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21.1 Background Because of the technical and economic benefits achieved by the use of externally bonded fiber-reinforced polymer (FRP) systems for the repair and strengthening of reinforced and prestressed concrete bridge structures, this method of reha- bilitation of bridge structures has become accepted practice in many state highway agencies. Such FRP systems are light- weight, exhibit high tensile strength, and are easy to install; these features facilitate handling and help expedite repair or construction, enhance long-term performance, and result in cost savings. In addition, the external bonding of FRP com- posites improves flexural behavior of concrete members and increases the capacity of concrete bents and columns. In spite of their potential benefits, the use of externally bonded FRP systems is hampered by the lack of nationally ac- cepted design specifications for their use in the repair and strengthening of concrete bridge elements. NCHRP Project 10-73 was initiated to review available information and to de- velop a recommended guide specification for the design of ex- ternally bonded FRP systems. This specification will help high- way agencies consider FRP systems among the options for the repair and strengthening of concrete bridge elements and select options that are expected to yield economic and other benefits. 1.2 Project Objective and Scope The objective of this project was to develop a recommended guide specification for the design of externally bonded FRP composite systems for their use in the repair and strengthen- ing of reinforced and prestressed concrete highway bridge elements. FRP composite systems covered in this project include thermoset polymers reinforced by carbon, glass, or aramid fibers. To achieve this project objective, the following tasks were carried out: Task 1. Information relevant to the design of FRP systems used in repair and strengthening of concrete bridge elements was collected and reviewed. This information was assembled from published and unpublished reports, contacts with trans- portation agencies and industry organizations, and other do- mestic and foreign sources, including the American Concrete Institute âGuide for the Design and Construction of Exter- nally Bonded FRP Systems for Strengthening Concrete Struc- turesâ (ACI 2002) and similar publications. Task 2. Based on the information gathered in Task 1, the items necessary for developing the guide specification were identified and categorized. These items addressed flexure, shear, axial loading, development length, detailing, and other design considerations in a manner similar to that provided in the AASHTO LRFD Bridge Design Specifications. Task 3. Based on the information obtained in Tasks 1 and 2, a tentative outline of the proposed guide specification and a work plan for developing the specification along with a com- mentary and design examples were prepared. The plan de- scribed the proposed approach for incorporating appropriate resistance factors and other design criteria in the specification. Task 4. The plan for developing the guide specification was executed. Based on the results of this work, the guide specifi- cation was developed. Task 5. Using the specification developed in Task 4, a com- mentary and design examples to illustrate use of the specifi- cation were prepared. Task 6. A final report that documents the entire research, including the recommended guide specification and commen- tary and the design examples was prepared. 1.3 Applicability of Results to Highway Practice The research products resulting from this project provide a technically sound and documented basis for using FRP re- inforcement in bridge rehabilitation and retrofit. The use of FRP reinforcement will have a significant impact on the eco- nomics of bridge maintenance and rehabilitation at state and national levels, and may permit them to upgrade the load- carrying capacity of bridge members through easy-to-install retrofits rather than replacement. The recommended guide C H A P T E R 1 Introduction and Research Approach
specifications gives FRP manufacturers a consistent basis for reporting material properties while at the same time allows bridge design and maintenance engineers to use such material property data for conditions similar to those under which these properties are obtained. The guide specifications and com- mentary presented in Attachment A are formatted to facilitate consideration and adoption by AASHTO. 1.4 Report Organization This report consists of four chapters and two attachments. Chapter 1 describes the objective and outlines the various tasks performed to accomplish the objective. Chapter 2 pres- ents the findings of this study, and Chapter 3 addresses the analytical formulations and the experimental data that formed the basis upon which the proposed Guide Specifications were developed. Chapter 4 presents the conclusions and recom- mendations for further research. Attachment A presents rec- ommended guide specifications and commentaries for the design of externally bonded FRP reinforcement systems for the repair and strengthening of concrete bridge elements. At- tachment B contains step-by-step illustrative examples that serve as a tutorial on how to approach bridge strengthening projects in practice. 3
