PSI - Issue 42

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

1235

5

Fig.3. Test setup (dimensions are in mm)

3. Experimental Results and Discussion Table 3 shows the summary of the test results in terms of the maximum attained load ( P n ), maximum shear force ( V n ) (calculated by statics as P n /2), mid-span deflection at the maximum shear ( δ max ), maximum strain in CFRP laminates ( ε max ), shear in concrete ( V c ), CFRP contribution to shear ( V f ), percentage increase in V n , and the observed failure modes. It should be noted that due to absence of steel stirrups in the beams, the shear capacity of NC and RC beams was considered V c for all NC and RC beams, respectively. Consequently, V f of the strengthened beams was calculated by subtracting V c from V n ( V f = V n - V c ).

Table 3. Summary of test results

ε max ( strain) V c (kN) V f (kN) - 30.0 -

Percentage increase in V n (%) a

Specimen

P n (kN)

V n (kN)

δ max (mm)

Failure mode b

NC RC NU RU

60.0 54.4 81.6 86.8

30.0 27.2 40.8 43.4

8.9 8.6

- -

SC SC

-

27.2 30.0 27.2

-

17.8 10.2

2230 2347

10.8 16.2

36 60

SC & D SC & D

a Percentage increase = 100[( Vn - Vn(NC/RC) )/ Vn(NC/RC) ] b SC: shear crack; D: debonding of the U-wraps

3.1. Failure modes Pictorial representation of the failure modes is shown in Fig.4. It can be seen from Fig. 4a that typical failure mode of specimens NC and RC is shear failure by the formation of a diagonal shear crack at an angle of 45º from the horizontal. The major shear crack propagated from the supports to the loading point. Minor shear cracks were also formed in the shear span, as shown in Fig. 4a. It is clear from Figs. 4b and 4c that the strengthened specimens RU and NU primarily failed by debonding of the U-wraps. Debonding occurred due to loss of bond between the U-wraps and concrete due to cracks formation. It was observed that the U-wraps that debonded from the concrete substrate were the ones that intersected the shear crack (middle three U-wraps), as shown in Figs. 4b and 4c. Although both control and strengthened beams failed in a brittle manner, the strengthened beams failed at a higher load and deflection than their control counterparts.

a

b

c

Fig. 4. Failure modes of specimens (a) NC/RC; (b) NU; (c) RU