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7 CHAPTER 2 Summary of Major Findings 2.1 Use of FRP for Shear 2.2 Field Applications Strengthening of Although there are several field projects related to FRP Concrete Girders strengthening systems, detailed information on these projects A survey of state departments of transportation (DOTs), is not available and most of these projects were strengthened Washington, DC, and Puerto Rico, was conducted to deter- for flexural rehabilitation. The following six projects were iden- mine the extent of using FRP for shear strengthening. This tified as directly related to FRP shear strengthening of concrete survey included a written questionnaire (followed by either a bridge girders: telephone briefing or a written response) aimed at determin- A single span, reinforced concrete T-beam bridge in New ing the practices for designing concrete girders strengthened in shear using FRP and their perceived deficiencies. York State was strengthened in flexure and shear with exter- nally bonded FRP laminates in November 1999 (Hag-Elsafi The responses received from 39 agencies revealed that only et al., 2001b). 7 state DOTs used FRP for shear strengthening of concrete The Grndals Bridge in Sweden is a prestressed concrete box girders and 32 DOTs have never used FRP for shear strength- bridge approximately 1,300 feet in length and a free span of ening of concrete girders. Fourteen DOTs indicated no need 394 feet. CFRP laminate strips were applied to the inside for shear strengthening of concrete girders, and 12 DOTs walls with steel plate anchorage system to increase the shear expressed a concern about the lack of proper design specifica- strength (Taljsten et al., 2007). tions or provisions for FRP shear strengthening. Some DOTs The Langevin Bridge in Calgary, Canada, is a six-span, four- considered the use of FRPs less efficient when compared to cell, continuous box-girder bridge constructed in 1972. The other strengthening techniques. internal webs were found to be deficient at the right end of The DOTs using FRP for shear strengthening follow the span 2 where the internal prestressing tendons are horizon- design methods contained in ACI 440.2R-02 (ACI 440, 2002) tal and thus contribute nothing to the shear resistance. To because it was the only design guidelines document available correct these deficiencies, CFRP sheets were bonded to the in the United States. Some DOTs (e.g., New York, Oregon, inside face of the external webs and to both faces of the inte- and Pennsylvania) have made slight modifications to ACI rior webs. 440.2R-02 (ACI 440, 2002). Design guidelines and specifica- The John Hart Bridge in Prince George, British Colum- tions provided by FRP manufacturers and course notes from bia and the Maryland Bridge in Winnipeg, Manitoba, are a workshop provided by several organizations were used by two bridges in western Canada that have been strength- some state DOTs. Most state DOTs identified provisions ened in shear with externally bonded CFRP. The John Hart regarding properties of FRP composite materials and control Bridge consists of seven simply supported spans with six of failure modes as the most important issues to be addressed I-shaped prestressed concrete AASHTO girders per span, in future design specifications. An in-depth explanation on and the Maryland Bridge consists of two sets of five continu- FRP strengthening schemes and fatigue and durability issues ous spans with seven I-shaped prestressed concrete AASHTO were also noted as major issues to be addressed. girders per span (Hutchinson et al., 2003).