Issue 58

R. Capozucca et alii, Frattura ed Integrità Strutturale, 58 (2021) 402-415; DOI: 10.3221/IGF-ESIS.58.29

100 120 140 160

edge of compressive concrete

D1 = D2 4kN = 8 D3 kN = 16 kN D4 = 24kN

0 20 40 60 80

-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 h [mm] ε ‰ level of tensile steel level of tensile GFRP

Figure 17: Distribution of strain at mid length cross section at D i , with i=1,2,3 - beam B2 with NSM GFRP rod.

The entity of stress-strain la g can be estimate considering the ratios (1) and (2) (Tab. 5), where ε FRP is the strain that CFRP and GFRP rod should exhibits if the Bernoulli's plane section hypothesizes is verified. The calculus of k 1 and k 2 coefficients was made both for the strengthened RC beams B1 and B2, considering the levels of damage D 1 to D 4 thus until values of steel strain greater than yield strain of steel. It can be observed that the average values k 1,av ≅ 0.93  0.99 and k 2,av ≅ 0.24  0.18 (respectively for B1 and B2), are quite different and lead to results more or less conservative. Nevertheless, in the study of the behaviour of RC section with the presence of NSM FRP rods, it can be a good strategy the adoption of one of the coefficient k 1,av (or k 2,av ) to prevent overestimation of the beam’s strength.

ε

 FRP

k

(1)

1

ε

s



ε *

ε

FRP FRP



(2)

k

2

ε *

FRP

k 2 = ε * FRP - ε FRP / ε * FRP

k 1 = ε FRP / ε s

Damage steps

Load, P [kN]

RC beams

D 1 D 2 D 3 D 4 D 1 D 2 D 3 D 4

4.00 8.00

0.60 1.06 1.06 0.98 0.87 0.91 1.07 1.15

0.51 0.13 0.13 0.19 0.28 0.25 0.12 0.05

B1

18.00 24.00

4.00 8.00

B2

16.00 24.00

Table 5: Lag coefficients k .

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