PSI - Issue 42

Jamal A. Abdalla et al. / Procedia Structural Integrity 42 (2022) 1223–1230 Abdalla et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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Table 3. Summary of test results

Percentage increase with respect to BU (%)

P u (kN)

δ u (mm)

V n (kN)

V f (kN)

Specimen

ε f (mm/mm)

Failure mode c

a

b

V n

V

f

BC BU

147 213 249 231 246 232

6.1 8.6

73

-

- -

- -

-

SC

106 124 115 123 116

33 51 42 50 42

0.002070 0.003200 0.002634 0.003120 0.002665

D

BAU 75/10/45 BAU 50/12/90 BAU 75/12/45 BAU 50/12/45

11.3

17

55 27 51 29

SC, PD, PDA SC, PD, PDA SC, PD, PDA SC, PD, PDA

7.4 9.0 8.5

8

16

9

a Percentage increase = 100[( Vn - Vn(BU) )/ Vn(BU) ] b Percentage increase = 100[( Vf – Vf(BU) )/ Vf(BU) ] c SC: shear crack; D: debonding of the U-wraps; PD: partial debonding of the U-wraps; PDA: partial debonding of the anchors.

3.1. Failure modes and shear force-deflection curves The failure modes of the tested specimens are shown in Fig. 5. It can be seen from Fig. 5 that the unstrengthened control beam failed by formation of the critical shear crack that extended from the support in the web to the loading point in the flange. The shear force-deflection response curve of specimen BC indicates a linear increase in the shear capacity that is followed by a sudden drop (failure) after attaining the maximum shear force. On the other hand, failure of the strengthened beams was initiated by the formation of the critical shear crack. As the load increased, the crack widened and caused debonding of the middle U-wraps (beam BU), or debonding of the U-wraps with anchors (BAU beams). The presence of anchors caused the U-wraps not to fully debond from the concrete substrate, but instead, partial debonding of the U-wraps and anchors was observed, as shown in Fig. 5(c). It should be noted that the strain values from the concrete strain gauges indicated that none of the specimens failed by concrete crushing (maximum strain in the concrete was less than 0.003). The shear force-deflection curves of all strengthened beams showed an enhanced shear and deformation capacity compared to specimen BC. However, similar to BC, the failure of all strengthened specimens was sudden due to debonding of the laminates from the concrete substrate.

Fig. 5. Failure modes of specimens: (a) BC; (b) BU; (c) typical failure of BAU beams

3.2. Shear force The results shown in Table 2 and Fig. 4 indicated a gain in the shear capacity from 45 to 70% in all strengthened beams compared to the control unstrengthened beam. The benefit of anchorage was pronounced in the enhancement of the shear capacity of the anchored specimens compared to the unanchored U-wrapped specimen. Particularly, the shear capacity and FRP contribution to shear capacity of BAU specimens improved by 8-17% and 27-55% compared to BU, respectively. In addition, it can be noticed from Table 2 and Fig. 4 that the maximum shear force of the anchored specimens occurred at higher deflection than the unanchored specimen. Furthermore, a slight enhancement in the