AASHTO-ACI 2013

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Title no. 110-S39

ACI STRUCTURAL JOURNAL TECHNICAL PAPER

ACI Structural Journal, V. 110, No. 3, May-June 2013.MS No. S-2011-204.R1 received July 11, 2011, and reviewed under Institute

publication policies. Copyright 2013, American Concrete Institute. All rightsreserved, including the making of copies unless permission is obtained from thecopyright proprietors. Pertinent discussion including authors closure, if any, will bepublished in the March-April 2014ACI Structural Journalif the discussion is receivedby November 1, 2013.

Performance of AASHTO-Type Bridge Model Prestressed

with Carbon Fiber-Reinforced Polymer Reinforcement

by Nabil Grace, Kenichi Ushijima, Vasant Matsagar, and Chenglin Wu

Carbon fiber-reinforced polymer (CFRP) composite material has

been widely studied and applied in bridge engineering as an alter-native solution to the corrosion-related problems posed by steelreinforcement. Nevertheless, adoption of CFRP reinforcementto replace conventional steel reinforcement in highway bridgeshas not been fully realized yet in the field. Therefore, large-scale

experimental investigations on bridges with CFRP reinforcementare essential to encourage its widespread application in highwaybridges. This paper presents an experimental investigation conductedon a one-third-scale AASHTO-type bridge model prestressed withcarbon fiber composite cable (CFCC) strands. The bridge model

was designed, constructed, instrumented, and tested to thoroughly

investigate its flexural behavior, strain response, and ultimate loadfailure. A separate one-third-scale single AASHTO-type I-beamwas also constructed and tested to study its flexural and shearbehavior as a control beam. In general, both the control beam and

the bridge model experienced compression-controlled failure asanticipated. Significant cracking and deflection were experienced

prior to failure. The ultimate strength of the control beam and thebridge model were in close agreement with the values estimatedusing the Unified Design Approach.

Keywords:AASHTO; carbon fiber composite cable; carbon fiber-reinforcedpolymer; ductility; fiber-reinforced polymer; flexure; prestress; reinforcement.

INTRODUCTIONCorrosion of steel strands and reinforcement is one of the

major reasons the structural integrity of prestressed concretebridges is compromised before the bridges reach their fulllife span. The viable solution to eliminate the corrosion-related problems associated with conventional prestressedand reinforced concrete bridges is the application of fiber-reinforced polymer (FRP) materials. The high strength-to-weight ratio, superior fatigue resistance, ease of handling,low thermal expansion, and low relaxations are some ofthe advantages of the FRP materials over conventionalsteel reinforcement. These excellent characteristics madecarbon fiber-reinforced polymers (CFRPs) a potential futureconstruction material in the bridge construction industry.

The various types of I-beam cross sections specified inAASHTO1have been extensively used in the recent construc-

tion of prestressed concrete bridges.2 Features such as asimpler cross section, higher flexural capacities, and reducedmanufacturing costs make the AASHTO beam a modestchoice for constructing long-span bridges. In addition, FRPmaterials can help sustain a longer life span with minimalmaintenance costs. To adopt the innovative CFRP materialsin the bridge construction industry, thorough investigationsare essential; however, an extensive review of the literaturereveals that limited research is available on the application ofCFRP materials in AASHTO-type beams.

In 1997, Fam et al.3 tested five I-beams prestressedand reinforced with CFRP materials with a span of 9.5 m(30.5 ft) and one conventionally reinforced beam prestressed

and reinforced with steel with the same geometry and span.

In this study, it states that the flexural behavior of the beams

prestressed with CFRP strands exhibited stiffness similar to

the beam prestressed with steel strands. Also, the variation

of the web reinforcement ratio did not significantly influ-

ence the flexural behavior of the beams, and the failures

were controlled by bending capacity. Further, the shape of

the stirrups did affect the shear failure of the beam.

To further investigate the load-deflection relationship of

concrete beams fully prestressed with CFRP, Abdelrahman

and Rizkalla4conducted an experimental study that included

four prestressed concrete T-beams with a total length of

6.3 m (21 ft) and a depth of 330 mm (13 in.). The results of

the study show that the load-deflection relationship of these

beams was bilinear up to failure, and negligible residual

deformations were experienced during the tests.

To provide guidelines in the design and construction of the

Bridge Street Bridgethe first concrete bridge prestressed

with CFRP materials in the United StatesGrace et

al.5conducted a full-scale test on a CFRP prestressed double-

tee beam. It was concluded that the anticipated prestressing

levels were maintained during the test. The strain-compat-

ibility-based Unified Design Approach was proposed by

Grace and Singh,6 which was validated by experimental

results conducted on a double-tee beam bridge model

reinforced and prestressed using carbon fiber composite cable

(CFCC) strands. Furthermore, a compression-controlled

failure mode was recommended as the design failure mode

for CFRP prestressed concrete beams.7 This recommenda-

tion was based on the better ductility characteristics of over-

reinforced sections. Also, an ultimate concrete compressive

strain of 0.0025 was reported, as experienced in the experi-

mental work.

In typical designs of concrete highway bridges prestressed

with conventional reinforcement, tension-controlled failure

mode dominates, as higher ductility is exhibited by yielding

of the steel reinforcement. CFRP, however, is a brittle mate-

rial exhibiting a linear stress-strain relationship up to rupture.Because a compression-controlled failure mode provides

better ductility than a tension-controlled failure mode in

terms of extensive deflections, ACI 440.1R-068 recom-

mends a compression-controlled design failure mode for the

concrete bridges reinforced and prestressed with the CFRP

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2 ACI Structural Journal/May-June 2013

ACI member Nabil Grace is the Dean of the College of Engineering, University

Distinguished Professor, and Director of the Center for Innovative Materials Research

(CIMR) at Lawrence Technological University (LTU), Southfield, MI.

Kenichi Ushijimais a Senior Engineer at Cable Technologies North America, Inc.

He received his bachelors degree in engineering from Yamaguchi National University,

Yamaguchi, Japan.

ACI member Vasant Matsagaris a Visiting Professor at the Center for Innovative

Materials Research (CIMR) at LTU.

Chenglin Wuis a former Research Assistant at the Department of Civil Engineering

at LTU.

materials. In this experimental investigation, therefore, thecompression-controlled design failure mode was adopted.

RESEARCH SIGNIFICANCEThe experimental study presented in this paper explains

the design philosophy, construction techniques employed,and flexural performance of AASHTO I-beam and bridgemodel reinforced and prestressed with CFCC strands.Experimental results of this investigation were validatedwith the Unified Design Approach.6This investigation alsocompliments the ongoing research on merits gained by using

the CFRP reinforcement for the construction of highwaybridges. Further, the results presented in this paper shouldallow engineers and designers to take full advantage of thispotential, emerging technology to overcome the corrosion-related problems in the current practice of AASHTO-typebeam bridges.

CONSTRUCTION DETAILSThe control beam and bridge model was constructed,

instrumented, and tested at the Center for Innovative

Materials Research (CIMR) at Lawrence TechnologicalUniversity (LTU). The AASHTO Type IV I-beams9weredesigned as over-reinforced sections as per the flexuraldesign philosophy8 to be used in the experimental inves-tigation. The one-third-scale (1:3.6) control beam consistedof a single precast prestressed AASHTO I-beam with a spanof 12,141 mm (39 ft 10 in.) and a 64 mm (2.5 in.) thickCFCC-reinforced composite deck slab. The cross section ofthe AASHTO I-beams used in this investigation was 502 mm(19.75 in.) deep with top and bottom flange widths of 203 mm

(8 in.) and a web thickness of 95 mm (3.75 in.), as shown inFig. 1. The one-third-scale (1:3.6) bridge model consisted offive AASHTO I-beams placed at a center-to-center distanceof 502 mm (19.75 in.), joined with five equally spaced 64 mm(2.5 in.) thick transverse diaphragms (404 mm [15.875 in.]in depth below the deck slab soffit), and topped with a 2.5 m(98.75 in.) wide and 64 mm (2.5 in.) thick deck slab,9 asshown in Fig. 2. The structural integrity of the bridge modelwas ensured by extending transverse reinforcement of thediaphragms into the beams and tying protruded verticalreinforcement of the diaphragms and protruded stirrups ofthe beams to transverse reinforcement of the deck slab.10

Each precast prestressed AASHTO I-beam consisted ofthree longitudinal CFCC prestressed strands and seven longi-tudinal non-prestressed CFCC strandsall with a diameterof 15.2 mm (0.6 in.)as flexural reinforcement distributedvertically along the depth of the beam. The CFCC stir-rups, measuring 7.5 mm (0.3 in.) in diameter and spaced ata center-to-center distance of 102 mm (4 in.), were usedas shear reinforcement and protruded in the deck slabby 38 mm (1.5 in.). The details of the CFCC reinforcementin the I-beam are presented in Fig. 1 and 3. Each beam wassubjected to a total prestressing force of 266.89 kN (60 kip)equally distributed among the three longitudinal CFCC

Fig. 1Cross-sectional details of I-beam.

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ACI Structural Journal/May-June 2013 3

prestressed strands. A rectangular end block 533 mm (21 in.)long, 203 mm (8 in.) wide, and 502 mm (19.75 in.) deep

was provided on each side of the beams to resist burstingstresses generated during the transfer of the pretensioningforces. Moreover, confinement in the end-block regions wasprovided with rectangular stirrups spaced at a center-to-center distance of 51 mm (2 in.), as shown in Fig. 3.

The deck slab of the bridge model was reinforcedby 20 longitudinal non-prestressed CFCC strands 15.2 mm(0.6 in.) in diameter and 62 transverse non-prestressed CFCCstrands 7.5 mm (0.3 in.) in diameter spaced at a center-to-center distance of 203 mm (8 in.). CFCC strands 7.5 mm(0.3 in.) in diameter were passed through transverse holesprovided at the web of the I-beams as diaphragm reinforce-ment for the bridge model. The mechanical properties of

the CFCC strands and stirrups are shown in Tables 1 and2, respectively. Because the CFCC stirrups were bent at

two ends by 90 and 180 degrees, tensile strength tests wereconducted on different portions of the CFCC stirrups todetermine the actual strength. The minimum strength wasselected as the design strength of the CFCC stirrups.

Construction of AASHTO I-beamsUpon completion of constructing the formwork for the

AASHTO I-beams, CFCC reinforcement cages were assem-bled and placed inside the formwork. The required concretecover (38 mm [1.5 in.]) at the bottom of the beams wasprovided by attaching 76 mm (3 in.) diameter plastic circularchairs under the cages. The CFCC prestressing strands werepassed through the reinforcement cages at designated layers

Fig. 2Dimensions of bridge model.

Fig. 3Cross-sectional details of control beam.

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and positioned between two bulkheads. Calibrated load cellswere mounted on the prestressing strands at the dead endand connected to a data acquisition system to monitor andrecord the level of pretensioning forces applied. In addition,the strain gauges mounted on the prestressing strands andthe pressure gauge installed on the hydraulic jack were usedto monitor the applied pretensioning forces.

The pretensioning force was applied through a 305 mm(12 in.) center hole hydraulic jack positioned at the live end.

A custom-made steel chair was attached to the hydraulicjack and supported on the bulkhead to transfer the reactionsgenerated during the application of the pretensioning forces.Moreover, to verify the pretensioning force applied, elon-gations experienced in the CFCC prestressing strands weremeasured during the prestressing operation by measuringram displacement of the hydraulic jack. Each prestressingstrand was stressed to an average jacking force of 88.96 kN(20 kip) to achieve a total pretensioning force of 266.89 kN(60 kip) on each beam. The applied pretensioning force of88.96 kN (20 kip) in each CFCC prestressing strand wasapproximately 30% of the average breaking load (Table 1).

After the prestressing operation, the concrete was placedin the formwork and proper uniform compaction was

achieved using three electrical pencil vibrators. The average28-day compressive strength of the concrete was 44.82 MPa(6500 psi). After placing the concrete, the beams were wet-cured by covering them with soaked burlap for 7 days. Whenthe concrete attained the required compressive strength,pretensioning forces were released by saw-cutting theCFCC prestressed strands simultaneously from both ends ofthe beams.

Construction of control beam and bridge modelOne of the six AASHTO I-beams was selected as the

control beam and was moved to the testing area underneath aloading frame and was positioned on steel supports 762 mm

(30 in.) tall, measuring 356 x 1372 mm (14 x 54 in.). Elas-

tomeric bearing pads 25.4 mm (1 in.) thick were placedbetween the beams and steel supports at each end to simulate

the field conditions. Upon placing the control beam underthe loading frame, a CFCC-reinforced 64 mm (2.5 in.) thick

and 502 mm (19.75 in.) wide deck slab was cast. The averagecompressive strength of the concrete for the deck slab was

44.82 MPa (6500 psi). After the concrete in the deck slabgained adequate strength, the control beam consisting of the

single AASHTO I-beam and the cast-in-place deck slab wasinstrumented and tested for flexure.

The other five AASHTO I-beams were moved to anothertesting area underneath a loading frame, and the beams

were positioned on steel supports to allow the constructionof the deck slab and transverse diaphragms for the bridge

model. The five beams were maintained at a center-to-centerdistance of 502 mm (19.75 in.). Non-prestressing CFCCstrands 7.5 mm (0.3 in.) in diameter were passed through the

holes kept in the beams and epoxied to brace the beams inthe transverse direction. Vertical reinforcement of the trans-

verse diaphragm was attached to its transverse reinforcementand formwork was provided around the reinforcement. Prior

to the deck slab reinforcement placement, formwork for thedeck slab was attached to the beams and diaphragm form-

work and supported on the ground as typically practiced inshored construction. The deck slab reinforcement consisted

of 20 No. CFCC 1 7 15.2 mm (0.6 in.) strands in thelongitudinal direction and CFCC 1 7 7.5 mm (0.3 in.)

strands at 203 mm (8 in.) in the transverse direction. Theconcrete was placed in the diaphragms and the deck slab, and

compacted properly with pencil vibrators and metallic rods.After finishing the top surface of deck slab the bridge model

was covered with soaked burlap for 7 days. Upon hardeningof the concrete for 7 days, supports of the formwork were

removed. The average 28-day compressive strength of the

Table 1Mechanical properties of tested CFCC prestressing and non-prestressing strands

Types Transverse non-prestressing strands Longitudinal prestressing strands Longitudinal non-prestressing strands

Diameter, mm (in.) 1 x 7, 7.5 (0.3) 1 x 7, 15.2 (0.6) 1 x 7, 15.2 (0.6)

Effective area, mm2(in.2) 30.97 (0.048) 115.48 (0.179) 115.48 (0.179)

Breakingload

Maximum, kN (kip) 95.01 (21.36) 305.99 (68.79) 305.99 (68.79)

Minimum, kN (kip) 91.02 (20.46) 274.99 (61.82) 274.99 (61.82)

Average*, kN (kip) 91.99 (20.68) 295.98 (66.54) 295.98 (66.54)

Tensile strength, MPa (ksi) 2972 (431) 2558 (371) 2558 (371)

Modulus of elasticity, MPa (ksi) 164,000 (23,786) 157,000 (22,771) 157,000 (22,771)*Five specimens were tested.

Table 2Mechanical properties of tested CFCC stirrups

Types CFCC rod at straight portion CFCC rod at 180-degree bent end CFCC rod at 90-degree bent end

Diameter, mm (in.) 7 (0.28) 7 (0.28) 7 (0.28)

Effective area, mm2(in.2) 30.97 (0.048) 30.97 (0.048) 30.97 (0.048)

Breakingload

Maximum, kN (kip) 72.02 (16.19) 37.2 (8.36) 40.5 (9.10)

Minimum, kN (kip) 60.00 (13.49) 30.4 (6.83) 25.6 (5.76)

Average*, kN (kip) 64.99 (14.61) 34.0 (7.64) 38.6 (8.68)

Tensile strength, MPa (ksi) 2096 (304) 1098 (159) 1246 (181)

Modulus of elasticity, MPa (ksi) 145,000 (21,030) 145,000 (21,030) 145,000 (21,030)*Five specimens were tested.

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concrete in the deck slab and the transverse diaphragms was27.58 MPa (4000 psi).

Instrumentation and test setupPrior to the casting of the AASHTO I-beams, electrical

strain gauges were attached to the CFCC prestressingstrands to measure the strain responses. After the concretein the deck slab gained adequate strength, two linear motiontransducers were installed at the quarter-span and midspan,respectively, to measure the deflections of the control beamduring the flexural load test. Two strain gauges were mountedon the top surface of the deck slab at midspan to record thestrain response of the extreme compressive concrete fiber ofthe control beam. Meanwhile, to observe the strain response

of the CFCC stirrups, five DEMEC stations (Rosette type)were also installed at the shear-critical sections. A steelloading framethat is, a spreader with two loading pointsspaced at a distance of 965 mm (38 in.)was placed on thedeck slab at midspan. An actuator with a maximum loadingcapacity of 889.64 kN (200 kip) was used to apply load atthe center of the spreader. A load cell with a capacity of889.64 kN (200 kip) was connected to the actuator to recordthe applied load. To prevent the possible twist that mightbe caused during the loading process, custom-made steelguides were installed around the beam at both quarter-spanpoints and beam ends. The test setup for the control beam isshown in Fig. 4.

The control beam was subjected to several loading andunloading cycles to separate the elastic and inelastic ener-gies. These loading cycles were 13.34, 31.14, 35.59, 53.38,66.72, 88.96, and 111.21 kN (3, 7, 8, 12, 15, 20, 25 kip) andultimate load cycle. Figure 5 shows the control beam duringthe flexural load test.

Different sensors were installed and used to analyze thebehavior of the bridge model according to the test program.The test program for the bridge model consisted of the flex-ural performance, decompression and cracking load, andultimate load tests.

In the flexural performance test, each beam of the bridgemodel was loaded at quarter-span and midspan with a singlepoint load of 66.72 kN (15 kip). Linear motion transducers

were installed at both quarter-span and midspan to measurethe deflections of the beams under different loading cases.

In the decompression load test, a 1.22 m (48 in.) longspreader was used to load the bridge model at midspan.Linear motion transducers were installed at the midspan ofthe bridge model to monitor and record the deflection. Straingauges were attached at the bottom surface of the centerbeam at midspan to determine the decompression load.

In the ultimate load test, the bridge model was loadedusing a steel square tube with a length of 1.22 m (48 in.)mounted at the midspan covering the center beam and itstwo adjacent beams, as shown in Fig. 6. The strain gaugesinstalled on the CFCC strands, linear motion transducers

Fig. 4Test setup for control beam.

Fig. 5Flexural load test of control beam.

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installed at midspan, and strain gauges installed on the topsurface of the deck slab at midspan were used to analyze thebehavior of the bridge model. Similar to the flexural loadtest conducted on the control beam, the bridge model wassubjected to several loading and unloading cycles beforefailure to separate the elastic and inelastic energies. Thesecycles were conducted at 311.38, 355.86, 422.58, 444.82,489.30, 533.79, and 578.27 kN (70, 80, 95, 100, 110, 120,and 130 kip) and at ultimate load.

RESULTS AND DISCUSSIONThe control beam failed with an ultimate load-carrying

capacity of 162.05 kN (36.43 kip) and a correspondingdeflection of 292 mm (11.5 in.). The ultimate load-carryingcapacity of the control beam is in close agreement with thedesigned value of 164.58 kN (37 kip) using the UnifiedDesign Approach proposed by Grace and Singh6(importantsteps in the design procedure are shown in the Appendix *).Because the control beam was over-reinforced with a

*The Appendix is available at www.concrete.orgin PDF format as an addendum tothe published paper. It is also available in hard copy from ACI headquarters for a feeequal to the cost of reproduction plus handling at the time of the request.

reinforcement ratio of 0.0046 (the balanced reinforce-

ment ratio for the section was calculated as 0.00196), a

compression-controlled flexural failure initiated by theconcrete crushing at the midspan was observed. The load-

deflection behavior of the control beam experienced a

bilinear response, as shown in Fig. 7, with cracking load of

28.91 kN (6.5 kip). The load-strain responses of the top and

bottom layers of the CFCC prestressing strands also experi-enced a bilinear response, as shown in Fig. 8. However, the

strain gauges on the strands stopped functioning at a load

of 62.28 kN (14 kip). The CFCC prestressing strands werefurther examined after the beam failure and no damage was

experienced. Meanwhile, the load-strain response of theextreme compressive concrete fiber was also recorded, as

shown in Fig. 9. The maximum strain experienced by the

extreme compressive concrete fiber was 2000 at failure.

The ductility of the control beam was evaluated by the

energy ratio, which was calculated using the energy-based

approach.11Accordingly, the failure of a structure is defined

as brittle failure if the energy ratio is lower than 70%.

Therefore, the failure of the control beam was defined as a

brittle failure with an energy ratio of 46.88%, as shown in

Fig. 10. However, a sufficient warning prior to the failure

Fig. 6Test setup for ultimate load test of bridge model.

Fig. 7Load-deflection behavior of control beam.

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Fig. 8Strain experienced by CFCC prestressing strands in control beam.

Fig. 9Compressive strain of top concrete fiber at midspan of control beam.

Fig. 10Ductility of control beam.

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was provided by the excessive deflection and extensivecracks of the control beam before reaching the ultimate loadof 162.05 kN (36.43 kip).

A significant number of diagonal cracks were observed inthe shear zone (between the loading points and beam ends)of the control beam. Details of the cracks mapped at differentload levels are shown in Fig. 11. As the control beam wasdesigned to have a flexural failure, adequate CFCC stir-rups were provided to avoid any premature shear failure.Therefore, the widths of the cracks were insignificant andthe maximum width of the shear cracks was approximately0.2 mm (0.009 in.) at a corresponding load of 111.21 kN

(25 kip). Thus, the CFCC stirrups provided in the AASHTOI-beams in the desired bent shapes served the intendedpurpose satisfactorily.

The strain responses of the CFCC stirrups at DEMECStation 2 were recorded and compared to the estimatedvalues using ACI 440.4R-047and ACI 318-0512approaches,as shown in Fig. 12. It can be seen that both the sheardesign approaches proposed by ACI 440.4R-047 andACI 318-0512 conservatively predicted the strains of theCFCC stirrups at a load of 111.21 kN (25 kip). However, theestimated strain responses of the CFCC stirrups using theapproach proposed by ACI 440.4R-047were closer to the

Fig. 11Cracks developed in control beam.

Fig. 12Strain experienced by CFCC stirrup at DEMEC Station 2.

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actual strains experienced as compared to those estimatedusing ACI 318-05.12Furthermore, the maximum strain of theCFCC stirrups measured at DEMEC Station 2 was 500 ,which was less than the ultimate strain of the CFCC stirrups(756 ). This fact signifies adequate strength of the CFCCstirrups during the flexural load test. The shear failure loadfor the control beam, predicted based on the strains experi-enced, was 178 kN (40 kip).

As mentioned previously, the test program conducted onthe bridge model included the flexural performance test,decompression and cracking load test, and ultimate loadtest. In addition, the flexural performance test was repeated

after the decompression and cracking load test to examinethe behavior of the bridge model at the cracked stage.

The decompression and cracking load test was conductedto determine the effective prestress and the cracking loadof the bridge model. During the test, the bridge model wassubjected to a single point load positioned on a 1.22 m(48 in.) long spreader located on the center beam (B-3) atmidspan. The first flexural crack was observed at the bottomof Beam B-3 at the midspan with the corresponding load of104.53 kN (23.5 kip). The bridge model was then unloadedto allow installing a set of four strain gauges at both sidesof the initial flexural cracks. Upon completing the installa-tion, the bridge model was reloaded. The strain of the bottomconcrete fiber increased proportionally to the applied load

immediately after the reloading started. When the stress of thebottom concrete fiber approached zero, however, the strainstopped increasing and remained constant as the load appliedon the bridge model was still increasing, as shown in Fig. 13.The decompression load determined through the load-strainresponse of the bottom concrete fiber was 57.83 kN (13 kip).The overall prestress loss was subsequently calculated as 11%based on the decompression load, which is less than the typical15% prestress loss, as usually reported for beams prestressedusing steel strands.13At the end of the test, the bridge modelwas loaded up to 266.89 kN (60 kip) to allow the developmentof the flexural cracks. The flexural performance test was thenrepeated after the bridge model was extensively cracked.

The ultimate load test was conducted by applyinga uniformly distributed load on a 1.22 m (48 in.) longand 152 mm (6 in.) wide steel square tube placed acrossthe bridge model at the midspan. After several loadingand unloading cycles, the bridge model failed at a loadof 689.47 kN (155 kip) with the corresponding deflectionof 240 mm (9.45 in.) at center beam, B-3. This ultimate load-carrying capacity of the bridge model was in close agree-ment with the designed6value of 733.96 kN (165 kip). Thefailure was initiated by concrete crushing at top compres-sion fibers at the midspan of the bridge model, and theCFCC prestressing strands were still intact after the bridge

model failed. The load-deflection behavior of the bridgemodel, as shown in Fig. 14, showed bilinear response dueto the concrete cracking, similar to what was observed inthe control beam. The load-strain response of the extremecompressive concrete fiber for the bridge model was alsorecorded, as shown in Fig. 15. The maximum concrete strainreached by the extreme fiber was 2520 in compression.The strain responses of the CFCC strands in the bridgemodel were monitored throughout the test. The load-strainresponses of different layers of the CFCC strands and theextreme compressive concrete fiber during the ultimate loadcycle are shown in Fig. 16. The maximum strain reachedby the bottom prestressing strands was 10,000 , whichwas 66.7% of the ultimate strain for the CFCC strands

(15,000 ). This fact suggests that perhaps a higher preten-sioning force can be applied to increase the cracking load.

The energy ratio of the bridge model was 26.67%, whichwas calculated using the energy-based approach,11as shownin Fig. 17. Although the ductility of the bridge model waslow in the terms of the energy ratio and the excessive deflec-tion and extensive cracks experienced, the bridge modelprovided significant warning before failure.

CONCLUSIONS AND RECOMMENDATIONSThis paper presents an experimental investigation

addressing the application of CFRP strands in prestressedAASHTO I-beams and bridges. The ACI 440.4R-047design

Fig. 13Strain experienced at bottom concrete fiber in bridge model.

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guidelines and the Unified Design Approach proposed byGrace and Singh6were used in the flexural and shear designof the control beam and bridge model. The test results wereanalyzed and compared with the estimated values, andseveral conclusions are drawn as follows.

1. Both the control beam and the bridge model experienceda compression-controlled failure as expected. The calcu-lated ultimate load-carrying capacities for both the control

beam and the bridge model were 164.58 and 733.96 kN(37 and 165 kip), respectively. These values are in close agree-ment with the experimental values (162.05 kN [36.43 kip]for the control beam and 689.47 kN [155 kip] for the bridgemodel). This verified that the Unified Design Approach6 issuitable in designing the AASHTO I-beams and bridges.

2. The maximum strain of the CFCC stirrups measured atthe shear-critical sections was 500 , which was less thanthe ultimate strain of 756 . This demonstrates the excellentperformance of the CFCC stirrups in resisting the shear loadexperienced by the AASHTO I-beams.

3. The calculated strain of the CFCC stirrup usingACI 440.4R-047approach was conservative as compared to

the experimental value experienced at the load of 111.21 kN(25 kip). This fact further indicates that ACI 440.4R-047sheardesign approach can be adequately used in the design of theAASHTO I-beams using CFCC stirrups.

4. An 11% prestress loss was calculated through thedecompression test conducted on the bridge model, whichis less than the typical 15% prestress loss, as traditionallyreported for beams prestressed using steel strands. This

further demonstrates the excellent performance of the CFCCstrands in prestressed concrete AASHTO I-beams.

5. The CFCC strands were not damaged after the failure ofthe control beam and the bridge model. The maximum strainexperienced by the prestressing CFCC strands was 66.7%of the ultimate strain. Therefore, a higher pretensioningforce may be recommended to be applied on the CFCCprestressing strands.

6. The energy ratios of the control beam and bridge modelwere 46.88% and 26.67%, respectively. These values clas-sified the failures of both the control beam and bridgemodel as brittle failure.11However, the excessive deflec-tions and the extensive cracks provided sufficient warning

Fig. 14Load-deflection behavior of bridge model.

Fig. 15Compressive strain experienced by extreme concrete fiber ofbridge model.

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prior to the failure for this type of AASHTO I-beam bridge

with CFCC strands.

ACKNOWLEDGMENTSThis investigation was supported by the U.S. Department of Transpor-

tation (US-DOT) (Contract No. DTOS 59-06-G-0030) and MDOT-LTU

Center of Excellence. The support and guidance of B. Jacob, Senior Policy

Analyst, US-DOT; and L. N. Triandafilou, Senior Structural Engineer,

FHWA, are truly appreciated. Moreover, the Tokyo Rope Manufacturing

Company Limited, Japan, supplied the CFCC reinforcement.

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Bridge Design Specifications, third edition, American Association of State

Highway and Transportation Officials, Washington DC, 2004.

2. Martin, R. D.; Kang, T. H.-K.; and Pei, J.-S., Experimental and Code

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PCI Journal, V. 56, No. 1, Dec. 2011, pp. 54-74.

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10. MDOT, Bridge Design Manual, Bureau of Highway Development,MI, 2006, 466 pp.

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Fig. 16Strain experienced by CFCC strands at ultimate load of bridge model.

Fig. 17Ductility of bridge model.

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