Frp For Sustainable Precast Concrete Structures - 北海道大学
Proceedings of US-Japan Workshop onLife Cycle Assessment of Sustainable Infrastructure MaterialsSapporo, Japan, October 21-22, 2009FRP FOR SUSTAINABLE PRECAST CONCRETE STRUCTURESSami RizkallaDepartment of Civil, Construction, and Environmental Engineering, North Carolina State University, Raleigh,NC 27695, USAABSTRACTThe use of FRP for sustainable precast concrete structures has become a commonpractice. The precast industry has recognized the advantage of this life-cycleapproach and has begun to implement FRP materials in innovative applications.This paper summarizes some of the emerging developments and establishedapplications. The selected applications presented in this paper are double-teebeams, insulated sandwich precast load bearing panels, architectural cladding andprecast concrete filled FRP tubes. Several possible future opportunities are alsopresented.1 INTRODUCTIONThis paper presents some of the emergingdevelopments and established applications related tothe use of FRP materials for precast concreteStructures. The paper focuses on the innovative useof FRP materials in several selected precasttechnologies including double-tee beams, insulatedprecast wall panels, architectural cladding andprecast concrete filled FRP tubes (CFFT). Theunique advantages of the FRP reinforced systems arehighlighted and the primary action mechanisms ofthe FRP materials are presented.The paperconcludes by identifying several areas of possiblefuture opportunities in which FRP materials can beused for further advancement of the precast industryand for civil engineering infrastructure in general.2 DOUBLE-TEESPrecast double-tees are commonly used inconstruction of parking decks and roof structures inwhich the top flange of the members are subjected tosevere environmental exposure including rain, snowand de-icing salts. Since precast members areoptimized to provide the most structurally and costefficient use of materials, the flanges of thesemembers are relatively thin, in the range of 2 to 4inches. These thin top flanges are typically lightlyreinforced with steel welded wire fabric to controlshrinkage and thermal cracks and to transmit theload from the flange to the stems of the double-teesin one-way slab bending action. Under harshexposure conditions, and over time, the flanges aresubjected to penetration of moisture and chlorides.This can lead to corrosion of the reinforcement,cracking and spalling of the cover concrete andpossible discoloration of the member. The noncorrosive properties and high strength-to-weightratio of carbon FRP (CFRP) grids make thesematerials ideally suited to replace conventional steelwelded wire fabric as reinforcement for the flangesof double-tees as shown in Figure 1(a). In additionto enhancing the durability of precast concretemembers, lightweight CFRP grids are commerciallyavailable in rolls which can be installed using anautomated process, as shown in Figure 1(b), therebyaccelerating the construction process.
(a)CFRP grid(b)Figure 1: (a) Schematic of CFRP reinforced double-tees (b) Apparatus for automated installation of CFRP gridin flanges of precast double-tees (courtesy of Metromont Corporation)Due to the brittle nature of CFRP materials,there is some concern regarding the possibility of abrittle failure of the flange reinforced with CFRPmaterials. To address these concerns, two full-scale12DT(30) double-tees, with CFRP grid reinforcedflanges were subjected to a uniformly distributedload and tested to failure.The uniformlydistributed load was applied using atmosphericpressure by constructing a pressure chamber aroundthe beams and applyingsuction within the chamber using high-poweredvacuums as shown schematically in Figure 2. Thetwo tested double-tees were identical except that thefirst, DT1, had a top flange thickness of 2 incheswhile the second, DT2, had a flange thickness of 3.5inches. Both beams were tested according to theload test requirements of chapter 20 of the ACI 31808 building code [1] which requires application of asustained factored load for 24 hours. The beamswere subsequently tested monotonically to failure.The test setup is shown in Figure 3(a).
Figure 2: Schematic of pressure chamber to apply uniformly distributed load to double-tee beams(a)(b)Figure 3: (a) Setup for testing precast double-tees under uniformly distributed loading (b) Cracking of DT2under concentrated load (crack enhanced)Both of the tested double-tees were capable toresist the maximum factored load for 24 hours whileexhibiting minimal residual deflections uponrecovery.The subsequent monotonic tests tofailure indicated that beams DT1 and DT2 were ableto sustain a maximum load equal to 1.3 and 1.9 timesthe full factored load respectively. DT1 failedalong the entire span of the double-tee due to theformation of a large longitudinal crack in theoverhanging flange near one of the stems, crushingof the concrete and rupture of the CFRP grid whichwas evident by total separation of the overhangingflange from the rest of the beam. The observedlinear failure along the entire length was due to thenature of the uniformly distributed load that wasused to test the member. The member exhibitedsignificant deflection and cracking prior to failure.DT2, which had a 3.5” thick top flange did notfail and the test was halted when the applied loadwas equal to 1.9 times the maximum factored load ofthe double-tee due to an inability to increase thesuction inside the test chamber. The test resultsindicated that the flange bending behavior of thedouble-tees was quite sensitive to the flangethickness. Therefore, the possible brittle flangebending failure mode can be avoided by properlydesigning the thickness of the top flange. For thetwo tested double-tees, increasing the flangethickness from 2” to 3.5” increased the flexuralmoment of inertia of the overhanging flange by morethan five times which resulted in a correspondingincrease of the cracking load and reduction of theflange deflections.The double tee wassubsequently tested under the effect of concentratedload as shown in Figure 3(b) and the resultssatisfied the recommendations of the PCI DesignGuideline [2].3 PRECAST CONCRETE SANDWICH WALLPANELSThese panels consist of two concrete wythesseparated by a rigid foam core. These highlyefficient precast members can serve multiplepurposes within the same structural member. Thewall panels can act as a part of the primary loadcarrying system of the structure to transfer gravityloads and lateral loads, due to wind or seismic events,to the foundation of the structure. Further, thepresence of the foam core increases the overallinsulation properties of the panel thereby improvingthe overall thermal characteristics of the structure.Finally, the exterior face of the precast panels can beconstructed with an architectural finish to contributeto the overall aesthetics of the structure. The panelscan be designed to act in fully composite action,partial-composite action or non-composite to achievethe intended purpose of the panel. The level ofcomposite action depends on the type of shearconnection provided between the two wythes.For conventional precast concrete fullycomposite structural wall panels, the shearconnection is typically provided between the innerand outer wythes by casting concrete solid zoneswithin the core of the panels or by using throughthickness steel ties.One series of tests wasconducted on panels in which the inner and outerwythes were connected with a steel truss assembly[3]. Test results indicated that the panels behavedas nearly fully composite up to failure. Other
research has indicated that solid concrete zones withan area of 1 percent or steel pin connectors with anarea of 0.1 percent of the panel area can reduce theTypicalprecastconcretesandwich wall panel systeminsulation properties (R-value) of a wall panel by upto 40 percent [4]. The locations of the shear‘hotspots’ at locationsof concrete solid zonesFigure 4: Thermal ‘leaking’ of precast concrete wall panel system due to thermal bridges at locations ofconcrete solid zones (courtesy of Composite Technologies Corporation)connectors thus form hot spots on the exterior of thestructure, as shown in Figure 4, in the thermal imageof these walls. For these panels heat is transmittedout of the structure through the shear connectors.This results in a thermally inefficient structure withincreased heating costs and energy consumption.Recently some of the precast producers in theUnited States adopted the use of FRP ‘shear truss’type shear connectors for fully composite wall panels.These panels are structurally and thermally efficientand behave as fully composite wall panels utilizingthe inner and outer wythes of precast concretesandwich panels. One method to achieve the ‘sheartruss’ mechanism consists of cutting square CFRPgrid at a 45o angle as shown in Figure 5(a). Thegrid is then embedded through the foam core intoboth wythes of the sandwich panel as shown in thefigure. Alternatively, GFRP bars can be pultrudedin a truss configuration as shown in Figure 5(b) andembedded in the wall panels in a similar manner.In both cases the FRP grid or bars are oriented todirectly resist the maximum shear stresses through atruss mechanism. The cross section of a typicalpanel is shown in Figure 5(c). The presence ofinternal pilasters helps to transmit vertical loads fromthe roof system to the foundation while providingadditional rigidity to the overall panel. In one studya total of six full-scale wall panels were fabricatedusing different types of foam cores and differentconfigurations of CFRP grid shear connectors [5].The panels were tested under the combined effect ofsimulated vertical gravity loads and lateral cyclicloads to simulate wind loading over the lifespan of atypical structure. The measured deflections andstrains indicated that the CFRP shear truss providedfully composite action at service load levels.Further the testing indicated that the degree ofcomposite action was highly dependent on the typeof foam used in the core material. A companionanalytical study indicated that varying the type offoam core material can approximately double theshear transfer between the two wythes [6]. Typicaltesting of a full-scale wall panel is shown in Figure5(d). The type of foam core can also affect theinsulating and vapour barrier characteristics of thepanel and therefore should be designed incollaboration with the panel producers.Theanalytical study further indicated that the degree ofcomposite action of the panels decreased withincreasing load level. At the service load level thepanels acted in nearly fully-composite action whilenear the ultimate load level the degree of compositeaction was slightly reduced.Based on the experimental and analytical study,a design guide was established to design the requiredamount of shear connection required for a given wallpanel using CFRP grid as shown in Figure 5(e) [7].The required shear force at the interface between thetwo wythes, and therefore the overall amount ofCFRP required is based on the required momentcapacity of the wall panel and the level of compositeaction desired. The design of a wall panel withGFRP truss connectors is based on the assumptionthat the panel exhibits 80 percent composite actionunder service loading conditions and 50 percentcomposite action under ultimate loading conditions[7].
(a)(b)(d)(c)(e)Figure 5: FRP shear connectors for fully composite precast concrete wall panels (a) CFRP grid ‘shear truss’connectors (b) GFRP shear truss connectors (courtesy Hughes Brothers Inc.) (c) Typical wall panel crosssection (courtesy Altus Group) (d) Testing of a full-scale composite sandwich wall panel (e) Proposed guidelinefor design of CFRP shear connection for precast concrete wall panels [7].
In some applications it is desirable that theprecast sandwich panels act in non-composite action.In this case one wythe of the panel, typically theinner wythe, is load bearing while the outer wythe isnon-load bearing and provides the architecturalfinish for the structure. This type of behaviour isdesirable, for example, in regions where a highthermal gradient exists between the exterior andinterior of the structure.In this case fullycomposite panels can exhibit thermal bowing causedby differential expansion of the two wythes due tothe thermal gradient across the panel. This thermalbowing can result in several undesirable effectsincluding increased P-delta effects, lack of fitbetween adjacent panesl due to differential thermalbowing and intentional cracking of wythes. Byeliminated the shear connection between the twowythes, each wythe in the panel is free to deformindependently thereby foregoing the problemsassociated with thermal bowing. It is still necessary,however, to provide a limited degree of connectivitybetween the wythes to prevent wrinkling of thewythes and through thickness separation of the panelfrom the core.Conventionally wythes areconnected to each other with discrete metallic pins orconnectors.However, as discussed, theseconnectors provide thermal breaks through the coreof the panel resulting in thermal inefficiency.Alternatively, glass fiber reinforced vinyl ester resinpins have been developed which facilitate themanufacture of thermally efficient, non-compositeprecast sandwich panels. A typical GFRP pinconfiguration is shown in Figure 6.Figure 6: Typical GFRP pin for construction ofnon-composite sandwich wall panels4 ARCHITECTURAL CLADDINGFRP materials have also been used as secondaryreinforcement for non-structural, architecturalcladding. For architectural products uniformity ofcolor, crack mitigation, and thermal efficiency areprimary considerations and structural demands areminimal.Precast architectural cladding panelstypically consist of a thin exterior concretediaphragm face, on the order of 1 to 2 inches thick.This layer is supported by a steel reinforcedVierendeel concrete frame with intermediate verticaland/or horizontal members, as shown schematicallyin Figure 7(a). This frame is attached to theprimary load carrying frame of the structure. Thetwo components of the frame are separated by aninsulating foam core layer and connected by a 45oCFRP shear grid similar to that used for compositewall panels. CFRP grids are also used as al diaphragm to prevent thermal andshrinkage induced cracking. The use of noncorrosive CFRP materials prevents staining andcracking of the architectural finish which can occurdue to corrosion and expansion of conventional steelreinforcements. The CFRP reinforced panels canweigh as little as 30 percent of the weight of similarconventional steel reinforced precast architecturalcladding panels. The primary weight savings aredue to the reduction of the required concrete coverthickness to protect the secondary reinforcementfrom corrosion for conventional steel-reinforcedcladding.
Triangularribofsupporting Vierendeeltruss-like frameCFRP shear-grid connectionbetween outer diaphragm andsupporting frameCFRP grid reinforcementof outer diaphragmFoam insulationlayerExterior architecturaldiaphragmPlan view (not to scale)(a)CFRP shear-gridVertical back rib configurationHorizontal back rib configurationBack ribs designed to accommodatepunched openings(b)Figure 7: (a) Schematic representation of CFRP reinforced architectural cladding panels (courtesy HighConcrete Group) (b) Different configurations of the Vierendeel truss-like supporting frame to accommodatedifferent panel configurations (courtesy Altus Group).5 PRECAST CONCRETE PILES (CFFT)These members consist of a filament woundGFRP tube which acts as a stay-in-place form for aconcrete core. In addition to acting as a stay-inplace form, the GFRP tube acts as the primarylongitudinal reinforcement of the piles and providesconfinement for the concrete core. The presence ofthe GFRP tube eliminates the need for internalreinforcement and prevents ingress of moisture andsulphates into the concrete thereby enhancing theenvironmental durability of the piles.Theenhanced durability of the CFFT piles makes themwell suited for application as bridge piles and also inmarine applications including as supports for lightmarine structures, fender piles and pile clusters.Due to their enhanced durability and their similarperformance to conventional piles, ten CFFT pileswere used to construct one bent of the Route 40bridge in Virginia is shown in Figure 8(a) [8]. Thepiles exhibited similar axial load response andsimilar driving characteristics to conventionalprestressed precast concrete piles. The CFFT pileswere connected to the pile bent cap using a similar
detail to that used for the conventional piles. Aftertwo years in service the piles did not exhibit anyindication of deterioration.To increase the flexural cracking load of thepiles and reduce lateral deflections, prestressedCFFT (PCFFT) piles have also been developed.The piles can be internally prestressed using similarmaterials and methods to those used for conventionalprestressing as shown in Figure 8(b).Anexperimental investigation was conducted toevaluate the behaviour of the PCFFT piles [9].Two types of precast concrete piles were tested.The first tested pile was a circular PCFFT pile whilethe second was a conventional precast concrete pilethat was designed with similar dimensions andconfiguration of prestressing as the PCFFT. Theconventional pile was reinforced with a transversesteel spiral to compare the confinement effect of theGFRP tube and a conventional steel spiral. Thenormalized moment-deflection responses of the twopiles are shown in Figure 8(c). Comparison of thebehaviour indicates that both piles exhibited similarinitial stiffnesses.However the PCFFT pileexhibited a higher post-cracking stiffness, ultimatecapacity and energy absorption prior to failure ascompared to the conventional pile.This isprimarily attributed to two mechanisms: (1) theGFRP tube provided additional reinforcement to thepile in the longitudinal direction and (2) the presenceof the GFRP tube on the outer surface of the pileprovided confinement to a greater volume ofconcrete as compared to the internal steel spiraltypically used in conventional piles.CFFT pilebent(a)(b)(c)Figure 8: Prestressed CFFT piles (a) Route 40 CFFT pile bridge bent (b) Fabrication of typical PCFFT piles(c) Comparison of flexural behavior of PCFFT and conventional prestressed concrete circular piles (courtesy Dr.A. Fam, Queens University)
Hollow CFFT, with a circular void within thecentral core region of the pole, represent an efficientuse of concrete materials and can be used tosignificantly reduce the weight of CFFT members.These lighter weight members can be effectivelyused in applications in which the poles are subjectedprimarily to flexural loading conditions such as forlighting poles, highway sign support structures andas support structures for wind turbines. The hollowCFFT are commonly fabricated using the spincasting fabrication method in which the concrete isplaced into the circular GFRP tubes which aresubsequently spun at a high rate of revolution toconsolidate the concrete and to form the central void.In one study a series of spun-cast CFFT poles werefabricated with different sizes of interior voids andsubsequently tested to failure [10]. The resultsindicated that, for the specific type of CFFTconsidered, the diameter of the inner void could beincreased to 60 percent of the pole outer diameterwithout reducing the flexural strength of the pole ascompared to a similar CFFT member with a solidcross--section. The study further indicated that theultimate strength of the poles can be increased andthe strain demand on the external GFRP tube can bereduced by reinforcing the concrete portion of themember with additional internal mild steelreinforcement.6 FUTURE OPPORTUNITIESRecent developments of construction materialshave highlighted the advantages of using FRPmaterials and revealed a number of opportunities inwhich FRP materials can be used for sustainableprecast concrete Structures.FRP materials can be used as a reinforcement forseveral precast sections, including precast deckpanels, hollow core slabs and hollow core concreteplank bridges. The use of FRP reinforcement forthese profiles could potentially reduce the requiredcover concrete thereby resulting in lighter, moreefficient and sustainable members. FRP grids canalso be used as combined longitudinal and transversereinforcement for precast concrete piles therebyeliminating the possibility of corrosion andpotentially extending their serviceable life.Thin FRP grid materials can also enable theconstruction of thin precast concrete plate and shellstructures which serve both structural andarchitectural purposes while completely optimizingthe use of the materials and enhancing buildingaesthetics. The potential to use FRP materials forslender concrete structural members has beenhighlighted in a recent study in which precastconcrete lighting pylons were prestressed with 4 mmCFRP tendons [11]. The 9.2 m long poles had anouter diameter of 185 mm and a wall thickness ofonly 40 mm. The cantilevered poles were capableof achieving tip deflections up to 925 mm orapproximately L/100. The use of prestressed CFRPtendons in conjunction with high-strength concreteresulted in an overall flexible system despite thebrittle nature of the materials themselves. Similarhigh-strength, slender and flexible structures can bedeveloped by innovative application of FRPreinforcing and other new technologies includinghigh-strength concrete, self-consolidating concreteand reactive powder concrete.Through the ingenuity of the new generation ofengineers, and based on a thorough knowledge andunderstanding of structural behavior, FRP materialscan be used to develop a new generation of precastconcrete structures and systems to address thesustainability challenges of the 21st century.7 CONCLUSIONSThis paper summarized the recent developmentsand common applications of FRP materials for theconstruction of sustainable, durable and structurallyefficient precast products.The technologiesdiscussed in this paper represent some of the selectedadvancements in the precast industry.Theydemonstrate the distinct advantages of using FRPmaterials which result in improved structural,thermal and architectural characteristics of thecompleted precast product. Typically the use ofFRP materials can result in long-term economicbenefits when the life-cycle costs are considered.The advancements described in this paper representthe growing acceptance of FRP in the engineeringcommunity and symbolize what can be achievedwhen new technologies are combined with ingenuity.The applications described in this paper paint thepicture of a bright future for composite materials, inthe precast industry specifically and in civilengineering in general. These advancements leadthe way towards exciting new future opportunities inthe use of FRP materials and open the doors for thefuture success of the use of new and advancedmaterials, structures and systems in the years tocome.8 ACKNOWLEDGEMENTSThe authors would like to acknowledge thecooperationofAltusGroup,CompositeTechnologies Inc., High Concrete Group, HughesBrothers Inc., and Metromont Corporation, forproviding much of the necessary backgroundinformation needed for the preparation of this paper.9 REFERENCES[1] American Concrete Institute.(2008)Building
code requirements for structural concrete (ACI 31808) and commentary.Farmington Hills, MI:American Concrete Institute.[2] Precast/Prestressed Concrete Institute. (2004).PCI design handbook: Precast and prestressedconcrete (6th ed.). Chicago: Precast/PrestressedConcrete Institute[3] Benayoune, A., Samad, A. A. A., Ali, A. A., andTrikha, D. N. 2007. Response of precast reinforcedcomposite sandwich panels to axial loading.Construction and Building Materials, 21(3), 677-685.[4] Eina A., Salmon, D.C., Fogarasi, G.J., Culp, T.D.and Tadros, M.K. (1991). State-of-the-art ofprecast concrete sandwich panels, PCI Journal,36(6), 78-98.[5] Frankl B.A., Lucier, G.W., Hassan, T.K. andRizkalla, S.H. . Behavior of insulated precastprestressed concrete wall panels reinforced withCFRP grid. ACI Structural Journal. (submittedfor publication)[6] Hassan, T.K. and Rizkalla, S.H. Analysis anddesign guidelines of precast/prestressed compositeload-bearing sandwich wall panels. ACI StructuralJournal. (submitted for publication)[7] Aslan Pacific Ltd. (2008). Nu-Tie sandwichwall connector: Aslan FRP. Hong Kong: AslanPacific Ltd.[8] Fam, A., Pando, M., Filz, G., and Rizkalla, S.(2003). Precast piles for Route 40 bridge inVirginia using concrete filled FRP tubes. PCIJournal, 48(3),[9] Fam, A. and Mandal, S. (2006). Prestressedconcrete-filled fiber reinforced polymer circulartubes tested in flexure. PCI Journal, 51(4), 42-54.[10] Qasrawi, Y. and Fam, A., (2008). Flexuralload tests on new spun-cast concrete-filled fiberreinforced polymer tubular poles. ACI StructuralJournal, 105(6), 750-759.[11] Terrasi, G.P. and Lees. J.M. (2003). CFRPprestressed concrete lighting columns.InRizkalla,S. And Nanni, A. (Eds.), Field applicationsof FRP reinforcement: Case studies (ACI SP-215)(pp. 55-74).Farmington Hills, MI: AmericanConcrete Institute.
precast wall panels, architectural cladding and precast concrete filled FRP tubes (CFFT). The unique advantages of the FRP reinforced systems are highlighted and the primary action mechanisms of the FRP materials are presented. The paper concludes by identifying several areas of possible future opportunities in which FRP materials can be
ASTM E84 Flame Spread for FRP Consult data sheets for specific information. Asbestos/Cement Halogenated-FRP Halogenated/ w/Antimony-FRP Red Oak Non-Halogenated 0 100 200 300 400 X X Plywood 25 75. Surge and Water Hammer-Surge wave celerity 0 200 400 600 800 1000 1200 1400 1600 CONC DI CS FRP PVC PE50 Wave Celerity-m . Usage of FRP World Wide- Literature Survey. Usage of FRP World Wide .
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2. PRECAST CONCRETE CONSTRUCTION IN BRIEF 3 3. METHODOLOGY 3 3.1 Precast Yard Role 3.2 Advantages of Precast Concrete 3.3 Disadvantages of Precast Concrete 4. SOLUTION STATEMENT 7 4.1 Concrete Batching Plant 4.2 M-beams 4.3 Viaduct Segments 5. PROCESS MANAGEMENT CONTROL 11 5.1 Numbering of elements 5.2 Stacking 6. LESSONS LEARNED 12
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majority of traditional design challenges (Precast/Prestressed Concrete Institute, 2010). Various uses of precast concrete exist in the form of double and single tees, slabs, panels, beam and girders, stairs, and columns (Canadian Precast/ Prestressed Concrete Institute, 2007) (Figure :1). In South Africa, precast floor systems are the most com
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