PSI - Issue 10

M. Petrov et al. / Procedia Structural Integrity 10 (2018) 303–310

306

M. Petrov et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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Table 1. Maximum compressive stresses of the samples studied.

Concrete without reinforcement

Type of reinforcement

GFRP – RC

RC

1 rebar 2 rebars

34 MPa 35 MPa 23 MPa

33.5 MPa

33 MPa

45 MPa

47.5 MPa

Cage made of 12 rebars

–

31 MPa

As can be seen from Table 1, strength changing of concrete laboratory models reinforced with a single rod is not observed comparing to the samples without reinforcement. The presence in the concrete samples of two reinforcing bars, and the more so of the reinforcing cage, leads to an increase in the maximum stress that the samples withstand. Internal mechanical stresses arise in the concrete sample as a result of uniaxial compression. The distribution of internal stresses is uneven and is affected by the presence of structural heterogeneities. During compression, stresses in various regions may rise to equal the tensile strength, at which point the cracking process begins. The computational simulation has been carried out in order to better understand how the presence of reinforcement in concrete affects the distribution of internal mechanical stresses. In the ANSYS software package, the mechanical stress distribution within the volume of a reinforced concrete cube subjected to uniaxial compression has been calculated using the finite element method, considering concrete a homogeneous medium. A compressive load is applied to the one cube face which is parallel to reinforcing bar. A condition of slipping along the rigid plane is applied to the opposite face of the cube. The elastic characteristics of materials specified in the calculations are given in Table 2.

Table 2. Elastic properties of concrete, steel and fiberglass. Properties Concrete

Steel

Fiberglass

4.2 ×10 3 2.35 ×10 3

5.7 ×10 3 7.8 ×10 3

4.9×10 3 2.0 ×10 3

Speed of sound (m/s)

Density (kg/m 3 ) Poisson’s ratio

0.2

0.3

0.25

Young’s modulus (GPa)

44

200

48

Determination of the beginning of the crack formation process in reinforced concrete under uniaxial compression was performed by calculating the destructive stresses at the boundary of the reinforcement with concrete. The strength calculation was performed according to the quadruple (energy) theory of strength (according to Mises). The calculation of the equivalent stresses corresponding to the compression stresses, equal to the stress state considered hazardous, was carried out. Let ’ s consider in more detail, the numerical calculation results for concrete samples with size of 100 × 100 × 100 mm, containing single steel or fiberglass reinforcing bar. The calculation results are shown in Fig.3. The figure shows the distribution of internal stresses in the surrounding areas of the reinforcing bar. a b

Fig. 3. Distribution of stresses in concrete samples reinforced with (a) steel and (b) fiberglass reinforcement.