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.
123 chapter eight State-of-Current-PraCtiCe Survey A survey questionnaire was disseminated to the state DOTs and Canadian Ministry of Transportation (provincial ministries) in cooperation with the AASHTO Subcommittee on Bridges and Structures (SCOBS). The purpose of this survey is to establish the state-of-current-practice of FRP technolo- gies in highway infrastructure, including present implementation, concerns, suggestions, and future directions. Survey results are also considered as a metric to identify the gap between the state-of-the- art research and actual practice. overview The survey was designed to provide information on the following items: â¢ How state DOTs are using FRP, with a summary of use by application. â¢ Whether FRP use is experimental or an institutionalized standard practice. â¢ Lessons learned by state DOTs in applications of FRP. â¢ Challenges to implementation. â¢ What specifications have been used by state DOTs. â¢ What design guidelines have been used by state DOTs. â¢ Procurement and contracting methods. â¢ Long-term durability and performance. â¢ Performance evaluation and qualification testing being conducted by state DOTs. â¢ Research being conducted by the state. â¢ Cost considerations in the use of FRP, how cost impacts the decision for FRP use, and how FRP is incorporated into life-cycle cost analysis. â¢ How FRP is being used in repair and retrofit versus new construction projects. Forty-six (46) transportation agencies responded to the questionnaire (44 U.S. DOTs and two Canadian Provincial MOTs: an 88% response rate for the U.S. agencies). To facilitate the survey process, an online survey program was employed. Phone interviews were conducted to better under- stand the responses and suggestions of the agencies (18 respondents, excluding the agencies showing similar responses and those with the panel members). The survey data were summarized in three content groups as follows: â¢ Historical aspect of FRP composites in highway infrastructure: the first part of survey was concerned with the general experience of the responding agencies (e.g., when FRP applications began, how many projects had been completed, and which bridge members were constructed with FRP composites). â¢ Use of FRP composites: specific information was gathered on how the respondents utilized FRP technologies for their construction projects in terms of specifications, testing and evaluation, maintenance, durability assessment, technical challenges, life-cycle costs, research activities, procurement, and overall assessment. â¢ Project planning with FRP composites: future construction trends using FRP were briefed in this content group. A discussion on why some agencies did not use FRP composites was provided, although there are a number of advantages.
124 HiStoriCal aSPeCt of fiber-reinforCed Polymer ComPoSiteS in HigHway infraStruCture More than 80% of the respondents used FRP composites for their projects (38 agencies), as shown in Figure 62(a). Bridge girders were the most frequently used members (68.4%), including CFRP- prestressed concrete girders, followed by bridge decks and piers (63.2% and 63.2%, respectively), and piles (26.3%). Other FRP applications (23.7%) include concrete pavement (FRP dowels), a floating bridge, fender piles, bridge drains, shear walls, bent cap wrapping, and culvert invert liners. It can be noted that significant portions of the âOthersâ category were left blank or were redundant with the items listed in Figure 62(b). Although the agencies did not specifically indicate FRP types used in their proj- ects, according to the interview, GFRP bars were employed as reinforcement for bridge decks and buried structures, and CFRP and GFRP sheets were used to strengthen bridge girders and columns. Figure 63 exhibits the application history of FRP materials. A pioneering effort was observed during the period between 1990 and 1995 (21.1%), when FRP technologies were transferred from the mechanical and aeronautics industries to the civil structure community. A significant increase was achieved up to 65.8% during the 1996â2000 (39.5%) and 2001â2005 (26.3%) periods. For the last ten years (2006â2016), 13.2% of the responding agencies had begun to adopt FRP for construction projects. Depending on structure types, some transportation agencies consider FRP technologies to be a stan- dard practice, whereas others still regard them as experimental (or developmental). The term âstandard practiceâ is defined as a technique that can be readily implemented by a state DOT with familiar con- struction materials (FRP composites in the present survey), based on established specifications. Accord- ing to Table 27, strengthening constructed bridge piers (columns) accounts for 44.7% of the âStandard Practiceâ category. It can be noted that a bridge pier consists of vertical and horizontal load-bearing (a) (b) FIGURE 62 Has your agency used FRP composites for highway infrastructure? (45 answers from 45 responding agencies) (a) previous experience; (b) application of FRP (multiple items selected). FIGURE 63 When was the first time for your agency to use FRP composites? (38 answers from 38 agencies experiencing FRP).
125 members (column and pier-cap, respectively), and CFRP strengthening can be implemented for both members. CFRP-confinement is a convenient and competitive solution compared with steel jacketing, as discussed previously in âAxial Behavior.â Reasonable numbers of bridge decks and girders account for the âStandard Practiceâ category as well (13.2% and 26.3%, respectively). The distribution of the âExperimentalâ category was as follows: bridge decks (63.2%), bridge girders (44.7%), bridge piers or columns (28.9%), bridge piles (28.9%), bridge abutments (17.9%), buried structures (17.9%), and others (15.4%). Table 27 enumerates the outline of various FRP applications at the member level, rather than specific implementation details including several sub-branches that are not readily achievable in an online survey program with numerous respondents [e.g., the bridge decks category can be subdivided into new deck construction and strengthening (retrofit and repair) with EB and NSM methods based on GFRP or CFRP materials]. These observations imply that FRP has been used for many projects; how- ever, it requires more development in terms of implementation techniques and specifications (further dis- cussions follow). The âOthersâ item included a number of redundant responses that could be answered in the listed âMemberâ items (e.g., FRP rebar, FRP strengthening, FRP wrap, pier cap, deck overhang with NSM FRP, repair for impact damage, prestressing and post-tensioning strands, and substructure repair), except some answers concerning GFRP dowel bars for concrete pavement and sidewalks over wingwalls. Some respondents noted that the âExperimentalâ and âStandard Practiceâ categories are determined on an element basis. The follow-up interview revealed that more field projects with FRP composites would be required for state DOTs to consider this technology as a standard practice. More than 40% of the jurisdictions had 10 or fewer FRP-based projects, as shown in Figure 64, indicating that the use of FRP composites is still premature from an application standpoint. Spe- cific reasons for this low adoption rate are explained in subsequent sections. More than 40% of the agencies reasonably employed FRP (22.9% for 11â20 projects and 17.1% for 21â30 projects). It is remarkable to note that 14% of the respondents used FRP materials more than 40 and 50 times (8.6% and 5.7%, respectively). This illustrates that, once transportation agencies become accustomed to using FRP materials, they can be a strong alternative to conventional materials with notable benefits. Member Experimental Standard Practice Not Applicable Bridge decks 63.2% 13.2% 23.7% Bridge girders 44.7% 26.3% 26.3% Bridge piers 28.9% 44.7% 21.1% Bridge abutments 17.9% 5.1% 66.7% Bridge piles 28.2% 5.1% 51.3% Buried structures 17.9% 10.3% 59.0% Others 15.4% 10.3% 48.7% Multiple items selected; 38 answers from 38 agencies experiencing FRP. TABLE 27 DOES YOUR AGENCY CONSIDER WHETHER FRP USE IS ExPERIMENTAL OR A STANDARD PRACTICE, BASED ON PREvIOUS ExPERIENCES? FIGURE 64 Estimate how many projects were completed with FRP composites in your agency thus far (38 answers from 38 agencies experiencing FRP).
126 More field-demonstration projects are necessary to actively promote FRP composites, including technology transfer in professional meetings, workshops, and conferences. During the telephone interviews, several agencies mentioned that technical training is necessary to better understand FRP materials and their applications in highway infrastructure. Some agencies specifically indicated webinars, while others preferred on-site training that provides direct interaction with the instructors. uSe of fiber-reinforCed Polymer ComPoSiteS The majority of the transportation agencies referenced design and practice guidelines published by AASHTO and ACI 440, as shown in Figure 65. The portion of in-house specifications accounted for 21.1% of the responses (California, Florida, Georgia, Indiana, Iowa, New York, vermont, and virginia). These in-house documents were developed based on the agenciesâ own experience (according to phone conversations with the agencies), which might fill specific application gaps that were not stated in other national-level documents, such as the AASHTO guide specifications and ACI 440 manuals. Although Canadian standards were used by some agencies (5.3%), the dependency on international documents (i.e., fib Bulletins and Intelligent Sensing for Innovative Structures Network design manuals) was vir- tually nil. The âOthersâ category (15.8%) included the following comments: FRP manufacturers, ICC Evaluation Service-ESR-2103 for material qualification standards, and consultant design. The need for unified practice standards for FRP arises, as in the case of the AASHTO LRFD Bridge Design Speci- fications (several agencies mentioned these unified standards during the interviews), which result in the uniform application and management of FRP-based structures, regardless of performing agencies. Figure 66 demonstrates technical and administrative challenges experienced by the responding jurisdictions when employing FRP composites. More than 70% of the agencies answered that they had challenges [Figure 66(a)]. Specifically, insufficient experience (68.0%) and a lack of design guidelines (60.0%) were the top ranked, followed by a lack of skilled designers and workers (52.0%), as shown in Figure 66(b). These responses clarify the reasons (1) why FRP was not actively used in many state agencies and (2) why the agencies familiar with FRP employed it more than 40 times in their projects. As discussed earlier, the transportation agencies generally acknowledge the benefits of FRP application and, accordingly, active technology transfer will facilitate the adoption of this prom- ising construction material. Nontechnical issues such as insufficient budget (20.0%) and procure- ment (20.0%) also influenced the use of FRP for infrastructure projects. Given that procurement in state DOTs is sometimes processed with pre-registered vendors, FRP manufacturers might be admin- istratively disadvantageous when competing with others. Although many agencies did not provide answers to the âOthersâ category [Figure 66(b)], several commented on the following challenges (quoted from the survey with the removal of respondersâ identification and to present a dual unit): â¢ Durability issues. â¢ Wearing surface on bridge decks. FIGURE 65 Which design guides/specifications for FRP have been used in your agency? (multiple items selected; 38 answers from 38 agencies experiencing FRP).
127 â¢ FRP deck failure/delamination. â¢ Lack of experience with fabrication, lack of standardization in the composites industry, and lack of inspection standards for composite. â¢ With regard to internal FRP reinforcement (rebar) there is widespread skepticism about its efficacy, even though such has been demonstrated in the laboratory and the field and there is a correspond- ing lack of experience/ignorance. There is less skepticism with regard to externally bonded repair applications using FRP materials. There is virtually universal agreement among engineering staff that FRP composite members such as beams or bridge decks (i.e., fully composite material) have not evolved to the point that they can be relied upon and can economically be employed. â¢ Sole source/proprietary design is biggest hurdle; cost is also a detractor because of high initial cost. â¢ FRP deck product was well-designed, but the attachment details and overlay details were poorly conceived. â¢ We have used column wrap or column shell casement in five projects, as best as I can tell. These projects were built between 1995 and 2002 and installed 8,150 ft2 (757 m2) of wrap/shell on columns. The design code changed, which lowered the stateâs seismic risk. Therefore, we had no real need to wrap other columns. â¢ High cost; limited availability for competition. About 45% of the respondents conducted qualification tests for FRP materials, as shown in Figure 67. Mechanical testing was 75.0% and durability testing was 56.3%, which are the most impor- tant aspects in FRP applications on site. Other methods utilized were bond examinations using non- destructive evaluation (NDE), pull-off tests, scaled column tests, and shake tables including multi-span bridges. One agency contracted with a university to develop environmental reduction factors. The (a) (b) FIGURE 66 Has your agency had any challenges in using FRP for infrastructure projects? (35 answers from 38 agencies experiencing FRP): (a) response; (b) sources of challenges (multiple items selected). (a) (b) FIGURE 67 Has your agency conducted qualification testing (e.g., strength, durability, and the like) for FRP materials or FRP-based structures? (35 answers from 38 agencies experiencing FRP): (a) response; (b) details (multiple items selected).
128 respondents were interested in the performance of structural members constructed with FRP compos- ites (Figure 68). The most common method was visual inspection (83.3%), which is relatively easy to conduct with minimal costs. The portion of the performance evaluation using special equipment was remarkable: nondestructive testing (61.1%) and condition rating (44.4%). The 16.7% response in the âOthersâ category included load testing, along with computer-based modeling (basically redundant with the condition rating item). The performance of FRP-based structures was satisfactory, as shown in Figure 69. In most cases, the maintenance and repair of these structures were not required (76.5%). The occurrence of techni- cal action for structural members reinforced with FRP bars was none and for the members strength- ened with FRP sheets was insignificant (only three states indicated that maintenance and repair were necessary for FRP-strengthened members: three times over the last 16 years in one state, one time over the last 10 years in another state, and eight times over 10 years in the other state). Other FRP types required technical action; for instance, FRP decks were delaminated owing to stiffness incompatibility or inappropriately designed connections details, and ultimately had to be replaced with a conventional reinforced concrete deck (one state indicated eight times over 5 years). Although a comparative analysis with conventional materials (e.g., steel) was outside the scope of the present study, it could be concluded that FRP applications need negligible maintenance and repair action, supported by the survey results and interviews with the participating agencies. Also of interest was the long-term durability of installed FRP composites, as evidenced by the 69.4% response in Figure 70(a). Durability is a major concern to most transportation agencies, because the application history of FRP materials is relatively short and their actual time-dependent behavior on (a) (b) FIGURE 68 Has your agency conducted performance evaluation for structures constructed with FRP? (35 answers from 38 agencies experiencing FRP): (a) response; (b) details (multiple items selected). FIGURE 69 Has your agency conducted maintenance or repair for structures constructed with FRP? (34 answers from 38 agencies experiencing FRP).
129 site is not well documented (a limited amount of information is available, as discussed in Chapter Five, State-of-the-Art of Fiber-Reinforced Polymer Composites in Highway Infrastructure.) Most agencies conducted visual inspections (88.0%) to examine the durability performance of structures with FRP [Figure 70(b)]. Nondestructive testing (32.0%) was used in preference to destructive test- ing (24.0%), which is typical since the agencies did not want to damage existing structures. Another method belonging to durability assessment was accelerated laboratory testing. Specific comments on long-term durability are: â¢ We have sponsored research on mechanical properties of GFRP bars exposed to concrete envi- ronment of laboratory specimens exposed to the exterior environment for 7 years, and have assisted/cooperated in research performed by others on GFRP bars that have been in service in one of our bridge decks for 15 years. â¢ Follow-up testing after more than 10 years of panels hung in a bridge environment (i.e., in the field for decaying in material properties). â¢ Primarily our durability issues have been with FRP decks. â¢ We also have a bridge deck that was built with carbon FRP grids in 1999. We worked with a university on this project, so all the material was thoroughly tested as to its ability to withstand loads. The only real problem with the grids was cost, as the CFRP was about three times higher than epoxy-coated rebar. That bridge was load tested after completion of construction, as well as about 10 years after that and all performed well. Life-cycle cost analysis is an important component in FRP application (see Chapter Six, Life- Cycle Cost Analysis.) However, only 8.6% of the responding agencies examined the life-cycle costs associated with FRP-based projects (Figure 71). These agencies used present worth and risk analyses, (a) (b) FIGURE 70 Has your agency considered or examined the long-term durability of installed FRP? (36 answers from 38 agencies experiencing FRP): (a) response; (b) details (multiple items selected). FIGURE 71 Has your agency considered or performed life-cycle cost analysis using FRP? (35 answers from 38 agencies experiencing FRP).
130 and assessed the costs of CFRP-prestressed concrete girders relative to those of conventional steel- prestressed girders. Effort on life-cycle cost analysis appears insufficient to quantify the long-term benefit of FRP applications in highway infrastructure. The investment of the respondents in research is substantial [Figure 72(a)]. The responding agen- cies supported structure-level and in situâlevel research projects [Figure 72(b)], and 53.8% were interested in material-level research. Some agencies checked the âOthersâ category (26.9%) with the following comments (most answers in this category were redundant with the foregoing categories): barrier static load testing and appropriateness of design standards (ACI versus AASHTO and others). The agencies responding to the previous question (Figure 72) stated that research activities can facilitate the use of FRP composites in practice [Figure 73(a)]. All research subjects listed in Fig- ure 73(b) received similar responses (about 50%), except the Failure Characteristics (62.5%), Perfor- mance Evaluation (62.5%), and Spec Development (62.5%). Several agencies added the following comments through the âOthersâ category (taken directly from the survey response without editing), which may be of interest to research personnel: â¢ New FRP applications. â¢ Repair/rehabilitation techniques; designs that directly compete with conventional methods. â¢ Performance effects of repair/rehabilitation/widening of structures reinforced with FRP bars. Deck/barrier interaction, effects of concrete removal tools on FRP in new construction practice and rehabilitation/maintenance practice. â¢ NCHRP Pendulum Testing and Crash Testing of bridge rails. (a) (b) FIGURE 72 Has your agency conducted or supported research activities related to FRP application? (35 answers from 38 agencies experiencing FRP): (a) response; (b) details (multiple items selected). (a) (b) FIGURE 73 Do you believe research can facilitate use of FRP composites in practice? (35 answers from 38 agencies experiencing FRP): (a) response; (b) details (multiple items selected).
131 â¢ For one FRP bridge deck, we performed a full-scale load test to measure structural response of the structure. â¢ IBRD research project. â¢ Literature review/spec development. â¢ Field-tested panels. As shown in Figure 74 (some agencies checked both Yes and No options, and this type of answer was not counted), the majority of the responding jurisdictions did not prefer FRP-based rehabilitation to conventional approaches and provided the following comments (directly taken from the survey responses with the respondersâ identification deleted): â¢ It is a tool, but not âpreferredâ tool . . . one of many. â¢ There is not a uniform policy for the use of FRP. It all depends upon the design engineersâ comfort level in designing with FRP. â¢ Concrete encasement more economical. â¢ Lack of familiarity with composite repair procedures and long-term durability. â¢ Many factors go into considering FRP if the deterioration is more than 10%, costs donât support use of FRP as a rehabilitation method. Also, unknowns such as repair of impact-damaged FRP repaired components, environmental factors, limitation on the strengthening allowed by codes, and uncertainty of short- and long-term failure modes. â¢ The design service life of the rehabilitation has significant impact on outcomes of life costâ benefit analysis and does not warrant the increase in initial capital cost or associate risks/ limitations of the material from an infrastructure management perspective. â¢ The solution chosen is not as simple as the question asked. It totally depends on the type of repair needed and the location. We do often use FRP pile jackets and FRP wrap for girders. â¢ More conventional methods of repairs are favored as a result of comfort level with materials and case history of good long-term results. FRP is a tool that we are using more frequently in the right situations. â¢ At this time, we have no preference or go-to repair methods. We consider all appropriate repair techniques and select the one that best meets the situation. We do not consider FRP repairs to be nonconventional. â¢ We do not have enough experience with the long-term effectiveness of FRP to know if the cost is justified. The performance appears to be very sensitive to installation and we are not yet comfortable that we are actually achieving the intended results from FRP. â¢ Too expensive and lack of trained contractors. â¢ Limited experience with FRP. â¢ Not enough experience with FRP to answer. â¢ This is not a yes/no question. We used FRP-based rehabilitation where it makes sense and we have confidence that it is the best approach. We have used FRP for concrete columns and a couple of pier caps. The condition of the concrete must not be so deteriorated. We also still do FIGURE 74 Does your agency prefer FRP-based rehabilitation (repair/retrofit) for deteriorated structures to conventional techniques? (32 answers from 38 agencies experiencing FRP).
132 conventional repairs as well. FRP repairs in the state are gaining acceptance from designers and contractors. We still have many more contractors that prefer conventional repairs over FRP repairs. Most general contractors in the state will hire a specialty sub-contractor to perform the FRP repairs. â¢ No established preference. â¢ Applications where weight is an overriding issue (movable bridges), so some extra cost to meet the weight specs can be reasonable . . . our designers claim that FRP rebar costs less installed than stainless steel rebar, but the cost basis for their comparisons have not been apples to apples. â¢ Not really a preference; however, it is frequently used where possible deteriorated; i.e., in pier extensions, high load impact, insufficient moment carrying capacity of existing structures need- ing increase in capacity. â¢ It depends on the component. â¢ Cost savings has not been evaluated, long-term performance has not been evaluated, and effec- tive installation procedures/standards have not been fully established. â¢ Lack of familiarity and cost. â¢ Conventional methods are still accepted by the majority. It can again be confirmed that the transportation agencies are not certain about the long-term performance and durability of installed FRP composites. Attention from the research community is required to address this fundamental concern associated with FRP-based construction. More than 28% of the agencies preferred structural rehabilitation with FRP (Figure 74) for the following reasons (taken directly from the survey responses): â¢ FRP column wraps have been successfully used to help prevent future spalling of deteriorated columns. â¢ FRP-wrapping is primarily used as a method to contain repair patches. It has been our experience that concrete repairs of columns, girders, and bent caps have a longer life if they are wrapped with FRP to contain the patch and seal the patch than if just patching with no FRP-wrapping. â¢ When appropriate, these repairs save significant funds. â¢ In some cases it does have benefits such as less invasive construction method versus replacement (e.g., pier cap repair and confinement versus pier cap replacement). â¢ Bonded repairs save money . . . FRP decks are used for very specific repairs. â¢ Yes for column retrofits; no for deck retrofits. â¢ Strengthening with removal shear deficiency or increasing load-carrying capacity. â¢ Lower costs, higher efficiency and effectiveness. â¢ It has proven to be an economical alternative. Open-ended questions were asked, as listed here (taken directly from the survey responses): â¢ Procurement of FRP materials: â Contractor supply. â Designate as research project and follow state procurement laws for sole sourcing. This is not viable on a production basis. â Specification based; contractor finds the supplier meeting the material requirements; DOT reviews and approves. If sole source or specialized (such as prestressing tendons), a procure- ment special provision or separate contract is issued. â Typically, when the application is considered experimental weâll purchase the FRP material directly, then as the application becomes common practice weâll competitively bid the material. â With specs and pre-qualification programs, performance spec. â Performance-based or through university; some private sales. â Special provisions with proprietary materials called out. â FRP work would be a subset of the total rehabilitation required on a given bridge structure. Unlikely that we would do a project just for FRP work. â¢ Selection of consulting firms or contractors for FRP application: â Pre-qualified bridge consultants; no FRP-specific requirements. â Same as conventional projects.
133 â The selection of consultants and contractors for projects involving FRP is done the same as it is for all projects. â Required that the FRP system supplier be present as the contractorâs QC [quality control] agent. Design for externally bonded FRP retrofits done in house with ACI codes at present. New structures and/or components are designated by consultant/university. â Written in specs that contractor must have at least three transportation-related projects using FRP within last 3 years. â Selected for its ability to develop bridge plans. â We work closely with the transportation center at a state university. The center conducts the design, deployment, and monitoring of FRP retrofit projects in the state. We did two or three projects through advertisement with contractors, but not many contractors expressed interest in using FRP. â¢ Does your agency have any current FRP projects or anticipated near future projects? â YesâCFRP prestressing; FRP structural system for marine fenders. â If rehabilitation projects arise that could utilize FRP wrap technologies they would be con- sidered on a case-by-case basis and evaluated using life-cycle cost analysis as well as risk analysis. Usually related to superstructure or substructure strengthening. â DOT currently has two hybrid composite beam bridges and at least two bridges using GFRP under construction. Weâre currently looking at using composite piles or composite SIP forms on a couple of upcoming projects. Other FRP bridge elements, such as bridge drains, are standard practice and are continuously in use. â Yes, prestressing strand in bulb tee-topped girders (current); post-tensioning strand for adja- cent box beam structures (three so far); FRP for deck and beam reinforcement (two so far), and PS tendon; bring in backpack (two so far). â Yes, many. Column casing and confinement, arch bridge seismic retrofit including the arch and spandrels. Strengthening deck overhangs in negative moment region using the NSM technique for higher AASHTO demand requirements. Girder strengthening including box girder and shear-strengthening. â Yes, major research process in place now. â A minimum of three FRP repair/strengthening projects of existing bridges in the next 2 years. â¢ Have you had any positive or negative experience in using FRP materials for your projects? â We have had positive performance with FRP wrap systems. They are performing well in protected areas. Protective coatings have deteriorated, but the systems remain bonded. Maintenance of the protective coatings will be an ongoing issue and may affect long-term performance. â Although our experiences have been mostly positive we have experienced some fabrication issues, construction issues, and performance issues. Weâre willing to share more details on these issues in the future if requested. â Yes, having the QC inspection during FRP laminate layup is valuable and ensures quality product. We also require a 2-year warranty on FRP laminates. No reports to date of debond- ing, Negatives are high cost, variances in design codes (such as how resistance factors are implicitly or explicitly defined, FRP strain limits, etc.), unknowns on long-term performance, creep-rupture concerns, and extreme events (fire, high load hits). â Only negative experience was with a FRP deck system for which we had not done thorough in-house evaluation that experienced some durability issues related to loosening and dete- rioration of mechanical fasteners and bond of the high-friction wearing surface. Handling of CFRP prestressing, particularly the anchorage system needed for stressing, is a challenge. â We had failure and delamination of a FRP bridge deck connections that were not detailed correctly (i.e., design flaw). Connection to pier cap included premature delamination. Even after many well-designed repairs, we were not able to stop delamination due primarily to the stiffness incompatibility between FRP deck and reinforced concrete pier cap. Deck was eventually removed and replaced with a conventional bridged deck. â Some failures; always in details, not FRP. â Negative: FRP bridge decks delaminated and failed. â We have had positive experiences, although we do not use it for structural purpose. â We have had positive experience with FRP in new bridges (two FRP pedestrian bridges, GFRP and CFRP reinforcement in bridge decks, stay-in-place GFRP forms, and CFRP
134 prestressed bridge girders). We have also had very good experience with FRP in retrofitting/ strengthening existing bridges. Figure 75 documents the opinion of the transportation agencies on FRP costs. Almost 60% of the responders answered that costs are a barrier to accepting FRP technologies [Figure 75(a)], and 28.6% indicated that costs are significantly high [Figure 75(b)]. Figure 76 shows an overall evaluation of FRP-based projects from the perspective of transportation agencies. The agencies were generally satisfied with the use of FRP composites. Phone interview with 18 agencies revealed the same result: 17 agencies did not have a serious concern about the performance of installed FRP composites within their observation ranges; however, one agency was not sure about the costâbenefit of FRP applications. ProjeCt Planning witH fiber-reinforCed Polymer ComPoSiteS Figure 77 shows fundamental reasons why responding jurisdictions were reluctant to consider FRP composites in their projects. Critical issues were a lack of experience (48.5%) and design guides (51.5%), as well as of skilled designers/workers (39.4%), which are similar to the challenges the agen- cies experienced when pursuing FRP projects. Several agencies mentioned during the phone inter- views that contractors need to be knowledgeable about FRP applications. Comments on the âOthersâ category were: â¢ Material costs (cost too high; no benefit). â¢ Questionable durability and performance. â¢ Skepticism about FRP compared with conventional materials. (a) (b) FIGURE 75 Do you think costs are a barrier in accepting FRP technologies? (36 answers from 38 agencies experiencing FRP): (a) response; (b) details. FIGURE 76 How do you rate your overall experience in FRP composites for your projects? (35 answers from 38 agencies experiencing FRP).
135 â¢ Unavailability of quality FRP deck products and existing installations with inadequate attach- ment and overlay details. â¢ No appropriate candidates. â¢ The use of FRP has been limited to concrete repair projects. â¢ Conventional materials work well. â¢ We donât consider it to be a structural enhancement; mainly used as a sealant. â¢ Long-term durability, high cost. More than 85% of the responding agencies positively answered regarding the potential of using FRP composites in future projects (29.7% for very likely and 56.8 for likely), as shown in Figure 78. By contrast, 13.5% of the agencies were not in favor, primarily because of the reasons discussed previously (see Figure 77). The following is a summary of observations from field work, which may be of interest to state agencies when planning infrastructure construction with FRP materials: â¢ FRP-reinforced concrete: the responding agencies did not indicate specific lessons belonging to FRP-reinforced concrete members. â¢ FRP-prestressed concrete: anchor systems for CFRP tendons need attention, because stress concentrations may damage the tendons during prestressing. When transporting CFRP tendons, at least two workers hold both ends of the tendons as straight as possible to prevent the local bending of the tendons. Improper handling such as excessive bending can degrade the tendonâs load-carrying capacity (i.e., fiber kinking). FIGURE 77 Why has your agency not considered using FRP for infrastructure projects? (multiple items can be selected; 33 answers from 46 responding agencies). FIGURE 78 Is your agency planning to consider use of FRP composites for a future project? (37 answers from 46 responding agencies).
136 â¢ FRP strengthening: although premature FRP-debonding has not been reported, protective coat- ings may deteriorate. Regular inspection detects this nonstructural problem, and maintenance action may follow, depending on the extent of peeled coatings. When unidirectional FRP sheets are bonded for shear strengthening, including U-wrap anchorage, the fiber direction needs to be checked (i.e., perpendicular to the longitudinal span). If fiber direction is parallel to the span, the strengthening effect does not conform to what was intended for the FRP sheets. Prior to bonding FRP sheets or laminates, an inspection for quality control (e.g., surface preparation) precludes potential debonding problems caused by poor workmanship. It is particularly impor- tant for wet lay-up application, including the complete saturation of dry fibers. Documentation of all procedures and material details is necessary for future maintenance purposes. â¢ FRP decks: preassembled FRP components increased construction productivity. Improperly designed or detailed deck connections, however, failed prematurely. The leveling and fabri- cation of FRP deck panels during installation were crucial, because differential deflections between the panels can accelerate connection failure. FRP decks are generally durable, whereas delamination often caused problems and required maintenance. No particular solutions were proposed to prevent delamination failure.