RESEARCH AND DEVELOPMENT BULLETIN RD063.01R

State-of-the-Art Report on Prestressed Concrete Ties for

North American Railroads by Amir N. Hanna

Reprinted with permission from the PCI Journul.

September-October 1979, pages 32-61

PORTLAND CEMENT ASSOCIATION Research and Development/ Construction Technology Laboratories

This publication is based on the facts, tests, and authorities stated herein. It isintended for the use of professional personnel competent to evaluate the signifi-cance and limitations of the reported findings and who will accept responsibilityfor the application of the material it contains. Obviously, the Portland CementAssociation disclaims any and all responsibility for application of the statedprinciples or for the accuracy of any of the sources other than work performed orinformation developed by the Association.

State-of-the-Art Remrt on

Prestressed Concrete Ties for

North American Railroads

Amir N. HannaPrincipal Engineer—Track StructuresTransportation Development DepartmentPortland Cement AssociationSkokie, Illinois

In most countries of the world,

there is a growing interest inthe use of concrete ties.

The interest is justified bygreater consistency in product

quality that can be achieved by

the use of prestressed concrete,

and inherent suitability of con-crete ties for use with continu-ously welded rails,

Experience to date indicates

that use of concrete ties is desira-ble for reasons of economy as wellas for the superior structural prop-erties that add considerably to the

overall stability and performanceof the track structure.

Performance of concrete ties intrack is influenced greatly by thefunctioning of both the rail fas-

tening system and the ballast sec-tion. Therefore, rails, ties, fasten-ings, and ballast should all be

considered integral parts of thetrack structure.

The Concrete Tie

The first concrete ties were de-signed in France by Monier in 1884.In the United States, the first recordeduse of concrete ties was in 1893 when200 were installed by the ReadingCompany in Germantown, Pennsyl-vania+1

Since that time, several types ofconcrete ties have been developedand used in track systems. Thesetypes include prestressed monoblock,prestressed two-block, reinforcedtwo-block, and longitudinal concreteties. Fig. 1 illustrates general config-urations of two-block and monoblockconcrete ties.

The prestressed monoblock con-crete tie is today the most widely usedtype. It is estimated that more than120 million concrete ties were laid intracks of railroads all over the worldprior to 1972. Of these, more than 100million ties were prestressed mono-block ties,2 Pretensioned concrete ties

1

Table 1. Recent Prestressed Concrete Tie Installation in North America.

*All ties are preteneioned monoblock unless otherwise is noted.TT and U designate threaded and threadlees type fastenings, respectively.

2

account for more than 70 percent ofthis number. Also, it is estimated thatof the 15 million prestressed concreteties produced annually all over theworld, 12 million are pretensioned. z

The first use of prestressed concreteties on American railroads was in1960, when 500 were installed on theAtlantic Coast Line Railroad and 600on the Seaboard Air Line Railroad,Since that time, over 100 concrete tietrack installations were built. Theseranged from several ties on ballastedbridges or grade crossings tothousands of ties on mainline track.

The first major use of prestressedconcrete ties in the United States wasin 1966, when 74,000 were installedon the Florida East Coast Railway. 3Recent concrete tie installations onmainline track in North America aresummarized in Table 1.

Methods of FabricationAs with other prestressed concrete

products, ties may be either pre-tensioned or post-tensioned.

For pretensioned concrete ties, pre-stressing is accomplished by tension-ing rods, strands, or wires prior toplacing concrete in the forms. Afterthe concrete has reached a specifiedstrength, the prestressing force is re-leased and transmitted to the concreteby bond.

‘ For post-tensioned concrete ties,prestressing is accomplished by highstrength rods that are appropriatelycoated or encased in conduits to pre-vent bond with the concrete. The pre-stressing force is applied after theconcrete has reached a specifiedstrength,’ This force is transmitted tothe concrete by end bearing,

Pretensioned concrete ties havegenerally been used in NorthAmerica, Therefore, only preten-sioned concrete ties will be discussedin this paper.

Pretensioned concrete ties are man-ufactured by one of three methods,These are the long-line, stress-bench,and individual form methods.

. Long-Line Method—In thelong-line method, several forms areset end to end on a prestressing bed.Pretensioning tendons, common to allforms, are stressed between twoabutments located at the ends of thebed. After placement of fastening andother inserts, the tendons are ten-

(b) MonoblockFig. 1, Types of conorete ties,

sioned. Then concrete is placed in theforms, vibrated, and cured.

After the concrete has reached aspecified strength, the prestressingforce is transferred to the ties bydetensioning the tendons, In thismethod, the turn-around time of theforms is within a 24-hour cycle. Fig, 2shows 600-fi (183 m) long productionlines for tie fabrication by the long-line method.

Another configuration of the long-line method utilizes a fixed concretingplant, In this system, forms are placedtwo at a time in the middle of the pre-stressing bed. After the concrete isplaced and vibrated, the forms are slidwit% their contents towards the end ofthe bed where the concrete is vibratedfor a second time.

. Stress-Bench Method—Thestress-bench method utilizes mobilebenches made of structural steel, Eachbench accommodates forms of four orfive ties in the longitudinal direction,The benches are operated mechan-ically and can be moved in both thelongitudinal and transverse directions.This permits production operationssuch as preparation and tensioning oftendons, placement and vibration ofconcrete, or curing to be performed atdifferent working locations.

. Individual Form Method-Theprestressing tendons are tensionedagainst the forms in the individualform method. Therefore, forms mustbe strong to resist the pretensioningforces. As with other methods, theprestressing force is transferred to the

Fig. 3. Indented tendons for pretensioned concrete ties.

tie after the concrete has reached aspecified strength,

Each fabrication method has inher-ent advantages and disadvantages. Forexample, the long-line method re-quires a large number of forms andconsequently large capital investment,The individual form and stress-benchmethods achieve high form utilizationwith relatively less capital. However,fewer man-hours are required to pro-duce a concrete tie by the long-linemethod than by the other methods. Inaddition, it is generally agreed thatthe long-line method provides betteruniformity in tie quality. The long-line method is used in most tie plantsin North America,

Materials

Concrete and prestressing tendonsare the principal materials in concreteties.

Concrete—Use of high strengthconcrete is necessary for the produc-tion of prestressed concrete ties forthe following reasons:

1. High compressive strengtA at anearly age permits transfer of theprestressing force to the concreteearly and results in better formutilization,

2. Prestress losses are reduced,

3. High flexural strength improvesresistance to cracking under ser-vice loads.

In the United States, a minimumcompressive strength of 7000 psi (48,3MPa) at 28 days has been generallyspecified, 4,5,8,T In Canada, however, aminimum compressive strength of6000 psi (41.4 MPa) at 28 days hasbeen used, A minimum compressivestrength of 4000 psi (27.6 MPa) attransfer has been considered satisfac-tory.e Also, a minimum 28-day flexuralstrength of 75o psi (5,2 MPa) has beenproposed.e,l

To obtain these strength levels andimprove freeze-thaw durability, thefollowing guidelines have been used:

1.

!2.

3,

4,

5.

6,

Maximum size of coarse aggre-gate should not exceed ?4 in. (19mm).Cement content should not beless than 650 lb/cu yd (386kg/ins),Water-cement ratio should bekept at a minimum, not to exceed0.40 by weight, This is accom-plished by the use of water-re-ducing admixtures.Curing should be accomplishedby low-pressure steam, radiantheat and moisture, or similarmeans to accelerate strengthgain.Proper consolidation of the con-crete should be accomplished byvibration,Air-entraining admixtures shouldbe used to improve freeze-thawdurability, where environmental

4

and other factors make it neces-sary,

Prestressing Tendons—Highstrength prestressing tendons are gen-erally used in pretensioned concreteties. Tendons should be selected toinsure adequate bond with the con-crete, to reduce bond transfer lengthand thus produce maximum prestressat the rail seat region, and also to re-duce prestress losses. To accomplishthese goals, the following guidelineshave been used:

1,

2,

3.

Tendons should be stress-re-lieved wires or strands with astrength of 225 ksi (1552 MPa) ormore,The nominal diameter of- thetendon should not exceed % in.(9.5 mm).Tendons should consist of in-dented wires or indented wirestrands. Fig. 3 shows three typesof indented tendons: 0.2-in.(5-mm) diameter wires, %-in,(6.4-mm) diameter 3-wire strandsand 3Ys-in. (9.5-mm) diameter7-wire strands.

Production Operationsand Control

When producing pretensioned con-crete ties by the long-line method, thefollowing operations are generallyperformed in sequence:

1,

2.

3,

4.

5.

6,

7.

8.

9.

10.

11.

Cleaning and oiling of forms,

Positioning of fastening andother inserts.Placement and tensioning ofpretensioning tendons.Placement and consolidation ofconcrete.Surface screeding, if required,

Curing,

Tests to verify compressivestrength.Transfer of prestress by deten-sioning.Separating of ties by sawingconcrete and tendons, or ten-dons only if end gates are usedbetween forms.Lifting of ties from forms andstoring of ties, Forms can beused again for Step 1,Tie inspection and daily qualitycontrol testing.

Although the process for fabricatingconcrete ties is straight forward, ade-q,uate quality control should be main-

tained during each stage of manufac-ture to insure consistency in qualityand performance. A proper quality as-surance program generally addressesthe following material properties,production operations, and tolerances:

1.

2.

3.

4,

5,

6,

7,

8.

9.

10,

Quality of concrete materialsincluding aggregates, cement,water, and admixtures,

Quality of concrete includingstrength, durability, and worka-bility,

Quality of prestressing tendonsincluding strength and physicalproperties.

Form dimensions and locationof fastening inserts.

Location of prestressing ten.dons.

Concrete proportioning andweight-batching.Mixing, placing, consolidation,and curing of concrete.

Application of prestressingforce,

Detensioning of prestressingtendons.

Handling and storing of ties.

Design Considerations

The design of concrete ties is acomplex problem because of variableloading conditions. However, designbending moments can be easily de-termine-d if loads imposed on the railseats and ballast support reactions areknown.

Rail seat loads depend on rollingstock characteristics, operating condi-tions, and track structure details. Bal-last support reactions depend on tieconfigurations and spacing, ballastcharacteristics, and maintenance stan-dards.

Based on extensive field measure-ments, simplified loading and supportconditions have been developed byEuropean railroads as a basis for tiedesign.8 These conditions representthe variation in support conditionsduring tie life.

Rail Seat Load—Static and dynamicloads are transmitted to the tie at therail seats. Static rail seat loads are de-termined from track analysis methods,Dynamic loads are accounted for byusing an impact factor.

Extensive measurements by Euro-pean railroads have shown that dy-namic stresses in railroad track de-

allast

UDDOrt

(a) Shortly after Tamping,,

Reoctian

(b) After Some Traffic

(c) After Extensive Traffic

P’

I

IIM(d) On Curves

Fig. 4. Tie support reactions for various loading conditions.

penal on the condition of track androlling stock, and speed of operation.A dynamic impact model has beendeveloped to account for these factors.

For analysis of concrete ties, Euro-pean railroads have used impact fac-tors that reflect the most severe trackconditions, A similar approach is usedin the American Railway EngineeringAssociation’s Manual for Railway En-gineering.4

Based on track analysis methods,the rail seat load, R, is given by thefollowing equation:’”

where

P = static wheel loada = tie spacing, generally ranges

from 20 to 27 in, (508 to 686mm)

k = track modulus which is theload per unit length of the railnecessary to produce a rail de-flection equal to unity, gener-ally ranges from 4,000 to 20,-000 lb/in./in. (28 to 138 kN/m/mm)

E = modulus of elasticity of railstee 1

I = moment of inertia of rail crosssection

a = impact factor, generally rangesfrom 0.5 to 1.5

The American Railway EngineeringAssociation’s Manual for Railway En-

o

ELEVATION

PLAN IIJ

L 8’-3” to 9’-0” (2.515 to 2.743m)

b 10% to 12” (267 to 305 nun)

h 9 to 10” (229 to 254 mn)

d 6 to 7J5° (152 to 191 I@

Prestressing force110 to 150 kips (489 to 667 kii)

Fastenina

Shoulder;%

Prestressing

< d

Fig. 5. Tieconfiguration and typical dimensions.

gineeringll recommends Cooper E72

loading with a 36,000-lb (160 kN)wheel load for the design of concretestructures on mainline track.

This load may be reduced for de-sign of structures on branch lines andother locations where the loading islimited to the use of light equipmentor cars only. However, for concreteties, the American Railway En-gineering Association’s Manual forRailway Engineering assumes a41,000-lb (182 kN) wheel load to de-rive concrete tie performance re-quirements.

Ballast Support Reaction—Nor-mally, ballast under a tie is tamped ateach side under the rail with littletamping at midlength, As a result thetie initially lacks support in its centralportion as shown in Fig. 4a. However,as a result of repeated traffic loads, thetie support conditions change causingsome pressure in the middle portionas shown in Fig. 4b or even along thetotal length of the tie as shown in Fig.4C.

The ratio of pressure intensity at thetie center to that under the rail seatsmay be referred to as the center

6

binding coefficient. This coefficient islarge in areas where insufficient trackmaintenance is performed or wherefrost-heaving occurs. However, thecenter bound condition can be greatlyreduced or even eliminated if propermaintenance is performed. Therefore,several railroads have considered acenter-bound coefficient of 0,5 or lessadequate for concrete tie designs

To account for the most severe trackconditions, the tie bending moment atthe rail seats is calculated for a cen-ter-binding coefficient of zero whilethe bending moment at tie center iscalculated for a center-binding coeffi-cient of 0.5. In calculating tie bendingmoments, consideration should begiven to load distribution through railbase and rail pad,

On curves, vertical and lateralforces are transmitted to the tie at therail seats, Where lateral forces occur,the magnitude of vertical force is in-creased on the outer rail and reducedon the inner rail. Under this condi-tion, tie support is similar to thatshown in Fig. 4d.

Because of normally reducedspeeds on curves, dynamic effects oncurved track may be less than thosefor tangent track, As a result, bendingmoments for ties on curved trackscould be lower than for those on tan-gent track, Loading conditions usedby some railroads 12 for concrete tiedesign confirm this assumption.

Selection of Tie Dimensions andPrestressing Tendons—In selectingtie dimensions, consideration shouldbe given to proper selection of tielength and width. Tie length shouldbe sufficient to assure development ofthe prestressing force by bond withinthe distance between the rail seat andtie end. Also, the tie bottom widthshould be sufficient to produce a bal-last pressure within permissiblelimits.

It should be recognized that undercritical loading conditions, tensilestresses occur on the bottom surface atrail seats and on the top surface at thetie center. Therefore, a shallower sec-tion at the tie center than that at railseats permits locating the prestressingforce towards the tensile surface atboth locations and thus reduces ten-sile stresses in the concrete,

Also, consideration should be givento the proper selection of diameter -.

Table 2. Material Properties.-r-–-

Concrete Properties

Coarse aggregate 3/4 in. (19 mm) maximum size

Cement content 650 lb/cu yd (386 kg/m3) minimum

Water-cement ratio 0.40 by weight maximum

Air entrainment Where environmental factors make itsuse necessary

Compressive strength at28 days~7 7000 psi (48.3 MPa) minimum

Compressive strength attransfers 4000 psi (27.6 MPa) minimum

Flexural strength at28 days6,7 750 psi (5.2 MPa) minimum

Tendons

Tensile strength 225 ksi (1552 MPa) minimum

Nominal diameter 3/6 in. (9.5 mm) maximum

and surface treatment of prestressing tendon strength. Table 2 lists thesetendons. Tendons should provide compressive strength values. In addi-short transfer lengths to insure ade- tion. concrete flexural strength andquate resistance to bond failure and tendon tensile strength values gener-s-lip. This can be accomplished by ally used for prestressed concrete tieroughening tendons without reducing production are listed in Table 2.the strength below that needed and by Design Criteria—In developing tie

using small diameter tendons.13’14!15 designs, permissible stresses specified

It should be recognized that tie in applicable codes and standards

strength depends on dimensions as should not be exceeded, This gener-

well as on marznitude and location of ally requires an evaluation of concrete

prestressing force, Therefore, atrade-off is required to obtain op-timum dimensions, and amount andlocation of tendons. Fig. 5 illustrates ageneral configuration and ranges ofdimensions for prestressed concreteties.*

Material Properties—Use of highstrength concrete and tendons is re-quired for production of prestressedconcrete ties. Thus, prestress lossesare reduced and resistance to crackingunder service loads is increased,

No nationally acceptable standardor recommended practice has yetbeen developed for material prop-erties. However, material propertiesspecified in the American RailwayEngineering Association’s Manual forRailway Engineering have beenadopted for recent concrete tie pro-curements.5

These recommendations covercompressive strength requirements forconcrete, but do not address theflexural strength of the concrete or

*In Canada, ties with dimensions smaller thanthose shown in Fig. 5 have been used.

stresses for two conditions:1. Immediately after prestress

transfer, and2. At service loads.In estimating concrete stresses im-

mediately after transfer, considerationis given to short-term prestress lossescaused by elastic shortening and otherfactors.

In calculating concrete stresses atservice loads, instantaneous andtime-dependent prestress losses areconsidered. These include lossescaused by the following factors:

1. Slip at anchorages.2. Elastic shortening.3, Creep of concrete.4. Shrinkage of concrete,5. Relaxation of steel.

In addition, steel stresses im-mediately after transfer should not ex-ceed those specified in applicablecodes and standards.

Because a concrete tie is subjectedto tens of millions of load repetitionsduring its service life, developmentof cracks in the tie should beminimized. lz~lc Thus, occurrences of

bond failure and tendon fatigue willbe reduced’7 and long life can beachieved under fatigue loads,

Therefore, a tie design based on theprevention of cracks under normalservice conditions after considerationof concrete fatiguels is required forgood performance and long life,

The American Railway EngineeringAssociation’s Manual for Railway En-gineering states this requirement asfollows:4

In order to give satisfactoryservice a prestressed monoblockconcrete tie should be capableof withstanding without crackingthe maximum loads likely to befound in service,

Rail Fastening Systems

In concrete tie track, the rail fas-tening system has four primary func-tions, It maintains gage and align-ment, restrains longitudinal railmovements, provides resilience, andassures electrical insulation. To pro-vide these functions during their ser-vice life, rail fastenings should be ca-pable of withstanding repeated trafficloads and environmental effects with-out deterioration or damage,

Concrete ties often use threadlessflexible-type fasteners. This fastenertype consists of four components:

1,

2.

3,

4,

Two inserts or fastening shoul-ders cast into the tie duringmanufacture. These inserts pro-vide means for anchoring theclips to the tie.A tie pad placed under the rail toprovide resilience and insula-tion,Two spring clips placed betweenthe inserts and W,e rail to restrainrail movements.Two insulators placed betweeneach clip and the rail to provideelectrical insulation.

Fig. 6a shows the different compo-nents of one type of threadless fas-tening. Fig, 6b shows the assembledfastener. Fig. 6C shows a second typeof threadle ss fasteners,

other designs of threadless, elas-tic-type fasteners utiIize a coating onthe inserts to provide electrical insu-lation, This eliminates the need forinsulators placed between the clipsand the rail. The different componentsof one of these fastening types is

7

Fig, 6 a throughc (above andleft). Threadlessflexible typefasteners withinsulators.

Fig. 7 a throughd (below).Threadlessflexible type

fastenerswithoutinsulators.

shown in Fig, 7a. The assembled fas-tener is shown in Fig, 7b. Two othertypes of threadless fasteners that relyon insert insulation rather than exter-nal insulators are shown in Figs. 7Cand 7d.

Other types of fastening systemsutilize spring clips fastened with boltsthat screw into inserts embedded inthe tie. Fig. 8a shows the componentsof one of these fastening types, Theassembled fastening is shown in Fig.8b.

8

Fig. 8 a and b (above). Fastener with bolts and spring clips.

Another fastening type capable ofproviding vertical and lateral rail ad-justment is shown in Fig, 9, This fas-tening consists of a slotted tie platewith built-in shoulders for springclips. To hold the tie plate in place,anchor bolts screw into inserts em-bedded in the tie, Vertical adjustmentis accomplished by loosening thebolts and inserting wood shims be-tween the tie and the tie plate. Lateraladjustment is accomplished byloosening the bolts and displacing thetie plate,

Ballast Materials

In recent years, field tests wereconducted on several designs of con-crete ties installed on different typesof ballast materials, These tests con-cluded that ballast properties shouldbe considered in the design of thetrack structure, lo

Ballast must provide adequate sup-porting strength and resistance to ver-tical, lateral, and longitudinal loadsimposed on track. It must also provideresilience, stability, and drainagecapabilities. Therefore, ballast mater-ial must perform in track in such amanner that particle degradation, if itoccurs, does not restrict drainage orinduce undesirable changes in basicloading patterns of the ballast section.

There are many physical andchemical properties that determine

qualities of a suitable ballast material.However, the preferred ballast mate-rial should be clean and gradedcrushed stone aggregate andlor pro-cessed slag that provides the follow-ing qualities:

1.

2,

Hard, dense, angular particleswith sharp comers and cubicalfragments to provide good drain-age and particle interlock.High wear and abrasive qualitiesto withstand impacts of trafficloads without excessive degra-dation.

3,

4,

5.

Minimum longitudinal fragmentsto enable better consolidation.High resistance to temperaturechanges and chemical attack,high electrical resistance, andlow absorption.Free of cementing properties.-that will cause small particles tocement together and reducedrainage capabilities, and pro-vide undesirable distribution oftrack loads.

These prime qualities of a ballastmaterial provide the maximum stsbil-

Fig. 9. Fastener with rail adjustment capabilities.

9

Fig. 10. Rail seat lmsitive moment test.

Fig. 11. Tie center negative moment test.

Fig. 12. Bond development test.

10

ity in the ballast section and reducepermanent deformations jn trackstructure and thus assure proper fimc-tioning and performance of concreteties in track,

In addition to the need for a goodquality ballast for concrete tie track,the subgrade should provide adequatestrength and stability. Excess sub-grade moisture contributes to foulingand degradation of ballast, Therefore,provisions should be made for ade-quate subgrade drainage. Also,stabilizing processes may be used tostrengthen poor subgrades,

Laboratory Testing

To assure the ability of ties andfastenings to provide their intendedfunctions, specifications set forthminimum performance requirements.Compliance of ties and fasteningswith specification requirements isevaluated by laboratory tests. Detailsof selected tests are outlined.

Tie Tests

Static and dynamic tests are gener-ally performed to evaluate tie abilityto carry specified bending moments atthe cross sections directly beneath therails and at tie center, Some spec-ifications require that no cracking oc-curs during the tests, while otherspermit cracks of specified length. Re-quired tie tests include the following:

1,

2,

3.

4.

5.

Rail seat moment test to evaluatethe ability of the tie to carry aspecified bending moment at therail seat.~5 Fig, 10 shows a railseat positive moment test.Tie center moment test toevaluate the ability of the tie tocarry a specified bending mo-ment at the center.4~5 Fig. 11shows a tie center negative mo-ment test.Bond development test, shownin Fig, 12, to evaluate the abilityof the tie to withstand over-loading without tendon slip-page.~5Tie center moment and torsiontest, shown in Fig. 13, toevaluate the ability of the tie tocarry a specified combination ofbending moment and torsion attie center,5Repeated load tests to evaluate

the ability of the tie to withstandrepeated loading,~s Figs. 14 and15 show rail seat and tie centerrepeated load tests, respectively.

Faatening Tests

Static and dynamic tests are gener-ally performed to evaluate fasteningperformance under specified loads orin specified environment, Typicalfastening tests include the following:

1.

2.

3.

4.

5.

60

Insert pull- out test, shown inFig, 16, to evaluate the ability offastening inserts to resist pull-outforces without slippage orcracking of the surrounding con-crete,~5Fastening uplift test, shown inFig. 17 to evaluate the ability ofthe fastening system to resistuplift forces without damage offastening components.~5Longitudinal restraint test,shown in Fig, 18, to evaluate theability of the fastening system torestrain longitudinal rail move-ments,~5Lateral restraint test, shown inFig. 19, to evaluate the ability ofthe fastening system to restrainlateral rail movement and to holdproper gage.4Repeated load tesg shown in Fig,20, to evaluate the ability of thefastening system to resist re-peated vertical and lateral loadswithout damage of fasteningcomponents. ~5Electrical test to evaluate theability of the fastening system toprovide electrical insulation,~5

Simulated Track Tests

Assembled track components can beevaluated by laboratory tests, In suchtests, tie support condition and load-ing environment are simulated.

In the test of assembled trackcomponents shown in Fig, 21, twopieces of rail are attached to the tieusing fastening components. The tie issupported on representative ballastand subgrade. A loading cycle, fol-lowing the time versus force relation-ship shown in Fig, 22, is applied. Thisloading simulates the effects of axleand truck spacing as well as car lengthand speed of operation.

Fig. 13, Tie center moment and torsion test,

Fig. 14, Rail seat repeated load test.

Depending on traffic conditions,as much as 12 million gross tons ofsimulated trai%c can be applied in 24hours of test, Thus, each year of ser-vice on a track with a traffic density of30 million gross tons per year, can besimulated in only 2Y2 days of test.

Evaluation of track componentsduring this accelerated test is accom-plished by visual inspection in com-bination with monitoring strains,movements, and pressures.

Field Installationsand Performance

In the last 20 years, several concretetie test sections were built in theUnited States. Early installations indi-cated several problems primarily dueto improper tie and fastening designs.However, installations built in thepast decade featured improved tie andfastening designs,

11

Fig. 16. Insert puii-out teat.

Fig. 15. Tie center repeated load test.

Fig, 17. Fastening upiift test.

Fig. 20. Fastening repeated ioad test.

Fig. 18. Longitudinal restraint teet.

Fig. 19. Laterai restraint test,

Fig, 21. Simuiated track test.

12

These recent test sections per-formed satisfactorily. Ties used in re-cent installations were pretensionedand were manufactured by the long-line method. Some of these installa-tions are described in References 20and 21.

Alaska Railroad Test Section

This test section, shown in Fig. 23,was built in October 1973 on theAlaska Railroad some 100 miles (160km) north of Anchorage, Alaska. Traf-fic on the track is only about 5 milliongross tons annually. However, clima-tic and support conditions are ex-tremely unfavorable. Winter temper-ature reaches – 60 F (– 51 C) and frostheave up to 6 in. (152 mm) occurs.

The 9-ft (2.74 m) long ties used onthe Alaska Railroad were prestressedwith eight, %-in, (9.5 mm) diameter,7-wire strands. Ties were spaced at 26in. (66o mm) center to center and sup-ported on crushed gravel ballast, Arail fastening system that providesvertical and lateral rail adjustments,shown in Fig. 9, was used.

Recent inspection of the test sec-tion22 indicated that the ties haveperformed very well. Cracking at tiecenter and rail seat has not been ob-served, Also, the fastening system hasperformed very well.

Although some pad movement oc-curred shortly after installation, nomovement was detected after fieldwelding of rail joints. The fasteningwas capable of providing trackadjustment needed to accommodatefrost heaving during the wintermonths,

Chessie Test Section

This test section, shown in Fig, 24,was built in March 1974 on the Ches-sie System near Lorraine, Virginia.Traffic on the track is about 40 milliongross tons annually.

Two tie designs were used: a 9-ft(2.74 m) long tie prestressed witheight, %-in. (9.5 mm) diameter, 7-wirestrands and an 8Y2-ft (2.59 m) long tieprestressed with 26, 0.2-in. (5 mm) di-ameter wires. All ties were spaced at26 in. (660 mm) center to center andsupported on crushed stone ballast.Three fastening types, similar to thoseshown in Figs. 6b, 6C and 7d, wereused,

Recent inspection of the test sec-tion22 revealed that the ties have per-

Time

Force

Fig. 22. Loading pattern for simulated track tests.

Fig. 23 Concrete tie track on the Alaska railroad.

Fig. 24 Concrete tie track on the Chessie system.

13

Fig. 26. Concrete tie track on the Norfolk& Western.

formed very well, Also, tie fasteningsystems have performed satisfactorilyexcept for some pad movement. Therecent pad movement appears consid-erably less than that observed shortlyafter installation, Also, skewing ofsome fastening clips appear to be thecause of insulator breakage,

Santa Fe Test SectIon

A test section, shown in Fig. 25, wasbuilt in November 1974 on the SantaFe mainline track near Streator, 11-

linois, Traffic on the track is about 20million gross tons annually.

Two tie designs were used: a 9-ft(2.74 m) long tie prestressed witheight %-in. (9.5 mm) diameter, 7-wirestrands and an 8V2-ft (2.59 m) long tieprestressed with 28, 0,2-in. (5 mm) di-ameter wires. All ties were spaced at24 in. (610 mm) center to center andsupported on crushed granite ballast.Three fastening types, similar to thoseshown in Figs. 6b, 6c, and 7C wereused.

Recent inspection of the test sec-tionzz indicated that the ties haveperformed very well and no load-in-duced cracking has been observed.Also, all fastening types have per-formed satisfactorily. Pad movementand clip skewing observed shortlyafler ins@dlation have stabilized, Nofurther pad movement has occurredand no extremely skewed clips or bro-ken insulators were found.

Norfolk & Western Test Section

The test section shown in Fig. 26was built in December 1974 on theNorfolk and Western at Kumis nearRoanoke, Virginia. Traffic on the trackis about 45 million gross tons annu-ally.

Two tie designs were used: a 9-ft(2.74 m) long tie prestressed witheight, %-in, (9,5 mm) diameter, 7-wirestrands and an 8V2-fl (2.59 m) long tieprestressed with 28, 0,2-in. (5 mm) di-ameter wires, Ties were spaced at 24and 26 in, (610 and 660 mm) center tocenter and supported on crushed gra-nite ballast, one fastening type, simi-lar to that shown in Fig, 6b, was used,

Recent inspection of the test sec-tion22 indicated that the ties haveperformed very well. Also, fasteningsperformed well. No appreciable paddisplacement has occurred. However,some broken insulators were found.

Faclllty for AcceleratedSewIce Testing

Operation on the Facility for Accel-erated Service Testing (FAST) of theU.S. Department of Transportation atPueblo, Colorado, started in Sep-tember 1976 at a rate of approximately1.0 million gross tons per day, Esti-mated tonnage by the end of 1978 is350 million gross tons. The facility in-cludes about 6000 ft (1829 m) of con-crete tie track as shown in Fig. 27,Ties are located in tangent and on 3-and 5-degree curves.

Six designs of prestressed concreteties were used: five 8%-ft (2.59 m)long and one 9-ft (2,74 m) long, Allties were spaced at 24 in. (610 mm)center to center and supported ongranite ballast. Four fastening &pes,similar to those shown in Figs. 6b, 7b,7d, and 8, were used,

Recent inspection of the test sec-tionzz indicated that all ties have per-formed well. Also, all fastening types

14

have performed well in both the tan-gent track and the 3-degree curve.However, breakage of a number offastening clips was observed in the5-degree curve.

Advantages ofConcrete Ties

Concrete ties have been in use inEurope for over 30 years. More re-cently, Japan, Canada, and the UnitedStates installed concrete ties in sev-eral projects, This extensive experi-ence has demonstrated many of theadvantages of concrete ties,

These advantages have been re-ported in a recent study,2s and includethe following:

1.

!2.

3,

4.

5.

6.

7.

8.

It

Concrete tie track provides bet-ter vertical and lateral stiffnessthan wood tie track, due to thegreater mass of concrete ties andthe more rigid fastening system.

Concrete tie track settles moreuniformly than wood tie track,thus providing a smoother, saferride and greater comfort for pas-sengers.

Concrete tie track maintainsalignment and gage for a longerperiod than wood tie track.

Concrete ties retain gage betteron curves than do wood ties withconventional fasteners,

The chances of a derailment areless on a concrete tie track due tothe more stable track system.

Concrete ties have an estimatedservice life twice as long as thatof wood ties.

Concrete tie track has fewer ir-regularities than wood tie track,thus requiring less maintenanceand providing better ride stabil-ity,Concrete tie track has a lowerlife-cycle cost than wood tietrack.

should be recognized that thegreater weight of con~rete ties makesit more difficult to handle during in-stallation and replacement operations.However, with use of modern andsuitable mechanical equipment, han-dling of concrete ties is no more dif-ficult than wood ties.

Fig. 27. Concrete tie track on the Facility for Accelerated Service Testing.

In addition, greater weight contrib-utes to greater track stability and in-creased safety, Fig. 28 shows a trackrenewal machine used for installing aconcrete tie track on Amtrak’s North-east Corridor Improvement Program.

Generally, concrete ties are moreexpensive to buy than wood ties.However, because of the rigidim andlarger dimensions of concrete tiesthey are generally placed at a largerspacing than wood ties, Furthermore,concrete ties are more effective than

wood ties in limiting gage wideningand alignment changes. Therefore,maintenance requirements for con-crete ties are less than those for woodtie track, Because of these factors,life-cycle costs for concrete tie trackare often less than for wood tietrack, XVM

These features indicate that con-crete ties are not only more economi-cal than wood ties; they also providesuperior operating characteristics.These features were important factors

15

in the recent decisions by the Cana-dian National Railway to proceed witha 5-year concrete tie program involv-ing 1,5 million ties,zs and by the Na-tional Railroad Passenger Corporation(Amtrak) to procure 1.1 million con-crete ties for the Northeast CorridorImprovement Program.zd

Concluding Remarks

There is growing interest in the useof monoblock prestressed concreteties, This is justified by the consis-tency in product quality, low annual

1. Weber, J. W., “Concrete Crossties inthe United States,” PCI JOURNAL, V.14, No. 1, February 1969, pp. 46-61.

2. Madhava R., Parameswaren, V. S., andAbdul Karim, E., “Prestressed Con-crete Monoblock Sleepers, ” IndianConcreteJournal, August 1978, p. 321.

3. “FEC’s New Main-Track Design:Concrete Ties, Welded Rail,” RailwayTrack and Structures, July 1966, p. 25.

4. “Concrete Ties (and Fastenings),” Palt10, Chapter 3-Ties and Wood Pres-ervation, Manual for Railway En-gineering, American Railway En-gineering Association, March 22,1978.

5. Concrete Tie Technical Provisions,Attachment to a Request for TechnicalProposals, National Railroad PassengerCorporation (Amtrak), August 1977 andamendments of October andNovember 1977.

6. Hanna, A. N., Preliminary Spec-ifications for Standard Concrete Tiesand Fastenings for Transit Track, Re-port No, UMTA-MA-06-0100-79 -3,prepared for the U.S. Department ofTransportation, March 1979.

7. Contract Specifications Book—TrackFastening Procurement, Mass TransitAdministration, Baltimore RegionRapid Transit System, November 16,1978.

8. Sikka, N. K., and Singh, S. F., “SomeAspects of Design of Monoblock Pre-stressed Concrete Sleepers, ” Pro-ceedings, International Symposium onPrestressed Concrete Pipes, Poles,Pressure Vessels, and Sleepers, V. 2,Paper SL2, Madras, India, February14-16, 1972,

9. “Stresses in the Rails, the Ballast andin the Formation Resulting from Traf-fic Loads,” Office for Research and

cost, and superior performance. It isestimated that 15 million prestressedconcrete ties are produced annuallyfor railroads all over the world. Pre-tensioned concrete ties account for 12million ties per year.

General methods of tie fabrication,material requirements, and designconsiderations are presented, Re-quirements for rail fastening systemsand ballast materials are outlined.Methods of laboratory testing of tiesand fastenings, and field installationand performance of concrete tie trackin the United States are presented.Finally, advantages of concrete tiesare summarized.

REFERENCESExperiments of the InternationalUnion of Railways, Question D-71,Stresses in Rails, Report No. 1, Ut-recht, Netherlands, April 1965.

10. Hanna, A. N., Railway Track Zle-search—Theoretical and Experimen-tal, (RD030.oIR), Portland CementAssociation, 1975,

11. “Plain and Reinforced Concrete Mem-bers,” Part 2, Chapter 8—ConcreteStructures and Foundations, Manual

for Railway Engineering, AmericanRailway Engineering Association,March 22,1978.

12. Eisenmann, J., The Concrete Tie,Betonstein-Zeitung, June 1965, p. 345.

13. Hanson, N. W., and Kaar, P, H.,“Flexural Bond Tests of PretensionedPrestressed Beams,” ACI Journal, V.55, January 1959, p. 783. Also BulletinD28, Portland Cement Association,Skokie, Illinois.

14. Kaar, P, H., LaFraugh, R. W., andMass, M. A., “Influence of ConcreteStrength on Strand Transfer Length,”PCI JOURNAL, V. 8, No, 5, October1963, pp. 47-67, Also Bulletin D71,Portland Cement Association, Skokie,Illinois.

15. Kaar, P. H., and’Hanson, N. W., “BondFatigue Tests of Beams SimulatingPretensioned Concrete Crossties,” PCIJOURNAL, V. 20, No. 5, September-October 1975, pp. 65-80. Also BulletinRD042.OIR, Portland Cement Assoc+ation, Skokie, Illinois.

16. Ager, J. W, A., “Prestressed ConcreteRailway Sleepers,” Proceedings, Sym-posium on Mass-Produced PrestressedPrecast Elements, Madrid, Spain, June1968, p. 81,

17. Rabbat, B. G., Kaar, P. H., Russell, H.G., and Bruce, Jr., R, N,, “Fatigue

Experience to date indicates thatthe prestressed concrete tie has out-grown the experimental stage and be-come an important constituent of themodern railway track structure, This isevidenced by the extensive use ofprestressed concrete ties in othercountries and recent procurements bythe Canadian National Railway andthe National Railroad Passenger Cor-poration.

Basic features and design parame-ters of concrete ties appear to be es-tablished. However, some refine-rqents may be desired to obtain op-timum and economic track systems atspecific locations,

Tests of Pretensioned Girders withBlanketed and Draped Strands,” PCIJOURNAL, V, 24, No. 4, July-August1979, pp. 88-114.

18. “Fatigue Life of Prestressed ConcreteBeams,” Bulletin No, 19, The Rein-forced Concrete Research Council,American Society of Civil Engineers.

19. Lynch, J, K., “Factors Which Affect theStability, Testing Selection and Per-formance of Suitable Aggregates forRailroad Ballast,” AREA Bulletin 668,June-July 1978, p. 368.

20. “Concrete Ties: In Four Test Installa-tions, They Have Performed VeryWell,” Railway Age, August 9, 1976, p,28.

21. “Concrete Ties: Tests Still On, JuryStill Out,” Railwag Age, August 14,1978, p, 34.

22. Weber, J. W., “Service Tests of the“New’’&oncrete Ties,” Railway Trackand Structures, August 1978, p. 20.

23. Northeast Corridor ImprovementProject-Concrete Tie Cost and Per-formance For Track Structures, Re-port No, FRA-NECPO-77-2 by De-Leuw, Cather/Parsons, Federal Rail-road Administration, october 1977.

24. White, D, W., Arnlund, R. C. andPrause, R, H,, Economics of Con-crete-and Wood-Tie Track Struc-tures, Report No. FRA/ORD-78/2 pre-pared for the U.S. Department ofTransportation, August 1978,

25. “CN Goes for Concrete-Tie Track,”Progressive Railroading, November1976, p. 47.

26. “Concrete Ties for Northeast CorridonRationale Behind DOT Decision,”Railway Track and Structures, Sep-tember 1977, p. 42,

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mPORTLAND CEMENT I I ASSOCIATIONAn organizaticm of cement manufacturers to improve and extend the uses of portland cement and concrete through scientific research, engineering field work, and market development.

5420 Old Orchard Road, Skokie, Illinois 60077

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