Precast Piles for Route 40 Bridge in Virginia Using ... · Precast Piles for Route 40 Bridge in...

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This paper summarizes the construction details and findings of laboratory and field tests of a new generation of precast composite piles used for the first time in the construction of the Route 40 highway bridge over the Nottoway River in Virginia. The piles consisted of 24.6 in. (625 mm) diameter concrete-filled glass fiber reinforced polymer (GFRP) circular tubes, with a 0.21 in. (5.3 mm) wall thickness. The composite piles extended above the ground level and were directly embedded into the reinforced concrete cap beam supporting the superstructure. Laboratory tests included two full-scale composite piles loaded to failure using four-point bending configuration. Field testing included a full-scale precast composite pile and a conventional 20 in. (508 mm) square concrete pile prestressed with fourteen 1 / 2 in. (12.7 mm) diameter strands. This paper presents details of the construction and driving of the piles, comparisons between the behavior of the composite and prestressed concrete piles under axial and lateral loading, the observed failure modes, and the details of the connection between the piles and the reinforced concrete cap beam. P iles used for bridge foundations are typically pro- duced using traditional materials such as concrete, steel, and timber. In recent years, high repair and re- placement costs have led North American highway agen- cies and researchers to investigate the feasibility of using fiber-composite materials for transportation and civil engi- neering infrastructure, including pile foundations for Precast Piles for Route 40 Bridge in Virginia Using Concrete Filled FRP Tubes 2 PCI JOURNAL Amir Fam, Ph.D. Assistant Professor Department of Civil Engineering Queen’s University Kingston, Ontario, Canada Miguel Pando, Ph.D. Assistant Professor Department of Civil Engineering University of Puerto Rico – Mayaguez Campus Mayaguez, Puerto Rico George Filz, Ph.D., P.E. Associate Professor Civil and Environmental Engineering Department Virginia Polytechnic Institute and State University Blacksburg, Virginia Sami Rizkalla, Ph.D. Distinguished Professor of Civil Engineering and Construction and Director of the Constructed Facilities Laboratory Civil Engineering Department North Carolina State University Raleigh, North Carolina

Transcript of Precast Piles for Route 40 Bridge in Virginia Using ... · Precast Piles for Route 40 Bridge in...

This paper summarizes the construction detailsand findings of laboratory and field tests of a newgeneration of precast composite piles used for thefirst time in the construction of the Route 40highway bridge over the Nottoway River inVirginia. The piles consisted of 24.6 in. (625 mm)diameter concrete-filled glass fiber reinforcedpolymer (GFRP) circular tubes, with a 0.21 in. (5.3mm) wall thickness. The composite piles extendedabove the ground level and were directlyembedded into the reinforced concrete cap beamsupporting the superstructure. Laboratory testsincluded two full-scale composite piles loaded tofailure using four-point bending configuration.Field testing included a full-scale precastcomposite pile and a conventional 20 in. (508mm) square concrete pile prestressed withfourteen 1/2 in. (12.7 mm) diameter strands. Thispaper presents details of the construction anddriving of the piles, comparisons between thebehavior of the composite and prestressedconcrete piles under axial and lateral loading, theobserved failure modes, and the details of theconnection between the piles and the reinforcedconcrete cap beam.

Piles used for bridge foundations are typically pro-duced using traditional materials such as concrete,steel, and timber. In recent years, high repair and re-

placement costs have led North American highway agen-cies and researchers to investigate the feasibility of usingfiber-composite materials for transportation and civil engi-neering infrastructure, including pile foundations for

Precast Piles for Route 40 Bridgein Virginia Using Concrete FilledFRP Tubes

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Amir Fam, Ph.D.Assistant ProfessorDepartment of Civil EngineeringQueen’s University Kingston, Ontario, Canada

Miguel Pando, Ph.D.Assistant Professor

Department of Civil EngineeringUniversity of Puerto Rico –

Mayaguez Campus Mayaguez, Puerto Rico

George Filz, Ph.D., P.E.Associate ProfessorCivil and Environmental EngineeringDepartmentVirginia Polytechnic Institute and State UniversityBlacksburg, Virginia

Sami Rizkalla, Ph.D.Distinguished Professor of Civil

Engineering and Constructionand

Director of the Constructed FacilitiesLaboratory

Civil Engineering DepartmentNorth Carolina State University

Raleigh, North Carolina

bridges in corrosive environments.1,2

For most projects, high quality con-ventional precast, prestressed concretepiles will continue to be the preferredsolution for deep bridge foundations;but for piling exposed to high-corro-sive environments, the precast FRPcomposite piles described in this papermay provide better durability.

A number of commercial productsknown as “composite piles” have re-cently become available for structuralapplications. The term “compositepiles” refers to piles composed of fiberreinforced polymers (FRP), recycledplastics, or hybrid materials. Thispaper focuses on precast concrete-filled tubular FRP piles, where theFRP tube serves as permanentlightweight non-corrosive formworkand a reinforcement element for con-crete.

The FRP tube is composed of sev-eral layers of fibers embedded in apolymeric resin. The layers of fibersare oriented in different directionswith respect to the longitudinal axis ofthe tube in order to provide strengthand stiffness in both the axial and cir-cumferential directions. The circum-ferential stiffness and strength of theFRP tube provides confinement to theconcrete core under axial stresses,which increases the strength and duc-tility of the pile, while the strength andstiffness of the tube in the axial direc-tion contributes to the flexural strengthof the pile.

During the relatively brief history ofcomposite pile use, applications havebeen limited mainly to marine fenderpiles, loadbearing piles for light struc-

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Fig. 2. The old Route 40 Bridge over the Nottoway River in Virginia.

Fig. 1. Location ofthe Route 40 Bridge(Structure No. 1006)in Sussex County,Virginia.

tures, and demonstration projects.2

Composite piles have not yet gainedwide acceptance in practice primarilybecause of the lack of a long trackrecord of performance and higher ini-tial cost. However, appropriately de-signed precast FRP composite pilescan result in longer service life, signif-icantly improved durability in harshenvironments, and substantially re-duced life-cycle costs.

The short-term structural behavior ofconcrete-filled tubular FRP piles, underaxial and flexural loading, has beenstudied by several researchers.3-6 Thegeotechnical behavior of these piles hasalso been investigated.7-9 While thesestructural and geotechnical studies haveadvanced the state of knowledge aboutthe behavior of composite piles, fieldapplications of composite piles inbridges are limited. This paper de-scribes the application of composite

piles in the new Route 40 Bridge inVirginia, which is the first bridgeknown to the authors to utilize compos-ite piles in its foundation pier.

BACKGROUND ANDBRIDGE DESCRIPTION

The following sections provide a de-tailed description of the old Route 40Bridge in Virginia as well as the newbridge. Details of the prestressed con-crete piles as well as the new compos-ite piles used in the new bridge arealso provided.

The Old Bridge

In 1998, the Virginia Department ofTransportation (VDOT) decided to re-place the existing Route 40 Bridge(Structure No. 1006) over the Not-toway River in Sussex County, Vir-

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ture supported by four piers and twoend abutments, as shown in Fig. 4.Each pier consists of a reinforced con-crete beam-type elevated pile cap sup-ported by ten piles. Based on the de-sign requirements, the VDOTspecified a 20 in. (508 mm) pre-stressed solid square pile, as shown inFig. 5(a). The design axial load ofeach pile was 150 kips (667 kN).

As a part of an ongoing study spon-sored by the Federal Highway Admin-istration (FHWA), the VDOT took theinitiative to use an alternative compos-ite pile system, consisting of concrete-filled FRP tubes, for the entire group ofpiles supporting Pier No. 2 (see Fig. 4).

The objectives of the VDOT initia-tive were to examine the feasibility ofusing composite piles for bridge sub-structures (particularly their drivabilityusing conventional pile drivers), per-formance under axial and lateral load-ing conditions using full-scale fieldtests, and comparison to conventionalprestressed concrete piles. The follow-ing sections provide a brief descriptionof both the conventional prestressedpiles and the precast composite piles.

Prestressed Concrete Piles

Details of the 20 in. (508 mm)square prestressed concrete piles spec-ified for the superstructure supportsare shown in Fig. 5(a). Each pile isprestressed using a total of fourteen 1/2

in. (12.7 mm) diameter seven-wirestrands of 270 ksi (1861 MPa) ulti-

Fig. 4. Schematic of the four piers of the new Route 40 Bridge.

Vertical cracks in columns Spalling and cracking ofbearing seats

Map cracking in beams

Fig. 3. Deterioration of the substructure of the old Route 40 Bridge.

ginia, which was built in the early1930s. Fig. 1 shows the location of thebridge. The old bridge, which con-sisted of a steel truss supported byconcrete piers, as shown in Fig. 2, suf-fered from excessive deterioration inboth the superstructure and substruc-ture.

Deterioration included full heightvertical cracks in the concretecolumns of the piers, spalling andcracking of the concrete bearing seats,and map cracking, up to 1/16 in. (1.6mm) in width, in the abutment bearingseats (see Fig. 3).

In addition to the deterioration of

the substructure, excessive corrosionwith large section losses was observedin the roller bearing devices of thetruss supports. Additionally, the floorbeams suffered from section losses upto 1/8 in. (3.2 mm) in both the web andbottom flanges. The bridge was func-tionally obsolete with a roadwayclearance of only 24 ft (7.3 m) curb-to-curb and was rated as scour critical.

The New Bridge

The new bridge, which is 280 ft(85.3 m) long and 50 ft (15.2 m) wide,has a five-span slab-type superstruc-

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mate strength, pretensioned to producea prestress level of 0.809 ksi (5.6MPa) in accordance with VDOT stan-dards. The piles are 43 ft (13.1 m)long. The specified concrete compres-sive strength at 28 days is 5.8 ksi (40MPa). The ties consist of No. 5 gaugespiral wire.

Precast Composite Piles

The composite piles used in thisproject consist of concrete-filled circu-lar glass FRP (GFRP) tubes. TheGFRP tube is fabricated using the fila-ment-winding technique, where E-glass continuous fiber rovings are im-pregnated with polyester resin andwound over a rotating steel mandrel,following a predetermined windingpattern. The fiber volume fraction ofthe tube is 51 percent. Fig. 5(b) pro-vides details of the composite pile.

The GFRP tube has an outer diame-ter of 24.6 in. (625 mm) and a totalwall thickness of 0.263 in. (6.68 mm).The tube has a 0.05 in. (1.27 mm)thick liner at the inner surface, whichresults in a net structural wall thick-ness of 0.213 in. (5.41 mm).

The wall structure of the tube con-sists of three layers. The inner andouter layers are each 0.074 in. (1.88mm) thick, and they contain layers offibers oriented at ±34 degrees with re-spect to the longitudinal axis of thetube. The middle layer, which is sand-wiched between the inner and outerlayers is 0.065 in. (1.65 mm) thick andcontains fibers oriented at 85 degreeswith respect to the longitudinal axis.

The GFRP tubes are filled with aconcrete mix that includes an expan-sive additive to reduce the effect ofshrinkage and therefore improve thebond between the concrete and theGFRP tube. It should be noted, how-ever, that concrete shrinkage in closedforms is significantly less than conven-tional concrete members.10 The speci-fied compressive strength of the con-crete fill at 28 days is 6 ksi (41.4 MPa).The mechanical properties of theGFRP tubes are provided in Table 1.

LABORATORY TESTING OFTHE COMPOSITE PILES

Prior to construction of the bridge, acomprehensive experimental study was

Mechanical property Axial direction Hoop directionTensile strength (ksi) 31.6* 30.0† 36.2‡ 51.2‡

Compressive strength (ksi) 15.1‡ N/AElastic modulus (ksi) 2196* 2199† 2404‡ 2567‡

Poisson’s ratio 0.32‡ 0.34‡

* Coupon test.13

† Manufacturer.‡ Lamination theory.Note: 1 ksi = 6.89 MPa.

Table 1. Mechanical properties of composite GFRP tube.

Fig. 5. Details of piling: (a) Prestressed concrete pile; (b) Composite pile.

Fig. 6. Test setup for laboratory bending tests of the composite piles.

conducted to study the structural be-havior of concrete-filled FRP tubes.3-6

The behavior of the composite pileswas investigated using full-scale labo-ratory testing, in which the flexuralstiffness, strength, and failure mode ofthe composite piles were determined.

Test Setup and Instrumentation

Two full-scale specimens withGFRP tubes identical to those pro-posed for the composite piles of theRoute 40 Bridge were tested in bend-ing under four-point loads. The tubes

(a) Prestressed concrete pile

(b) Composite pile

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about 0.37 in. (9.4 mm). Both labora-tory test specimens exhibited flexuraltension failure by rupture of the fiberson the tension side, as shown in Fig.8(a). Despite the brittle nature of rup-ture of the FRP tube, the specimen re-mained intact and was able to supportthe dead weight after failure, as shownin Fig. 6.

Fig. 8(b) shows the cross section ofthe specimen at the failure locationafter removal of the FRP shell. Thecompression zone of the concrete corecould be distinguished from thecracked zone of the section by exam-ining the texture of the cross section.The measured depth of the compres-sion zone was about 6 in. (152 mm).

Material Testing

To validate the manufacturer’s data,the mechanical properties of the com-posite tubes were measured usingcoupon tests and calculated using clas-sical lamination theory. Strips, 1 in.wide x 30 in. long (25 x 762 mm),were cut from the tube in the longitu-dinal direction.

Since the stress concentration at thegripping location can severely influ-ence the strength of FRP coupons, thetwo ends of the GFRP strip were in-serted inside hollow steel tubes, 1 ft(305 mm) long each, and epoxy resinwas used to fill the steel tubes. Theclear length of the GFRP coupon be-tween the two steel tubes was 6 in.(152 mm).

After curing of the epoxy, thecoupons were tested in tension, wherethe gripping was applied to the steeltubes. Fig. 9 shows the coupons aftertension failure and a typical stress-strain curve for a GFRP coupon com-pared to the stress-strain curve ob-tained from classical laminationtheory11 and the manufacturer’s data.Table 1 provides a summary of the me-chanical properties of the GFRP tube.

Comparison Between Behavior ofComposite and PrestressedConcrete Piles

The moment-curvature behavior ofthe prestressed concrete piles was pre-dicted analytically using the conceptof equilibrium and strain compatibil-ity. A modified Ramberg-Osgood

(a) Tension failure by rupture of FRP tube (b) Cross section at failure location

Tension (cracked) zone

Compression zone

6 in.

Fig. 8. Flexural tension failure of the composite pile.

Fig. 7. Moment-curvature responses of both the composite and prestressed concrete piles.

were filled with 4.8 ksi (33 MPa) con-crete at Lafarge Canada, in Winnipeg,Manitoba, using the same procedurespecified for casting the compositepiles for the bridge. The span of thetest specimen was 16.4 ft (5.0 m), andthe distance between the two appliedloads was 4.9 ft (1.5 m).

Fig. 6 shows the test setup of thespecimens in bending. The tests wereconducted using stroke control with arate of loading of 0.05 in. per minute(1.3 mm/min). The specimens wereinstrumented to measure the midspandeflection, the extreme fiber strains atthe tension and compression sideswithin the constant moment zone, andthe relative slip between the concretecore and FRP tube at the ends.

Test Results and Failure Mode

The measured moment-curvaturebehavior of the composite piles for thetwo identical specimens is shown inFig. 7. The average ultimate momentcapacity of the composite piles is 370kip-ft (502 kN-m). The cracking mo-ment, 93 kip-ft (126.1 kN-m), is rela-tively small compared to the ultimatemoment. Since the composite pileswere tested under stroke control, thebehavior shows vertical drops in themoment when cracks occurred, andthe behavior after first cracking wasalmost linear.

At the end of the test, the total slipmeasured between the concrete coreand the FRP tube at each end was

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function was used to model the stress-strain relationship of the prestressingsteel strands. A generalized expres-sion, given by Popovics, was used tomodel the nonlinear stress-strain rela-tionship of concrete.12 The moment-curvature response based on the analy-sis of the prestressed concrete pile isshown in Fig. 7. The response was ter-minated when the compressive strainin the concrete reached 0.003.

For the concrete-filled GFRP tube,the moment-curvature behavior wasalso predicted using an equilibriumand strain compatibility approach. Thecross section was divided into hori-zontal layers to account for the circu-lar geometry of the concrete and theGFRP tube, which forms continuousreinforcement around the concrete. Alinear stress-strain relationship of theGFRP composite tube, based on thelinear regression of the experimentalresults shown in Fig. 9, was used. Theforces in both the concrete and theFRP tube were obtained by numericalintegration.

The forces were then used to calcu-late the internal moment resistance atdifferent strain levels, which wereused to generate the predicted mo-ment-curvature response. Details ofthe analytical model can be foundelsewhere.13 Fig. 7 shows that the pre-dicted moment-curvature response ofthe composite pile agrees well withthe measured response.

Fig. 7 also shows that the flexuralstiffness of the composite pile beforecracking is very similar to that of theprestressed concrete pile. However,after cracking, the stiffness of thecomposite pile is significantly re-duced. This is attributed to the pre-stressing effect and the lower elasticmodulus of GFRP in comparison tothat of steel strands.

The cracking moment of the com-posite piles is 40 percent lower thanthe prestressed concrete pile due to theabsence of prestressing. However,cracking of composite piles should notcause concerns regarding durability,since the internal steel reinforcementhas been eliminated from this system.The maximum moment capacities ofthe two piles are very similar, despitethe differences in geometry, size, andmaterials.

(a) Tension failure

(b) Stress-strain curve in the axial direction

Fig. 9. Failure mode and behavior of longitudinal tension coupons tests of the GFRP tube.

Fig. 10.Fabricationand handlingof precastcompositepiles.

(a) Pumping concrete into the upper end

(b) Rear end showing wooden plugs

(c) Handling of the pile using eight-point supports

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Fig. 13(a). Driving of composite test pile. Fig. 13(b). Driving of prestressed test pile.

Prestressed pile

Composite pile

FIELD TESTING OFCOMPOSITE AND

PRESTRESSED PILESPrior to installation of the produc-

tion piles for the new Route 40Bridge, a test pile program was com-pleted at the bridge site. Axial and lat-eral loading tests were performed ontwo full-scale, 43 ft (13.1 m) longpiles, one a composite pile and theother a prestressed concrete pile.Based on the subsurface conditions atthe bridge site, it was anticipated thatthe axial load capacity of the pilewould be governed by the geotechni-cal capacity, i.e., the soil support ca-pacity rather than the axial structuralcapacity of the pile.

Fabrication of the Piles

The GFRP tubes were shipped to theprecast plant and were filled with con-crete while they were placed in an in-clined position and supported by asteel beam along the full length of thetubes, as shown in Fig. 10. Wooden

Fig. 11. Fabrication of prestressed concrete pile. Fig. 12. Instrumentation of test piles.

The predicted axial load capacitiesof the prestressed and composite pilesare 2071 and 2812 kips (9212 and12508 kN), respectively. These valuesare based on the specified concrete

compressive strengths of the pre-stressed and composite piles, respec-tively, as well as the properties of thesteel strands and the GFRP tube.

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end plugs were used to seal both endsof the tube. The plugs were secured inposition using metal straps connectedto both the plug and the compositetube in radial directions, as shown inFig. 10(b).

Concrete was pumped into the upperend through a hole in the woodenplug. The concrete-filled compositetubes were handled using eight-pointlifting devices along the length of thepile, as shown in Fig. 10(c). The pre-stressed concrete piles were fabricatedat the precast plant in accordance withVDOT standards, as shown in Fig. 11.After fabrication and curing, the pileswere shipped to the bridge site.

Instrumentation

Both the composite and the pre-stressed concrete test piles were in-strumented with strain gauges in theaxial direction at three levels along thelength of the piles. At each level, twostrain gauges were placed near the twoopposite faces of the pile, as shown inFig. 12. The strain gauges weremounted on 36 in. (914 mm) long No.4 steel reinforcing bars, which wereembedded inside the concrete core.

Each test pile was also instrumentedwith eight lateral motion sensors tomeasure the lateral displacement pro-file of the pile during the lateral loadtests. The sensors were placed insidePVC tubes embedded inside the testpiles. The locations of the lateral mo-tion sensors are shown in Fig. 12.

To measure the axial stresses duringdriving, pairs of special strain gaugesand accelerometers were installed onthe concrete surface of the piles at adistance of 4 ft (1.2 m) from the top.For the composite pile, this wasachieved by cutting 5 x 5 in. (127 x127 mm) portions of the FRP shell inorder to attach the instrumentation tothe concrete surface.

Pile Driving

Both the composite and prestressedtest piles were driven using a hy-draulic impact hammer, Type ICEModel 160S, which was also used todrive the production piles for thebridge. The ram weight was 16,000lbs (71.2 kN). A 7.5 in. (190 mm)thick plywood pile cushion was used

during pile driving. Both of the testpiles were driven to a depth of about33.5 ft (10.2 m). The blow count wassix blows per 1 in. (25.4 mm) of pilepenetration for the composite pile andfour blows per 1 in. (25.4 mm) for theprestressed concrete pile.

Figs. 13(a) and 13(b) show the com-posite pile during and after driving, aswell as the prestressed pile duringdriving. Table 2 provides some of themeasurements obtained during piledriving. It can be seen that the wavespeeds, maximum compressivestresses, and maximum tensile stressesare each similar in the different piletypes. The measured stress levels are

lower than the allowable stresses rec-ommended for prestressed piles.14 Nostandards are available yet for drivingprecast composite piles.

Axial Load Tests

The composite and prestressed pileswere both subjected to axial loadsusing the Statnamic Testing System,as shown in Fig. 14. This system ap-plies the load to the pile by launchinga heavy reaction mass upwards atclose to 20g (twenty times the gravityacceleration). When the reaction massis launched upwards, an equal and op-posite reaction force acts on the test

Pile typeMeasurement Prestressed Composite

Wave speed 12,150 ft/s 11,840 ft/sMaximum compressive stress

2.55 ksi 2.78 ksimeasured during driving

Maximum tensile stresses0.7 ksi 0.42 ksi

measured during driving

Allowable stressesTension < 1.02 ksi No standards

Compression < 4.5 ksi available

Note: 1 ft = 0.305 m; 1 ksi = 6.89 MPa.

Table 2. Pile driving measurements for prestressed and composite piles.

Fig. 14. Axial loadtest using Statnamictest setup.

Load cell

Pressurechamber

Laser beam device

Composite pile

Reactionmass

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pile. The Statnamic load does not havethe impact nature of the hammer blow,but rather a more gradually increasingforce with a typical duration of 0.2 to0.3 seconds.

During the Statnamic test, severalmeasurements are taken, including theapplied load, the pile head displace-ment using a laser beam device shownin Fig. 14, and strains. A detailed de-scription of the Statnamic techniquecan be found in Brown.15 Each testpile was subjected to three loading cy-cles with increasing the magnitude ofthe applied load. The equivalent axialstatic load is determined by subtract-ing the inertia and damping forcesfrom the total measured force usingthe Unloading Point Method (UPM).16

The equivalent static load versuspile head axial displacement for theprestressed concrete and compositepiles is shown in Fig. 15 for the threecycles. The behavior during the lastcycle in both piles shows that thegeotechnical capacity of the piles wasfully mobilized, as evident from therapid increase of the pile displacementnear the end of the test. The ultimateequivalent static loads of the pre-stressed concrete and composite pilesat failure were 942 and 980 kips (4190and 4359 kN), respectively. Both pilesexhibited similar axial capacities, eventhough their shaft and end areas wereslightly different.

Fig. 16 shows the equivalent axialstatic load versus axial strain behaviorof both the composite and prestressedpiles based on the peak load and corre-sponding strain during each of thethree load cycles. The axial strain isbased on the average strain of the twouppermost strain gauges (closest to theloading end), since they measured themaximum axial strain induced in thepile.

Fig. 16 shows that the behavior ofthe two piles is relatively similar, withthe composite pile being slightly stifferthan the prestressed pile. The figurealso shows the design load of the piles,150 kips (667 kN), which is signifi-cantly lower than the ultimate load.

The variation of the axial strainsalong the length of both the pre-stressed and composite piles is shownin Fig. 17. It can be seen that the mea-sured strains along the depth are simi-

Fig. 16. Axial load versus axial strain behavior of test piles.

Fig. 17. Variation of axial strain levels along depth of pile.

Fig. 15. Variation of pile head displacement with equivalent axial static load.

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lar in both piles. The figure also showsthat the strain level is reduced as thedepth is increased. This is attributed tothe gradual transfer of axial load fromthe pile to the soil through skin fric-tion along the pile shaft.

Lateral Load Tests

Following the axial load tests, lat-eral load tests were conducted on boththe composite and prestressed piles,using the Statnamic Testing Systemshown in Fig. 18. The loading systemis similar to that used for the axialload test; however, the setup wasplaced horizontally in order to producea lateral load. During the Statnamictest, several measurements were taken,including the applied load and the lat-eral displacement of the pile at differ-ent depths. Each test pile was sub-jected to four loading cycles byincreasing the magnitude of load.

The equivalent lateral static load ver-sus the lateral deflection behavior ofthe two piles at the loading points isshown in Fig. 19. The figure showsthat the behavior has a similar moment-curvature response as shown in Fig. 7,for both the prestressed concrete andcomposite piles. For the compositepile, the sudden change in stiffness at alateral load of 11 kips (48.9 kN) re-flects the cracking point. For the pre-stressed pile, the initial stiffness is highdue to the prestressing effect and thehigher elastic modulus of steel.

Composite pile

Reactionmass

Pressurechamber

Fig. 18. Lateral load test using Statnamic test setup.

Fig. 20. Lateral deflection distribution along length of pile.

Fig. 19. Lateral load versus displacement response of piles using Statnamic test.

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Fig. 20 shows the lateral deflectiondistribution along the length of thepile at the peak load for each of thefour loading cycles, for both the com-posite and prestressed concrete piles.The figure indicates that lateral deflec-tions become insignificant at a certaindepth between 15 and 20 ft (4.5 and6.1 m) measured from the loadingpoint. The figure also indicates that,for the last two load cycles, the deflec-tion profile along the depth of thepiles is almost bilinear, with a sudden

change in slope occurring at a depth ofabout 16 ft (4.8 m), measured from theloading point. This suggests that, dur-ing the last two cycles, failure mayhave been initiated in both piles at thelocation of the change in slope.

CONSTRUCTION OF THENEW ROUTE 40 BRIDGE

Based on the results of the field andlaboratory testing of the compositeand prestressed concrete piles, the

Fig. 21. Precast composite piles for Pier No. 2 after driving.

Fig. 22. Details ofpile head

showing barsused to connect

pile to cap beam.

VDOT decided to use the compositepiles in the construction of Pier No. 2(see Fig. 4) of the new Route 40Bridge. The pier consists of a rein-forced concrete cap beam supportedby ten composite piles.

The composite production piles areidentical to the composite test pile interms of size, laminate structure of thetube, and the methods of constructionand driving. Fig. 10 shows the com-posite piles during casting and han-dling, while Fig. 13 shows the piledriving process. The installed compos-ite piles of Pier No. 2 are shown inFig. 21.

After all the piles were driven, andprior to casting the cap beams, specialpreparation of the pile heads was nec-essary to facilitate connecting the pilesto the cap beams. Eight, 1 in. (25.4mm) diameter holes were drilledthrough the top flat surface of eachpile, using a regular rock drill. Theholes were 18 in. (457 mm) deep, par-allel to the longitudinal direction ofthe piles.

In the prestressed concrete piles, theholes were equally spaced in a 13 in.(330 mm) square pattern, whereas inthe composite pile, the holes wereequally spaced in a 17.6 in. (447 mm)diameter circular pattern as shown inFig. 22. These arrangements allow fora 3 in. (76 mm) concrete cover foreach hole. Eight, 48 in. (1219 mm)long, No. 7 steel reinforcing bars wereinserted in the holes, and epoxy resinwas used to secure the bars inside theconcrete. Fig. 22 shows the details ofthe pile head and the steel dowels inboth pile types.

The formwork arrangement of thecap beams were placed such that thebottom surface of the cap beam is 6 in.(152 mm) below the upper surfaces ofthe piles to allow for embedment ofthe piles inside the cap beam. Fig. 23shows details of Pier No. 2. Fig. 23(b)shows the No. 7 steel bars, which areembedded 30 in. (762 mm) inside thecap beam.

Fig. 24 shows close-up views of PierNo. 2 and the connection between thecomposite pile and cap beam. A gen-eral view of the new completed bridgeis shown in Fig. 25. The bridge hasbeen in operation for over two years.

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Fig. 23. Connection of composite piles to cap beam at Pier No. 2.

Fig. 24. Pier No. 2 showing composite piles and reinforced concrete cap beam.

Reinforced concretecap beam

Cost Comparison

The cost of the composite piles in-cluding the costs of the GFRP tube,concrete, casting, and shipping was$95 per ft. The cost of driving thecomposite piles was $20 per ft. Thisresulted in a total cost of $115 per ftfor the installed composite pile, incomparison to a total cost of $65 per ftfor the installed square prestressedconcrete pile. Therefore, the initialcost comparison indicates about 77percent higher unit cost for the com-posite pile. Part of this higher costmay be due to the fact that compositepiles are not currently produced on alarge-scale basis. Further, current pro-duction of composite piles is mostly in

Precast compositepiles

Fig. 25. The new Route 40 Bridge over the Nottoway River in Virginia.

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smaller sizes for marine fendering ap-plications.

The higher costs may also be associ-ated with a lack of contractor experi-ence in handling and lifting compositepiles, which require special arrange-ments and equipment. Nevertheless,precast composite piles may gainwider acceptance in the constructionindustry when life-cycle costs are con-sidered because annualized mainte-nance and replacement costs for thenon-corroding composite piles are ex-pected to be less than for conventionalprestressed concrete piles in corrosiveenvironments.

CONCLUSIONSBased on the testing and construc-

tion experience gathered so far, thefollowing conclusions can be drawn:

1. The use of concrete-filled FRPtubes as piling for bridge piers is prac-tical and feasible. The FRP tubeserves as permanent formwork and re-inforcement at the same time, elimi-nating the need for internal reinforce-ment and temporary formwork.

2. The flexural strength of the 24.6in. (625 mm) diameter composite pilewith a 0.213 in. (5.4 mm) thick GFRPtube is similar to the flexural strengthof the 20 in. (508 mm) square concretepile prestressed with fourteen, 0.5 in.(12.7 mm) diameter strands. However,the stiffness of the composite pile afterfirst cracking was lower.

3. The composite pile failed inbending by fracture of the GFRP tubeon the tension side, whereas the pre-stressed concrete pile failed by yield-ing of the strands in tension, followedby crushing of the concrete in com-pression.

4. Both the composite and pre-stressed concrete piles performed sim-

ilarly during pile driving, as evidentfrom the measured wave speed gener-ated by the driving hammer and themeasured compressive and tensilestrains.

5. Both the composite and pre-stressed concrete piles performed sim-ilarly under the axial load tests. Fullgeotechnical capacity was mobilizedin both cases before structural failureof the piles. The axial load at failurewas significantly higher than the de-sign pile load.

6. The lateral load field tests on boththe composite and prestressed pilesshowed a similar behavior to that ob-tained from the laboratory flexural testand analysis.

7. Similar pile-to-cap beam connec-tions were used for the composite andprestressed concrete piles, includingeight No. 7 steel dowels embedded 18in. (457 mm) inside the piles from oneend and extending 30 in. (762 mm)into the cap beam. The piles them-selves were embedded 6 in. (152 mm)inside the cap beam.

8. An initial cost comparisonshowed a unit cost for the installedcomposite piles 77 percent higher thanfor the installed prestressed piles.However, as production volume in-creases, and by considering life-cyclecosts of the low-maintenance compos-ite piles, the cost comparison mayshift in favor of composite piles incorrosive environments.

9. To date, no indications of unsatis-factory performance of the compositepiles of the Route 40 Bridge havebeen reported.

Further research is still needed toexamine the following aspects of com-posite piles:

1. Behavior under combined load-ing.

2. Methods of improving the bond

between the tube and the concretecore.

3. Methods for increasing the flexu-ral stiffness, such as prestressing.

4. Shear behavior.5. Behavior under cyclic loads. Additional case histories and long-

term performance data are needed. De-tailed life-cycle cost analyses are alsoneeded to determine the cost effective-ness of these piles.

The VDOT and FHWA are cur-rently engaged in another compositepile research project associated withthe new Route 351 Bridge over theHampton River in Virginia. This pro-ject is a continuation of the compositepile research of VDOT and sponsoredby FHWA to contribute to the scarcedata available on projects with com-posite piles. This project is differentfrom the Route 40 Bridge in themethod used for the field test, wherestatic load tests are performed usingconventional hydraulic jacks insteadof the Statnamic tests.

ACKNOWLEDGMENTThe authors want to acknowledge

the Federal Highway Administration(FHWA), the Virginia Department ofTransportation (VDOT), the VirginiaTransportation Research Council(VTRC), and the Network of Centersof Excellence, ISIS Canada Program,for supporting and sponsoring the lab-oratory and field tests.

The authors would also like to ac-knowledge Lancaster Composite forproviding the composite tubes andproviding valuable guidance duringthe construction of the compositepiles.

The authors are also grateful to thePCI JOURNAL reviewers for theirconstructive comments.

May-June 2003 15

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