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41.1 Background Fiber-Reinforced Polymer (FRP) systems have shown potential for use in rehabilitating and retrofitting existing structures. They can be used to provide increased ductility as well as shear and flexural strength to structural elements such as columns, beams/girders, slabs/decks, and walls. Typi- cal applications include compensation for increased traffic volumes on bridges, dampening of vibration, corrosion reha- bilitation, correction of deficient design, etc. (Busel and Barno, 1995 and ACI 440.2R-08, 2008). FRP systems have been used on a project-specific basis for the last two decades. They are now becoming a widely accepted method of strengthening concrete structures. FRP systems used for strengthening reinforced or prestressed concrete girders consist of externally bonded laminates or near-surface mounted bars. These systems may contain either carbon or glass fibers and thus carbon fiber reinforced poly- mer (CFRP) or glass fiber reinforced polymer (GFRP). The acceptance and use of these strengthening techniques depend on the availability of clear design guidelines, installation pro- cedures, and construction specifications. Standard specifica- tions exist for all materials commonly used in civil engineering structures. However, design specifications for FRP use are not readily available. Most research has focused on strengthening of axially loaded or flexural members with limited experi- mental and analytical data on the use of FRP systems for shear strengthening of girders. This research, performed under NCHRP Project 12-75, was initiated to address FRP- related shear design issues and related specifications and design methods. 1.2 Research Objectives The objective of this project was to develop design methods, specifications, and examples for design of FRP systems for strengthening concrete girders in shear. 1.3 Research Plan and Methodology The following tasks were performed to achieve the following project objectives: 1. Review of relevant practice, data, specifications, and re- search findings from both foreign and domestic sources on the strengthening of concrete girders in shear using FRP systems containing carbon or glass fibers and identi- fication of FRP systems available for shear strengthening. 2. Identification of criteria that influence design of FRP shear strengthening systems. 3. Evaluation of existing design methods and the identifica- tion of appropriate shear design provisions that account for FRP and preparation of a work plan for further devel- opment of potential design methods. 4. Execution of the work plan and development of the design methods. 5. Preparation of recommended specifications and com- mentary for shear design of FRP-strengthened concrete girders together with design examples to illustrate the application of the recommended design methods and specifications. 6. Preparation of a report that documents the entire research. Figure 1.1 shows the process used to determine the criti- cal issues that were addressed in the project. Figure 1.2 illus- trates the process used to develop the design methods and specifications. 1.4 Organization of the Report This chapter presents the background, objectives, method- ology, and scope of the project. Chapter 2 summarizes the findings of the research, including the literature review as well as experimental and analytical investigations. Chapter 3 C H A P T E R 1 Introduction
5Literature Review Identify Criteria that Influence Design of FRP-Strengthened System Comparison and Evaluation of Existing Design Methods Annotated Outline of the Proposed AASHTO LRFD Design Specifications Recommend Design Methods and Prepare work plan Critical Issues to be Addressed in this Project Survey Results Field Problems Collection of Existing Experimental Investigations Collection of Existing Analytical Models Limits of Number of Testing Requires selections of the most efficient/practical methods in the experimental program. Other methods can be considered in the analytical work by finite element analysis methods. Parameters that influence shear capacity provided by FRP Design Detailing 1. CFRP vs. GFRP vs. Aramid 2. Complete Wraps vs. U-Wrap, vs. Side Bond 3. Continuous wraps vs. discontinuous (Strips) 4. Fiber directions (45 vs. 90 degree) 5. Anchorage system types Parameters well documented in the current database 1. FRP properties 2. Internal shear reinforcement 3. Shear-span-to depth ratio 4. Scale Effect 5. Effect of Longitudinal reinforcement Parameters not fully documented in the current database 6. Influence of anchorage/configuration 7. Concrete strength 8. Fatigue 9. Precracking 10. Prestress 11. Beam continuity Causes for Inaccuracy of the Existing Models Recommendations for the Research Program to develop design methods Construction of Database Figure 1.1. Process to determine potential critical issues.
discusses the application and implementation of the rec- ommended design method and specifications. Chapter 4 presents the conclusions and suggestions for future re- search. Attachments A and B present suggested changes to AASHTO LRFD Bridge Design Specifications (AASHTO, 2008) and recommended design guidelines, respectively. Appendix A provides more details on all aspects of the research including, the literature review, survey of state DOTs, existing analytical models, experimental investiga- tions, and data analysis. Appendix A is not published herein but can be found on the NCHRP Report 678 summary web- page at http://www.trb.org/Main/Blurbs/164622.aspx. 6 15 Main Parameters and 37 Sub-Parameters to be investigated to fully understand the behavior of concrete girders strengthened in shear with FRP 12 Main Parameters and 27 Sub-Parameters These are not fully covered by the previous experimental research projects Other Parameters Experimental Works Analytical Works Provide experimental data for the calibration of FE Models Provide anticipated critical issues for tests and provide predictions of test girders Results of Experimental Parametric Study Develop Design Methods Development of the AASHTO LRFD Specifications Existing Experimental Database Existing Analytical Models Reliability Analysis Results from this Project Figure 1.2. Process for developing design methods and specifications.
