PSI - Issue 64

Mehdi Aghabagloo et al. / Procedia Structural Integrity 64 (2024) 1516–1523 Mehdi Aghabagloo/ Structural Integrity Procedia 00 (2019) 000 – 000

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strain gauges (for the case of HB specimens). For the determination of the experimental bond-slip laws, shear stresses (  ) are calculated using Eq. (1), where E f and t f represent the FRP elastic modulus and thickness, respectively, ε f is the strain measured by DIC, and x indicates the position along the bonded length. These positions are specifically located 2.5 mm above ( x i ) and below ( x i +1) the indicated four positions in Fig. 1c. In the case of HB, these positions coincide with the locations of the strain gauges. ( ) ( ) , 1 , 1 2 , 1 , f f f i f i i f i f i E t x x    + + + − =− − (1) The slip ( s ) along the FRP can be obtained from integration of the strain profile using Eq. (2). Finally, the average slip between two gauges can be calculated. As a result, the experimental bond-slip law can be obtained. ( ) ( ) ( ) ( ) , 1 , - - 1 1 2 f i f i s x s x x x i i i   + + =  + + (2) The result of the predicted bond-slip curve for the EBR specimen is shown in Fig. 4a, along with the experimentally derived bond-slip laws at four distinct locations from the loaded end. Results reveal a close alignment between the predicted and experimental bond-slip laws, showcasing the enhanced prediction accuracy achieved by employing a multi-linear shape. Similarly, the comparison between predicted and experimentally determined bond-slip laws for the HB specimen is shown in Fig. 4b, demonstrating again a remarkable alignment between them. According to the predicted bond-slip law, as the test progresses toward the end, the shear stabilizes, indicating the presence of residual bond stress caused by friction from the compressive stress applied by the metal anchor. Furthermore, Fig. 4c displays the predicted bond slip law for the second test performed to the HB specimen, referred to as the HB post-failure. In this case, comparison between predicted and experimental bond-slip laws is not feasible due to the loss of strain gauge data after the first single shear test on the HB specimen.

Fig.4 Comparison of predicted and experimental bond-slip law at different locations

4. Discussion From the comparison between bond-slip laws of EBR and HB specimens (Fig. 4a and 4b), higher initial stiffness and maximum bond stress are visible for the anchored specimen, as expected. After attaining the bond strength, the descending branch of the EBR specimen diminishes until reaching a null stress, whereas for the case of the HB specimen, a plateau friction part is observed. This friction part is also observed in the bond-slip law of the HB post failure specimen (Fig. 4c), with some differences for small values of slip that are attributed to the damaged surface when the HB post-failure test is performed. Fig. 5a compares the addition of predicted bond-slip laws of EBR (purple solid line) and HB post-failure (green solid line) with the predicted bond-slip law of the HB specimen (blue solid line). The addition (black solid line) is obtained by adding the shear values for identical slip values. As observed in the plot, the combined bond-slip law