were both track tested andmodeled and the balance were only modeled. In almost everycase, the railcars had a demonstrable performance improvementwith the simple application of LT-CCSBs. The AAR quicklyreacted by requiring all new cars and cars meeting certainconditions to have LT-CCSB (Rule 88) [Ref. 2].

Following this test program two other independent tests wereconducted, which demonstrated the advantages of LT-CCSBs.The first was a rail service test of two diesel tank cars and thesecond was a series of controlled tests on a tank car that hadderailed at high speed. In both cases performance was markedlyimproved by the application of LT-CCSB.

Finally the industry needed to update the side bearingspecification M-948, in order to reliably control theperformance of LT-CCSBs and preserve the benefit derivedfrom their use. In preparation, a 2-year rail service test was

7

conducted on three different cars, which were a refrigeratedorange juice boxcar (operated in high speed intermodal or "Z-train" service), an intermodal car, and a coal gondola. Using thedata from these cars and knowledge from participants in theCCSB supply industry, the M-948 specification was revised torepresent and preserve the operational benefits derivedfrom CCSBs. This paper will also document an audit ofthe specification to highlight advantages from the revisedM-948 specification.KEYWORDSConstant contact side bearings (CCSB),freight cars, and rail service testing.

long travel (LT),

NOMENCLATURE AND TERMSAAR - Association of American RailroadsFRA - Federal Railroad AdministrationCCSB -Constant contact side bearingLT-CCSB - Long travel CCSBIWS - Instrumented WheelsetSide Bearing - A load bearing surface originally designed as asolid steel block that is located 25 inches from the center of thecenter bowl on both sides. The side bearing typically has a0.25-inch air gap between the carbody bottom and the sidebearing surface. The side bearing aids in vertical loaddistribution across the bolster as the car rocks or twists fromside to side.Roller Side Bearing - A side bearing constructed with one ortwo steel rollers to aid in bolster rotation while contacting thecarbody bottom (under load from rocking or twisting). Whilenot loaded this side bearing typically has a 0.25-inch air gap.Constant contact side bearing (CCSB) - A side bearing designthat remains in contact with the body bolster at all times. Theforce at this contact point is determined by an internal spring.The contact point slides longitudinally when the bolster rotatesproviding frictional rotation resistance. This side bearing hasthree typical designs.

Copyright 2006 by ASME

1. Standard travel - The CCSB compressesapproximately 0.25 inches before hitting a solid stop.

2. Long Travel - The CCSB compresses approximately0.63 inches before hitting a solid stop.

3. Roller Assist - Exists as either a standard or longtravel version but employs a roller for the solid stop toaid in reducing tuming resistance.

IWS - An instrumented wheelset utilizing data from strain gagecircuits, which are collected and manipulated to produce real-time lateral, vertical, and longitudinal wheel forces.

INTRODUCTIONThe freight car in North America has slowly but surely changedas greater demands were placed on performance. Thetraditional three-piece truck has provided a long history ofservice that though enhanced is still utilized today. Othercomponents like the axle bearings have seen the benefit of newtechnologies as they emerge and are proven. Side bearings areanother component that has improved but this history is morerecent. Railcar side bearings have traditionally had a singularrole of limiting the amount of carbody roll. As railroadcapacity improved by handling higher loads at higher speedrequirements from side bearing performance changed also. Thefirst prominent change was from a non-contacting side bearingto one that was designed to stay in contact with the side bearingwear plates on the car body. The initial design function was toimprove carbody roll control. Later, with the increased speeds,the benefit of better truck hunting control was discovered andsoon became the primary objective of CCSB design. Thispaper documents research and performance advantages fromthe latest evolution of increased travel in constant contact sidebearings.BACKGROUNDApplying CCSB to railcars has elicited polarizing responsesdepending on the geographic location. The paradigm of thetime (2000) was that CCSB were only necessary in the west buta costly disadvantage in the east. Railroads running railcars inthe eastern US avoided CCSB applications, given their pastexperience that it greatly increased truck-turning resistance.Conversely, railroads in the western US relied heavily on theapplication of CCSBs to offer protection from rail car huntingpotentially causing damage to sensitive lading or unfavorablecar performance. An industry resolution to reduce the stressstate of the railroad initiated an industry wide directive to equipall railcars with CCSBs. Following the resolution an extensiveresearch program was initiated to determine the effects ofCCSBs on the performance of various car types.CONTROLLED TESTING OF CARS WITH CCSBUnder the direction of two AAR committees, a test plan wasdeveloped that would quantify performance in curving, twistand roll and high-speed stability (these regimes are all definedin an AAR specification) [Ref. 3]. The two committees werethe Equipment Engineering Committee (EEC), which wastasked with oversight and execution, and the MechanicalResearch Committee (MRC), which provided funding andadditional oversight. The EEC selected and prioritized a list ofcars to test and model as shown in Table 1. These cars wereselected based on the FRA accident / incident database and onrailroad experiences with the cars.

Table 1: Rail Cars Selected for Testing and ModelingCar Type

Aluminum Coal GondolaBulkhead Flat CarShort Covered HopperLong Tank CarGrain Covered HopperPlastic Pellet Covered HopperCenterbeamShort Tank CarMill Gondola (52 ft)Boxcar (60 ft)

Test/ ModelYes / YesYes / YesYes / YesYes / YesNo / YesNo / YesNo / YesNo / YesNo / YesNo / Yes

RESULT SUMMARYTrack tests and modeling studies indicated that the use of LT-CCSBs provided the best overall performance in combinedissues of curving, roll control, vertical load equalization, andhigh-speed stability. It was also surprising to discover thatCCSBs generally performed well in comparison to doublerollers in loaded truck turning resistance tests.Once the EEC and MRC reviewed the results from these tests

they added language to Rule 88 which reads, "...after January1, 2003, all new cars and cars that are rebuilt, cars givenextended service, or increased in gross rail load, in accordancewith AAR Office Manual Rule 88, must be equipped withmetal-capped LT-CCSBs." Since that time, LT-CCSB retrofitplans benefiting other car types have been scheduledaccordingly.INSTRUMENTATION METHODOLOGIES ANDMATHEMATICSThree AAR M-1001 Chapter XI test regimes were chosen toquantify the differences in car performance due to CCSBs,high-speed stability, constant curving, and dynamic curving.In order to quantify the differences in each of theseregimes instrumentation was applied to allow thefollowing measurements:

* Lateral, vertica* Truck tuming r* Truck warp* Truck rotation* Lateral carbod~* Carbody Roll

1l, and longitudinal wheel forcesmoments

y acceleration

Lateral, vertical, and longitudinal wheel forces weremeasured directly using two AAR designed instrumentedwheelsets (IWS). The IWS were placed in axle positions oneand two on the leading end of the car. Truck tuming momentsare derived from both the lateral and longitudinal forcesmeasured by the IWS. The total truck turning moment isdefined as:Warp Moment + Steering Moment = Truck Turning Moment

Copyright 2006 by ASME8

The warp moment is calculated from the wheelset's lateralforces, which are vector-summed on each axle and thenmultiplied by the one half of the wheelbase. The vector sum isnecessary because the IWS do not follow a conventional righthand rule coordinate system (the lateral forces for a wheelsetare positive when pushing outward on the rail). The steeringmoment is computed by multiplying the longitudinal force withthe distance between the wheels' contact position and summingthe two axle couples together along with the two momentscalculated from the warp or lateral components. Thecalculation is performed using time series data, which creates adynamic measurement of the total truck turning moment(see Figure 1).

rl*uu.c -. I '-pi .1.r - Oe ... tUOVU LJ rVrnabu,V fI u%. vvarpwith (Bottom) A Close-Up of the Displacement Transducer's

Connection to the Side Frame

Turning Moment =Wament + Steer rc Mom ent

DETAILED CONTROLLED TESTING RESULTSThe amount of data collected from this series of controlled testshas been documented in several TTCI Technology Digests;[Ref. 4,5,6,7, and 8]. A complete graphic documenting tracktesting results is shown in Table 2. With limited funding, notall combinations could be tested; therefore, please note that *means in was not tested or modeled.Table 2: Controlled Testing Results from Four Rail Carswith Various Side Bearings. Results Demonstrate theConsistent Performance Benefit from using LT-CCSBs

Figure 1: Truck Turning Moments used to Compare CCSBswith Traditional Roller Side Bearings

Truck warp was measured by locating a beam on each end ofthe bolster parallel to the side frame, then measuring thedisplacement between the beam and the side frame. Figure 2 isa picture of the warp measurement arrangement. Themeasurement in radians is based on the difference in the deltadisplacement at each end divided by the distance between them.It is a trigonometric calculation utilizing the small angletheorem since warp angles are typically less than 5 to 15milliradians. Truck rotation was measured at the end of thebolster with respect to the carbody. Truck rotation is computedby the arc tangent of the delta displacement divided by one halfthe bolsters width (d).Truck Rotation = Arc-tangent * (displacement delta / d)

Carbody roll in degrees was calculated using two lateralaccelerometers at a known vertical distance apart, which wereratioed based on the similar triangle theorem. The difference intheir amplitudes produced the angle of carbody roll and the rollcenter. The remaining measurement, lateral carbodyacceleration, was used to quantify high-speed stabilityperformance for hunting.

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Chapter Xi Roller ST STRA STNM LT LTRA LTSHTank Loaded Yes Yes Yes Yes Yes

Empty No No Yes YesHopper Loaded No No Yes Yes

Empty No No No NoBulkhead Loaded Yes Yes Yes Yes

Empty Yes Yes Yes YesGondola Loaded No No No Yes

Empty No Yes Yes Yes

Legend:* ST - Standard Travel* STRA - Standard Travel Roll Assist* STNM - Standard Travel Non Metal Cap* LT - Long Travel* LTRA - Long Travel Roll Assist* LTSH - Long Travel Shear

Table 2 documents the improvement in performance byindicating whether or not the car met M-1001 Chapter XIrequirements. All four cars (having every other aspect heldconstant) experienced marked improvement against Chapter XIcriteria by simply changing to a LT-CCSB design. In similarfashion the results from modeling are reported in Table 3 whereagain LT-CCSB performed consistently within the criteriaof chapter XI.

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Table 3: Modeling Results from Four Rail Cars with VariousSide Bearings. Results Demonstrate the Consistent

Performance Benefit from using LT-CCSBsChqaptrXl Rolle IST ISTRA #TNM L LTRA LTSI

Center Beam Yes Yes YesLoaded e e

Empty Yes Yes Yes60-foot Box car Ye YeYs

Loaded Yes Yes YesEmpty No No Yes

Grain Hopper Yes Yes YesLoadedEmpty No No Yes

Pellet Hopper Yes Yes.

YesLoadedEmpty No No Yes

Short Tank Yes Yes YesLoadedEmpty No No *Yes

52-Foot Mill-Go" e YesYeLoaded Ye

Empty No NoYe

The next two sections will document the specificperformance results measured on a short covered hopper and along liquid propane tank car. These two cars were chosen sincethey represent both ends of the spectrum of performance for allthe cars tested. The long tank car enjoyed many benefits withthe use ofLT-CCSBs, whereas the short covered hopper did notgarnish a similar increase in benefits.SHORT COVERED HOPPER RESULTSThe short covered hopper (BNSF409040) is equipped with110-ton Barber S-2-D trucks cast in June-98 employing sevenD5 outer, and four D5 inner and inner-inner coils. Thelightweight and load limits were 57,100 and 228,900 pounds,respectively. Car length is 40 feet over strikers with truckcenters of 29.5 feet. All side bearings were tested withoutlubrication and truck center plates were left in dry condition asreceived. The car had accumulated more than 60,000 servicemiles prior to testing. The hopper was filled with sand inloaded tests to approximate the center of gravity of the typicallading of cement.One issue with curving is maintaining vertical wheel load in

the entry and exit spirals. Two plots show how the hopper carperformed in this arena. The first is from the loaded hopperrunning in dynamic curving. This test combines elements ofcurving, with twist and roll. Figure 3 shows that the long travelside bearing consistently provided more vertical wheel loadthan the other side bearing designs. Whether or not the dip (18mph) in the long travel result is realistic, it is important toconcentrate on the fact that vertical wheel loads stayed wellabove the minimum criteria of 10 percent as compared to theother side bearings.

In spiral negotiation vertical wheel loading was not as goodwith the long travel as it was with the double roller. Thecumulative histograms of each side bearings' performance aredemonstrated in Figure 4. Since the car has a short truck centerthe difference in twist from lead to trail in the exit spiral iseasily accounted for in the 0.25 inch air gap of the double rollerside bearings.

10

4'

0

70%60%

50%

40%30%20%h -10'h -

0% -10 15 20

Speed (mph,-4- Double Rollers-fr-Long Travel

25 30 35

-_ Non-Metal-.*- Standard Roll Assist

Figure 3: Statistical Minimums from Each of the SideBearing Designs Running in the Dynamic Curve

100% -r

60

440% - = = _ ---

E 20%

0%0 2 4 6 8 10

Vertical Load (kips)-Double Roller - Non4Metal-Long Travel - Standard Travel RA

Figure 4: Cumulative Histograms of Vertical Loads for FourTypes of Side Bearings on the Short Covered Hopper

However, since typical maintenance standards allow thedouble roller air gap to degrade to zero before maintenance, avalid argument could be made that vertical loadingperformance with the long travel design would provecomparable to the double roller given the additional travelclearance under tight conditions. The two conditions, optimaland tight, are compared in Figures 5 and 6, which areNUCARSTM predictions of the percent wheel load retained inthe limiting spiral (specified in AAR's Chapter XI). The lightblue line in Figures 5 and 6 represents the equivalent cross-level of the hopper (approximately 1.5 inches) given its 29.5-foot truck centers. In the optimal condition no side bearingstands apart as best for negotiating the spiral. However, undertight conditions, the long travel design demonstrates the benefitof the additional travel (Compare remaining vertical wheel loadfor each condition (optimal and tight) for the three side bearingtypes using the light blue line).

Copyright C) 2006 by ASME

v N.. - -'101,\ NI-11

1111_91n.

0%-0

1 80%j 0%40%

E

30%0 0.5 1 1.S 2 2.5 3

Crosslbvel (in)- Roder- mdard Trael- Long Travel- Ncn-Metal

Figure 5: Empty Car - Lead Outside Wheel Vertical Load -Short Hopper Modeling Results

Finally, truck-turning resistance indicated elevated levels(10 to 35 percent) when using LT-CCSBs as compared todouble rollers in optimal conditions. The result is notsurprising since rotation under optimal conditions is onlyresisted by the centerbowl when using double roller sidebearings. This expectation would however, quickly reversegiven tight side bearing conditions resulting in turningmoments that could almost be equivalent.

100%

_ 90%

II 80%0-J8 70%

e 60%E 50%ir 40%

30%0 0.5 1 1.5 2 2.5 3

Crosslevel (In)- Roller - Standard Travel - Long Travel - Non-setal

Figure 6: Empty Car - Lead Outside Wheel Vertical Load -Short Hopper Modeling Results with Tight Side Bearings

LONG TANK CAR RESULTSTrucks used during empty car tests were new, 110-ton BarberS-2-HD cast in August-99 with a standard suspension (sevenD5 outer coil springs and six D5 inner coil springs). Loaded cartests were performed with the higher mileage truck borrowedfrom an aluminum gondola previously tested (AAR TD-02-021). The lightweight and load limits were 98,200 and 164,800pounds, respectively. Car length was 66 feet over strikers withtruck centers of 55 feet. Side bearings were tested withoutlubrication and center plate bowls were left in dry condition asreceived. The car was new and had acquired less than 5,000service miles prior to testing. In loaded car tests, the tank wasfilled with water resulting in a center of gravity below thenormal location.

Benefits from using LT-CCSBs on this tank car were muchmore pronounced. During initial empty car tests with rollerside bearings the tank car derailed on an exit spiral from a 12-degree curve. The following tests, performed with long traveldesigns, allowed safe spiral negotiation without any issue. Thekey to this incident was primarily vertical wheel loading whichis demonstrated in Figures 7 and 8. Side bearings providingadditional travel allow the trucks to freely rock (rotate aroundthe longitudinal axis) below the carbody and maintain verticalloads during negotiation of cross level variations.

| 60- 40

A 30

1 20e 10

a 10 20Sned (mohi

30 40

_ Doubb Roler _ Standard Tmvel-*- Long Travel Rot Assist -- Long Travel

Figure 7: Vertical Wheel Loading Comparison in theDynamic Curve on a Long Propane Tank Car with Various

Side Bearings

10^ ..

166%- .-

146%___

%.- ''- ....................6 4 a 12 1I

Doubl ROlOM Stlad Trtl-La" Travl RA -La Travw

Figure 8: Vertical Wheel Loading Comparison in the 12-Degree Exit Spiral on a Long Propane Tank Car with

Various CCSBUsing NUCARS" modeling methods, vertical load plots were

constructed to illustrate the performance differences betweenthe various side bearing applications. Figure 9 demonstrates thepercent vertical load response of the long tank car in spirals.The light blue vertical line indicates the tank car's performancein the limiting spiral, which would subject the car (based ontruck centers) to approximately 2.6 inches of crosslevel. Notethe long travel design is predicted to provide more vertical loadequalization than the other side bearing designs, which wasconfirmed in test. The performance with traditional doubleroller or block side bearings degrades more with tighter sidebearing clearances.

Copyright 2006 by ASME11

A"!

.A."

Yls.lbNhm16

I I

0 I 2

\ N1*3 4

Crosslevel (in.)-Rolbr 8Standard Trel _ Long Travel

this test. Figure 11 provides a map of the routes that werecovered during the 4,100 miles of testing.

Figure 10: Two BNSF Diesel Oil Tank Cars used in RailService Tests

Figure 9: NUCARSTm Prediction of Remaining PercentVertical Load in the Limiting Spiral

(approximately 2.6 inches of Crosslevel)CONTROLLED TEST RESULTS CONCLUSIONThe body of evidence produced from testing and modelingclearly indicated the favorable performance of LT_CCSB withlittle downside. The AAR committees took the results with theintention of requiring the best side bearing for each car type butended up simplifying the requirement by using LT-CCSB in allcars. The EEC recommendation to the Technical ServicesWorking Committee was, "after January 1, 2003, all new carsthat are rebuilt, and cars given extended service or increased ingross rail load, be equipped with long-travel CCSBs inaccordance with AAR Office Manual Rule 88." The rule wasaccepted and made effective in 2003.

INDEPENDENT OFFSET LOAD TESTIn 2001, one additional test was performed using intermodaldouble stacks with offset loads. This test and the result arecritical to understanding the risk in allowing loads to travel inthis condition. The test indicated that offset loads will produceresults that nearly exceed Chapter XI criteria, obviously themore the offset the more risk in derailment. The use of otherside bearings does not necessarily relieve this conditionbecause the result will be higher truck turning forces andreduced vertical wheel loading capacity making legacyconfigurations susceptible to derailment. Better loading rulesand inspections should warn and watch for this condition in aneffort to avoid any potential issues.

INDEPENDENT RAIL SERVICE TESTING RESULTSFollowing the initial LT-CCSB work performed under thedirection of the MRC and the EEC, there were severalproprietary test programs conducted that produced findings,which also support the benefits derived from applyingLT-CCSBs.

BNSF RAIL SERVICE TESTIn the first quarter of 2003, two diesel oil tank cars from BNSFwere used in a rail service test see Figure 10 [Ref. 9]. The carswere identical in setup with the only exception being that onehad LT-CCSB and the other had block style side bearings.Both cars traveled in the empty condition for the duration of

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83NS1P

,b Theit1 D ocf.r,4 1111

Figure 11: Route Traversed by the Two Tank Cars during aBNSF Test Covering 4,100 Miles

For one of two configurations, IWS were placed in the leadaxle of each car providing real-time vertical, lateral, andlongitudinal wheel forces. Vertical and lateral accelerometerswere placed on each end of the tank cars.The initial move leaving LaJunta, Colorado, ran at speeds of

50 mph, however the tank car with block side bearings had toomany severe hunting incidents. The test plan was revised andmaximum test speeds were reduced to 45 mph to avoid tank carhunting. CCSBs have long been known for improving high-speed stability. Unfortunately the wheelsets were not alwayslocated in the configuration discussed above, which would haveallowed comparison of the two cars with respect to verticalloading and LN ratios. The author only states the following,"the car equipped with long travel constant-contact sidebearings still performed slightly better than the car equippedwith solid-block side bearings, based on measured single wheelL/V ratio and lateral car-body accelerations results."TANK CAR TEST RESULTSAnother independent test involving LT-CCSBs was conductedat the request of CN [Ref. 10]. In 2003, CN experienced ahigh-speed hunting derailment with a privately owned, tank car.Derailments of this type are not frequent but can be very costly.In discussions, CN indicated that most of their empty tank carderailments occurred in exit spirals at low speeds. They wantedTTCI to determine if the block side bearings had any impact onboth types of these derailments.

Copyright 2006 by ASME

90%I80% 7 c1hiie70% -60%IfliL

40%30%

ieI.1

~1E

4 UU

The test parameters required the car to remain in the asreceived condition. No condemnable conditions were observedon the car. The side bearings met the current FRA rules by notbeing in contact with the car body; however, the clearance oneach of the side bearings and their respective locations turnedout to be a significant factor in the car's performance. Earlier adiscussion was offered regarding the increased risk ofperformance issues resulting from a reduction in side bearingclearance. It turns out this test highlighted this condition.Table 5 documents the clearances measured in the four sidebearing positions.Table 4: Side Bearing Clearances of the Tank Car Measured

in as-Received Condition before TestingLocation B-Left B-Right A-Left A-Right

Side Bearing Gap 1/8th 5/16th 7/16th 1/64th

The key here is that the clearances diagonally opposed fromeach other, B-left and A-Right, were tight. With the B-endleading this set up a circumstance that restrained the truck in aleft-hand entry spiral from equalizing vertical load to theleading inside wheel. The suspension in the empty condition istoo stiff to provide any compliance. Figure 12 is a cumulativedistribution comparing long travel side bearings to the asreceived block side bearing performance. The position Al (anIWS label) is located on the lead axle right side (inside curveB-end leading) position. Note that railcar performanceimproved by distributing 7 to 8 kips more load to the insidelead wheel and the outside (axle 3 left wheel) when the truck isallowed to distribute the load side to side (please note the A3 isan IWS label). Fortunately, in this direction, derailment is notimminent since the most important railcar wheel (not shown inthe plot) is carrying significant vertical load. However, in aright hand exit spiral, the situation would reverse and causeundesirable wheel unloading as the track twists away to atangent level geometry. A rail climb derailment under thisscenario would be likely.

higher vertical loads to the wheels. It should be stated that thepoor results measured during block side bearing tests wereexacerbated by the uneven clearances. Figure 13 shows theminimum vertical wheel loads for each of the noted speeds inthe twist and roll test. The test for the block side bearings wasstopped after 50 mph for two reasons. First the car began toseverely hunt just prior to entering the test zone and then, at 50mph, the lowest vertical load of the test series was recorded.These two events, truck hunting and wheel unloading, couldoccur simultaneously and lead to a rail climb derailment at highspeed, which is what was described in the original derailmentthat lead to the investigation.

90%

60%

, 70%

1 60%

X 50%01-: 40%

* 30%

*A 20%

10%

0%0 10 20 30 40 50 60

Sped (mph)Block * CCSB

Figure 13: Twist and Roll Vertical Wheel Load Statistics forthe Tank Car

With over 2 years of testing and modeling to support thebenefit of LT-CCSBs, the rules for upgrading side bearingsbecame an integral part of reducing the stress state of therailroad. What remains now is the fact that no specificationexists to detail the performance requirements ofCCSBs.UPDATING THE CCSB SPECIFICATIONWithin the AAR Manual of Standards and RecommendedPractices, is the historical side bearing specification M-948-1997. The specification was mostly designed to control theperformance of block and roller side bearings with only a shortsection that tested the vertical fatigue of the CCSB. Thespecification had no criteria for success or failure, just a basicapplication and approval process. Once the rail industry knewhow a CCSB needed to perform, an updated specificationbecame essential.The AAR sponsored a Technical Advisory Group (TAG)

staffed with members from the railroads, side bearing suppliers,and TTCI. The first objective outline by the TAG was to definethe railroad environment. The rail service testing wassponsored by an AAR research program and conducted byTTCI. Three high utilization car types were selected to acquirethe environmental data of CCSBs.

Figure 12: Cumulative Distribution of Vertical Wheel LoadsComparing the Two Side Bearing Types

The tank car was then tested using the twist and roll regime.In comparing the two side bearing configurations the LT-CCSBrecovered after the resonance point in carbody roll to provide

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CCSB ENVIRONMENT IN RAIL SERVICEIn 2003, three cars known to experience high mileage in servicewere selected to ascertain the environment experienced by LT-CCSBs [Ref. 11]. The three cars were a refrigerated boxcar(runs in high-speed service), an intermodal well car, and a coal

Copyright c 2006 by ASME

160%

80%

60%a.Ila 40%'3

20%

0%6 6

Vertical Wheel Load (kips)---__ ..-.

-

.. 1. -.u-,- - - ____-

gondola. Each of the cars was instrumented to measure bolsterrotation (CCSB longitudinal sliding), car body roll in the centerbowl (CCSB vertical cycles), lateral accelerations at each end,speed, and GPS. The purpose for the instrumentation was toquantify the inputs into LT-CCSBs. It was anticipated at thetime that three cars and the services they operate in would be achallenging factor in LT-CCSB performance; this, however,was not realized in all cases. The total mileage from colleteddata was over 25,000 miles for the three cars.The first test was conducted on a 76-foot refrigerated boxcar

owned by Tropicana and used to ship orange juice in high-speed traffic lanes from Tampa, Florida to Los Angeles,California (Figure 14).

CCSB VERTICAL CYCLESConsidering the available data set the most notable observationis the absence of any challenging inputs into LT-CCSB fromthe three cars. It was anticipated that plentiful high-speedinstability events would give an indication of the frequenciesand amplitudes that a LT-CCSB experiences while in railroadservice. Those cycles would then be quantified and used whendeveloping inputs for a CCSB laboratory test. Instead only oneof the three cars (the boxcar) produced Over-the-Road (OTR)inputs that could provide validation to lab test inputs. Theother two cars had good truck performance, which meantthat nothing was recorded that would challenge CCSBs.Focusing on the data from the boxcar there were a fewuseful observations.The available service data was analyzed for the vertical

displacements of the CCSB. Table 5 provides the cycle countsmeasured in the vertical direction as compared to thosepublished in the updated M-948-2004 [Ref. 12] specification.

Table 5: Comparison of Vertical Cycle Counts betweenService Tests and the Updated M-948-2004

0.1250.250U.3730.5000.625

2,841,318 1,200,000140,966 240,00024,215 40,0006,551 10,0002,591 2,500

Figure 14: 76-foot Refrigerated Boxcar from TropicanaUsed in Assessing the LT-CCSB Environment

The Tropicana cars frequently ran at high speeds (60 to70 mph) given the time sensitive nature of the orange juice theycarry. The route was traversed three times between Tampa andLos Angeles as depicted in Figure 15. The car is equipped withASF Super Service Ride Master trucks using Lord primarysuspension pads and A.Stucki SSB-5000 side bearings.Tropicana does an exceptional job of maintaining their railcarfleet, which proved beneficial on the wear and tear ofcomponents like trucks and CCSBs.i ~~~~Ap

Figure 15: Path Traversed by the Tropicana Boxcar

14

The cycle counts (at normal operational frequencies of 0.1 to2.5 Hz) at the lower amplitude range are not particularlychallenging to typical side bearings, so the difference in cyclecounts at 0.125 inches is assumed insignificant. The M-948-2004 mid-range cycles are more numerous making the testmore conservative. Since rail cars have frequent rest periodswhile in service, the fact that the vertical lab inputs arecontinuous should also facilitate a more conservative test.CCSB LONGITUDINAL CYCLESGleaning any correlation to longitudinal CCSB cycles proveddifficult with the good performance measured from the threecars. Only the boxcar experienced a brief incident that couldprovide a snapshot of how severe hunting can become. Therefrigerated boxcar made three trips between Tampa and LosAngeles totaling 14,000 miles. In one of those trips, theleading truck (B-end) experienced high-speed instabilitycontinuously for over two miles. Figure 16 shows the tracesfrom this event. Using this brief occurrence the data iscompared to the inputs specified in M-948-2004. M-948-2004requires that for 37-hours and 20-minutes, a CCSB be subjectedto hunting cycles that combine both vertical and lateraldisplacements in phase. The vertical cycle (peak-to-peak) is0.125 inches at 3.0 Hz, and the longitudinal cycles are0.25 inches. Figure 17 shows the Fast Fourier Transform (FFT)of the filtered (FIR filter at 10 Hz) displacement signals fromthe boxcar; note that the frequency in both cases is about3.0 Hz. When analyzing the time series data from Figure 16the signals were determined to be out of phase. Since theforces into the side bearing are the same the phase is notconsidered to be important.

Copyright c 2006 by ASME

Figure 16: Three Miles of Data Recorded on theRefrigerated Boxcar near Wilcox, Arizona

A final segment in the lab test in the simulated service lifesection is intended to replicate curving. The data from over theroad was not analyzed to provide any correlation to the labrequirements. It has been suggested that this segment is toosevere and far removed from conditions in service. Given theseverity of all the lab inputs, side bearings that meet theseperformance levels should provide reliable performance inservice. In order to validate this statement, the AAR conducteda test on two typical LT-CCSBs that have significantpopulations in service.

Figure 17: FFT of Vertical and Longitudinal CCSBFrequencies Matching the M-948-2004 Lab Requirements

TESTING OF TWO LT-CCSBTwo typical LT-CCSBs being used in rail service were selectedto undergo M-948-2004 requirements in two of the testprocedures [Ref. 13]. Those procedures were the VerticalFatigue Cycling test (M-948-2004 4.1.2) and the SimulatedService Test (M-948-2004 4.1.3). The tests were performed onMTS controlled two-axis load fixtures (Figure 18) having a50-kip vertical and 10- to 35-kip longitudinal capacity.

Figure 18: Dual Axis MTS Load Frame Used in LT-CCSBTests

The remaining requirements from M-948-2004 were notperformed, as they are requirements for defining the function ofa CCSB (preload, travel, etc.).VERTICAL M-948-2004 RESULTSThe vertical test took a little over 10 days at 24 hours a day foreach LT-CCSB. A vertical stifffiess plot was generated at thebeginning and end of both tests to document the vertical fatigueperformance. In addition, load values were recorded followingthe 30-minute static squeeze per M-948-2004 requirements.Figure 19 illustrates the force/displacement curves for the oneofthe side bearings.

Figure 19: Hysteresis Curves (Initial and Final) From M-948-2004 Testing of a Typical LT-CCSB

M-948-2004 has two ratings for side bearings, which arepremium (65 percent preload retention) and standard (50percent preload retention). Both side bearings met premiumrequirements in the vertical fatigue test.LONGITUDINAL M-948-2004 RESULTSLongitudinal hysteresis curves have a unique shape since theyrepresent several conditions as the side bearing is loadedlongitudinally. In a typical metal-capped side bearing the firstevent offers almost zero resistance because the cap is merelytranslating with respect to the base due to the clearance (the

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spring element is shearing). Once the inner cap hits the limit ofthe outer base longitudinal force builds under static friction.Then when the force has increased to the break away point theside bearing is no in full slip or friction is saturated. This shapeis outlined in Figure 20 below where each of the components ofthe cycle can be observed.

na.

0U-

-0.3 -0.2 -0.1 0 0.1 0.2 0.3Displacement (in)

I-Start -End -Theoretical HysteresisFigure 20: Typical Longitudinal Hysteresis Curves from a

Metal Capped LT-CCSBSeveral other pieces of information are included in Figure 20.

The red rectangle is a theoretical longitudinal cycle of a sidebearing. The starting and ending hysteresis areas are alsodemonstrated. It is the ratio of the final to the initial hysteresisareas that is specified. In M-948-2004, standard performance isspecified with a ratio > 25 percent and for premium the ratio> 45 percent. In the test cases of the two LT-CCSB, both unitsmet the premium requirements.The loss in area is caused by the degradation of the spring

load. The polymer element used by many CCSB designsdegrades with the intense heat that is caused from the inputs ofthis testing. It is important to realize that this is notrepresentative of service conditions; therefore meeting theserequirements should give the industry confidence in the long-term performance of these LT-CCSBs.A companion requirement to the ratio is the loss in the length ofthe slipping region where friction is saturated. To guard againsta side bearings' clearance wearing this criteria requires that thedifference in the "gap" or leading edge of impending CCSBslip cannot exceed 0.125 inch for the standard requirement and0.0625 inch for a premium designation. This requirement isillustrated in Figure 21. Again, both our test specimens metpremium requirements.

Figure 21: Methodology to Measure Reduction in SaturatedFriction (a - b = longitudinal slip)

CONCLUSIONBy using LT-CCSBs, rail operations can be improved bymaintaining better vertical wheel loads, providing high-speedstability, and providing more predictable truck turning forces.This observation was well supported with several years ofmodeling and testing conducted under the AAR strategicresearch program. Understanding how the CCSB works andwhat the rail industry needs from its performance was also abenefit from the testing. The updated M-948-2004specification now captures this knowledge and preserves theCCSBs' function.Using M-948-2004, two typical CCSBs were evaluated and

determined to meet premium performance levels. The corollaryis that these units are also known to be performing better inservice than earlier CCSB designs. Presently, this indicatesassurance that the new specification benefits the industry byensuring the stringent lab performance requirements willfacilitate excellent LT-CCSBs..ACKNOWLEDGMENTSRussell Walker Senior 1I Engineer TTCIA. Stucki CompanyAmstead Rail GroupBNSFCanadian National Railway CompanyCSX TransportationMiner EnterprisesStandard Car TruckTTX CompanyUnion Pacific Railroad Company

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REFERENCES1 Association of American Railroads, "Manual of Standards

and Recommended Practices," Section D, Specification M-948, 1997.

2 Association of American Railroads, "2005 Office Manualof the AAR Interchange Rules," Pueblo, Colorado, Rule88.C.3.c.18.m, pp. 28. 2005.

3 Association of American Railroads, "Manual of Standardsand Recommended Practices," Section C,Chapter XI, 1986.

4 R. Walker, "Side Bearing Performance Under AdverseConditions," TTCI, TD-02-014, Pueblo, CO, 2002.

5 D. Iler, "Assessing Constant Contact Side BearingPerformance for an Aluminum Coal Gondola," TTCI,TD-02-02 1, Pueblo, CO, 2002.

6 D. Iler, "Assessing Constant Contact Side BearingPerformance for an Short Covered Hopper," TTCI, TD-02-023, Pueblo, CO, 2002.

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7 D. Iler, Walker, R., "Assessing Constant Contact SideBearing Performance for a Long Tank Car," TTCI TD-02-027, Pueblo, CO, 2002.

8 D. Iler, Walker, R., "Assessing Constant Contact SideBearing Performance for a Bulkhead Flatcar," TTCI, TD-03-006, Pueblo, CO, 2003.

9 D. Li, Bidwell, R., Malone, J., "Over-The-Road Test:Track Geometry and Tank Car Performance," TTCI, P-03-016, Pueblo, CO, 2003 (proprietary).

10 D. Iler, "Tank Car Derailment Study," TTCI, P-03-036,Pueblo, CO, 2003 (proprietary).

11 D. Iler, "Constant Contact Side Bearing Environment,"P-05-027, Pueblo, CO, 2005.

12 Association of American Railroads, "Manual of Standardsand Recommended Practices," Section D, Specification M-948, 2004.

13 D. Iler, "Testing of Constant Contact Side Bearings UsingAAR Specification M-948," TTCI, P-05-028, Pueblo,CO, 2005.

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