Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
137 chapter nine Summary and ConCluSionS This report presents a comprehensive overview of fiber-reinforced polymer (FRP) composites for highway infrastructure along with the state of current practice in the United States. The approaches used were: (1) a review of published literature covering laboratory experiments, design and practice guidelines, specifications, and in situ projects; and (2) a survey questionnaire to examine the use of FRP materials with positive and negative aspects in conjunction with phone interviews (an 88% response rate of the U.S. agencies). The state-of-the-art review of FRP applications provided the following information: â¢ FRP materials: FRP consists of high-strength fibers and a polymeric resin. Typical FRP com- posites in highway infrastructure include CFRP (carbon), GFRP (glass), AFRP (aramid), and BFRP (basalt). Various resin types are available, depending on the nature of applications such as epoxy, polyester, and vinylester. FRP materials are produced by pultrusion, wet lay-up, fila- ment winding, and several other techniques. Numerous test methods are suggested by standards organizations and professional societies. â¢ Application guidelines, codes, and specifications: a number of documents were published by AASHTO: Design of Bonded FRP Systems for Repair and Strengthening of Concrete Bridge Elements, GFRP-Reinforced Concrete Bridge Decks and Traffic Railings, and Design of FRP Pedestrian Bridges, and Design of Concrete-Filled FRP Tubes; by American Concrete Institute (ACI) Committee 440 (Fiber-reinforced Polymer Reinforcement): Guide for the Design and Construction of Structural Concrete Reinforced with Fiber-Reinforced Polymer (FRP) Bars, Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures, Guide Test Methods for Fiber-Reinforced Polymers (FRPs) for Reinforcing or Strengthening Concrete Structures, Prestressing Concrete Structures with FRP Tendons, Specification for Construction with Fiber-Reinforced Polymer Reinforcing Bars, Specification for Carbon and Glass Fiber-Reinforced Polymer Bar Materials for Concrete Reinforcement, Guide for Design and Construction of Externally Bonded FRP Systems for Strengthening Unreinforced Masonry Structures, Specification for Carbon and Glass Fiber-Reinforced Polymer Materials Made by Wet Layup for External Strengthening of Concrete and Masonry Structures, and Guide to Accelerated Conditioning Protocols for Durability Assessment of Internal and External Fiber-Reinforced Polymer (FRP) Reinforcement; by Canadian Standards Association (CSA); International Federation for Structural Concrete ( fib) and Intelligent Sensing for Innovative Structures. â¢ FRP-reinforced concrete: FRP reinforcing bars can replace steel reinforcement in concrete structures. GFRP bars are predominantly used, whereas BFRP bars appear promising. The design approaches for FRP-reinforced concrete are similar to those for conventional reinforced concrete with steel bars, except for the linear elastic nature of FRP composites and tension- and compression-controlled failure modes. Environmental reduction factors are employed to address the potential degradation of FRP materials. The deflection of FRP-reinforced concrete members is of interest, because FRPâs low modulus results in more deflection relative to steel- based members. Deformability is another important consideration in FRP-reinforced members owing to the brittle nature of FRP. Unlike flexural and shear cases, limited information is available on FRP-reinforced concrete columns. A number of site projects were reported using GFRP bars, including bridge decks, culverts, and railings. â¢ FRP-prestressed concrete: FRP-prestressed concrete is an alternative to steel-prestressed concrete, particularly for pretensioned highway bridge girders (short and medium spans). CFRP tendons
138 are employed in preference to other FRP types (i.e., GFRP has creep-rupture concerns). Similar to FRP-reinforced members, FRP-prestressed members are designed based on the methods used for steel-prestressed members with additional considerations (e.g., failure modes, creep- rupture, and deformability). In some cases, CFRP stirrups were placed in CFRP-prestressed concrete girders. FRP tendons may be spliced using a steel coupler wrapped with shrink rubber (to alleviate corrosion). Limited site applications were reported in comparison with FRP-reinforced concrete cases. â¢ FRP-strengthened concrete: this rehabilitation technique has been studied extensively and, accordingly, is widely accepted by transportation agencies. All major structural members can be strengthened to upgrade flexural, shear, and axial capacities (e.g., bridge girders, decks, and columns). Two types of strengthening techniques are used: externally bonded and near- surface-mounted FRP composites. The durability of FRP-strengthened members is satisfactory. However, the properties of FRP materials are susceptible to elevated temperatures, because their engineering properties change. Specific design approaches are necessary to prevent the premature failure of the FRP, such as through debonding. A large number of field projects were conducted to strengthen deficient bridge elements. â¢ Other applications: FRP decks and FRP stay-in-place members are usable for highway infra- structure. In these cases, GFRP is preferred because of the reasonable costs. Several types of GFRP decks were used in practice (e.g., honeycomb and hexagonal structures). Typical failure modes of these decks include cracking, delamination, and punching shear. FRP is a good candidate material for pedestrian bridges. â¢ Life-cycle cost analysis: long-term economic benefits associated with FRP composites are quantified by life-cycle cost analysis. Case studies reveal that the overall expenses of structures constructed with FRP (from planning to demolition) were less than those of the structures with conventional materials, although the former required higher material costs than the latter. Despite the extensive endeavors delineated earlier, further research and development are necessary to advance the state of the art and state of the practice of FRP composites in highway infrastructure: â¢ FRP-reinforced concrete: â Globally acceptable expressions for deformability. â Long-term in situ monitoring for durability assessment. â Further testing of FRP-reinforced columns and developing design guidelines. â Material characterization of BFRP and application, including fatigue investigations. â¢ FRP-prestressed concrete: â Time-dependent prestress losses. â Prediction of long-term camber and deflection. â In situ behavior of installed FRP tendons and anchorage. â¢ FRP-strengthened concrete: â Specification development for strengthening steel and timber structures. â Size effect on the behavior of strengthened members. â Environmental reduction factors for various exposure conditions. â Anchoring techniques to preclude debonding. â¢ Others: â Integrated FRP decks to prevent premature delamination failure. â Specification development for FRP stay-in-place members and FRP decks. â Examination of life-cycle costs for constructed FRP-based structures. A comprehensive survey was conducted to understand the state of current practice of FRP com- posites in highway infrastructure. According to the responses and comments of the participating juris- dictions (from 44 U.S. departments of transportation and two Canadian agencies], various technical and administrative aspects were examined. The findings of the survey questionnaire and follow-up interviews are presented here: â¢ More than 80% of the responding agencies used FRP materials for their projects; specifically, bridge girders, decks and piers (columns), piles, abutments, buried structures, concrete pavement, drains, and culvert liners. The application began in the early 1990s (21.1% of the respondents),
139 whereas most agencies adopted FRP technologies during the period between 1996 and 2005 (65.8% of the respondents). â¢ FRP applications were considered as a standard practice or experimental, depending on struc- tural members. CFRP wrapping for upgrading bridge piers (columns) was the most accepted standard practice (44.7% of the respondents), followed by bridge decks and girders with GFRP reinforcing bars and CFRP strengthening, respectively. A number of agencies, however, still considered FRP applications to be experimental. Almost 45% of the respondents conducted fewer than 10 projects using FRP composites, whereas 14.3% of the respondents had more than 40 projects with FRP. â¢ When implementing FRP technologies, the agencies referenced guidelines published by AASHTO and ACI 440. In-house specifications were also used. By contrast, foreign recourses such as fib bulletins (European guides) were not used at all. Unified practice manuals or specifications con- cerning FRP composites help produce uniform application quality and management procedures in highway infrastructure. â¢ Most responding agencies (71.4%) had the following challenges in FRP-based projects: insuffi- cient experience, a lack of design guidelines and skilled personnel, procurement, and budget. The agencies conducted qualification tests to evaluate FRPâs mechanical and durability performance, including the bond behavior of FRP. Although limited effort was made on supporting research activities, the responding agencies revealed that research can facilitate the use of FRP in practice. â¢ The performance and long-term durability of constructed structures with FRP were of interest to the transportation agencies. As such, several evaluation methods were employed (e.g., visual inspection, nondestructive testing, and load rating with computer modeling). It was found that the performance of structures was satisfactory, with negligible demand for maintenance and repair. Nonetheless, long-term durability requires further examination. Life-cycle cost analysis also requires more attention to better quantify the economic benefit of FRP application. â¢ On procurement and contractor selection for FRP-based projects, procedures were basically the same as those of conventional projects. Some agencies, however, noted that sole sourcing is necessary for FRP with a special provision or separate contract. â¢ The respondents were mostly satisfied with FRP in their projects, even though there were some minor problems (e.g., deteriorated surface coating). Several agencies have current and planned projects using FRP composites; for instance, CFRP-prestressed girders, CFRP wrapping for columns, hybrid and GFRP decks, and composite piles.