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3 General The sustainability of highway infrastructure is one of the most crucial research and practice needs in the United States. Constructed facilities deteriorate owing to physical and environmental fac- tors, and may become structurally deficient. There are a number of contributors to such deterio- ration; for example, water, ultraviolet radiations, temperature, freeze-thaw, traffic load, impact, and chemicals. Accordingly, structural members do not meet their expected design life. The load- bearing capacity of these members may decrease as their physical properties change, leading to public safety concerns. The membersâ durability performance is also affected by the degree of deterioration (e.g., steel reinforcing bars become vulnerable to corrosion, when concrete sur- rounding the bars cracks or spalls). Transportation agencies are eager for alternative construction materials, which will enable them to extend the longevity of existing structural members in an economical manner. Fiber-reinforced polymer (FRP) composites are a promising material and have shown excellent performance with numerous advantages (Mirmiran et al. 2004). Examples include favorable strength- to-weight ratio, noncorrosiveness, reasonable labor, rapid implementation, and reduced long-term maintenance costs. The application range of FRP materials is broad from internal reinforcing to external strengthening. Various FRP materials and types (e.g., sheets, laminates, structural shapes, bars, and ten- dons) are available for highway infrastructure, as shown in Table 1. Although significant advancements have been made over the last two decades, FRP composites have not been widely adopted by state departments of transportations (DOTs), including the Ministry of Transportation in Canadian provinces, because of their high material costs, a lack of design guidelines or specifications, procurement, and relatively short application history. NCHRP Topic 47-12 discusses the state of the art and state of current practice of FRP com- posites for highway infrastructure. This document covers FRP materials, test methods, design and practice guidelines, FRP-reinforced and -prestressed concrete, structural strengthening, stay- in-place FRP systems, durability, life-cycle cost analysis, and case examples (detailed descriptions follow). These fundamentals and applications help transportation agencies to better understand the use of FRP composites in their construction projects, with an emphasis on planning and implementation. Objectives The overarching goals of this synthesis are (1) to provide critical information to DOT engineers and other practitioners who are interested in FRP technologies and (2) to identify current challenges requiring technical and administrative efforts to facilitate the use of this promising construction material. All major aspects associated with FRP composites are taken into consideration. This report is a link between research and practice. The specific objectives of the study are: â¢ To synthesize published literature on FRP materials in highway infrastructure, based on a state- of-the-art review of national and international resources. â¢ To establish the state of current practice of FRP applications in transportation agencies along with a survey questionnaire, followed by interviews with responding agencies. chapter one intrOductiOn
4 scOpe and apprOach A holistic endeavor was made to collect information relevant to the study subject. Although the scope of this topic is relatively broad, the following topics are expounded upon in this report: â¢ FRP materials in highway infrastructure: fundamental characteristics and engineering proper- ties of commercially available FRP composites are discussed in tandem with material composi- tion, constituent fibers and resins, comparison with conventional construction materials, and macroscopic constitutive behavior. â¢ Test methods to determine material properties: FRP composites show different mechanical responses relative to steel, because of FRPâs tailorable properties and orthotropic nature. Available test standards or guidelines are compiled, including short- and long-term test proto- cols as well as durability assessment methods. noitacilppA PRF etatS Florida â¢ Decks: One application (removed from service) â¢ FRP fender systems: 22 systems or more are in place (6,250 linear feet) â¢ GFRP Reinforcement/Carbon Fiber Reinforcement: one pile jacket application Standards and Specifications are in place to begin implementation. Design Standards for Bearing Piles are published (Index 22,600) and Structures Design Guidelines define mandatory use for intermediate pile bents in extremely aggressive locations. A planned project (letting date 6/15/16) will include HC beams, GFRP reinforcement in the deck, pier cap, and sheet pile, as well as CFRP in the piles and sheet piles. Two other projects will have GFRP reinforcement in the bulkhead caps. â¢ NSM repairs using CFRP: three or more repairs â¢ Repairs to concrete using externally bonded FRP: a fully implemented repair procedure that has been used for over 25 years. Kansas â¢ Column strengthening with FRP wrap: 20 bridges (approximate) â¢ Concrete beam strengthening (RC & P/S): 10 bridges (approximate) â¢ Bridge decks with GFRP reinforcement: one bridge â¢ FRP bridge superstructure: one bridge â¢ FRP bridge decks: three bridges (decks have been replaced) Maine â¢ Bridge drains: 10 bridges â¢ CFRP cable stays: one bridge (used alongside steel) â¢ CFRP transverse post-tensioning (CFCC): two bridges â¢ CFRP prestressing (CFCC): one bridge â¢ Concrete-filled FRP tube arch: nine bridges â¢ Culvert invert re-lining with FRP: three projects â¢ Fender piles: one bridge â¢ GFRP deck reinforcement: three bridges + several in design â¢ Hybrid beams (HC bridge): four bridges â¢ Load bearing piles: four research trials but not yet deployed â¢ Non-proprietary flexural strengthening system for concrete slabs: developed but not yet deployed Michigan â¢ CFRP prestressing and transverse post-tensioning (CFCC): four bridges â¢ Column wraps: 11 bridges â¢ Beam shear strengthening: two bridges â¢ FRP reinforcement: one bridge â¢ Concrete-filled FRP tube arch culvert: one bridge Missouri â¢ Hybrid beams (HC bridge): three bridges â¢ FRP drainage systems standard practice â¢ Repair/retrofit of concrete several times, district repair crews have retrofitted concrete columns by bonding FRP Nebraska â¢ FRP reinforcement bridge deck: one bridge â¢ FRP pier cap protection/strengthening: one pier cap â¢ FRP girder strengthening (shear and flexure)/protection: one bridge Oregon â¢ Arch rib strengthening with CFRP strips: one bridge â¢ Deck strengthening for rail LL with NSM CFRP rods: four bridges â¢ Deck strengthening with NSM CFRP rods: four bridges â¢ GFRP reinforcement (45,000 ft2): two bridges â¢ Girder flexure strengthening with CFRP strips: eight bridges â¢ Girder shear strengthening with CFRP strips: 32 bridges â¢ Modular FRP bridge decks: four bridges (9,516 ft2 state, 17,200 ft2 local owners) â¢ Pier cap flexure strengthening with CFRP strips: one bridge â¢ Pier cap shear strengthening with CFRP strips: 12 bridges Source: Frankhauser et al. (2016). TAblE 1 USE OF FRP COMPOSiTES iN SElECTED STATE DOTs
5 â¢ Codes, standards, and design guidelines: design-oriented documents are reviewed for the inter- nal and external applications of FRP materials; for example, AASHTO guide specifications, ACi Committee 440 (Fiber-reinforced Polymer Reinforcement) guidelines, Canadian standards, Federation internationale de beton ( fib) bulletins, and intelligent Sensing for innovative Structures design manuals. â¢ FRP-reinforced concrete members: FRP reinforcing bars can enhance the performance of reinforced concrete members owing to corrosion resistance, which is particularly beneficial for bridge decks where detrimental deicing agents are spread. Of interest are the flexure and shear of FRP-reinforced concrete members, serviceability, durability, and development length. â¢ FRP-prestressed concrete members: FRP tendons to prestress concrete girders are discussed. Several tendon types such as rods and strands are used, which may replace 7-wire, low- relaxation steel strands. Carbon FRP (CFRP) composites are predominantly used, because of their high strength and modulus. Glass FRP (GFRP) is not preferred as a result of long-term concerns (e.g., creep-rupture). Technical contents include anchorage, flexure and shear of CFRP-prestressed concrete, serviceability, transfer and development lengths, and bonded and unbonded applications. â¢ FRP-strengthened constructed members: deterioration of existing structural members is unavoid- able with time. From a financial stand point, FRP strengthening or retrofitting may be implemented in preference to reconstruction. installation methods, the behavior of strengthened structures, and failure modes are dealt with. Time-dependent durability of FRP-strengthened members (e.g., freezeâthaw) is contemplated. â¢ FRP stay-in-place members and FRP decks: although not common, concrete-filled FRP forms can be used as load-bearing elements integrated with conventional structures (e.g., bridge piers and piles). This type of application may extend the longevity of members constructed in a marine environment. The structural behavior of concrete-filled FRP elements and their potential are reviewed. FRP decks are limitedly employed in practice. Available deck types, field applications, and possible failure modes are presented. â¢ Durability: the durability performance of FRP materials is elaborated on for both internal and external applications. Existing research results are largely based on accelerated laboratory testing (mostly for concrete structures), whereas limited in situ investigations are reported. The extent of degradation in mechanical properties, induced by aggressive service conditions, and correspond- ing performance is discussed. â¢ Life-cycle cost analysis: when transportation agencies make a rational decision, the economy associated with relatively expensive FRP composites for structural design and construction is crucial to consider. An appropriate understanding of life-cycle costs in FRP applications enables or facilitates the use of such a promising material, although initial construction costs are higher than those of conventional materials. The principle and background of life-cycle cost analysis are provided, in conjunction with relevant literature with case study examples. â¢ Site application and case studies: a number of field projects have been conducted nationally and internationally using FRP composites to construct new structures and to strengthen existing members. Notable case studies are collected for transportation agencies to reference how FRP is used on site. information provided in this report was acquired through a review of literature related to FRP composites for highway infrastructure. An online survey was distributed to elucidate the state of current practice of FRP in transportation agencies, with the aid of the AASHTO Subcommittee on bridges and Structures. Follow-up interviews were conducted to complement or clarify the responses of participating agencies. OrGanizatiOn Of repOrt The report consists of five major sections. â¢ General: an overview of constructed highway infrastructure and the use of FRP composites is provided. Also expounded upon are FRP materials and their properties, manufacturing techniques, pertinent codes, standards, and design guidelines.
6 â¢ State-of-the-art of FRP composites in highway infrastructure: in accordance with an extensive review of published literature, various technical aspects associated with FRP applications are presented. Specific applications are elaborated on with discussions on FRP-reinforced concrete, FRP-prestressed concrete, FRP-strengthened concrete, FRP decks, FRP stay-in-place mem- bers, life-cycle cost analysis, and constructability. â¢ State-of-current-practice survey: the results of survey questionnaires are analyzed with the historical aspect and utilization of FRP composites in practice, followed by project planning with FRP. Technical and administrative challenges are included. â¢ Conclusions: technical contents and findings are summarized with research needs to further advance FRP technologies. â¢ Design examples: to guide transportation agencies that are not familiar with FRP technologies five design examples are provided. These examples are fundamentally aligned with the design of conventional bridge structures; hence, bridge engineers can readily understand and learn the basics of FRP-reinforcing and -strengthening techniques.