Published Monthly by thePRESTRESSED CONCRETE INSTITUTE

Lip I. IL

December 1962Vol. 8, No. 12

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Ben C Gerwick, nc., Son Francisco Calif.

PR~STRESS~D CONCRIETE INSTITUTE

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Construction of a wharf for the Encinal Terminals inAlameda, Calif. which employed extensive use of precast prestressed concrete. Precast prestressed 18 in.piles, pile caps, and deck slabs were used. Stirrupscan be seen extending up from the slab to engage thecomposite deck.

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PRESTRESSED CONCRETE FOR FOuNDATIONSAND MARINE STRuCTuRES

One obvious requirement of all structures is that they have a foundation.While not as glamorous as the latestmode in solar screens or expressions inwall panels, the foundation is vastlymore important. Without an adequate,dependable foundation little in the structure can survive. Piles and spread foottings are the most common foundations.

The length of pile required for astructure is a function of foundationconditions. For deep foundations usingnormal reinforced piles, the pile size andreinforcement is determined by t h ehandling stresses. By using prestressedpiles the entire section modulus is ableto work for you, while with reinforcedpiles a smaller transformed area mustbe considered. Therefore, prestressedpiles can be made smaller, lighter, andstronger. This in turn allows prestressedpiles to be more easily handled. Mosttimes a one or two point “pick” is allthat is required.

Driving Prestressed PilesPiles made of prestressed concrete

are one of the most rugged types known.Several prestressed test piles have beendriven with impressive results. In 1950the U.S. Naval Research and EvaluationLaboratory in Port Hueneme drovesome 14 inch octagonal prestressed piles.The piles were driven to resistances ashigh as 200 blows to the 1/2 inch withno damage to the piles.

There are three basic types of stressthat can develop in a pile during driving: compression, tension and torsion.The cause of the compression stress isobvious as it is produced by the force

of the pile driver. Concrete, being strongin compression, is capable of easily taking large compressive stresses. It is estimated that the maximum compressivestress induced by most pile driving liesbetween 1,000 psi and 2,500 psi.

The cause of the tension stress canbe explained by likening a pile to anumber of billiard balls all lined up andtouching one another. If the first ballis struck by the cue ball, the last ballwill shoot off by itself. If the balls weretied together, the tying element will thenbe subjected to tension in restraining thelast ball from flying off. These sameconditions can exist in piling, when thedriving is being done in soft soil. Asthe compression wave in the pile travelsdown its length, tension forces can beproduced at its end. These same tensionforces can also occur as a pile is driventhrough a tough strata with an extremely soft one below. This can produce alarge tension force near the end becauseof the little restraint. Here prestressedpiling is superior to any other concretepiling, as it is able to resist large tensionforces because of the built-in compression force induced by prestressing.

These tension forces can also occurin hard driving by rebound as the compression wave travels down the pile andis reflected back up as a tension wave.

In practice the returning tensile waveis reduced markedly by the frictionalresistance of the soil.

Stress readings taken on a 70 ft. long,14 inch square pretensioned pile indicated maximum compressive stresses offrom 1200-1500 psi created by driving,and a reflected maximum tensile stress

of 500 psi.Higher tensile stresses have also oc

cured and the magnitude of the potential tensile stress is a function of:

1. Pile length2. Foot Resistance3. Side friction4. Maximum compressive stress

from the hammer blow5. Length of t h e compressive

wave.It can be shown that the total com

pressive stress in the pile varies directlywith the energy of the blow. The lengthof the compressive wave increases withan increase in E and with the durationof the hammer blow. The longer thecompressive wave the better, since successive compressive waves will cancelout reflected tensile stresses.

The duration of the hammer blowincreases with the ratio of the hammerblow to the weight of the pile and itreduces with increased stiffness of thehead packing. Therefore, in order toeliminate or reduce reflected tensilestresses a prestressed pile is ideal because of its high E. Using a heavy hammer and a relatively “soft” packing canreduce tensile stresses. It has also beenfound helpful to reduce the hammerstroke when the driving is easy until afirm resistance is met.

The most common type of packing isa 6 inch layer of softwood or a 2-3 inchlayer of plywood. These cushions mustbe continuously replaced during drivingas they become compressed or burnedout. Sometimes two or more cushionsare required while driving a long pile.A cushion is also valuable in evenly distributing the hammer blow across thetop of a pile.

The other stress produced in a pileis torsion. This is usually produced bythe driver and the leads imparting atwisting action on the pile head. As thepile is driven the soil fixes it and torsionstresses are set up. It has been found thata driving head having a snug fit on thepile and extending well over the pilefor several inches (±12) sets up theconditions which may produce excesstorsion stresses in a pile. Eliminatingthese conditions reduces or eliminatestorsion stresses.

DurabilityOne of the best reasons for using pre

stressed concrete is its superior durability characteristics. Prestressed pilesare made of high quality dense concrete which is maintained permanentlyin compression. For this reason pre

Ben C. Gerwick, Inc., San Francisco, Calif.

Pillar Point Small Craft Harbor, San Moteo County, California employed 18 in. Octagonal prestressed piles, and precast prestressed deck slabs. Also used and seen in thebackground is a sea wall mode of prestressed sheet piles 3 ft. x 1 ft. x 40 ft.

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Bridge for the State of California whichemployed 20 in. square prestressed pilebents, 30 ft. prestressed slab spans, and105 ft. post-tensioned girders. This entirelyprecast prestressed bridge, with the exception of the cast-in-place deck slab, wasshipped by barge 350 mi. to the site.

Ship unloading dock the New Haven TerminalCorp. employes 120 ton 18 in. octagonal bearingpiles. Note the excellent condition of the headsof the driven piles.

IBen C. Gerwick, Inc., San Francisco, Calif.

24 in. square prestressed piles 125 ft. longfor the Napa River Bridge for the state ofCalifornia. 54 in. pretensioned cylinderpiles also 125 ft. long were also used onthe project.

Ben C. Gerwick, Inc., San Francisco, Calif.

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Blakeslee Prestress, New Haven, Conn.

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24 in. round prestresséd piles for a channel crossing for the California Division of Highways. Dowels have been grouted into place forconnection to the pier cap.

Ben C. Gerwick, Inc., San Francisco, Calif.

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Continued from Page 2stressed concrete has been specified inareas subject to a harsh corrosive environment. The Lake Maracaibo Bridgewas built of prestressed concrete because of the corrosive atmosphere, ashave several buildings for the AmericanCyanimid Company.

Prestressed concrete piles provendurability is exemplified in the RaymondInternational tests started in 1939. Prestressed piles were placed in New Yorkharbor subject to both the corrosive seawater and alternate freezing and thawing. 13 years later they were examinedand the only indication of deteriorationwas a small amount of rusting at theends of the unprotected strands whichonly penetrated 1/8-1/4 of an inch.

Recent studies sponsored by theCorps of Engineers at Treat Island alsohave shown the excellent durabilitycharacteristics of pretensioned piles. Airentrained pretensioned beams have beenexposed to over 400 cycles of alternatefreezing and thawing in sea water for4 years with only small amounts ofsurface scaling.

Prestressed concrete piles are produced by pretensioning on long beds orby post-tensioning cylindrical segmentstogether. The pretensioned piles aremost commonly available in square oroctagonal cross-sections. Recently asystem for manufacturing pretensionedcylindrical piles has been developedwhich is discussed later. The usualresidual prestress force after losses isfrom 700-900 psi for highway bridgepiles, while 300.500 psi has proven adequate for short building piles. Thisamount of prestress force has provenadequate for both applications, and provides a superior pile to the usual alternates at competitive costs.

This residual prestress force produces

a pile capable of taking large verticalloads plus having a high moment resistance. This moment resistance makesthe piles easier to handle and also allowsthem to double as a structural column.Several buildings have been built inwhich prestressed piles are driven to agiven resistance and then allowed to extend out of the ground acting as acolumn to take roof and floor loads.This is economical because it eliminatesdriving several piles, casting a footing,and then casting a separate column.While the load capacity depends on thesoil conditions, 18 inch octagonal prestressed piles have been test loaded upto 500 tons with a net settlement of only3/16 of an inch.

Prestressed piles have also had greatsuccess in the highway bridge field.Many bridges have been built employ-

ing the pile-column principle discussedabove and many have been built usingprestressed piles in typical footings. AJoint Committee of the American Society of Civil Engineers and the Prestressed Concrete Institute has developed a set of comprehensive standards forprestressed piles for highway bridges.The standards cover both square andoctagonal piles in sizes from 10 in.-24in. (see page 5)

Marine ConstructionMarine construction can take many

aspects; ranging from sea walls to docksand harbor structures, and prestressedconcrete has proven an excellent application in all cases.

Because of their location, pier andwharf structures must be supported onpiling. Considerations of fire proof-ness, large load carrying capacity, durability, and economy have promoted theextensive use of prestressed concrete piling in many new water-front structures.

Prestressed Concrete piles have an inherent advantage in their being smallerand more able to accomodate a relatively large concrete strain without cracking. They are therefore capable of absorbing the large impact forces so oftenencountered in marine structures.

Some of these applications of prestressed marine structures are: At PearlHarbor 50 ton capacity prestressed pileswere used because of the requirementof the facilities to carry a live load of750 lbs. per sq. ft. The piles rangedin length up to 155 feet.

The Port of Seattle’s Pier 28 project,costing $6 million is making extensiveuse of prestressed concrete. The deckstructure is designed to support a 50ton traveling gantry crane, Coopers E-50railroad loading, and a 30 ton fork-lift

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T. Y. Un & Assodc,tes

Sea wall at Santa Crux, California constructed of prestressed single tees. The wall is888 ft. long and was designed for full hydrostatic pressure. Each tee is 6 ft. wideby 23 ft. long and is pretensioned with 8-~/2 in. strands.

T. Y. Un & AssociatesCloseup of the Santa Crux sea wall. The single tees were topped by cast in placeconcrete. The tee flanges are 5 in. thick, they are grooved to provide a 2 in. x 3 in.grout key between adjacent units. The tee’s were jetted into position.

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truck, or a uniform live load of 750lbs. per. sq. ft. The deck is composedof precast prestressed concrete slabs 6ft. wide and 20 ft. long.

These deck slabs are prestressed forpositive moment and are reinforced withmild steel in the composite deck to provide full live load continuity.

Two sizes of prestressed piles areused to support the deck; 161/2 in. octagonal sections with a design load on100 tons and 14 in. square sections witha design load of 85 tons. The pilesrange up to 130 feet in length.

In Norfolk Virginia, 24 inch prestressed piles 80 ft. long will support apier able to accomodate 35,000 and 45,-000 ton colliers.

San Francisco is planning a newArmy Street Terminal with the mar-

ginal pier supported by 75 ft. longprestressed piles.

These are just a few of the many applications of prestressed concrete to pierand wharf construction.

Prestressed Sea WallsAnother excellent application is in

sea wall construction. Prestressed concrete sheet piles or heavy duty buildingsections, such as single tees, have beenused successfully to produce miles ofsea walls. The prestressed sea walls aredesigned either one of two ways, ascantilevers, or with tie backs to a deadman.

Cantilever walls can consist of iñdividual members driven into the grounduntil sufficient moment capacity is produced or the “King Pile” system. In the

“King Pile” system, heavy prestressedpiles are driven and prestressed slabsare slipped horizontally between spacedking piles which are long enough toresist the overturning loads of the back.fill.

The prestressed sea wall members areusually put in place by a combinationof driving and jetting. The bottom edgeof the sheet pile is usually clipped offin one corner to force them closer tothe ones already in place.

The connection between adjacent prestressed sheel piles is usually made oneof two ways; the two basic methods aretongue and groove or a grout key. Bothhave been successful.

Cylinder PilesBasically, cylinder pile fabrication can

Continued on Page 6

Blakeslee Prestress New Haven Conn

While not a suggested way to handle prestressedpiles this photo illustrates the moment capacityof a typical prestressed pile.

Driving thirteen hundred 12 inchsquare prestressed piles for theUnited Illuminating Company’s generating Unit Foundation in Bridgeport, Conn. The piles ranged inlength from 40 ft. to 75 ft. Theywere bid lowest in competition withpipe and monotube piles. The excellent condition of the pile headseven though they were driven to BIakes~ee Prestress New Haven Connbearing on rock, can be noted.

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Piles cast with pre-attached drivingcushions.

PILE PROPERTIES00a,dI L’,,it Appree Area of .Seotea, Aiao

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The /et~th ¶L’i, the Otheec. aeM 60 end ofpit. ioo/odrg a/terse/cpile tp .8cc Coed. TaL,o/at.d /~r9th.. ‘ag be coed for ‘toasea,,pAl 0p ~s the 0/. the aetoret. hoc ottoired a oot/tpreaat-.eyhd.,- o/rergth of4O00poi Ifp/leo arc pie/ed ~a -her the0.00,-ct. Ot-w,gth /0 thea b/a,, 4OOOpa~ the rro,i,nes, p/oh-op leegthohs/I be fh. tobe/oted /.s~Th redeced bg 3%.

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‘The /,n9th L’,A the d,ataceo and to and ofpile Ate/ca/hg alternate pile t~e 08cr oteet heAl/atoM/a~qtha a’s,,t ha teed far roan/stoat p,ak-tip length, e’hao the aerarate ha. otto/ned a eoatpreaoiaag//sOar .~frenqth of 4000psi If p//ca Al-c p/shed ‘p oMan the e000ratc .ttr~rtqth At lea..titan 4000pp the ,ttaiiroc,n p0k-op length ohs//ba/ho tabola/ed/etyth redecad 3%.

AASHO-PCI STANDARD PRESTRESSED CONCRETE PILESCopies of the complete standards are available from PCI Headquarters for 30c each.

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be divided into the two general categories of pre.tensioned and post-tensioned.

Post-tensioned piles are made by acentrifugal casting process much likeordinary concrete pipe. A cage of reinforcing m e s h and post-tensioningducts is “spun” while concrete is slowl)added. The concrete builds up on thecage until the desired wall thickness isattained. These spun segments are curedto the necessary compressive strengthand then joined together like beads ona string by means of steel stressingstrands. Any desired pile length can beproduced by this method. The standardindividual segment lengths are 12 or 16ft. The strands are post-tensioned andthen grouted. When the grout hardensthe strand end anchors are released,producing a continously prestressed pile.

The manufacture of pretensionedlarge diameter piling is performed bya still more ingenious process. Thevoid is produced by an interior slipform. This slip form, or mandrel, isinserted into a cylindrical outside form,in which pretensioned strands and reinforcing steel has already been placed.The outside form has a longitudinalstrip removed from its top to permiteasy placement of concrete. As the concrete is poured along the length of thepile the mandrel is also moved. Theremoval speed of the mandrel is ratedto correspond with the set of the concrete. Speeds up to 12 in. per minutehave been used. Therefore as the mandrel passes out of a given portion of thepile, the concrete has attained enoughset so that it will not crumble or deform.This procedure calls for a very uniformconcrete slump and vigorous vibration.After the mandrel has been completelywithdrawn from the newly cast pile, theconcrete ~s given time to acquire lhenecessary compressive strength before

the pretensioned strands are cut and thepile is removed from the outside form.

Hollow prestresed concrete piles withdiameters up to 54 inches and lengthsup• to 200 feet are finding increasingapplication, especially in marine andhighway bridge construction.

The huge Chesapeake Bay Bridge.Tunnel Project calls for 12 miles of 2-lane highway to be carried on 54 in. di.ameter prestressed concrete pile bents.This piling provides not only a submarine foundation but also above watercolumns. Substructure constructiontime is drastically cut by the elimination of expensive caison work. Becauseof their exceptional flexural strength.these pile-columns need no bracing eventhough they extend a distance of from25 ft to 60 ft. between the mud line andthe surface of the water.

Splicing these large diameter pre.stressed concrete piles is no problemeither. A concrete plug that extends afew feet into either side of the joint does•the job.

Caps for these piles are generally ofprecast concrete construction. Reinforce.ment bars are cast into the caps so thatthey project into the pile void space.

After the cap is set on the piling, thetop few feet of the void is filled withconcrete by means of a hole throughthe top of the cap. This bonds the capand piling into a monolithic unit.

Durability, easy handling and economy made prestressed large diameterpiles the choice for the $2 million Pay.allup River Highway Crossing near Tacoma, Washington. Here again the pileswere employed in their dual role offoundation and pier columns, eliminating the need of formwork for footingsand cast in place columns. Since itwas necessary that the columns be drivenabsolutely plumb, the contractor de.vised a crane mounted “pile holder”for the job. This “pile holder” is amodified crane boom that holds a pilemuch as a carpenter holds a nail. Usingthis method in combination with largediameter prestressed concrete piles thecontractor was able to put the piling inplace at less than one half the price ask.ed by the other bidders.

Prestressed concrete piles have a history of proven success in many diverseapplications. Their versatility, non-corrosion and durability combine to pro.duce an economical solution to today’sfoundation problems.

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Courtesy Contractors and Engineers Magazine

The Chesapeake Bay Bridge-Tunnel Project. The machine in the center of the photo trimsthe piling with its foreward end and sets caps from the rear.

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Close-up shot of the device used to trim the large diameter prestressed Concrete piling on the Chesapeake BayBridge-Tunnel Project

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Superior Sand & Grovel. Everett, Wash.

Casting a large diameter pretensioned prestressed concretepile Mandrel is shown protruding from the end of theexterior form.

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54” pile being placed in position using a specially designed pile holder. Driving hammer is seen in left foreground.

Construction photo of the Tees Dock, No. 1 Quay, England, whichmade use of large diameter post-tensioned piling as caisons. 6’-3”diameter concrete cylinders having preformed post-tensioning ductswere placed in prebored holes and then stressed with bars. A concrete plug was then placed at the bottom of the cylinder and theremaining void is filled successively with sand and weak concrete.A precast, prestressed concrete superstructure is then placed on the

piles to produce a non corroding, quickly constructedmaritime shipping quay.

Courtesy Construction Methods

Changing overheated pile packing thatwas used to drive 54” prestressed concrete piles.

Courtesy Contractors and Enq~neers Magazine

Precast caps awaiting placement on the Chesapeake Bay Bridge-Tunnel Project.

A pretensioned prestressed concrete pile being loaded for shipment.

Courtesy Construction Methods

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WORLD’S LARGESTPRESTRESSED CONCRETERESERVOIR COMPLETED

The world’s largest prestressed concrete reservoir has recently been completed at Alderwood Manor, SnohomishCounty, Washington. The reservoir is370 feet in diameter and 36 feet deep.It hold 28 million gallons of water,which is almost twice as much as thepresent largest prestressed concrete reservoir. The unroofed structure was builtat a cost of nearly $600,000.

Probed Co., Weitbury, N. V.Newly constructed 28 millionprestressed concrete reservoir.

Prestressing of the reservoir wall wasperformed by the Preload Company ofNew York. Circumscribing laps of wirewere applied to the reservoir by meansof a self propelled machine. The machine was suspended along ~the outerface from a carriage that rode alongthe top of the wall. The stressed wireimparts an inward compressive forcewhich will codnteract the circumferential tensile force exerted by the tank’scontents in service.

The inward force at the top of thetank is 28 kips per vertical foot and 395kips per foot at the bottom. Eight wrapsof wire were applied per vertical footat the •top of the reservoir and 114wraps were applied-in five layers at thebottom. The, reservoir wall is 20 inchesthick at’ the bottom and tapers to 8inches at the top. -

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~ason S 9reelings

ROSTASY WINSMARTIN P. KORN AWARDThe Martin P. Korn Award for the

paper judged to be the best publishedin the PCI JOURNAL between September 1961, and August, 1962 was awarded to Ferdinand S. Rostasy for his paper,“Connections in Precast Concrete Structures-Continuity in Double-T Floor Construction.” The paper was publishedin the August, 1962 JOURNAL of thePrestressed Concrete Institute. TheAward, consisting of a Walnut Plaqueand $100.00 •was accepted by EivindHognestad, Manager of the StructuralDevelopment Section of the Researchand Development Laboratories of thePortlahd Cement Association on behalfof Dr. Rostasy who is in Europe.

The research.~pi-pje,ç~ reported on.in -~

the pajcer’was’ conducted under Dr.Hognestad’s direction.

gallon The competition for next year’s awardwill be open to all original papers published in the PCI JOURNAL fromOctober, 1962 to August, 1963. Theceremony conferring the Award will beheld at the 1963 PCI Convention inSan Francisco, .October 5-11.

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