CFRP Strand Application on Penobscot Narrows Cable Stayed Bridge

Rohleder, Jr., P.E., S.E., W. Jay Page 2<strong>CFRP</strong> <strong>Strand</strong> <strong>Application</strong> on Penobscot Narrows Cable Stayed BridgeABSTRACTMaine’s first cable stayed bridge opened to traffic on December 30, 2006. Designed as an emergency replacementfor the Waldo Hancock Bridge, the new bridge uses an innovative cradle system to carry the stays from bridge deckthrough the pylon and back to the bridge deck. Each strand is anchored independently, thus strands may beremoved, inspected and replaced while the bridge carries traffic. This advantage, coupled with Maine DOTconcerns over the premature loss of the Waldo Hancock Bridge due to corrosion, provided the interest in anopportunity to install and monitor representative carbon fiber reinforced polymer (<strong>CFRP</strong>) strands in the cable staysof this bridge. <strong>CFRP</strong> strands were installed for purposes of assessing performance in a service condition andevaluation for use on future bridges. Three representative stays in the bridge were designed to include two referencestrands each, which may be removed and not replaced, without change to the bridge’s structural integrity. Six epoxycoated steel strands were removed and successfully replaced with <strong>CFRP</strong> strands in June 2007. Data is beingcollected from the monitoring equipment installed on all of the strands (both traditional steel and <strong>CFRP</strong> strands) inthe bridge to evaluate <strong>CFRP</strong> strand performance for future bridge cable stay and post-tensioning installations. Thebridge location ensures that the test strands will be evaluated under a wide range of temperatures and variety of windloads.

Rohleder, Jr., P.E., S.E., W. Jay Page 3CFCC <strong>Strand</strong> <strong>Application</strong> on Penobscot Narrows Cable Stayed BridgePROJECT BACKGROUNDThe opportunity for incorporating carbon fiber reinforced polymer (<strong>CFRP</strong>) cable strands into a new cablestay bridge in Maine started in July 2003 when the Maine Department of Transportation awarded a contract forrenovation of the 75-year old Waldo-Hancock (steel suspension) Bridge. Based on the Maine Department ofTransportation inspection program, confirmed by a minor exploratory opening of the main cables, the Department’sadvisor theorized that the main suspension cable was structurally intact. However, as work progressed and the cablewas progressively unwrapped, it became evident a considerable amount of corrosion had taken its toll on the bridge.The bridge was immediately posted and extensive steps taken to reduce the superstructure weight and strengthen thebridge by adding supplemental cables to reduce the load on the corroded main cables. Simultaneously, planning anddesign started for a replacement structure (Figure 1), given that the strengthening project success was not assuredand that any immediate success could add only a limited number of years to the existing suspension bridge’s servicelife.The Maine Department of Transportation quickly contracted with FIGG, from a field of 14 interestedteams, as designer of the new bridge and initiated an ‘owner-facilitated’ design/build process to quickly deliver thenew bridge. Design decisions were made rapidly, while involving the public in evolving the bridge aestheticelements. The optimum new structure was identified as a 2,120’ (646M) cable stayed bridge with a main spanlength of 1,161’ (354M). By fall, just six months later, the Maine Department of Transportation had negotiated astaged contract for construction with Cianbro/Reed & Reed, LLC, a joint venture of the state’s two largestcontractors and ground was broken on December 3, 2003.FIGURE 1 – Penobscot Narrows Bridge Elevation View.CABLE STAY SYSTEM BACKGROUNDAs the new cable stay bridge design rapidly progressed, there was extensive discussion among the owner,contracting team and FIGG on details of the cable stay system. FIGG had worked with Ohio Department ofTransportation and the Federal Highway Administration to complete testing and receive approval in 2001 forinstalling the cradle system in a new cable stayed bridge, the I-280 Veterans’ Glass City Skyway in Toledo, Ohio.The Maine Department of Transportation elected to also use the cradle system, recognizing the advantages of longterm durability and ease of maintenance. Given Maine’s recent history with cable conditions, considerable effortswere directed toward developing a new cable stay system that prevented any opportunity for corrosion. Thepatented (U.S. 6,880,193; 4-19-05) new cradle that housed individual stay strands was seen as a significant means tohelp accomplish this goal.

Rohleder, Jr., P.E., S.E., W. Jay Page 4With the cradle design, cable stay strands serve as tensile elements that are individually threadedcontinuously from an anchorage at the bridge deck (see Figure 2), through a free length of HDPE external sheath(see Figure 3), through the cradle in the pylon (see Figure 4) and back through another sheath and anchorage atbridge deck on the opposite side of the pylon.FIGURE 2 – Cable Stay Block for Anchoring Individual <strong>Strand</strong>s Inside the Box Girder.FIGURE 3 – Cable Stay Sheath Containing Individual <strong>Strand</strong>s.

Rohleder, Jr., P.E., S.E., W. Jay Page 5Location of CradleEmbedded in thePylon WallFIGURE 4 – Cable Stay Cradle LocationFIGURE 5 – Cable Stay Cradle Pipes Prior to Installation.

Rohleder, Jr., P.E., S.E., W. Jay Page 7equipment allows for the selective replacement of steel strands with <strong>CFRP</strong> strands. The bridge location in coastalMaine provides a wide array of weather conditions for a testing opportunity that includes large temperaturevariations and high humidity in a brackish water environment. Testing of <strong>CFRP</strong> strands under these actual serviceconditions could be accomplished with a reasonable effort that could serve as a “Living Laboratory.” Financialsupport was provided by the FHWA and the State of Maine using federal Innovative Bridge Research andDeployment program funds for the <strong>CFRP</strong> applications.Maine DOT with FHWA, FIGG and Lawrence Technological University collaborated to develop thedesign details for incorporating <strong>CFRP</strong> strands into the bridge as special reference strands. One of the key challengeswas devising the method for anchoring these cable strands within the already designed and fabricated cable stayanchorage system for this bridge. This included developing the specific hardware for installing the strands and thentransferring the stressing force directly from the strand into the stay anchor. The design team was interested inselecting a representative number of strands to replace with <strong>CFRP</strong> that would serve as a comprehensivedemonstration at the least possible additional cost. Within this guideline, it was decided that we would replace tworeference strands in a short, medium and long stay. Variations in structural response due to thermal effects, initialversus long-term bridge stresses and flexibilities in the overall bridge system would be captured by testing a shortand long stay with the middle stay serving as an average representation. Additional selection criteria includedproximity to the existing data logger, utilizing stays with symmetrical strand patterns that worked best for design ofthe permanent anchor chairs, and coordination with concurrent final stay construction activities. Of the 20 possiblestays, the design team selected Stay 2 (short), 10 (average) and 17 (long) through the Western (observatory) Pylonas the representative stays for carbon fiber strand installation as shown in Figure 7. .The fast-tracked bridge construction was completed with traditional epoxy coated steel strands installed inthe stays and the bridge opened to traffic on December 30, 2006, just 42 months after identifying the need for anemergency bridge replacement. In June 2007, on the heels of a day long festival celebrating the bridge, six steelstrands (two each in three stays – short, medium and long) were removed and installation of the <strong>CFRP</strong> strandssuccessfully completed – while the bridge continued to carry traffic. The <strong>CFRP</strong> strands will be monitoredindefinitely and inspected over time to evaluate the structural behavior and long term durability as it relates to usingthe <strong>CFRP</strong> materials for many more future applications in long span bridge designs throughout the United States.FIGURE 7 – Location of Stays Containing Experimental <strong>CFRP</strong> <strong>Strand</strong>s.

Rohleder, Jr., P.E., S.E., W. Jay Page 8The University of Maine contributed to the project with lab testing and calibration of load cells and fiber opticsensors that are measuring forces on the <strong>CFRP</strong> strands. They also proof tested the permanent anchor chairs andtemporary stressing chairs. They will also provide long term data collection of forces, strains and temperatures onthese innovative <strong>CFRP</strong> strands. The collected data will be analyzed by the design team to compare results withexpected structural performance criteria for the <strong>CFRP</strong> and relative to the adjacent high-strength steel strands. Thecomparative performance criteria will include data such as initial prestressing elongations, force losses, and anchorset values along with long term expected design strand prestressing forces related to time dependent properties andthermal effects experienced by the bridge.BACKGROUND OF PREVIOUS CFCC USE IN VEHICULAR BRIDGESCurrently, advanced fiber reinforced polymer (FRP) materials find worldwide application in theconstruction of small and large structures 1-5 such as beams and bridges. However, prestressed concrete bridgesconstructed using CFCC reinforced polymer (<strong>CFRP</strong>) tendons are few in number 1-6 . The FRP is a linearly elasticmaterial which may not provide a ductile failure mode like steel, however a structural member that is prestressedand reinforced with CFCC can be designed to fail in a similar ductile manner as under-reinforced concrete members.The results of early research investigations 6-10 conducted in the Center for Innovative Materials Research atLawrence Technological University, Southfield, Michigan have shown that internally bonded <strong>CFRP</strong> tendons incombination with externally unbonded <strong>CFRP</strong> tendons can lead to reasonably ductile simply supported 6,7 andcontinuous 9,14 prestressed concrete bridge systems. These results formulated the basis for design of the BridgeStreet Bridge 11, located in Southfield, Michigan. The Bridge Street Bridge is the most recent <strong>CFRP</strong> prestressedconcrete bridge in the USA and the first to use CFRLeadline TM tendons, CFCC TM strands, and <strong>CFRP</strong> NEFMAC TM1The Bridge Street Bridge served as a resource during development of the Penobscot Narrows Bridge <strong>CFRP</strong>strand installation methods, details and material specifications.PROJECT <strong>CFRP</strong> MATERIAL QUALITITES AND CHARACTERISTICSThe specific <strong>CFRP</strong> material used for the Penobscot Narrows Bridge project is CFCC TM strand that isproduced by the Tokyo Rope Mfg. Co., Ltd. It comes in a variety of sizes, from 0.20" diameter single wire to 37individual helically wound wires with a total nominal diameter of 1.57". The actual CFCC TM strand used for thePenobscot Narrows Bridge cable stay test project is a 0.60" diameter, 7 wire strand, with 6 wires helically woundaround a center king wire. There is also a protective coating along the outside of the strand to shield the fibers fromnormal handling and exposure. The properties from the certification tests of the production strands used for thisproject are shown in Table 1. Note that the tensile rigidity for CFCC as included in Table 1 is defined as the slopeof a load-strain curve derived from the tensile tests. The CFCC tensile rigidity is the average value of results fromthe 20 test pieces from the load-strain curve obtained in accordance with a tensile test at 20% and 60% of theguaranteed tensile capacity.While the <strong>CFRP</strong> strand is similar in size to the steel strand, there are some significant material property differences.Due to the smaller effective cross sectional area and modulus of the <strong>CFRP</strong> strand, the elongations are approximately1.73 times that of the steel strand used for this project. The stress-stain relationship of the <strong>CFRP</strong> strand is also linearup to ultimate loading. Thus, there is no ductility within the strand. Compared to steel the <strong>CFRP</strong> strand isapproximately 5 times lighter, which makes handling and installation easier. The shear resistance for the carbonfiber reinforced polymer cable material is negligible; therefore precautions need to be taken to avoid applying anytransverse forces on the cable.Since there are no anchorages within the pylons, the friction between the strands and the cradle sleeves isan important design parameter. The actual friction coefficient was measured in the laboratory during thepreliminary design phase for the steel strand and before installation for the CFCC strand. The friction coefficientmeasured for the steel strand is 0.5 while the CFCC strand value is 0.3. While this decrease in friction for thereplaced strands do not affect the behavior of the Penobscot Narrows Bridge, this property would have to beconsidered for a stay completely constructed using <strong>CFRP</strong> strands or any other prestressing applications whichexperience friction resistance.

Rohleder, Jr., P.E., S.E., W. Jay Page 9Similar to conventional steel prestressing, care must be utilized during handling of <strong>CFRP</strong> strands.Excessive bending, abrasion, shearing, crushing, or heat will damage the <strong>CFRP</strong> strand. In general, the <strong>CFRP</strong> strandis more susceptible to damage than the steel strand, thus additional care is required during installation. It was alsoimportant to avoid twisting of the <strong>CFRP</strong> strand along its axis during installation.CFCC TM QUALITY REPORTMessrs.Maine DOT Penobscot Narrows Bridge & ObservatoryConfiguration CFCC 1×7 15.2φReport No.TEST-0890Date Sep. 29, 2006UnitSpecificationTest resultsItem(metric) Nominal(metric)English (metric) ToleranceEnglishEnglishLot No. - - - 1166 (d) 1168 (e)Diameter(mm)In.(15.2)0.60Effective cross sectional area (mm 2 ) (113.6)In 2 0.176Pitch(mm)In.-Linear density(g/m) (226)lb/ft 0.15Breaking load(kN)kipsTensile strength (kN/mm 2 )ksiTensile rigidity(kN)kips(199)44.8(1.75)254(15,600)3,510-Ave. (15.5)0.61(15.4)0.61- - - ---(199) orabove(1.87) orabove (a)(14,500~17,500)Tensile modulus (kN/mm 2 ) (137) (127~153)ksi 19,887(b)Elongation at break % 1.5 1.2 orabove (c)1 MPa = 0.145 ksi; 1 kN = 0.225 kips; 1 g/m = 0.000672 lb/ft; 1 in. = 25.4 mmAve. (193)7.6Ave. (225)0.15Ave. (246)55.3Max. (259)58.3Min. (232)52.2Ave. (2.20)319Ave. (15,980)3,596Ave. (141)20,468(190)7.5(222)0.15(241)54.2(250)56.2(234)52.7(2.10)305(16,160)3,636(142)20,613Ave. 1.5 1.5(a) Tensile strength = Breaking load / Effective cross sectional area(b) Tensile modulus = Tensile rigidity / Effective cross sectional area(c) Elongation at break = Breaking load / Tensile rigidity(d) CFCC test lot for Stay 02(e) CFCC test lot for Stay 10 and 17TABLE 1: CFCC 1x7 Prestressing <strong>Strand</strong> Properties (Tokyo Rope Mfg. Co., Ltd., Japan 15 )

Rohleder, Jr., P.E., S.E., W. Jay Page 10PROJECT CARBON FIBER SYSTEM COMPONENTS AND DESIGN DETAILSKey components for the <strong>CFRP</strong> strands installed into the Penobscot Narrows Bridge cable stay system are theanchorage sockets and permanent jacking chairs.<strong>CFRP</strong> strands are low in shear strength and subject to brittle fracture when using biting wedges. As such, gripingwedge style anchorages that are conventionally used for steel post-tensioning cannot be used for <strong>CFRP</strong> strands.Alternatively, the carbon strands for this project were bonded in a threaded socket using highly expansive grout (seeFigure 8 and 9). The socket is a long threaded rod with a voided center slightly larger than the diameter of thestrand. The annular space between the inside socket wall and the strand is filled with a cementatious based material,which exhibits a high degrees of expansion (HEM) during curing. As curing takes place expansion of the material isconstrained by the socket wall and the strand. This constraint ultimately produces a confining pressure ofapproximately 11 ksi, locking the socket and strand end together. This is described as approximate since the actualconfining pressure for a specific anchor is dependent on the actual grout thickness. General testing and experiencewith the Bridge Street Bridge 11 has shown that this confining pressure from the HEM is valuable for avoiding creepconcerns as might be found if an epoxy agent had been used to anchor the strand in the socket.FIGURE 8 – General View of CFCC TM Anchor Sleeve with Nut and <strong>Strand</strong>.FIGURE 9 – End View of CFCC TM Anchor Sleeve with HEM retaining the <strong>Strand</strong>.Custom permanent jacking/anchor chairs were fabricated (see Figure 10) for this application. These chairs weredesigned to straddle the existing anchorage elements. Extensive proof load testing was performed in the laboratoryto document the behavior of the chairs under actual field conditions. Force from the carbon fiber strand bears on acenter hole load cell and permanent anchor chair via the threaded socket nut (see Figure 10). The threaded portionof the socket provided plus/minus 4" of adjustment from the anticipated position. The load cells were initiallycalibrated prior to installation. The need for additional calibration throughout the life of the permanent installationwill be evaluated as time progresses. However, a primary value of the load cells will be to compare the relativestrain differences between the carbon fiber and epoxy coated steel strands.

Rohleder, Jr., P.E., S.E., W. Jay Page 11FIGURE 10 – Permanent Anchor Chair with <strong>CFRP</strong> Load Cell and Monitoring Lead Wires.The reference strands from stays 2, 10 and 17 over the western (observatory) pylon were replaced. Final loadslocked into the <strong>CFRP</strong> strands varied from 21.05 kips to 25.27 kips depending on strand location. Table 2 belowcontains a full description of the permanent initial loadings placed on the carbon fiber strands.LocationLength from Jacking ChairBack Face to Pylon Face(Length of <strong>CFRP</strong> <strong>Strand</strong>)(feet)Adjacent Steel <strong>Strand</strong>Force at Time of <strong>CFRP</strong><strong>Strand</strong> Stressing(kips)Actual <strong>CFRP</strong> <strong>Strand</strong>Lock-offStressing Force(kips)Stay 02 Back Span 134 25.20 25.27Stay 02 Main Span 149 22.20 22.02Stay 10 Back Span 303 22.00 21.05Stay 10 Main Span 346 21.10 21.66Stay 17 Back Span 459 22.20 21.66Stay 17 Main Span 526 21.30 20.58TABLE 2 – Carbon Fiber <strong>Strand</strong> Stressing Results.Other than an underestimation of initial length needed to take out slack in the cable as it was threaded intothe stay, and the additional stretch of the cable within the pylon (approximately 3 inches at all locations), theelongations as pre-calculated were within expected tolerance of actual installation values.

Rohleder, Jr., P.E., S.E., W. Jay Page 12<strong>CFRP</strong> INSTALLATION METHOD AND DETAILSThe Maine Department of Transportation contracted with the joint venture partners that had constructed thebridge, Cianbro/Reed & Reed, LLC, to also perform installation of the <strong>CFRP</strong> strands. The installation process wassupervised by representatives on-site from the Maine DOT, FHWA, FIGG, and Lawrence Technological University.The <strong>CFRP</strong> monitoring devices were installed and data recorded by the University of Maine staff during initialstressing of the strands.Each of the six <strong>CFRP</strong> strands were individually installed using the existing epoxy coated steel strands aspull lines. The initially installed epoxy coated steel strands were each detensioned by first utilizing a temporaryjacking chair bearing on the permanent anchor chair to apply a jacking force (see Figure 11) that allowed forremoval of the strand retaining wedges, followed by an incremental release of the strand force.FIGURE 11 – Permanent and Temporary Chairs with Destressing Jack and Bar.A custom coupler was created for gripping the steel strand on one end and connected to a high strengthstressing bar on the other end (see Figure 12). The destressing was performed using a center hole hydraulic posttensioningjack (refer back to Figure 11). The initial lift-off pressures were recorded to use as a reference whenapplying the stressing force to the replacement <strong>CFRP</strong> strands.A different specially fabricated custom designed coupler was then used to grip the king wire of thedestressed steel strand on one end and attach to the <strong>CFRP</strong> strand at the other end of the coupler (see Figure 12). Thesteel strand was removed by pulling it out from the cable stay while concurrently pulling the <strong>CFRP</strong> strand in behindthe removed steel strand. An anchor sleeve was then attached to the <strong>CFRP</strong> strand tail by pouring the cementatiousbased highly expansive material (HEM) into the sleeve socket that housed the strand tail (refer back to Figure 8 and9). The HEM was allowed to cure for 24 hours prior to stressing the strand. The anchoring sleeve is threadedaround the perimeter to engage the socket setting nut that bears against the permanent jacking chair (refer back toFigure 8). The strand and anchorage sockets were supplied by Tokyo Rope Mfg. Co., Ltd., and representatives fromthis company also assisted on-site with attachment of the anchorage sockets to the <strong>CFRP</strong> strand tails.

Rohleder, Jr., P.E., S.E., W. Jay Page 13FIGURE 12 – Various <strong>Strand</strong> Coupler Components:(The Steel <strong>Strand</strong> to Post-Tensioning Bar Coupler for <strong>Strand</strong> Detensioning and Removal is shown fullyassembled in the Top View with individual components displayed in the Center View. The Steel <strong>Strand</strong>King Wire to <strong>CFRP</strong> <strong>Strand</strong> Coupler components used for <strong>Strand</strong> Installation is shown in the BottomView.)Once the anchors were positively attached and the HEM completely cured in the <strong>CFRP</strong> strand tail sleeves,the load cells, fiber optic sensors, socket setting nut, temporary stressing nut, and jacking nut were placed in theproper order as shown in the layout detail of Figure 13.FIGURE 13 – <strong>CFRP</strong> End Anchorage System Layout.

Rohleder, Jr., P.E., S.E., W. Jay Page 14The <strong>CFRP</strong> strands were incrementally stressed to their final force against the permanent jacking/anchorchairs using a center hole hydraulic stressing jack. The temporary stressing nut was tightened against the socketsetting nut during the incremental stressing with each stroke of the jack until the socket setting nut could be fullyengaged upon the threads of the socket. Once the final force was placed on the strand, the temporary stressing nutand jacking chair were removed (refer back to Figure 10). The long-term monitoring lead wires and end sealing capwere then installed over the stay anchorage.With the understanding that care must be taken while handling <strong>CFRP</strong> strand, the design team aggressivelyprepared a Quality Control plan well before starting installation. A detailed installation manual was developed bythe design team, with the Contractor participating in all of our meetings during the development process. The teamprogressed through many iterations of the manual until satisfying all the participants that every possible handlingconcern had been addressed. The procedures included details such as handling of strand from the reel along aprotective trough (fabricated as a split plastic duct) into the anchor end of the stay system. The result was asuccessful installation with only one minor incident of scraping the protective strand coating.CONCLUSIONInstallation of six representative carbon fiber reinforced polymer (<strong>CFRP</strong>) strands in the Penobscot NarrowsBridge cable stay system was successfully demonstrated. These reference <strong>CFRP</strong> strands serve as contributingstructural elements of the permanent stay system and also as a proof test of their long-term performance.The long term <strong>CFRP</strong> strand performance will be determined by comparing the force over time as recordedby the monitoring load cells with the initial force and analytically expected long term forces. Another monitoringtool used for evaluation is the dyna-force strand sensors that were provided by Dywidag Systems International andplaced on three of the epoxy coated steel strands during initial stressing of the stays. The recorded forces on the<strong>CFRP</strong> strands will be compared to forces measured on the epoxy coated steel strands in the stays. The climateextremes in Maine will provide a valuable performance test for the use of <strong>CFRP</strong> under service conditions.It has been demonstrated with this project that various lengths of <strong>CFRP</strong> strand can be successfully handled,installed and stressed on a long span cable stay bridge in a construction environment. The successful deploymentand expected long term performance of the <strong>CFRP</strong> strands used in the Penobscot Narrows Bridge cable stays providetestimony in support of continuing to explore and advance the application of these advanced composite materials inmore long span bridge members. The recognized merits from eliminating potential corrosion related problems byusing <strong>CFRP</strong> prestressing and reinforcing components that will also not need to be grouted for protection along withtheir light weight characteristic provides exciting opportunities for use in future long span bridges.As has been successfully demonstrated from this project and earlier projects 2, 11 , it is feasible to easilydeploy <strong>CFRP</strong> strands as both cable stays and conventional external post-tensioning tendons in future conventionalbridge projects. The one lesson that was verified through this installation is that to advance the use of thistechnology for general post-tensioning tendons, a refinement of the currently used anchoring system will need to bedeveloped that allows for quick construction and efficient use of the anchorage area.Indeed, the success of this <strong>CFRP</strong> strand installation in the Penobscot Narrows Bridge sets the stage forpotentially even more conventional applications of the <strong>CFRP</strong> material in future long span bridges.

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