PSI - Issue 42

Jamal A. Abdalla et al. / Procedia Structural Integrity 42 (2022) 1231–1238 Abdalla et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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3.2. Shear force-deflection responses The shear force-deflection graphs of the tested specimens are shown in Fig. 5. It is clearly indicated that the strengthened specimens with CFRP U-wraps performed superior to the unstrengthened specimens, despite the type of concrete aggregate. Particularly, the percentage increase in the shear force was 36 and 60% in the NU and RU compared to NC and RC, respectively. In addition, strengthening the beams with U-wraps aided in enhancing the deformability of the beams, where the strengthened specimens failed at a higher deflection than their control counterparts. This conduct was more evident in NU specimen which attained a significantly higher deflection than NC, as shown in Fig. 5 and Table 3. It can be also seen from Fig. 5 that the prior cracking (up to 10 kN), all specimens had similar stiffness. However, post cracking, the advantage of the U-jacketing was evident in enhancing the stiffness of the strengthened beams, especially in specimen RU. Comparing NAC and RAC beams, it can be clearly indicated that without strengthening, the behavior of RC beams with 100% NAC and 100% RAC was identical. Particularly, the shear force-deflection graphs of specimens NC and RC are almost overlapping with a percentage difference of 5% in the shear capacity between both specimens. The inclusion of U-wraps also resulted in similar shear strength (percentage difference in shear capacity between NU and RU of 3%), but the deflection of the U-wrapped NAC beam (NU) outweighed that of RU. The maximum strain attained in the CFRP laminates before failure for specimens NU and RU was also comparable (2230 and 2347 strain, respectively). However, as it can be seen from Table 3, the percentage increase in the shear strength is higher for recycled aggregate beam (RU) than the normal aggregate beam (NU). This proves the effectiveness of external strengthening using CFRP on recycled aggregate RC beams. The results also indicate that recycled aggregates can be used as a very good alternative to normal aggregates without compromising the beam’s shear strength.

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3.3. Analytical predictions The shear strength of the tested beams was predicted using ACI 318-19 (2019) and ACI440.2R-17 (2017) for unstrengthened and strengthened specimens, respectively. According to the ACI design guidelines, the shear capacity of the RC beams is calculated by summing up the shear contribution of concrete ( V c ), steel ( V s ), and FRP ( V f ). The specimens in this study did not include steel stirrups; accordingly, the shear capacity of specimens NC and RC is V c ( V n = V c ), and the shear capacity of the strengthened beams is the summation of V c and V f ( V n = V c + V f ). Table 4 shows the results in terms of experimental shear capacity ( V n(exp) ) , predicted shear capacity ( V n(pred) ), and ratio of V n(exp) to V n(pred) . It should be noted that all reduction factors were set to unity to allow for true comparison with the experimental results. Analytical results shown in Table 4 indicate that the ACI shear strength predictions of the unstrengthened control beams NC and RC were underestimated and conservative. In particular, the ratio of experimental to predicted shear capacity of NC and RC is 1.20 and 1.11, respectively. On the other hand, the ACI design provisions provided unsafe predictions and overestimated the shear capacity of the U-wrapped specimens NU and RU, (ratio of V n(exp) to V n(pred) = 0.70 and 0.76, respectively). Despite that, the results are deemed reasonable considering that the reduction factors were not included in the analysis. The slight variation in the predicted capacities between the NAC and RAC beams