Recommended Practicefor

Precast Post-TensionedSegmental Construction

Reported by

Joint PCI-PTI Committee on Segmental Construction

WALTER PODOLNY, JR.(Chairman)

MAHMOUD Z. ARAFATTHOMAS J. D'ARCYC. S. GLOYDH. HUBERT JANSSENT. ROBERT KEALEYHEINZ P. KORETZKYRICHARD M. McCLUREVILAS MUJUMDARCARL A. PETERSON

PETER REINHARDTFRED ROBINSONCHARLES SLAVISMARIO G. SUAREZDAVE SWANSONMAN-CHUNG TANGY. C. YANGPAUL ZIAZENON A. ZIELINSKI

14

SynopsisThis Joint PCI-PTI committee report presents

basic recommendations for the design andconstruction of precast post-tensioned concretestructures which are composed of individualsegments that are connected by the use ofpost-tensioning. The recommendations cover thefabrication, transportation, and erection of theprecast component segments, details of theconstruction of joints, tendons and anchors, anddesign considerations applicable to segmentalconstruction.

It should be emphasized that this report ispublished as a guide on segmental construction andshould not be considered a specification. The reportcontained herein is an update of the report entitled"Recommended Practice for SegmentalConstruction in Prestressed Concrete," published inthe March-April 1975 PCI JOURNAL.

PCI JOURNALlJanuary- February 1982 15

CONTENTSChapter 1 Introduction .................................. 181.1 General

1.2 Historical Background1.3 Limitations of this Recommended Practice1.4 Scope1.5 Definitions

Chapter 2 — Examples of Segmental Construction .......... 192.1 General2.2 Airport Control Tower2.3 Liquid Natural Gas Storage Tanks2.4 28-Story Office Building2.5 Cement Clinker Silo2.6 Floating Vessel for Storage of Liquified Petroleum Gas2.7 Five Points Station, MARTA Rapid Transit, Atlanta, Georgia2.8 Precast Segmental Bridge Construction

2.8.1 Balanced Cantilever2.8.2 Span-by-Span2.8.3 Progressive Placing2.8.4 Incremental Launching

Chapter 3 — Fabrication of Precast Segments ............... 363.1 General Considerations3.2 Methods of Casting

3.2.1 The Long-Line Method3.2.2 The Short-Line Method

3.3 Formwork3.3.1 General3.3.2 Provisions for Tendons3.3.3 Provisions for Supplemental Reinforcement3.3.4 Tolerances

3.4 Concrete3.5 Joint Surfaces

3.5.1 Quality3.5.2 Holes for Tendons and Couplers

3.6 Bearing Areas

Chapter 4 — Transportation, Storage and ErectionofPrecast Segments ........................... 44

4.1 General4.2 Plant Handling and Transportation4.3 Erection Methods

16

4.3.1 Cranes4.3.2 Winch and Beam4.3.3 Launching Girder

4.4 Erection Considerations4.5 Erection Tolerances

Chapter5 -- Joints ........................................ 485.1 General5.2 Cast-in-Place Joints5.3 Dry-Packed Joints5.4 Grouted Joints5.5 Match Cast Joints

5.5.1 Epoxy Bonded Joints5.5.1.1 Selection of Epoxy5.5.1.2 Application of Epoxy

5.5.2 Dry Joints5.6 Metal Joints

Chapter 6— Post -Tensioning Tendons ..................... 536.1 Sheathing6.2 Tendon Couplers6.3 Anchor Plates

6.3.1 Anchor Plates Cast into Precast Segments6.3.2 Anchor Plates Placed against Precast Surface

6.4 Tendon Layout6.5 Placement and Stressing of Tendons6.6 Grouting6.7 External Tendons

Chapter 7 — Design Considerations ........................ 577.1 General7.2 Force Redistribution7.3 Handling and Storage of Segments7.4 Joint Design

7,4.1 Shear7.4.2 Keys7.4.3 Compression

7.5 Auxiliary Reinforcement7.6 Design of Segments for Box Girder Bridges7.7 Design of Segments for Decked I-Beams

References ............................................... 60

PCI JOURNAUJanuary- February 1982 17

CHAPTER 1 -- INTRODUCTION1.1 General

Precast post-tensioned segmentalconstruction is defined as a methodof construction for bridges, build-ings, tanks, silos, cooling towers,tunnels and other structures inwhich primary load carrying mem-bers are composed of precast con-crete segments post-tensioned to-gether.

1.2 Historical BackgroundThe concept of dividing precast

concrete structural members intosmaller segments and connectingthem with stressed rods or barsdates back as far as 1888 to 1907and early ideas about prestressedconcrete by Dohring, Mandl, Lundand others.'

Five bridges designed in Europeof a segmental precast girder typewere constructed between 1946and 1950. These girders were pre-stressed longitudinally, verticallyand transversely. The 240-ft (73 m)spans were flat two-hinged portalframe structures with adjustablehinged bearings to compensate forshortening due to shrinkage andcreep of concrete. 42 In 1951, asmall number of bridge girders inthe United States were built of pre-cast concrete blocks. These blockswere strung onto prestressing ca-bles, joints of the net section weremortared, harped tendons werepost-tensioned, and tendons weregrouted.s In the United States in1952 a single span girder bridgewas constructed by dividing eachgirder into three precast segments.After curing, the segments were re-assembled at the site with coldjoints and post-tensioned.4

Thirty-two major bridges outsideof North America were reviewed(in 1971) in a state-of=the-art paperabout segmental bridges." Thesebridges were built between theyears 1960 and 1969. Many designparameters resulted in variations inspan, number of segment cells,span-depth ratios, segment lengths,joints, types, and erection methods.Six more bridges in various coun-tries were reviewed in anotherstate-of-the-art paper published in1975.°

In North America well over 50box girder bridges of segmentalconstruction have either been builtor are under construction. In 1977 acable-stayed precast post-tensionedsegmental bridge was completed."

The Portland Cement AssociationIibrary has two annotated bibliog-raphies,9' 10 available for review,which list 195 articles on segmentaland cantilever cast-in-place bridgeconstruction between 1962 and1975.

Although the term segmental hasmost often been applied to bridgeconstruction the concept of usingsegmental construction has beensuccessfully utilized in many proj-ects other than bridges. For exam-ple: the Mutual Life Building inNorth Carolina; Gulf Life Tower inJacksonville, Florida; the FivePoints Station — MARTA RapidTransit, Atlanta, Georgia; the Velo-drome and Olympic Stadiumstructures in Montreal, Canada; andnumerous buildings using shellsand roof girders.","

Chapter 2 presents examples ofthe varied use of precast post-tensioned segmental construction.

18

1.3 Limitations of thisRecommended Practice

This report is a recommendedpractice on segmental construction,not a building code or specification.It is presented as a guide to the de-sign and construction of structuresusing segmental elements to insuresafety and serviceability. En-gineering judgment must beapplied to these recommendations.

1.4 ScopeThese recommendations are in-

tended to cover those conditionswhich affect segmentally con-structed members differently fromnon-segmentally constructed mem-bers. They consider the fabrication,transportation, and erection of theprecast component segments, theconstruction of joints, tendons andanchors, and design considerationsapplicable to segmental construc-tion.

1.5 DefinitionsAdhesive —A bonding material

used in joints.Anchorage — The means by

which the prestressing force istransmitted from the prestressing

steel to the concrete.Coating —Material used to pro-

tect the prestressing steel againstcorrosion and/or provide lubrica-tion.

Couplers — Hardware to transmitthe prestressing force from onepartial length prestressing tendonto another.

Grout —A mixture of cement,and water with or without admix-tures. (In some instances sand isused as a filler).

Joint — The region of the struc-ture between interfaces of precastsegments with or without adhesiveor grouting materials and with orwithout reinforcement.

Prestressing Steel —The part of apost-tensioning tendon which iselongated and anchored to providethe necessary permanent pre-stressing force.

Segment — A precast elementmade out of concrete, with or with-out reinforcement, prestressed ornon-prestressed.

Sheathing or Duct — Enclosurearound the prestressing steel.

Tendon — The complete assem-bly for post-tensioning, consistingof anchorages, couplers, and pre-stressing steel with sheathing.

CHAPTER 2- EXAMPLES OF SEGMENTALCONSTRUCTION

2.1 GeneralMany structures have been de-

signed and built using some varia-tion of the concept of segmentalconstruction. The following exam-ples are only a small portion ofthose built. These were recentlyreported in technical journals.

2.2 Airport Control TowerIn 1973 a 180-ft (54.86 m) high

airport control tower' 3 consisting offour service cores was segmentallyconstructed using box segmentsapproximately 10 ft (3 m) square inplan and 7' ft (2.3 m) high. Thefour cores are topped by a 16-ft

PCI JOURNAIJJanuary-February 1982 19

!1I ilFig. 1(a). Airport control tower. Structuralsteel platforms were set at 15-ft (4.57 m)intervals to connect the four service cores.

Fig. 1(b). Erection of precast boxsegments. Note that the modules werestacked to 180-ft (54.9 m) height.

VERTICALPOST -TEN SIONIN

PRECASTCOREELEMENT

DRY PACKEDJOINT

SHIM S

Fig. 2. Isometric view of stacked boxsegments. Sketch shows the majorcomponents of segment.Fig. 1(c). Setting of box segments.

ce

Fig. 3. Erection of precast panel for liquid natural gas storage tank.

(4.88 m) high steel cab housing thecontrol tower observation deck andfacilities. Vertical post-tensioningwas used to stabilize the core seg-ments during construction and pro-vide moment and shear capacity toresist service loads. Fig. 1 showsthe tower during construction. Fig.2 is an isometric view of thestacked and post-tensioned boxsegments.

2.3 Liquid Natural GasStorage Tanks

In 1974 in the United States, two900,000 bb] liquid natural gas stor-age tanks 14 were completed using 8x 60 ft (2.44 x 18.3 m) high precastwall panels. After completion oferection of the panels the structurewas post-tensioned circumferen-tially. The tanks are composed oftwo concentric walls, the outer wall

PCI JOURNAL/January-February 1982 21

Fig. 4a. Plan of liquid natural gas tank.

having a radius of 134 ft (40.8 m)and being 13 ft (4 m) beyond theinner wall. Three feet (0.9 m) of in-sulating material is placed in theannular space beside the innerwall. Mass concrete fills the other10 ft (3 m) providing resistance toexternal impact forces. Fig. 4a is aplan view showing the segmentsplaced side by side. Fig. 4b shows asection of the double wall and thecircumferential post-tensioning.

Figs. 4c and 4d show the tanks invarious stages of construction.

Fig. 4c. Precast panel being readied intoposition on tank wall. Note connecting

dowels on side of panel.

22

20'- 10 12" TO SUPPORTS

3/B"PL ROOFING

TRUSS POCKET

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MI PRECAST _~z WALL m m

SEGMENTS _'

- a

3.-0" SHOTCRETE

Fig. 4b. Section of double wall with post-tensioned precast wall segments.

Fig. 4d. Overall view of LNG tanks during construction.

PCI JOURNAUJanuary-February 1982 23

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Fig. 5. Plan view of 28-story office building.

2.4 28-Story Office BuildingIn 1974, a 28-story office build-

ing15 used a segmentally con-structed Vierendeel truss as theexterior support for the edges offloors. Truss segments were block-Ishaped, 17 ft (5.2 m) high, 10 ft (3m) wide at top and bottom andweighed a maximum of 9 tons (8.2t) each. The block-I's were erectedside by side at the site and the top

and bottom chords of the truss werepost-tensioned horizontally. Theends of the truss were then an-chored into large cast-in-place col-umns. Fig, 5 is a plan view showingthe location of the trusses and col-umns. Fig. 6 is an elevation of asegmental Vierendeel truss. Fur-ther design and erection details ofthis building can be found in theNov.-Dec. 1975 PCI JOURNAL."

24

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Fig. 6. Elevation of Vierendeel truss.

T ^' ^— LOADING R5 / G,11 \ `CONVEYOR

= FLOW 1

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LEGEND

P I - RADIAL TIE BEAM AND R I - RING BEAM NO. IANCHORAGE BLOCK R 2 - RING BEAM N0. 2

P 2 - SLANTED V- COLUMNR 3 - RING BEAM N0. 3

P3 - LOWER CONE ELEMENTR 4 - RING BEAM NO. 4P4 -WALL PANEL

P5 - CONICAL ROOF ELEMENT R 5 - RING BEAM NO. 5

Fig. 7. Cross section of cement clinker silo showing location of main precast concretecomponents.

2.5 Cement Clinker SiloA cement clinker storage silo'6

was built in 1975. It has a diameterof 214 ft (65.2 m), a height of 130 ft(39.6 m) above ground, and a depthof 79 ft (24.1 m) below grade. Threebasic elements were composed ofprecast concrete: (a) a conical shell

roof, (b) a segmental cylindricalwall which contained two levels ofpost-tensioned rings, and (c) an in-verted cone bottom, two-thirds ofwhich was below grade. Fig. 7 is across section of the silo showing itsvarious components. Fig. 8 showsthe individual precast components.

26

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IO'8"

DETAIL P5DETAIL P4

CONICAL ROOFWALL PANEL

Io.8u ELEMENT

Fig. 8. Dimensional details of major precast concrete components.

PC[ JOURNALJanuary-February 1982 27

a. Match Castings of Shell Segments

e. Placing Hull Tanks

b. Setting of Shells in Graving Dock

I. In-place Casting of "D" Platesand Deck

c. tn-place Casting of Longitudinal Bulkheads,Saddles and Transverse Bulkheads

g. Placing Deck Tanks and FinalOutfittingd. Launching Stage

Fig. 9. Construction sequence used for liquified petroleum gas storage vessel.

2.6 Floating Vessel forStorage of LiquifiedPetroleum Gas

In 1977, a prestressed concretefloating vessel" for liquified pe-troleum gas was completed. Thehull dimensions were 461 ft (140.5m) long by 136 ft (41.5 m) wide.The hull bottom is in the shape ofthree cylindrical barrel shells. Eachbarrel consisted of precast curvedsegmental shells approximately 11ft (3.4 m) long, 45 ft (13.7 m) wide

and a rise of 11 ft (3.4 m). Theseshells were match cast and post-tensioned longitudinally. Addi-tional cast-in-place bulkheads, sad-dles, stiffeners and decks resultedin the hull functioning as a multi-cell box girder and providing spaceand support for twelve 400-ton (363t) steel tanks. Fig, 9 shows the con-struction sequence. Figs. 10, 11,and 12 are photographs of a hullsegment being cast, delivered anderected.

28

Fig. 10. Match-casting, precast concrete bottom shell segments.

Fig. 11. Graving dock and delivery of 40-ton bottom hull segment.

PCI JOURNAUJanuary-February 1982 29

Fig. 13. Five Points Station, Atlanta Rapid Transit System, Atlanta, Georgia.

2.7 Five Points Station,MARTA Rapid Transit,Atlanta, Georgia

The massive roof structure forthis $42 million transit station (seeFig. 13) is made up entirely of pre-cast components (some 450 in all)except for the reinforced concretecolumns. In plan the roof is 167 ft(50.9 m) wide and 262 ft (79.86 m)long. It rises almost 50 ft (15.2 m)above the at-grade plaza level. Themajor elements of the roof structureare nine longitudinal beams 262 ft(79.86 m) long and eleven trans-verse beams, 167 ft (50.9 m) long.These beams are composed of up to20 precast segments, 13 ft (4 m)long, 10 ft 8 in. (3.15 m) high and 2ft 6 in. (0.76 m) wide. The mainbeams are match-cast constructionglued together with epoxy. The

heaviest precast pieces, weighingup to 23 tons (20.9 t) apiece, arethose that make tip the main beams.

2.8 Precast Segmental BridgeConstruction

In precast segmental bridge con-struction, short segments are cast ina plant or near the job site underfactory simulated conditions, butalways at some location other thantheir final position in the structure,and then assembled in place. Pre-cast segmental bridges may be clas-sified by their method of construc-tion.

Generally, the method of con-struction can be divided into fourtypes:' 8 ' 1$ (1) balanced cantilever,(2) span-by-span, (3) progressiveplacing, and (4) incrementallaunching or push-out construction.

30

2.8.1 Balanced CantileverIn this method segments are can-

tilevered from a pier in a balancedfashion on each side until midspanis reached and a closure pour ismade with a previous half-spancantilever from the preceding pieras shown in Fig. 14. This procedureis then repeated until the structureis completed.

Each segment added is immedi-ately post-tensioned to the alreadycompleted portion of the structure.Care must be exercised to maintaincompression over the entire jointarea by means of temporary or per-manent post-tensioning until allof the permanent tendons arestressed. The magnitude of stresses,segment alignment, and elevationsmust be evaluated at all stages ofconstruction.

The advantages of cantilever con-struction are minimal interference

with the environment, traffic flow isnot obstructed below, small laborforce required, and speed of erec-tion.

An interesting concept in bal-anced cantilever segmental con-struction is its incorporation withcable-stayed bridges. This concepthas been used in the United Statesfor the Pasco-Kennewick Bridge s-sin the State of Washington asshown in Fig. 15.2.8.2 Span-by-Span

This type of construction starts atone end of the structure and pro-ceeds continuously to the other endof the structure, span-by-span, asopposed to the balanced cantileverwhere construction starts at thepiers and symmetrically moves outfrom the piers. In this type of con-struction segments are supportedduring construction by a moveablefalsework. The Long Key Bridge in

Fig. 14. Balanced cantilever construction employing a launching girder at theSallingsund Bridge. Denmark.

PCI JOURNALJJanuary-February 1982 31

Fig. 15. Precast segments For balanced cantilever construction of the Pasco-KennewickBridge in Washington State.

Florida [see Fig. 16(a)] uses astructural steel trusswork soffitmounted on adjacent piers, whichis moved by a barge-mounted cranefrom span to span.20,2'

The segments could be assem-bled in final position on falsework(or fill), they could be assembled onthe ground and lifted into place, orthey could be assembled on false-work parallel to the final locationand pushed laterally into place.The segments could also be par-tially assembled on the ground,lifted onto falsework, and the as-sembly completed on the false-work. An experimental bridge con-structed at the Pennsylvania Trans-portation Research Facility 1 ' waserected on non-movable falseworkas shown in Fig. 16(b).2.8.3 Progressive Placing

Progressive placing is similar to

the span-by-span method describedabove in that construction starts atone end of the structure and pro-ceeds continuously to the other endof the structure. The progressiveplacing method is based on the bal-anced cantilever concept. In thismethod, the precast segments areplaced continuously from one endof the structure to the other in suc-cessive cantilevers on the sameside of the various piers, rather thanby balanced cantilevers on eachside of the pier.

Because of the length of can-tilever (one span) in relation to con-struction depth, the erectionstresses become prohibitive andtemporary supports such as cablestays or pier bents are usually re-quired. The erection procedureutilizing temporary stays is illus-trated in Fig. 17. The first few seg-

32

Fig. 16(a). Span-by-span technique using movable steel truss (Long Key Bridge).

Fig. 16(b). Span-by-span technique using falsework at Pennsylvania TransportationResearch Facility.

ments placed near the pier may beplaced in a cantilever fashion untilthe stresses become excessive. Atthis point temporary stays (or someother temporary support) are re-

quired to control the cantileverstress.

This method can be used to ad-vantage where site conditions pro-hibit the use of the span-by-span

PCI JOURNAl.JJanuary-February 1982 33

Fig. 17. Schematic of progressive placing technique (from Reference 4).

method. Where access to pier loca-tions is precluded, this method canbe used to transport equipment andmaterials for pier construction fromabove, over that portion of thecompleted structure. This methodis of interest for applications in the100 to 160-ft (30.5 to 48.8 m) spanranges.2.8.4 Incremental Launching

Another variant of the segmentalconcept has evolved in Europe. Inthe United States, it is referred to asincremental launching or push-outconstruction. The first increment-

ally launched segmental bridgeconstructed in the United States,carries two lanes of U.S. 136 overthe Wabash River near Covington,Indiana. It is a six-span structurewith end spans of 93 ft 6 in. (28.5m) and four interior spans of 187 ft(57 n).22,23

In this type of construction seg-ments of the bridge superstructureare positioned to the rear of theabutment and post-tensioned to-gether. The assembly of units islaunched stepwise forward one unitat a time to allow for succeeding

34

Fig. 18. Schematic of incremental launchingsequence (Courtesy of F. Leonhardt).

units to be positioned to the rear ofthe abutment.

Bridge alignment in this type ofconstruction may be either straightor on a curve; however, the curvemust be a constant radius curve,vertically and/or horizontally.

Longitudinal prestressing con-sists of two families of tendons:tendons concentrically placed andtensioned before launching, andtendons placed and tensioned afterlaunching, that is, negative momenttendons over the supports and pos-itive moment tendons in the bottomof the section in the central portionof the span.

Hydraulic jacks are used to pro-gressively launch successive con-centrically prestressed units in a

longitudinal direction as shown inFig. 18. To allow the superstructureto move forward, special slidingbearings are provided. To reducethe large negative bending mo-ments that the structure would besubjected to during launching, afabricated structural steel launchingnose is attached to the lead seg-ment. Long spans are subdividedby means of temporary piers tokeep negative moments at an ac-ceptable level.

Complete coordination of all op-erations is essential to prevent theoccurrence of a "runaway struc-ture," unexpected twist, or exces-sive displacement of the structurewhile on or between temporary orfinal supports.

PCI JOURNAL/January-February 1982 35

CHAPTER 3- FABRICATION OF PRECASTSEGMENTS

3.1 General ConsiderationsIt is generally preferable to use

as few units as possible, consistentwith economic shipping and erec-tion. During design of a segmentalstructure, consideration should begiven to the selection of cross sec-tions which simplify formwork,lead to production efficiency, andoverall project economy.

In the case of girder segments,economy and speed of productionmay be increased by:

(a) Keeping the length of thesegments equal and keeping themstraight, even for curved structures.

(b) Proportioning the segmentsor parts of them, such as keys, insuch a way that easy stripping ofthe forms is possible.

(c) Maintaining a constant webthickness in the longitudinal direc-tion.

(d) Maintaining a constant thick-ness of the top flange in the lon-gitudinal direction.

(e) Keeping the dimensions ofthe fillet between webs and the topflange constant.

(f} In case of variable depth,keeping webs vertical to avoid avariable bottom flange width.

(g) Avoiding interruptions of thesurfaces of webs and flanges causedby protruding parts for anchorages,inserts, etc.

(h) Using a repetitive pattern, ifpractical, for tendon and anchoragelocations.

(i) Minimizing the number ofdiaphragms and stiffeners.

(j) Avoiding dowels which passthrough the forms, when possible.

Because of economic consid-erations the variation of the crosssection of girder segments is gener-ally limited to changing the depthand the thickness of the bottomflange. Curves in the vertical andhorizontal direction and superele-vation of the structure can be easilyaccommodated.

If a segment is damaged beyondrepair in transportation or erection,a new segment should be cast. It ispreferable to match-cast it againstone or both of the mates but, if notpossible, a tolerance provisionshould be made for erecting thenew segment which will not ad-versely affect the geometry oraesthetics of the completed struc-ture. If damage occurs to the jointarea during transporting or erec-tion, the segment may be erected atthe discretion of the Engineer.Generally, this will be allowedwhen the damage is to a small areaand the damage is patched aftererection. This precludes destroyingthe fit of the match-cast surfaces.The location of the damage and itseffect on the segment's strength andserviceability should be consideredin the Engineer's decision.

Evaluation of segments havingmanufacturing defects should rec-ognize that many of the segments ina segmental bridge may have ex-cess capacity since concrete dimen-sions are kept constant for stan-dardization purposes and control-ling sections may be located else-where in the structure. Bottom slaband web dimensions, for example,are usually critical only in the sup-

36

port area. Honeycombing of ele-ments outside this area, provided itis suitably repaired, need not because for rejection.

3.2 Methods of CastingSegments to he erected with

wide joints may be cast separately.Match-cast joint members are castby the "long-line" or "short-line"method.3.2.1 The Long-Line Method

Principle — All of the segmentsare cast, in correct relative position,on a long line. One or more form-work units move along this line.The formwork units are guided by apre-adjusted soffit. An example ofthis method is shown in Figs. 19a to19c. For further practical details ofthe long-line fabrication methodsee Reference 24.

Advantages — A long line is easyto set up and to maintain controlover the production of the seg-ments. After stripping the forms itis not necessary to take away thesegments immediately.

Disadvantages — Substantialspace may he required for the longline. The minimum length is nor-mally slightly more than half thelength of the longest span of thestructure. It should be constructedon a firm foundation which will notsettle or deflect under the weight ofthe segments. Because the formsare mobile, equipment for casting,curing, etc., has to move from placeto place. In case the structure iscurved, the long line must be de-signed to accommodate the curva-ture. This, however, increases thecomplexity of the form and themore appropriate method to pro-duce curved bridges is by theshort-line method.

3.2.2 The Short-Line MethodPrinciple —The segments are

cast at the same place in stationaryforms and against a neighboringelement. After casting, the neigh-boring element is taken away andthe last element shifted to the placeof the neighboring element, clear-ing the space to cast the next ele-ment. A horizontal casting opera-tion is illustrated in Figs. 20athrough 20c. Segments intended tobe used horizontally may also becast vertically.

Advantages — The space neededfor the short-line method is small incomparison to the long-linemethod, approximately three timesthe Iength of a segment. The entireprocess is centralized. Horizontaland vertical curves and twisting ofthe structure are economically ob-tained by adjusting the position ofthe neighboring segment.

Disadvantages — To obtain thedesired structural configurationvery precise workmanship, qualitycontrol procedures, and geometrycontrol are required. The neigh-boring segments must be accuratelypositioned for each match-casting.

3.3 Formwork3.3.1 General

All forms should be carefully de-signed and it is highly recom-mended that forms be designed byEngineers with experience in thesegmental method and the proce-dure, as well as form design.Formwork should be designed tosafely support all loads that mightbe applied without undesired de-formations or settlements. Soil sta-bilization of the foundations may berequired, or the formwork may bedesigned so that adjustments can be

PCI JOURNAL1January-February 1982 37

Formwork

Fig. 19(a). Cross section of formwork using long-line method.

outside Formwork

Inside Formwork

ELEVATION

PLAN

Fig. 19(b). Formwork at start of casting (long-line method).

QQ

ELEVATION

n

Hil _PLAN

Fig. 19(c). Formwork after casting several segments (long-line method).

38

AFTER STRIPPING DURING CASTING

r INSIDEFORMWORK

CARRIAGE

TURN BU

Fig. 20(a). Formwork for short-line method. !t should be designed to facilitateinspection.

Fig. 20(b). Formwork just before separation of segments (short-line method).

Fig. 20(c), Formwork just before casting next segment (short-line method).

age

PCI J0URNALlJanuary-February 1982 39

Fig. 21. Form used to construct I-shaped girder segments. (Note: Planeof deck may be varied with respect to web of I-beam).

made to compensate for settlement.Since production of segments is

based on multiple reuse of forms,the formwork should be sturdy andspecial attention should be given toconstruction details. Forms shouldalso be easy to strip and handle. Anexample of a form used to construct1-shaped girder segments is shownin Fig. 21.

Cement paste Ieakage throughformwork joints should be pre-vented. This can normally beachieved by using a flexible sealingmaterial. Special attention shouldbe given to the junction of tendonsheathing with the forms.

The forms may need to be flex-ible in order to accommodate slightdifferences of dimensions with thepreviously cast segment. Theyshould be designed in such a man-ner that the necessary adjustmentsfor the desired camber, curvatureand twisting can be achieved accu-rately and easily.

Special consideration should be

given to those parts of the formsthat have to change in dimensions.To facilitate alignment or adjust-ment, special equipment, such asscrew or hydraulic jacks, should beprovided.

Attachments to the form such asanchorages, sheathing, blockoutsand inserts should be designed insuch a way that their position isrigid during casting. Fittings shouldnot interfere with stripping of theforms.

Accelerated curing may causetemperature gradients in the con-crete which may be harmful to thesegments especially in the coolingphase. Cantilever flanges and otherthin elements cool faster thanheavier parts of the section andcracking of elements has occurreddue to this phenomenon. Thisshould be guarded against by closecontrol of the heating and coolingprocess.

When using accelerated curing itis furthermore advisable to cure the

40

segment being cast together withthe segment it was cast against. Thisprevents temperature deformationsof the hardened segment duringcuring of the new segment whichmay lead to open joints upon erec-tion.

Internal vibration is commonlyused. If the form is designed forexternal vibrators they should beattached at locations that willachieve optimum consolidation andpermit easy replacement during thecasting operations. To break thesuction during stripping, air jetsmay be employed if required.3.3.2 Provisions for Tendons

Holes for prestressing tendonsmay be formed by:

(a) Sheathing which remains afterhardening of the concrete. Flexiblesheathing made of spirally woundmetal may be stiffened from the in-side by means of inflatable rubberduct tubes during the casting oper-ation.

(b) Rigid sheathing with smoothor corrugated walls may be usedthat will not deform excessivelyunder the pressure of vibrating theplastic concrete. Sheathing shouldbe carefully aligned and tied atclose intervals to avoid displace-ment.

Holes should be accurately po-sitioned, particularly when a largenumber of holes are required.Often, sheathing with tendons inplace require no stiffening. Furtherinformation on forming holes fortendons and tendon anchorages ispresented in Chapter 6.3.3.3 Provisions for SupplementalReinforcement

Supplemental mild steel rein-forcement is used to resist forcesnot provided for by prestressing.

Chapter 7 lists the requirementsfor supplemental reinforcement.

3.3.4 TolerancesTolerances as specified by appli-

cable codes of practice can gener-ally be used for segmental con-struction, It should be borne inmind, however, that tolerances ondimensions which directly influ-ence alignment or shape of theerected segmental structure requireparticular attention. Formwork forsegmental box girder bridge con-struction that meet the tolerancesshown in Table 1 (see next page)are normally considered accept-able.

Depending upon the detail atbridge piers, the tolerances for thesoffit of the pier segment may needspecial attention. The actual di-mensions of a segment should bedetermined immediately after re-moving the forms. If specified tol-erances are exceeded, acceptanceor rejection should be based on theeffect on final alignment and onwhether the effect can be correctedin later segments.

3.4 ConcreteUniform quality of concrete is es-

sential for segmental construction.Procedures for obtaining highquality concrete are covered inACI,25 PCI,E8 and PCA27 publica-tions.

Both normal weight and struc-tural lightweight concrete can bemade consistent and uniform withproper mix proportioning and pro-duction controls, Normally concretefor segmental construction willhave a slump of'3 to 5 in. (76 to 127mm) and 28-day strength greaterthan the strength specified bystructural design. It is recom-

PCI JOURNALJJanuary-February 1982 41

Table 1. Formwork tolerances for segmental box girder bridgeconstruction. (To correlate tolerances, see sketches on next page.)

Webthickness ...................................... ±Y4 in. (6.4 mm)Depth of bottom slab ........................ ±'1a to 0 in. (6.4 to 0 mm)Depth of top slab .....................................± % in. (3.2 mm)Overall depth of segment .............. ±rlax in.lft (2.6 mm/m), of depth,±' in. max, (12.5 mm)Overall top slab width .......+'/s2 in./ft (2.6 mm/m), ± 1 in. max. (25 mm)Length of match-cast segment (not cumulative) ................±¼ injft(10.4 mm/m), + 1 in. max. (25 mm)Diaphragmthickness .................................+ N in. (6.4 mm)Grade of form edge and soffit ...............± Yls in. in 10 ft (0.5 mm/n)Tendon hole location in bulkhead ................... ± '4 in. (1.6 mm)Positionof shear keys ................................ ±'/a in. (3.2 mm)Vertical plumbness ..................................±Vss in. (0.8 mm)End squareness ......................................'/ss in. (0.8 mm)

Finished segment tolerances should not exceed the following:Web thickness ...................................... ±% in. (9.5 mm)Depthof hottom slab ........................+ r to 0 in. (12.7 to 0 mm)Depthof top slab ............................... .....±'/4 in. (6,3 mm)Overall top slab width .......± %a in./ft (5.2 mm/m), ± I in. max. (25 mm)Diaphragm thickness ................................+ % in. (12.5 mm)Grade of form edge and soffit ................± ys in. in 10 ft (1.0 mm/m)Tendon hole location ............................... . ±% in. (3.2 mm)Positionof shear keys ................................ ±' in. (6.3 mm)Vertical plumbness ................................. ±ha in. (1.6 mm)Endsquareness .................................... ± Ii s in. (1.6 nun)

mended that statistical methods beused to evaluate concrete mixes.

The methods and proceduresused to obtain the characteristics ofconcrete required by the designmay vary somewhat depending onwhether the segments are cast inthe field or in a plant. The resultswill be affected by curing temper-ature and type of curing. Liquid orsteam curing or electric heat curingmay be used.

A sufficient number of trial mixesshould be made to assure uniform-ity of strength and modulus ofelas-ticity. Careful selection of aggre-gates, cement, admixtures andwater will improve strength andmodulus of elasticity and will alsoreduce shrinkage and creep. Soft

aggregates and poor sands shouldbe avoided. Creep and shrinkagedata for concrete mixes should beavailable or should be determinedby tests.

It is dangerous to use corrosiveadmixtures such as calcium chlor-ide or those containing substantialchlorides, nitrates, sulphates andfluorides. Water-reducing admix-tures and also air-entraining ad-mixtures which improve concreteresistance to environmental effects,such as deicing salts and freeze andthaw actions, are highly desirable,However, their use should be rig-idly controlled in order not to in-crease undesirable variations instrength and modulus of elasticityof the concrete.

42

/DVERALL TOP SLAB WIDTHIENDON HOLE

7DUCTS

0 0 0 0 o Q 0000000

° o 0o DEPTH OF WEB KEY TOP SLAB

OVERALL DEPTH WEB OF SEGMENT

SS 90, THIC N SS

0 0 __ o 0SQUARENESS —"— DEPTH OF(MEAS. ON GRADE OF BOTTOM SLABDIAGONALS) FORM EDGE

WIDTH OF WEB

SEGMENTAL BOX GIRDER

POSITION OF POSITION OFSHEAR KEYS --- - -SHEAR -- i SHEAR KEYS

^+-DIAPHRAGM t I

WEB KEY I I THICKNESS I--------4-4-------

GRADE OF SOFFIT —4— VERTICALPLUM RNESS

LONGITUDINAL SECTION

Isometric view and longitudinal section of box girder showingtolerances designated in Table 1.

Mixes should be designed tominimize creep and shrinkage. Re-liable data on the potential of themix in terms of strength gain andcreep and shrinkage performanceshould be used as a basis for im-proved design parameters.

Proper vibration should be usedto afford use of lowest slump con-crete and to allow for the optimumconsolidation of the concrete.

Consideration should be given todelaying erection of segments untiltheir internal moisture is reduced

to a level that subsequent dryingwill not produce unexpected de-formations.

3.5 Joint SurfacesRequirements concerning surface

condition should be stricter formatch-cast joints than for widejoints filled with mortar or concrete.3.5.1 Quality

Best results in match-casting areachieved if the joint surfaces areeven and smooth. Surface crushingor chipping off of edges during

PCI JOURNALJanuary-February 1982 43

post-tensioning caused by pointcontact are thus avoided.

Chamfers at match-cast joints arenot recommended since they aredifficult to manufacture and de-crease the joint contact area consid-erably. In case chamfers are con-sidered desirable, as may be ex-pected in buildings or specialstructures with exposed "architec-tural" surfaces, the effect of thearea reduction should be duly in-vestigated. For wide joints, roughsurfaces are preferable as they pro-duce better bond between segmentand filling material.3.5.2 Holes for Tendons andCouplers

holes or sheathing for tendonsshould be located very precisely

when producing segments joinedby post-tensioning. Care is requiredto prevent leakage or penetrationof joint-filling materials into theduct so as to prevent blocking thepassage of the tendons,

3.6 Bearing AreasBearing areas at reactions should

be smooth and in frill contact to as-sure uniform distribution of bearingforces. If possible, in view of man-ufacturing and erection tolerances,it may be desirable to place bearingelements like pads or steel plates inthe forms before casting. Other-wise, cement mortar or an epoxymortar may be required betweenthe segment and bearing area to en-sure full contact.

CHAPTER 4— TRANSPORTATION, STORAGE ANDERECTION OF PRECAST ELEMENTS

4.1 GeneralDue to the interdependence

which exists between design, fabri-cation, and erection, close coordi-nation is required and is of majorimportance. The design concept, byspecifying member size, generallydictates the choice of transportationmethods. Erection methods mayalso be dictated by the design con-cept.

4.2 Plant Handling andTransportation

Segments should he handledcarefully, without impact, in amanner that limits stresses to val-ues compatible with the strengthand age of the concrete. Location oflifting hooks and inserts should be

determined carefully to preventdamage of segments during han-dling. Lifting hooks or insertsshould have an adequate safetyfactor, a minimum of 4.0 on han-dling loads plus 50 percent impactis suggested. Transportation overuneven surfaces may produce staticand dynamic stresses which need tobe considered, especially at anearly age of a segment. Special careshould be exercised during han-dling and transportation to protectcantilevers or projections againstdamage or cracking.

Plant handling and transportationgreatly influence the constructioncost. The way the segment is trans-ported from the casting yard into itsfinal position, the site conditions,

44

Fig. 22, Winch and beam erection method.

segment weight and number of re-handlings are major parameters in-fluencing costs.

Since it is essential to preventdeformation of the segments causedby uneven settlement, especiallytwisting, storage should be onsound supports. Segments shouldnot be unnecessarily exposed touneven shrinkage caused by mois-ture loss due to excessive wind orpartial sunlight exposure. Storage ofsegments should be arranged tominimize damage, deflection, twist,and discoloration of the segments.Stacking should be limited to avoidexcessive direct or eccentric forces.

Stacking may induce deformationsin the segment which may"lock-in" because of creep and ad-ditional strength gain of segmentconcrete while in storage.

Inserts, anchorages, and otherembedded items may need to beprotected from corrosion, and frompenetration of water or snow duringcold weather. Contact surfaces tobe bonded with epoxy should bekept free of contaminants.

Scheduling of segments is veryimportant; fabrication, transporta-tion, and erection schedules shouldbe coordinated so that at least thenext matching segment is delivered

PCI JOURNAUJanuary-February 1982 45

to the job site before the previoussegment is erected.

Transportation may be by truck,rail, or barge or a combination ofsuch modes. Modification of trans-portation vehicles or equipmentmay be dictated by size and weightof the segment. Local hauling reg-ulations may limit width, length,height, and weight of segments fortransportation over highways with-out special permits.

4.3 Erection MethodsErection is commonly accom-

plished by truck, crawler, or bargemounted cranes; winch and hoist;launching girder; or at times, byspecially designed equipment cus-tom made for the project.

Several parameters will influencethe method of erection. The sizeand weight of the unit will deter-mine, or be determined by, theerection equipment available. Theheight of the structure above exist-ing terrain, or navigation clearance,will determine if the units can beerected by truck, crawler, or bargemounted cranes. In some cases,precast units may be Iifted up froma barge or truck by a winch andhoist located on the pier or com-pleted portion of the structure. Ifthe height of the structure is suchthat truck or barge cranes are notpractical or if the structure is a longviaduct, a movable launching girderor a movable falsework may henecessary and economically justifi-able.

4.3.1 CranesMobile cranes moving on land or

floating on barges may be used

where access is easily available.Portal cranes straddling or attachedto the decks have also been used.Cranes can be used with balancedcantilever, span-by-span, and pro-gressive placing types of con-structiou.4.3.2 Winch and Beam

The winch and beam (see Fig.22) is a lifting device that extendsover the completed portion of thebridge deck on a short cantileveredmechanism anchored to the bridgedeck. From this position, a segmentis lifted and held in place untilpost-tensioning can occur. Afterpost-tensioning, the winch andbeam is moved onto the newlyadded segment and the process isrepeated.

Precast column segments may beplaced on the column with thesame basic equipment cantileveredtemporarily out from a tower at-tached to the completed portion ofthe column. The winch and beam iscommonly used with balanced can-tilever and progressive placingtypes of construction.4.3.3 Launching Girder

The launching girder (see Fig.14) is a special mechanism thattravels along the completed deckspans and maintains the work flowat that level. The essential parts ofthe launching girder are a maintruss with a length somewhatgreater than the maximum bridgespan, three leg frames which areattached to the main truss, and atrolley which travels along thebottom chord of the girder and iscapable of moving the segment inthe longitudinal, transverse, andvertical directions, During con-struction, by assuming various po-sitions, the girder can place seg-

46

0

c = Real slope change

e = Theoretical slope change

I4-el 3%

Fig. 23. Longitudinal slope change tolerance.

ments in cantilever, place segmentsover piers, and can move to thenext span so that the constructionprocess can be repeated. This is thefastest method of cantilever con-struction, but it is limited to largeprojects because of the high initialcost of the launching girder,

4.4 Erection ConsiderationsSegments should be stabilized

and braced to resist constructionloads, impact, wind loads, acciden-tal forces, etc. Segments must befree from restraint during post-ten-sioning.

Depending on the type ofconstruction/erection methodsutilized, changes in post-tensioningforces may affect various conditionswhich should be considered in de-sign. These may be the redistribu-tion of forces at supports, stabilitydue to prestressing, effect of reac-tions (shear) at temporary supportsor the additional loads imposed byheavy handling, lifting equipmentor devices.

The shortening of the segmentsand jointing material due to previ-

ous post-tensioning, temperatureeffects, settlement or other loadingconditions should be investigatedbefore final post-tensioning of thestructure.

4.5 Erection TolerancesThe erection tolerances dis-

cussed below apply principally tosegmental box girder bridges.

Maximum deviation betweenoutside faces of adjacent segmentsin the erected position should notexceed 1/a in. (6 mm). Longitudi-nally, the angular deviation fromthe theoretical slope change be-tween two successive segments isrecommended not to exceed 0.3percent as shown in Fig. 23. Trans-versely, the angular deviation fromthe theoretical slope differencebetween two successive segmentjoints is recommended not to ex-ceed 0.1 percent as shown in Fig.24.

The most important item of toler-ance or acceptance is the finaloverall geometry of the erectedsuperstructure. The elevation of thedeck surface in the completedstructure should not vary substan-

PCI JOURNAWanuary-February 1982 47

W

w = Real slope difference

= Theoretical difference

Fig. 24. Transverse slope differencetolerance.

tially from the theoretical profilegrade elevation. In cantilever builtstructures the final elevation is ob-tained only after completion of theclosure sections between succes-sive cantilevers, subsequent post-tensioning, and after all creep andshrinkage have taken place.

For bridge decks more liberaltolerances may he accepted if the

design incorporates a wearing sur-face andlor separately cast trafficbarriers or edge beams which per-mit a smoothing out of smalI align-ment and elevation errors. For thisreason, it is recommended thattraffic barriers and edge beams becast separately (they may be cast inplace or precast) and not precastwith the segments.s

In case correction in the align-ment is required, adjustmentsshould be acceptable to the En-gineer. Stainless steel wire meshllia in. (1.6 mm) thick with mesh di-mensions of in. (3.2 mm) embed-ded in the epoxy joint have beenused for this purpose. Insertion of 8x 12-in. (200 x 300 mm) shims ofthis kind brings about a small an-gular change. However, undesira-ble stress concentrations should beguarded against. Solid steel platesare, for this reason, less suitable. Ifa larger joint is required, the seg-ments should be held in place untilan adequate cast-in-place joint isconstructed.

CHAPTER 5- JOINTS5.1 General

Joints separate the structure intoa number of segments. It is gener-ally preferable to use as few seg-ments as possible consistent withtransportation and erection eco-nomics. The joint surface is usuallyoriented approximately perpen-dicular to the centroidal axis of thestructure.

The capacity of a joint is a func-tion of the prestressing force nor-mal to the joint and development offriction on the joint face. ThisChapter discusses the joint types. A

further discussion of design consid-erations for joints is presented inChapter 7.

joints are either wide or match-cast. Wide joints may be cast inplace with concrete, dry packedwith mortar, or grouted. Match-castjoints are normally bonded withepoxy but dry joints have beenused in special instances. For alltypes of joints the surfaces must beclean, free from grease, oil or othercontaminates. Where epoxy bond-ing is to be used the joint surfacesshould be lightly sandhlasted while

48

maintaining the match-cast fit.Post-tensioning tendons crossing

joints should be approximately per-pendicular to the joint surface inthe direction of the smaller dimen-sion of the segment element con-cerned, i.e., flange or web thick-ness; but may be inclined in the di-rection of the larger dimension, i.e.,flange width or web depth. This isto minimize any unbalancedshearing force which could lead todislocation of edge zones at joints.

Holes for the passage of tendonsmust be located very precisely.Particular care is required to com-pletely seal tendon ducts at jointsin order to prevent penetration ofjoint filling material into the duct,thereby blocking passage of ten-dons, and also to prevent unsightlyleakage at joints during grouting.

5.2 Cast-In-Place JointsIn the case of cast in place or

other types of wide joints, prior toconstruction of the joint, the adja-cent concrete surfaces should beroughened and kept thoroughlywet, or a bonding agent approvedby the Engineer may be applied.

The design width of a joint mustallow access for coupling of con-duits, welding or lapping of rein-forcement, and thorough compac-tion of concrete. Typical jointwidths are equal to the deck slabthickness or one-half of the webwidth, but not less than 4 in. (100mm).

The compressive strength of thejoint concrete at a specified ageshould be equal to the strength ofthe concrete in the adjacent precastsegments. High early strengthportland cement may be used.Aggregate size should he selected

to ensure maximum compaction.Serration of the joint is recom-mended.

The height of each concreteplacement or lift must be limited sothat the concrete can be properlyconsolidated. Ports are normallyprovided in the joint form for in-spection. Formwork should besealed to prevent leakage of paste.Cast-in-place joints should be ade-quately cured.

The sharpness of line of assem-bled segments with wide joints de-pends mainly on the accuracy of themanufacturing of the joints duringerection and less on the accuracy ofthe segments. Curvature andtwisting of the structure may occurwithin the joints from the post-tensioning unless proper care istaken to prevent it.

5.3 Dry-Packed JointsThe width of dry-packed joints

should not exceed approximately2' in. (65 mm). Mortar should beintroduced into the joint in batchesnot exceeding 10 lbs (4.5 kg) byweight. Each batch should bethoroughly tamped and packed be-fore the next batch is placed. Mor-tar should be rammed into placeusing a heavy hammer and ram, or apneumatic tamper. Containmentformwork may be necessary, par-ticularly at the bottom of the joint.

The strength of the mortar in thejoint may be lower than that of theconcrete in the adjacent segmentsand this factor may be a critical de-sign consideration for the structure.The use of special high strengthmortars may have to be considered.The mortar should have a compres-sive strength of at least 4000 psi(281 kglcm2 ) measured on cubes in

PCI JOURNAL)January-February 1982 49

accordance with ASTM C-109. 2 Ifan expansive additive is used theU.S. Army Corp. of EngineersSpecification CRD-588 30 may beused. Mortar should be thoroughlymixed and have zero slump.Maximum aggregate size normallydoes not exceed is in. (5 mm).

5.4 Grouted JointsThe width of grouted joints

should not exceed approximately Iin. (25 mm). Grouted joints may bemade with either gravity or pres-sure methods. In either case provi-sions should be made to contain thegrout.

When gravity grouting is used,rodding or tamping should be usedto consolidate the grout. Problemsmay be encountered with gravitymethods, particularly on horizontaljoints. For this reason the groutshould consist of approximatelythree parts of cement, one part ofclean sand passing a #16 meshscreen, and a water-reducing agentwhich minimizes sedimentation.The total water content should bekept as low as practical. Shrinkagecompensating additives should beconsidered.

Pressure grouting of joints re-quires adequate preparations andequipment that is in good and cleancondition. The joint should betightly sealed in order to sustain thepressure. Pressure grouting is par-ticularly effective when joint formscan be easily used. Joint formsshould be vented. At the conclusionof the grouting operation, the ventshould be closed, and the pressureincreased a minimum of 15 psi (1kg/cros ) at the vent. Twenty-fourhours after grouting, the ventshould he opened and filled if

sedimentation has occurred.In both grouting methods venting

is of extreme importance. Horizon-tal joints should be vented at thehighest points and at several pointson each side. The vents shouldhave provisions for closure whichcan withstand grout pressure. Thestrength of the grout in the jointmay be lower than that of the con-crete in adjacent segments and thisfactor may be a critical design con-sideration for the structure. Thecompressive strength of the grout ata specified age should be at least4000 psi (281 kglcml) measured oncubes in accordance with ASTMC-109.2& If an expansive additive isused the U.S. Army Corp. of En-gineers Specification CRD-5883°may be used. Non-metallic groutmixes should he used when thegrout will be exposed to weather.

5.5 Match-Cast Joints5.5.1 Epoxy Bonded Joints

Epoxy resins used for bonding ofmatch-cast joints are high qualityproducts having compressive, ten-sile, bond, and shear strengthsequal or superior to concrete.These products are subject to strictspecifications and laboratory cer-tification of their chemical, physi-cal and mechanical properties.Manufacturers' recommendationsfor successful application in thefield should be strictly adhered to.

The three major purposes ofepoxies used in match-cast jointsare:1. Epoxy serves as an erection aid.

A. The epoxy, while in its gelform, serves as a lubricant betweensegments during the fitting process.

B. The epoxy serves as a mediumfor filling up unwanted voids and

50

surface flaws on the jointing sur-faces.2. Epoxy improves the durability cifmatch-cast joints.

A. Complete filling of the jointprovides weather tightness.3. Epoxy improves the structuralperformance of match-cast joints.

Since the tensile strength ofepoxy itself and the bond strengthbetween epoxy and concrete can beequal or superior to the tensilestrength of concrete, the use of asuitable epoxy restores "the tensilestrength of concrete" at the match-cast joints. The significance of thisis:

A. The use of epoxy increases theoverload at which the joint opensand makes the magnitude of thisequal to the load required forcracking the sections surroundingthe joints. Crack developmentunder overloading tends to besimilar to that in a monolithicstructure. This also improves thetightness of the closure of suchcracks upon removal of the load.

B. The joints are subjected tosecondary effects which make com-plete restoration of tensile strengthdesirable. For example, tempera-ture gradients in top slabs of boxgirder bridges can cause consider-able tensile stresses. Also, the dis-tribution of bending moments inthe top slab caused by wheel loadsis more effective across moment-resisting joints. It is evident thatjoints without epoxy do not havemoment capacity unless there issubstantial compression normal tothe joint face. Such compression isusually not provided in negativemoment areas of box girders de-signed for zero tension under fullloading. For a further discussion of

joints see Section 7.4.Bridge model tests and other

structural tests having epoxiedjoints with large keys have beentested up to failure and were foundto perform excellently. Breen statedthat "Epoxied joints did not induceany discernable weakness of thistype of construction. "31

If this high-performance epoxy isnot provided, the joint or key willbe a plane of weakness in thestructure. The durability, capacityto sustain overloads, and momentcapacity of the individual slabs atthe joints are affected, and must heattended to by using alternativemethods.5.5.1.1 Selection of Epoxy

The compressive strength of theepoxy should equal that of the con-crete in adjacent segments underany environmental condition thatmay be encountered during the lifeof the structure.

Only highly cross-linked epoxyadhesives that have beenthoroughly tested in accordancewith current ASTM32 and applica-ble industry standards should beused. Information which should heobtained from the manufacturer, orbe determined by test, must in-clude as a minimum:

(a) Workability, pot life and"open time" at various tempera-ture s.

(b) Compressive strength andmodulus of elasticity at varioustemperatures after curing for atleast 7 days at 68 F (20 C).

(c) Direct shear strength ofbonded concrete prisms at varioustemperatures, with notation ofwhether failure occurs in the jointor in the concrete.

(d) Ability to bond in such a way

PCI JOURNAUJanuary-February 1982 51

that the tensile strength of the con-crete is fully restored.

(e) Creep behavior of the epoxycompound.5.5.1.2 Application of Epoxy

The adhesive should be suppliedin preweighed packs or cans ofresin and hardener component.Resin and hardener should havedifferent colors.

Components of the epoxy mixshould be proportioned and mixedthoroughly until a uniform color isobtained, following the instructionsof the manufacturer. Each batchshould be assigned a number. Theadhesive should be applied im-mediately after mixing, and thejoint surfaces brought together be-fore the pot life expires. A record ofthe location of the joint where thebatch of epoxy is used, weather,temperature, and observed pot lifeshould be maintained. Tests shouldbe conducted to verify uniformityof mixing in the field.

The concrete surfaces which areto be bonded should not be wet; adamp but not dark, shiny surface ispermissible. A wet concrete surfacemay be dried with hot air prior toapplying the adhesive.

The adhesive should be appliedin a uniform thickness to both sur-faces. Some post-tensioning shouldbe applied within the "open time"of the adhesive. If the correctamount of adhesive has been used,a little will extrude from the jointwhen pressure is applied. It is rec-ommended that a minimum of 30psi (2 kglcm 2 ) be applied to thejoint. After the stressing has beencompleted, a wiper should bepushed into each open tendon ductor sheathing to remove or even outany epoxy that may have entered

the duct, and to seal any pocketsthat form at the joint.

In the case of unforseen inter-ruptions, the "open time" may haveexpired before the segments arefully joined. In such an event theepoxy should be completely re-moved according to the instructionsof the manufacturer. Sandblastingmay be necessary. Particular atten-tion to the manufacturer's recom-mendations and AASHT0 93 is re-quired in cold weather.5.5.2 Dry Joints

The requirements for the use ofdry joints are similar to those forepoxy bonded joints but with aneven greater emphasis on the qual-ity of the matching faces. Surfacesshould be carefully checked to en-sure that any high points or otherprojections are eliminated.

Care should be taken duringerection of segments to ensure thatjoints are completely closed beforeapplying the final prestress.

In bridge construction specialtreatment is required at the decklevel to seal the joints against pen-etration of moisture. In cold cli-mates where de-icing salts are usedspecial care should be taken to pre-vent salt penetration through thejoints into the tendon ducts. Forthis reason the use of dry joints isnot recommended where corrosiveenvironments exist or where bridgedecks are salted.

5.6 Metal JointsMating pairs of steel plates which

are joined by welding, or similarsuitable steel connections havebeen used. However, they shouldbe considered more as connectionsthan as typical joints between pre-cast elements in segmental struc-

52

tures. Special attention is requiredfor welded joints to prevent crack-ing or spalling of the concrete.Protection against corrosion should

be applied to prevent staining ofadjacent surfaces and to protect theintegrity of welds and contact sur-faces.

CHAPTER 6- POST TENSIONING TENDONS

6.1 SheathingSheathing is used to form the

holes or enclose the space in whichthe prestressing steel is located. Itis usually located inside the con-crete section; however, in somecases it has been located outsidethe section.

The prestressing steel can beplaced with the sheathing, or in-stalled after the concrete is placed.The cross section of the sheathingshould be adequate to allow properinstallation of the prestressing steeland to provide enough passage areafor filling the sheathing with groutsubsequent to stressing, The ratioof the net area of the prestressingsteel to sheathing cross-sectionalarea should comply with the GuideSpecification for Post-TensioningMaterials in Reference 34. For longten do , [more than 100 ft (30 m)linserttci into the sheathing after theconcrete is placed, it is recom-mended that slightly oversizedsheathing be used to facilitate in-stallation of tendons. (Note that thesheathing size given in Reference34 is considered a minimum.)

Sheathing should have sufficientgrouting inlets, vent pipes for es-cape of air, shut-off valves, anddrains to allow proper grouting andto avoid accumulation of waterduring construction in freezing cli-mates. For continuous structures,

ducts exceeding 400 ft (122 m) inlength should be vented over eachintermediate support, and at suchlocations as shown on the plans.Intermediate vents may not be re-quired for ducts less than 400 ft(122 m) in length.35

Sheathing placed inside the con-crete should be resistant to damagecaused during installation andplacing of the concrete and the in-stallation of pull-through tendons.If the sheathing wall has inade-quate strength to resist such dam-ages, it may be protected by in-serting inflatable duct tubes, steelpipe, etc. during the placement ofconcrete. The sheathing should beadequate to prevent leakage of con-crete into the void, and should besecured against buoyancy.

When semi-rigid sheaths areused, they should bend sufficientlyto follow the required tendon pro-file. All sheaths should be tiedeither to the reinforcing bar cage orto special supports. Semi-rigidsheathing of 23/4 in. (70 mm) diam-eter or larger should be tied at amaximum of 5-ft (1.5 m) intervals.Smaller diameter or flexiblesheathing should be tied more fre-quently to minimize wobble.

In certain applications, thesheathing is arranged outside theconcrete section either in voids ofthe section or along the outside of

PCI JQURNALJanuary-February 1982 53

the concrete cross section. In addi-tion to the requirements listedabove, all sheathing should beprotected against corrosion or madeof non-corrosive material such aspolyethylene.

Sharp curvature and/or changesof angle should be avoided andsheathing splices should he tightlyapplied and fastened to facilitatethe threading of tendons throughthe sheathing.

Sheathing may be connected atthe joints by:

(a) In the case of match-cast seg-ments, joining the two matchingsurfaces with the epoxy filler willestablish the connection and con-tinuity of the sheathing void.

(b) Telescopic sleeves pushedover the protruding ducts.

(c) Screw-on type sleeves.(d) Rubber or plastic sleeves.(e) Gaskets.In all cases, leak tightness should

be assured to avoid the entrance ofjointing materials into the sheath-ing, causing possible blockage.Sheathing protruding from the sur-face is easily damaged, and must berepaired prior to making the con-nection. Post-tensioning ductsshould be swabbed or wiped to en-sure the removal or smoothing outany epoxy that might have leakedinto the duct.

6.2 Tendon CouplersCouplers should be designed to

develop the ultimate strength of thetendons they connect. Adjacent tothe coupler, the tendon should bestraight for a minimum length of 12times the diameter of the couplerunless the curvature is very minoror the strength of the system is de-termined by tests. Adequate provi-

sions should be made to assure thatcouplers can move during prestress-ing. Large coupler void areasshould be deducted from gross sec-tion areas when computing stressesat the time of prestressing. Enclo-sures around the couplers must beprovided with a vent pipe.

6.3 Anchor PlatesThe anchor plate is the compo-

nent of a post-tensioning systemwhich transmits the prestressingforce from the tendon anchoringdevice directly to the concrete. Itsfunction is to distribute the con-centrated forces from the anchoringdevice over a larger bearing area tothe concrete. The bearing surfaceshould be perpendicular to the pre-stressing steel to prevent undesira-ble secondary stresses of the pre-stressing steel and to optimize theeffectiveness of the anchors. Theanchor plate should be of suchshape and dimensions as to limitthe bearing stresses to thosespecified in the Post-TensioningManual, 34 the AASHTO BridgeSpecifications, 33 or other applicablecodes. Mild steel reinforcementbehind the anchor plates should bedetailed to resist bursting stresses.6.3.1 Anchor Plates Cast intoPrecast Segments

This is the most commonly usedprocedure. The concrete should bethoroughly vibrated behind thebearing plate to avoid honeycomb-ing and to achieve proper strength.However, over-vibration may causesegregation of concrete.6.3.2 Anchor Plates Placed AgainstPrecast Surface

When the bearing plate is placedagainst the hardened surface of theprecast element, dry-packed mortar

54

or another suitable material shouldbe used between the plate and theconcrete to achieve a good degreeof stress distribution under thebearing plate. The strength of themortar or other material should notbe less than the concrete strengthon which it bears, and the thicknessof the joint should he limited to amaximum oft in. (50 mm).

The reinforcement of the con-crete underneath the dry-packedmortar or other material should bethe same as if the plate was castinto the precast segment.

The preparation of the surfaceunder the bearing plate will de-pend on the type of plate andplacing procedure used.

When the bearing plate is notcast into the concrete, the surfaceshould be clean and free fromforeign matter. The surface shouldbe wire brushed to remove all la-tents and loose concrete chips. Ifthe hearing plate is to be grouted,proper bond should be assured.

6.4 Tendon LayoutAttention should be given to the

tendon layout to make it compatiblewith:

(a) Sequence of the segmentalconstruction.

(b) Progressive and subsequentload conditions which the segmen-tal structure will undergo whilebeing erected,

(c)Concrete placement.(d) Effective section used in de-

sign.It is important to anticipate the

secondary effects (stresses due torestrained deformations) whichpost-tensioning may have on thestructure, and how these effects canbe influenced by changes in the

tendon profile. The effects of con-crete creep and changes of thestatical system during constructionshould be considered.

Anchorages, couplers and splicesof post-tensioning tendons shouldpreferably not be located in areaswhere yielding may occur underultimate load conditions.

6.5 Placement and Stressingof Tendons

When tendons are installed in thesegments before casting, they areusually coupled together at eachjoint. This construction methodpermits stressing of part of a ten-don, after installing one or moresegments, before the full length iscompletely installed.

Tendons may also be installedafter casting and erection in paritallengths and coupled together atspecial openings. Usually, how-ever, these tendons are installedfull length. It may be noted, thatthis coupling procedure permitsintermediate stressing of portions ofthe structure, by using tendons ofvariable lengths, stressing the shortones first and long ones later. Theprestressing steel should be free ofdetrimental rust when installed intothe structure. Special attentionshould be given to the temporarycorrosion protection of the pre-stressing steel until grouted.

6.6 GroutingThe purpose of grouting is to

provide corrosion protection to theprestressing steel, and to developbond between the prestressingsteel and the surrounding concrete.To accomplish this, the groutshould fill all the voids in andaround the post-tensioning tendon

PCI JOURNAL/January-February 1982 55

for its entire length. Grouting mate-rials, preparation of grout, andgrouting procedures should followthe Recommended Practice forGrouting of Post-Tensioned Pre-stressed Concrete 36 wherever ap-plicable.

Grouting of tendons should becompleted as soon as practical aftertensioning of the tendons. It is rec-ommended that all tendons whichare in the same group be groutedwithin a short period of time. Groutcrossing over from one duct intoanother, which sometimes occurs ata joint, will be easier to detect andremedy if all tendons in the groupare grouted in a short interval oftime.

As a consequence of this prac-tice, some time may elapse be-tween stressing and grouting ofthe first tendon in such a group. Ifthe period of time that a tendon isleft ungrouted exceeds 20 days,37 atemporary corrosion protectionsystem for the tendon should beemployed.

Grouting is preferably done fromthe lowest points of the tendon, to-ward the higher points, where ventpipes should be installed. Thegrouting should be done slowly andat low pressure to insure full dis-placement of the air. Highlypressurized and rapid grouting maycreate entrapped air. The tendonmay be flushed with water beforegrouting to avoid blockage wheninjecting the grout. Sufficientpurging of grout should be allowedto demonstrate that the exitinggrout has the same consistency as

the grout pumped into the sheath-ing.

Grouting should not be done ifthe temperature in the duct is lessthan 35 F (2 C) or if the surround-ing concrete temperature is lessthan 32 F (0 C).

When grouting vertical tendonsthe potential of segregation of thegrout is greater than with horizontaltendons. To minimize sedimenta-tion and to avoid dehydration andconsequent blockage of grout andpossible joint leaks, the groutshould have the property of in-hibiting water separation whenunder pressure. Additives for thispurpose may be used with approvalof the Engineer.

Precautions should be taken toreduce the danger of blockage ofgrout due to the couplers. Couplersare generally housed in a special,enlarged encasement, whichshould:

(a) Have the same open crosssectional area for passage of groutas the rest of the tendon.

(b) Be provided with a grout inletand/or vent pipe.

6.7 External TendonsExternal tendons have been used

in segmental construction. Atten-tion should be paid to the strengthof the anchorage in relation to thetendon, corrosion protection, andthe ultimate moment and shearcapacity of the structure.

If external tendons are used, con-struction details should prevent ac-cess of water into the ducts or an-chorages.

56

CHAPTER 7- DESIGN CONSIDERATIONS

7.1 GeneralThe analysis and design of seg-

mental structures are essentiallythe same as for monolithic pre-stressed concrete structures exceptthat due consideration should begiven to the following items:

(a) Redistribution of forces due tocreep of concrete, which changesthe stresses of the as built condi-tions, and erection conditions.

(b) Weather-proof tightness andstrength of connections and joints.

(c) Storage and handling of seg-ments before and during construc-tion.

(d) Camber, during erection andin the casting bed.

7.2 Force RedistributionIn most cases, the statical system

of the structure during constructionstages is not the same as in the finalstage under service load. Redis-tribution of forces due to creep andshrinkage of concrete should beconsidered.

As the structural system changesduring construction, creep of con-crete tends to redistribute the mo-ments and forces in the structure toapproach the conditions as if thestructure were built totally onfalsework. However, depending onenvironmental factors, concreteproperties and constructionschedules, the degree of this redis-tribution varies.

Calculation of the force redis-tribution may follow the recom-mendations of ACT Committee209311 or other recognized methods.

7.3 Handling and Storage ofSegments

Handling and storage of precastsegments requires special attentionso that no warping or bending ofindividual segments will takeplace. It is suggested that the En-gineer specify the method of sup-port during storage and handling.

7.4 Joint DesignThe joints between segments

should he capable of transferring thecompressive, shearing, and tor-sional forces determined by the de-sign. There should be no tensilestresses in extreme fibers when allpossible design loads such as liveload, temperature, wind, construc-tion loads, etc. are properly consid-ered. Longitudinal bending mo-ments in the top slab due to wheelloads should be included in theanalysis. Temperature variationthrough the cross section may causesignificant stresses in bridgesuperstructures and should not beneglected.

The joints are subjected to shearstresses. In box girder bridges, thejoints are generally perpendicularto the neutral axis. Shear forces actin the plane of the joint, and per-pendicular to that plane are pre-stressing forces. In many precastsegmental bridges, the ratio of theprestressing forces and shear forcesis seldom less than 5. For a drymatch-cast concrete-to-concretejoint, if the friction coefficient is as-sumed to be 1.0, the resultingsafety against sliding would equal5. Therefore, under those condi-tions, dry joints of this type wouldsafely transfer the shear even with-out keys or serrations. If the

PCI JOURNAL/January-February 1982 57

match-cast joint is filled withepoxy, the "friction concept"applies as well.

Shear in match-cast joints can besafely transferred without keys,using either dry or epoxied joints.The epoxy joint, however, is mostlyused because of its other desirableproperties. Note that all require-ments are satisfied only by usingepoxies with good bond capabilitiesand tensile strength. Tests per-formed on epoxy joints have dem-onstrated their adequacy.7.4.1 Shear

Shear-friction provisions aregiven in AASHTO Specifications "9

and in the AC! Building Code(318-77). 44 Diagonal or vertical webtendons may he used to reduceshear forces or to increase shearcapacity; however, attention shouldbe given to the location of thesetendon anchorages. If tendons areconsidered effective for increasingthe shear capacity they should meetthe applicable provisions of' theSpecifications" or Codes 44 for de-veloping shear reinforcement. Ifwide joints are used, they shouldcontain non-prestressed shearreinforcement equivalent to that inthe adjacent segments.7.4.2 Keys

Keys in the webs and slabs ofsegments are useful to facilitatealignment and to transfer shearduring erection. Two systems areused:

1. A large, single, reinforced keyusually designed for transfer ofshear caused by a number of seg-ments.

2. A large number of unrein-forced small multiple keys which,when properly arranged and de-signed, are capable of transferring

shear forces higher than possiblewith a single, large key.

The large key is easily designedas a corbel, and leaves ample op-.portunity for penetration of thematching surfaces by anchors, ten-dons, etc. The large keys are lo-cated in or near the neutral axis ofthe section. This ensures placementin a compression zone even in caseof moment reversals.

The shear capacity of' multiplekeys depends largely on the two-dimensional stress condition in thekeys caused by compression andshear very similar to the dryconcrete-to-concrete joint. As in anyother joint, the multiple key de-pends, for its strength, on compres-sion normal to the joint. As a con-sequence of this, multiple keys lo-cated in a precompressed tensionzone may have little to contributeto shear transfer under full load,because of a low ratio of normalforce to shear force.7.4.3 Compression

As indicated in Chapter 5, thecompressive strength of materialsused in a joint may be lower thanthat of the concrete in adjacentsegments and this factor may be acritical design consideration for thestructure. If a dry joint is used, con-sideration should be given to theprevention of spalling around theedges of the contact area. It is rec-ommended that dry joints be usedonly when previous performanceindicates acceptable transfer offorces and long-term weather-proofing.

7.5 Auxiliary ReinforcementIn addition to the primary rein-

forcement for transverse bending,shear and torsion, auxiliary rein-

58

forcement is normally required insegments for:

(a) Concentrated forces at reac-tions and at tendon anchorages.

(h) Volume change forces.(c) Temporary forces imposed

during fabrication, transportation,or erection.

(d) Temperature gradient stressesbetween the top and bottom of thesegment and between inside andoutside surfaces of exterior webs.

Horizontal and vertical rein-forcement should be placed be-tween segments in wide jointsfilled with mortar or concrete whenthe transverse thickness of the jointis more than 2 in. (50 mm).

7.6 Design of Segments forBox Girder Bridges

lror constant depth segmentalbridges, span-to-depth ratios from18 to 25 are currently consideredpractical and economical. Midspandepth of variable depth girders mayhave span-to-depth ratios of 40 to50; span-to-depth ratios of equal tothat of constant depth girders areused at the piers.

Simple single cell box girdersmay be used if the width of thedeck is less than 20 percent of thespan. This is based on the use ofsimple beam theory for which thedistribution of longitudinal stressesis limited to a deck width per webof 10 percent of the span length.For wider decks, multiple cells aredesirable and the webs should belocated to reduce moments in thetop slab and to minimize transversebending of the webs. Generally,these moments are computed withsufficient accuracy by consideringthe box section as a closed rigid

frame. Transverse prestressing inthe deck slab has often been used.

Deck slab design should also in-clude longitudinal local bendingmoment in the deck slab due towheel loads which can cause sig-nificant flexural stresses. If curvedtendons are used, radial forces dueto curvature of tendons should beconsidered. In some cases tendonsare given curvature in addition tothe principal tendon curvature atcertain locations in order to ac-commodate better distribution ofvoids in the concrete or arrange-ment of anchors; forces due to thesesecondary trajectories should becarefully evaluated. Fillets or rein-forcement may be added for thispurpose.

Diaphragms are normally re-quired at abutments, piers andhinges. Intermediate diaphragmscontribute very little to load dis-tribution and are not recom-mended.

Special consideration should hegiven to the effects of severe en-vironmental exposure.

For more information on seg-mental box girder bridges refer tothe Precast Segmental Box Girder

Bridge Manual.37

7.7 Design of Segments forDecked I-Beams

The spanning capability of typi-cal I-shaped sections is extendedwhen the beam and deck are pre-cast integrally.

Moment redistribution due tocreep of the concrete should beconsidered in order to estimate theinteraction between the beams andthe deck slabs if the structural sys-tem changes during construction.

PCI JOURNAL'January-February 1982 59

REFERENCES1. Leonhardt, Fritz, Prestressed Concrete

Design and Construction, WilhelmErnst & Sohn, Berlin, Germany, 2ndEdition, 1964.

2. Billington, David P., "Historical Per-spective on Prestressed Concrete," PCIJOURNAL, V. 21, No, 5, Sept,-Oct. 1976,pp. 48-71.

3. Bennett, W. Burr, Jr., "Manufacture andProduction of Prestressed Concrete,"PCI JOURNAL, V. 21, No, 5, Sept,-Oct.1976, pp. 191-203.

4. Muller, jean, "Ten Years of Experiencein Precast Segmental Construction,"PCI JOURNAL, V. 20, No. 1, Jan.-Feb.1975, pp. 28-61.

5. Lacey, Geoffrey C., Breen, John E., andBurns, Ned H., "State of the Art forLong Span Prestressed ConcreteBridges of Segmental Construction,"PCI JOURNAL, V. 16, No, 5, Sept.-Oct.1971, pp. 53-77.

6. Grant, Arvid, "Pasco-KennewickBridge—The Longest Cable StayedBridge in North America," CivilEngineeri ng-ASCE, V. 47, No. 8, August1977.

7. Grant, Arvid, "The Pasco-KennewickIntercity Bridge," PCI JOURNAL, V.24, No. 3, May-June 1979, pp. 90-111.

8. Bridges, Conrad, and Coulter, CliffordS., "Geometry Control for the IntercityBridge," PCI JOURNAL, V. 24, No. 3,May-June 1979, pp. 112-125.

9. Carlson, C., Ady, Nancy, "Special Bib-liography No. 185 — Segmented Post-Tensioned Construction," Portland Ce-ment Association, Skokie, Illinois,March 1968.

10. Carlson, C., Ady, Nancy, "Supplementto Special Bibliography No. 185 -Segmented Post-Tensioned Construc-tion," Portland Cement Association,Skokie, Illinois, October 1975.

11. Zielinski, Z. A., "Prestressed Slabs andShells Made of Prefabricated Compo-nents," PCI JOURNAL, V. 9, No. 4, Au-gust 1964, pp. 69-80.

12. Zielinski, Z. A., "Prefabricated BuildingMade of Triangular Prestressed Compo-nents," ACI Journal, Proceedings V. 61,No. 4, April 1964.

13. Lamberson, Eugene A., "Post-Tensioned Structural Systems —

Dallas-Ft. Worth Airport," PCI JOUR-NAL, V. 18, No, 6, Nov.-Dec. 1973, pp.72-91.

14. Arafat, Mahmoud Z., "Giant Precast Pre-stressed LNG Storage Tanks at StatenIsland," PCI JOURNAL, V. 20, No, 3,May-June 1975, pp. 22-33.

15. Martynowicz, A., McMillan, C. B.,"Large Precast Prestressed VierendeelTrusses Highlight Multistory Building,"PCI JOURNAL, V. 20, No. 6, Nov.-Dec.1975, pp. 50-65.

16. Perry, William E., "Precast PrestressedClinker Storage Silo Saves Time andMoney," PCI JOURNAL, V. 21, No, 1.Jan. -Feb. 1976, pp. 50-67.

17. Anderson, Arthur R., "World's LargestPrestressed LPG Floating Vessel," PCIJOURNAL, V. 22, No. 1, Jan.-Feb. 1977,pp. 12-31.

18. Ballinger, C. A., Podolny, W. Jr., andAbrahams, M. J., "A Report on the De-sign and Construction of Segmental Pre-stressed Concrete Bridges in WesternEurope — 1977," International RoadFederation, Washington, D.C., June1978. (Also available from FederalHighway Administration, Office of Re-search and Development, Washington,D.C., Report No. FHWA-RD-78-44.)

19. Podolny, W. Jr., "An Overview of Pre-cast Prestressed Segmental Bridges,"PCI JOURNAL, V. 24, No. 1, Jan.-Feb.1979, pp. 56-87.

20. Gallaway, Thomas M., "Design Featuresand Prestressing Aspects of Long KeyBridge," PCI JOURNAL, V. 25, No. 6,Nov.-Dec. 1980, pp. 84-96.

21. Muller, Jean, "Construction of Long KeyBridge," PCI JOURNAL, V. 25, No. 6,Nov.-Dec. 1980, pp. 97-111.

22. "First Incrementally Launched Post-Tensioned Box Girder Bridge to be Builtin the United States," Bridge Report,Post-Tensioning Institute, Phoenix,Arizona, December 1976.

23. "Wabash River Bridge, Covington, In-diana," Bridge Report, SR 201.01 E.,Portland Cement Association, Skokie,Illinois, 1978.

24. Walker, Homer M., Janssen, H. Hubert,and Kelly, John B., "The Kentucky RiverBridge — Variable Depth Precast Pre-stressed Segmental Concrete Structure,"

60

PCI JOURNAL, V. 26, No, 4, July-August 1981, pp. 60-85.

25. ACI Manual of Concrete Practice, PartI, American Concrete Institute, Detroit,Michigan, 1979.

26. Manual for Quality Control .for Plantsand Pr»duction of Precast PrestressedConcrete Products, Prestressed Con-crete Institute, Chicago, Illinois, 1977.

27. Design and Control of Concrete Mix-tures, Portland Cement Association,Skokie, Illinois, 1979.

28. "Proposed Recommendations for Seg-mental Construction in PrestressedConcrete," FIP Commission — Prefabri-cation, Third draft, September 1977.

29. 1980 Annual Book of ASTM Standards,Part 13, Cement; Lime; Gypsum,"ASTM C109-80 Standard Test Methodfor Compressive Strength of HydraulicCement Mortars (Using 2-in. Or 50-mmCube Specimens)," American Societyfor Testing and Materials, Philadelphia,Pennsylvania, 1980.

30. CRD-C588-60 Corps. of EngineersSpecification for Expansive Grout.

31. Kashima, S. and Breen, J. E., "Con-struction and Load Tests of' a SegmentalPrecast Box Girder Bridge Model," Re-search Report 121-5, Center Iar High-way Research, The University of Texasat Austin, February 1975.

32. 1980 Annual Book of ASTM Standards,Part 14, Concrete and Mineral Aggre-gates, "ASTM C881-78 Standard Speci-fication for Epoxy-Resin-Base BondingSystems for Concrete," American Soci-ety for Testing and Materials, Philadel-phia, Pennsylvania, 1980.

33, "Interim Specifications Bridges 1979,"Section 1.6.25, American Association ofState Highway and Transportation Offi-cials, Washington, D.C., 1979.

34. PCI Post-Tensioning Manual, Pre-stressed Concrete Institute, Chicago,Illinois, 1972. PTI Post-TensioningManual, Post-Tensioning Institute,Phoenix, Arizona, 1976.

35. Bezouska, T. J., "Field Inspection ofGrouted Prestressed Tendons," ProjectNo. 0906 71204, California Departmentof Transportation, Sacramento, Califor-nia, 1977.

36. PCI Committee on Post-Tensioning,"Recommended Practice for Grouting ofPost-Tensioned Prestressed Concrete,"PCI JOURNAL, V. 17, No. 6, Nov.-Dec.1972, pp. 18-25.

37. Precast Segmental Box Girder BridgeManual, Published Jointly by the Pre-stressed Concrete Institute (Chicago, Il-linois) and the Post-Tensioning Institute(Phoenix, Arizona), 1978, 116 pp.

38. Subcommittee 2, ACI Committee 209,"Prediction of Creep, Shrinkage, andTemperature Effects in ConcreteStructures," Designing for Effects ofCreep, Shrinkage and Temperature inConcrete, SP-27, American Concrete In-stitute, Detroit, Michigan, 1971.

39. Standard Specification for HighwayBridges, 12th Edition, American Associ-ation of State Highway and Transporta-tion Officials, Washington, D.C., 1977.

40. "Building Code Requirements forReinforced Concrete (ACI 318-77),"American Concrete Institute, Detroit,Michigan, 1977.

NOTE: Discussion of this report is invited. Please submityour discussion to PCl Headquarters by September 1, 1982.

PCI JOURNAUJanuary-February 1982 61