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19 4.1 Conclusions This research developed a set of Recommended Guide Speci- fication for the Design of Externally Bonded FRP Reinforcement Systems for Repair and Strengthening of Concrete Bridge Ele- ments. The provisions contained in these specifications utilize the load combination requirements found in the AASHTO LRFD Bridge Design Specifications 4th Edition (2007) and em- ploy the LRFD methodology. The load and resistance factors have been developed from structural reliability theory based on current probabilistic/statistical models of loads and struc- tural performance and are designed to achieve the reliability levels that are already embedded in current AASHTO design and rating guidelines. The recommended Guide Specification is accompanied by commentaries that are necessary for explaining the back- ground, applicability, and limitations of the provisions con- tained therein. The guide specifications and commentary are presented in a format resembling that of the AASHTO LRFD Bridge Design Specifications in order to facilitate their consid- eration and adoption by AASHTO. The Guide Specification consists of five sections. Section 1 addresses the scope, general requirements, and design basis of the proposed specifications. Section 2 defines the require- ments for polymeric composite material systems intended for use for repair and strengthening of concrete bridge elements. The material provisions contained in Section 2 give a consis- tent basis for reporting material properties and the condi- tions under which these properties are obtained. Sections 3, 4, and 5 contain the recommended design provisions based on the limit states governing the response of a steel-reinforced concrete member subjected to flexure, shear, and combined axial loading and flexure, respectively. In addition, step-by-step calculations in accordance with the Recommended Guide Specification are presented as exam- ples of common FRP strengthening applications. These ex- amples cover the five sections of the proposed Guide Specifi- cation and would serve as a tutorial of how to approach bridge strengthening projects in practice. 4.2 Implementation The successful implementation of the Guide Specification developed in this research will require in-depth training for bridge design engineers to become fully acquainted with the fundamental principles, assumptions, limitations, and inves- tigative procedures associated with the behavior and design of steel-reinforced concrete structural members reinforced with externally bonded FRP reinforcement. The training ma- terials must emphasize the underlying basis for, and the de- tails of, all relevant provisions of the Guide Specification. It is also recommended that the proposed Guide Specification be used for trial design by independent designers to identify potential improvements. 4.3 Recommendations for Further Research Based on the findings and limitations of this research, fur- ther research on FRP strengthening of reinforced and pre- stressed concrete structural members is recommended. The following topics are proposed: ⢠FRP Material Requirements. Material requirements in the proposed guidelines stipulate that the FRP reinforcement be conditioned in four distinct environments and for a du- ration of 1,000 hours and then tested to ensure that the property of interest retains 85% of its original value. These requirements have been derived from the work of Steckel et al. (1999a, 1999b), and Hawkins et al. (1999), under the sponsorship of the California Department of Transporta- tion (Caltrans), which called for property measurements after exposure intervals of 1,000 hours, 3,000 hours and 10,000 hours to allow estimates of degradation over the C H A P T E R 4 Conclusions, Implementation, and Recommendations for Further Research
projected service life. It is suggested that research be con- ducted to (1) examine the reasonableness of test durations of up to 10,000 hours and (2) establish a standard practice of how to analyze and report the data resulting from any long-term tests. ⢠Effect of Temperature on the Response of Reinforced Concrete Structural Members Externally Reinforced with FRP Reinforcement. The proposed guide specifications re- quire that the characteristic value of the glass transition tem- perature of the composite system and for the adhesive (when used) determined in accordance with ASTM D4065 shall be at least 40°F higher than the maximum design temperature, TMaxDesign, defined in Section 3.12.2.2 of the AASHTO LRFD Bridge Design Specification. Research is needed to examine the validity of the requirement proposed in the Guidelines. ⢠Experimental Studies Addressing FRP Reinforcement End Peeling. It is suggested that the FRP reinforcement end peel- ing design equation be further validated under static and fa- tigue loading conditions and with exposure to various envi- ronmental conditions in order to establish the validity of the limiting peel stress stipulated in the guidelines. ⢠Shear Strengthening of Reinforced and Prestressed Con- crete Girders with FRP Reinforcement. Data concerning 0 065. â²fc shear strengthening of concrete members are limited. Re- search on shear strengthening of bridge members with FRP reinforcement is needed. Such research should include (1) Complete wrapping of structural members, (2) The shear behavior of deep reinforced concrete beams fully wrapped with FRP reinforcement, and (3) Design guide- lines and specifications related to the shear behavior of shal- low and deep reinforced concrete beams reinforced with FRP reinforcement combined with mechanical anchorages. It is recommended that these studies include specifications for anchorage systems and design guidelines for anchor- ages for use in conjunction with the FRP reinforcement (Schuman and Karbhari 2004; Monti et al. 2004a, 2004b). ⢠Experimental Behavior of Confined Rectangular Columns Under Axial Loading and Combined Axial Loading and Flexure. Tests on eccentrically loaded compression slen- der and non-slender columns confined with FRP rein- forcement are needed to address (1) the most appropriate confinement model for design purposes, (2) the effective- ness of the FRP reinforcement with respect to the cross section aspect ratio, and (3) experimental behavior of con- fined reinforced concrete columns under axial tension and flexure. 20
