Splice length in Concrete Beams Reinforced with FRP Bars

The bond between concrete and tensile reinforcement is a major problem in RC structures, as far as strength and safety are concerned. Because of the complexity and the effect of a variety of parameters, researchers have not been able to theoretically include all parameters in their solutions for the bond phenomena. This paper proposes an equation for calculating the splice length of lap-spliced concrete beams reinforced with FRP bars. Firstly, equations for displacement modulus and local bond strength of FRP bars are obtained by available pullout test results. After wards, using the local bond strength equation and based on the experimental results of lapspliced FRP reinforced concrete beams, an equation for bond strength of splices is derived. Finally, an equation for splice length calculation is also presented. The splice lengths calculated by the proposed equation are compared with the values predicted by different code provisions and other models. The proposed equation is compared with the existing design equations (ACI 440.1R-06 4] and CSA S806-02 [5]) using a parametric study. According to Fig. 4, in specimens with concrete compressive strength of 28 MPa, the splice length obtained from the proposed and ACI 440.1R-06 [4] equations are almost the same. For specimens with concrete compressive strengths of 41 MPa and 55 MPa, the splice length obtained from the proposed equation is longer than that obtained from ACI 440.1R-06 equation, and as the compressive strength increases, the difference between these two equations increases. As seen in Fig. 4, for specimens reinforced with small diameter bars (db< 22mm), the splice length calculated by the proposed equation is greater than that calculated by CSA S806-02 [5] equation. For the specimens reinforced with large diameter bars (db≥ 22mm) and C/db 1.5, the difference between the values calculated by the proposed equation and CSA S806-02 equation are small.Based on the results of this study, the following conclusions were drawn:1- The proposed equation for determining the local bond strength of GFRP bars showed a good correlation with experimental results. The average ratio value of the experimental to calculated local bond strength obtained by the proposed equation was 1.022 with a standard deviation of 0.138.2- The average of the experimental over calculated bond strength ratios obtained by the proposed equation was 1.09 with a standard deviation of 0.164. These values were 0.649 and 0.187 for the ACI 440.1R-06 guideline. Therefore, ACI 440.1R-06 equation overestimates the bond strength of GFRP bars in splices of beams.3- A simple and practical equation was proposed for determining the splice length in beams with GFRP spliced bars. When compared to the ACI 440.1R-06 and CSA S806-02 codes, the proposed equation is generally conservative.