PSI - Issue 70

Oberoi Kabrambam et al. / Procedia Structural Integrity 70 (2025) 74–81

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3. Material constitutive model 3.1. Steel

Steel is elastic up to the yield point, so the property of the steel in the software can be taken care by the modulus of elasticity and Poisson’s ratio. The modulus of the elasticity of the steel is 200000 MPa and Poisson’s ratio is 0.3. The stress-strain values of steel for plastic region (SCS3) were obtained from the uniaxial tensile test result conducted by İlgün and Sancioğlu (2023). The values obtained from the tensile test are then converted into true stress and strain and specified in the software. 3.2. Concrete In CFST, the concrete core is confined by the steel tube so when specifying the property of concrete in finite element (FE) model, its confinement effect must be considered. Confined concrete model proposed by Ellobody et al. (2006) is used here. The strain for unconfined concrete ( ) c  is taken as 0.003. Eqs. (1) and (2) are proposed by Mander J. B. et al. (1988).

(1)

f

1 1 f k f = + c

cc

1  =  +    2 1 c c f k f 

(2)

cc  

Here, 1 f is the lateral confining pressure, the approximate value of 1 f can be calculated from the empirical equations given by (Hu et al., 2003). The factors 1 k and 2 k are taken as 4.1 and 20.5 respectively as given by Richart et al. (1928).

Fig. 5. Stress-strain curves for confined and unconfined concrete (Ellobody et al., 2006). In order to complete the equivalent uniaxial stress-strain curve for confined concrete, as illustrated in Fig. 5, it is necessary to identify three segments of the curves. The initial segment is considered to be within the elastic range up to the proportional limit stress, which is defined as 0.5 cc f according to Hu et al. (2003). The Young’s modulus for confined concrete is determined using Eq. (3) from the American Concrete Institute (1999), while the Poisson’s ratio for confined concrete is assumed to be 0.2.

4700

E

f

=

MPa

(3)

cc

cc