The use of fiber reinforced plastic reinforcement in reinforced and prestressed concrete structures is gaining increased attention. This paper describes the results of a preliminary experimental program in which strands made of carbon fiber composites (trade name CFCC - Carbon Fiber Composite Cable) were used as pretensioning reinforcement in two partially prestressed concrete T beams. The beams were ten foot in length and 12 inches in depth and contained, in addition to the carbon fiber strands, conventional reinforcing bars Experience gained with the stressing, anchoring, and releasing of CFCC strands is described. Relevant test results regarding load-deflection response, curvature, stress-increase in the reinforcement with increased load, cracking and crack widths, and failure modes are reported, and compared to results obtained from similar tests using prestressing steel strands. The load deflection response of beams prestressed with CFCC strands showed generally a trilinear ascending branch with decreasing slope up to maximum load. Deflections and crack widths were generally small but increased rapidly upon yielding of the non-prestressed steel reinforcement. The post-peak response was characterized by rapid step-wise decrease in load due to successive failures of the CFCC strands, and stabilization at about the load-carrying capacity of the remaining steel reinforcing bars. The presence of reinforcing bars helped the beams sustain large deflections before crushing of the concrete in the compression zone. Analytical predictions of the load-deflection response using a nonlinear analysis method were used and led to reasonable agreement with experimental results.

Four prestressed concrete T-beams were constructed with aramid-based prestressing and parallel fiber rods. Three beams included an externally applied fabric shear reinforcement. The beams were tested and the performance of beams with external fabric shear reinforcement were compared to a control beam without external shear reinforcement. The tests indicate that fiber rods serve as effective prestressing tendon with excellent bond characteristics and shear response predicted by ACI equations. The tests also indicate that the externally applied woven fabric can provide the shear resistance. External shear reinforcement using nonmetallic fabric offers significant opportunities for strengthening existing structures as well as for fabrication of nonmetallic structures.

Finite element analyses and experimental confirmation tests were conducted to evaluate epoxy-socketed anchors for fiber reinforced plastic prestressing tendons. The studies disclosed that a parabolically varying profile provides superior performance compared to a conventional linear conic anchor. It was also found that an anchor with a bond release agent on the surface between the socket and resin plug results in a lower peak shear stress compared to a bonded anchor. The combination of a parabolic anchor and bond release agent permits use of a wider range of resins as socketing agents and is less sensitive to construction tolerances. Additional research is suggested to optimize material selection, anchor geometry, and anchor construction.

PC members reinforced with FRP as tendons show brittle failure regardless of the failure mode. The authors' objective was to improve the ductility of PC members reinforced with FRP as tendons. First, the compressive properties of concrete confined with FRP as transverse reinforcement was investigated. Major improvement can be made in the stress-strain relationship of concrete laterally reinforced with FRP, and the concrete members can be given ductility characteristics similar to those of steel-reinforced members by confining the concrete with FRP. Secondly, several PC members reinforced with FRP as tendons and transverse reinforcement were tested and investigated. It was found that marked improvements could be made in the ductility of PC members with FRP tendons by confining the part of concrete subjected to flexural compression with FRP and forcing the members to undergo flexural compression compression failure. 235-493

An overview of a study on bond of glass fiber reinforced plastic (GFRP) reinforcing bars to concrete is presented. The 78 specimens to be tested include several variables, such as the mode of failure (i.e., pullout or splitting), concrete compressive strength, bar diameter, clear cover distance, and top bar effects. In addition, the effect of the radius of bend for hooked bars and the extension on the hooks are investigated. The study is currently in progress and the results of the specimens tested to date are presented. Preliminary results indicate that the top bar effects observed for steel reinforcing bars are also present for GFRP bars. For hooked bars, larger radii of curvature increase significantly the failure load of the bars.