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14 chapter four Codes, standards, and design guidelines Several specifications and design guidelines have been published, and some are currently under development or revision. Notable documents are summarized in this section. aasHto guide speCifiCations Four guide specifications are currently available to assist with the design and practice of highway bridges with FRP materials. The contents of these documents are briefly described as follows: â¢ Design of Bonded FRP Systems for Repair and Strengthening of Concrete Bridge Elements: the first edition of the guide specifications was published in 2012 and based on two NCHRP projects [NCHRP Report 655: Recommended Guide Specifications for the Design of Externally Bonded FRP Systems for Repair and Strengthening of Concrete Bridge Elements (Zureick et al. 2010) and NCHRP Report 678: Design of FRP Systems for Strengthening Concrete Girders in Shear (Belarbi et al. 2011)]. The document, consisting of five sections, handles technical contents spanning from selecting materials to implementing FRP strengthening methods for bridge members subjected to various loading conditions. The first section introduces the con- cept of FRP strengthening for constructed bridge members, in conjunction with design objec- tives and approaches. Conforming to the AASHTO LRFD Bridge Design Specifications, four limit states are established (Service, Strength, Extreme-event, and Fatigue Limit) for the mem- bers externally strengthened with FRP composites. A concise description of structural loads and their combinations is provided, according to corresponding articles in the AASHTO LRFD Bridge Design Specifications. The second section provides material requirements in terms of acceptability; testing, mechanical, and thermal properties; and adhesives. The third section is concerned with flexural strengthening for bridge girders and decks. Because FRP composites do not yield, unlike conventional steel reinforcement, the ductility of strengthened members is important (a subsection reports ductility requirements). Detailing is also given to specify the required development length of bonded FRP, as well as the limit of peel-off stresses to avoid premature bond failure at termination points of the FRP. The fourth section covers members under shear and torsional loadings. An increase in shear or torsional strength by the externally bonded FRP is stated and some design limitations are included (i.e., shear span-to-depth ratio, maximum FRP shear reinforcement, and maximum spacing of FRP shear reinforcement). The last section of the guide specifications discusses FRP wrapping for load-bearing members in bridge substructures. Both short and long columns are reviewed, when subjected to either axial compression or combined axial-bending loadings. â¢ GFRP-Reinforced Concrete Bridge Decks and Traffic Railings: these specifications, published in 2009, consist of five sections on the use of GFRP reinforcing bars for bridge decks and side rails. The design philosophy and limitations associated with GFRP-reinforced bridge mem- bers are stipulated in the first section. Various aspects to be considered when a bridge deck is constructed with GFRP bars, instead of steel bars, are presented in the second section. Two loading effects such as flexure and shear are separately handled with fundamental assump- tions required to establish several limit states (i.e., Strength, Service, Fatigue, Creep-rupture, and Extreme-event). Detailing requirements are available to suggest maximum and minimum spacings, shrinkage and temperature, development and splice lengths, and mechanical anchors. The third section outlines design considerations for traffic railings including end treatment, test level section criteria, curbs, and sidewalks. The fourth section provides material specifications.
15 The requirements for fibers, matrix resins, and other additives are specified in tandem with the manufacturing process, durability properties, and certification. The last section is about construction specifications dedicated to material delivery, storage, handling, fabrication, and execution. â¢ Design of FRP Pedestrian Bridges: this document, released in 2008, specifies structural loads and design requirements for FRP pedestrian bridges. The first section discusses general con- tents and specifies that the AASHTO Standard Specifications for Highway Bridges shall be referenced. The second section consists of wind loads and live loads associated with pedestrians and maintenance vehicles. The last section provides design details concerning deflection, vibra- tions, allowable stresses, minimum FRP thickness, connections, and half-through truss spans. It is worth noting that the design philosophy presented is based on the allowable stress design (ASD), rather than the load and resistance factor design (LRFD). â¢ Design of Concrete-Filled FRP Tubes: this publication was released in 2012 to assist bridge engineers in designing FRP tubular beams or columns filled with concrete. Three sections are presented. The first section is an introductory chapter detailing the scope of the guide specifications, limitations and assumptions in structural calculation, and the design philoso- phy employed (i.e., LRFD). The second section encompasses contents required to complete structural design: material properties, limit states, and design approaches for flexural and axial members, as well as structural elements carrying combined flexural and axial com- pression loads. The third section emphasizes material specifications similar to those of the GFRP-Reinforced Concrete Bridge Decks and Traffic Railings document discussed earlier (AASHTO 2009). ameriCan ConCrete institute Committee 440 doCuments ACI Committee 440 (Fiber-reinforced Polymer Reinforcement) has published several design guide- lines covering a variety of scopes from material specifications to construction with FRP composites. Selected documents are reviewed in this section. â¢ ACI 440.1R-15 [Guide for the Design and Construction of Structural Concrete Reinforced with Fiber-Reinforced Polymer (FRP) Bars]: this is a comprehensive guide for concrete structures reinforced with FRP bars, including 11 technical chapters and one reference chapter. The first chapter defines the scope of the guide with a brief background about FRP-reinforced con- crete, which is a promising alternative to conventional steel-reinforced concrete. Chapter 2 pre sents notations and definitions, and Chapter 3 covers historical development and demonstra- tion projects (primarily for bridge decks). Material characteristics and durability performance are discussed in Chapters 4 and 5, along with a literature review (i.e., physical and mechani- cal properties, time-dependent behavior, thermal effects, and accelerated durability testing). Chapters 6 to 8 are concerned with design methods; specifically, design philosophy and assump- tions (Chapter 6), flexural strength and serviceability (Chapter 7), and shear strength and stirrup detailing (Chapter 8). Chapters 9 and 10 are dedicated to miscellaneous subjects: reinforcing for shrinkage and temperature, development length, and splice. Eleven design examples are avail- able in Chapter 11 with regard to flexural and shear members, GFRP bars subjected to creep- rupture, crack control, and punching shear. â¢ ACI 440.2R-08 (Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures): technical guidance on the application of externally bonded FRP sheets and laminates is presented in this five-part document: General, Materials, Recommended Construction Requirements, Design Recommendations, and Design Examples. It is a revised version of the previous ACI 440.2R-02 document (another upgrade of the ACI 440.2R-08 version is currently underway). The first part discusses scope and limitations, the use of FRP strengthening systems, historical development, and commercially available FRP products. The second part focuses on the material characteristics of FRP with typical engineer- ing properties (e.g., densities, coefficients of thermal expansion, tensile strength, creep-rupture, fatigue, and durability). There are four subchapters in the third part, addressing the shipping, handling, installation, and inspection of FRP systems, as well as the repair of installed strength- ening systems. The fourth part expounds on the implementation of externally bonded FRP
16 strengthening systems to enhance the capacity of constructed concrete members. The coverage range involves design philosophy; strengthening limitations; design of members in flexure, shear, and axial loading configurations; bond issues; and drawings. The guide concludes with design examples based on the provisions specified in the fourth part. â¢ ACI 440.3R-12 [Guide Test Methods for Fiber-Reinforced Polymers (FRPs) for Reinforcing or Strengthening Concrete Structures]: a number of test methods are elaborated on to determine the properties of FRP materials with schematic drawings. The first part introduces needs for standardized test methods, with a summary of ASTM test methods relevant to FRP composites. The second part describes 12 test methods for FRP reinforcing bars: cross-sectional properties, longitudinal tensile properties, bond strength, transverse shear strength, strength of bent bars and stirrups, alkali resistance, fatigue, creep-rupture, long-term relaxation, anchorage, tensile properties of deflected bars, and the effect of corner radius. The last part comprises three test methods for FRP laminates: pull-off, tension, and overlap splice. â¢ ACI 440.4R-04 (Prestressing Concrete Structures with FRP Tendons): the contents of this design guide are devoted to FRP-prestressed concrete in various aspects described in ten chapters. Chapter 1 discusses an overview of prestressed concrete members with FRP tendons, historical development, a literature review of numerous research endeavors, and site demonstra- tion projects. Chapter 2 highlights commercially available AFRP and CFRP tendons with their material properties, anchorage for tensioning FRP tendons (e.g., clamp, plug and cone, sleeve, and split wedge anchors), and possible failure modes of FRP-prestressing systems. Chapters 3 through 6 explain design requirements from flexural, service, shear, and bond perspectives (some of which are subject to change because of the ongoing update work). Although the design approaches detailed in these chapters may appear to be similar to those for conven- tional steel-prestressed concrete, the unique characteristics of FRP tendons necessitate con- ceptually different technical considerations such as creep-rupture, compression-controlled section, progressive rupture of vertically aligned tendons (rather than yielding of the tendons), deformability, effective moment of inertia adjusted from the Branson equation, and empiri- cal transfer length dependent on tendon manufacturers. Chapter 7 specifies design details on the application of unbonded and external tendons, based on empirically derived parameters. Several case studies with FRP-prestressed concrete piles are presented in Chapter 8, which were collected from published articles. The document concludes with further research needs and design examples. â¢ ACI 440.5R-08 (Specification for Construction with Fiber-Reinforced Polymer Reinforcing Bars): this is a concise manual suggesting construction specifications when FRP reinforcing bars are employed. General requirements are discussed in the first and second parts (e.g., refer- ence standards, submittals, material delivery, storage, handling, and fabrication). The execution of FRP bars is detailed in the last part. To assist construction engineers, three checklists are provided: mandatory requirements, optional requirements, and submittals. â¢ ACI 440.6R-08 (Specification for Carbon and Glass Fiber-Reinforced Polymer Bar Materials for Concrete Reinforcement): this document presents fundamental considerations about the use of CFRP and GFRP bars for concrete structures. The first three sections describe introductory contents (scope, reference documents, and terminology), followed by classification (Section 4) and ordering information (Section 5). The acquisition methods for physical, mechanical, and durability properties are shown in Sections 6 to 9. Product assessment, sampling, certification, and markings are available in Sections 10 to 14. â¢ ACI 440.7R-10 (Guide for Design and Construction of Externally Bonded FRP Systems for Strengthening Unreinforced Masonry Structures): design guidelines for masonry structures are presented based on 13 technical chapters. Although masonry can be used for highway infra- structure, its actual application may be limited. The coverage of these guidelines encompasses constituent materials and properties, handling, installation, evaluation, in-plane and out-of- plane structural loadings for FRP-strengthened masonry members, specifications, and design examples. â¢ ACI 440.8R-13 (Specification for Carbon and Glass Fiber-Reinforced Polymer Materials Made by Wet Layup for External Strengthening of Concrete and Masonry Structures): this is another short specification document covering CFRP and GFRP sheets and laminates for external strengthening application. Contents include material classification; properties from physical, mechanical, and durability standpoints; data sampling; and product data sheets.
17 â¢ ACI 440.9R-15 [Guide to Accelerated Conditioning Protocols for Durability Assessment of Internal and External Fiber-Reinforced Polymer (FRP) Reinforcement]: durability test proto- cols and data interpretation are the focus of this guide document. Chapters 1 to 4 present the background and importance of durability performance, when FRP composites are used for concrete structures. Chapters 5 and 6 recommend test methods for FRP reinforcing bars and sheets and laminates subjected to accelerated environmental conditioning. Chapter 7 discusses future work and potential test approaches relevant to FRP products. Canadian standards Three Canadian standards are available for structures with FRP composites: one is for highway struc- tures (CSA-S6), a second for building structures (CSA-S806), and the third for material specifications (CSA-S807). A review of the CSA-S6 standard is given here with an emphasis on FRP-related articles: â¢ CSA-S6 (Canadian Highway Bridge Design Code): this bridge design code includes 16 sections (the use of FRP materials is presented in Section 16). The primary focus of Section 16 is on FRP-reinforcing bars and tendons. Technical contents involve durability, material properties, con- crete beams and slabs reinforced with FRP bars, FRP-prestressing tendons, and post-tensioned wood decks. An expression related to deformability index with two limits for rectangular and T-sections is given. fib (international federation for struCtural ConCrete) The fib (Federation Internationale du Beton) is a nonprofit organization based on the merger of two technical societies: the Euro-International Committee for Concrete (CEBâComitÃ© Euro-International du BÃ©ton) and the International Federation for Prestressing (FIPâFÃ©dÃ©ration Internationale de la PrÃ©- contrainte). Three bulletins have been published for FRP-based structures. â¢ Bulletin No. 14 (Externally Bonded FRP Reinforcement for RC Structures): design consid- erations when implementing FRP strengthening for concrete members are presented in nine chapters. Chapters 1 to 3 show the background of FRP-based rehabilitation, materials, safety, and ductility demand. Chapters 4 through 6 emphasize flexural, shear, and axial strengthening for beams and columns. FRP-bonding schemes and anchor systems are illustrated in Chapter 7. In situ quality control is the primary content of Chapter 8 (execution procedures, surface prepara- tion, finishing, material selection, technical personnel, and bond test methods). Chapter 9 is dedi- cated to the effects of physical and environmental loadings on the behavior of FRP-strengthened structures, including exposure to fire, moisture, freezeâthaw, ultraviolet radiation, alkalinity and acidity, creep, fatigue, impact, and galvanic corrosion. â¢ Bulletin No. 35 (Retrofitting of Concrete Structures by Externally Bonded FRPs with Emphasis on Seismic Applications): this is a compilation of various contents associated with externally bonded FRP composites for retrofitting existing concrete structures. Technical subjects encom- pass retrofitting concepts, durability, anchorage, strengthening of two-way slabs, seismic retro- fit, FRP-confinement of columns, and some modeling aspects. â¢ Bulletin No. 40 (FRP Reinforcement in RC Structures): this document comprises eight chapters regarding the design of concrete members using internal FRP reinforcement. The first chapter explains why FRP is an alternative solution to conventional steel reinforcement in terms of durability, electromagnetic neutrality, and high strength at low density. Chapter 2 is dedicated to specifying material characteristics and short- and long-term properties. Durability is the main content of Chapter 3, with a focus on the effects of water, chlorides, alkali, sustained stress, ultraviolet radiation, temperature, carbonation, and acid. Chapters 4 and 5 specify ultimate and serviceability limit states, respectively, based on the flexure, deflection, and cracking of FRP-reinforced concrete members. The requirements for shear resistance (shear-crack-induced failure and punching shear problems) are elaborated in Chapter 6. Other miscellaneous sub- jects such as bond, anchorage, and tension stiffening are covered in Chapter 7, along with macro- and meso-level modeling approaches. The last chapter briefs the design philosophy of FRP-reinforced concrete.
18 intelligent sensing for innovative struCtures A federally funded Networks of Centres of Excellence program in Canada, entitled Intelligent Sens- ing for Innovative Structures, has published three design manuals related to FRP composites for concrete structures, in addition to two other manuals about structural health monitoring with fiber optic sensors (Manuals 1 and 2). â¢ Manual No. 3 (Reinforcing Concrete Structures with Fibre Reinforced Polymers): upon explain- ing an overview of the Centres of Excellence Program and general guidelines on how to use the manual shown in Chapters 1 to 3, the background of FRP reinforcing materials is described in Chapter 4 (fibers and resins, fundamental engineering properties, and commercially available products). The concept of the limit states design (or LRFD) and design factors are provided in Chapter 5. For instance, material resistance factors for CFRP, AFRP, and GFRP bars are f = 0.8, 0.6, and 0.4, respectively. Chapters 6 to 11 are concerned with the design of FRP-reinforced concrete members in flexure, shear, and service (deformability is emphasized in Chapter 9). The constructability of these members is explained in Chapter 12. The last chapter of the man- ual demonstrates four case study examples employing FRP reinforcing bars in four Canadian provinces. â¢ Manual No. 4 (FRP Rehabilitation of Reinforced Concrete Structures): Chapters 1 and 2 have introductory contents, whereas technical contents are explained in Chapter 3, which is dedi- cated to FRP materials and associated properties. Chapter 4 presents evaluation methods for existing structural members before conducting FRP strengthening; namely, capacity estima- tion, structural integrity, surface conditions, and the causes of deficiency. Flexural rehabilita- tion against strength and serviceability requirements is detailed in Chapter 5, as well as design examples in accordance with the Canadian highway bridge design code. FRP-confinement and shear retrofit are discussed in Chapters 6 and 7, respectively, with approaches similar to the previous chapter in terms of specifying design equations and examples. Chapters 8 and 9 dis- cuss in situ work, such as the storage and handling of FRP materials, qualified technical staff, installation methods, curing, finishing, inspection, and field testing. â¢ Manual No. 5 (Prestressing Concrete Structures with Fibre-Reinforced Polymers): the first chapter provides general considerations about the design philosophy and limit states of FRP-prestressed concrete members. The next chapter is concerned with FRP tendons and six anchor systems for prestressing the tendons, in addition to the pictorial descriptions of anchors specifically designed for commercial FRP tendons. Chapter 3 recommends specific methods for the place- ment, handling, and construction of FRP prestressing tendons. Conventional topics related to prestressed concrete are covered in Chapter 4, in conjunction with allowable jacking and trans- fer stresses, eccentricities caused by harped or draped tendon profiles, and short- and long-term prestress losses (i.e., friction, anchor set, elastic shortening, creep, shrinkage, relaxation, and temperature change). Design guidelines for flexure, serviceability, deformability, shear, and bond and development length are presented in Chapters 5 to 9. The last chapter explains the use of unbonded tendons and external prestressing. The document concludes with four design examples in Appendix A: Flexural Design with Single and Multiple Layer Tendons, Deflection, and Shear.