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