PSI - Issue 47

Francesco Ascione et al. / Procedia Structural Integrity 47 (2023) 460–468 Author name / Structural Integrity Procedia 00 (2019) 000–000

466

7

instead, the material parameters required by the adopted bond-slip law, are equal to that employed for the validation test (see Table 1).

400

Load/2

Load/2

50

100

2 φ 12 φ6/ 2 φ 10

Steel plate

150

1550 1500 1000

FRP

1

25

Fig. 5. Geometry and boundary conditions of the tested reinforced concrete element.

Fig. 6a shows the loading curve of the nano-enhanced beam (CNT-E beam) predicted by the proposed model together with a comparison with the control beam (without FRP system). The FRP-plated beam provides a stronger structural response with respect to the control beam, mainly due to the reinforcing effect induced by the externally bonded FRP system. In particular, a higher energy absorption capacity is obtained by the CNT-E beam during the yielding stage with respect to the beam without the nano-modified FRP system.

a

b

60

50

40

30

20 Load [kN]

Control beam CNT-E beam

10

0 5 10 1520 2530 0

-80 -120 σ xx concrete stress [MPa] -100

Deflection [mm]

-60

-40

-20

0

Fig. 6. Global structural response of the tested beams: (a) loading curve and (b) deformed configuration at 15 mm deflection.

The benefic effect offered by the nanomaterials embedded in the epoxy resin is also evident in the crack pattern, reported in Fig. 6b. In particular, the beam is characterized by a diffuse cracking within the concrete cover mainly due to the higher shear strength along the concrete/FRP interface provided by the nano-materials incorporation, with respect to the tensile strength of concrete. 4. Conclusions In this work, a numerical investigation on the mechanical behavior of plain and reinforced concrete elements retrofitted with FRP sheets externally bonded with nano-enhanced epoxy resin is presented. In particular, a numerical model based on a cohesive zone approach is employed to simulate the damage phenomena occurring in the concrete phase and FRP system, such as concrete cracking and FRP debonding. Zero-thickness cohesive elements are inserted between the linearly elastic bulk elements and along the physical FRP/concrete interface. To take into account the presence of nanomaterials in the epoxy resin, a specific trapezoidal bond-slip law is employed to describe the bond