Issue 54

A.G. Pahlaviani et alii, Frattura ed Integrità Strutturale, 54 (2020) 317-324; DOI: 10.3221/IGF-ESIS.54.22







1    ln

(2)

true

nom

Figure 2: Stress-strain curve of concrete under heat increase [14].

In which nom  and σ nom are nominal strain of section and nominal stress of section, respectively. The real value of steel stress and strain has been given in Tab. 1.

Real Stress (MPa)

Plastic Strain

300 350 375 394

0.000 0.025 0.100 0.200 0.350

400 Table 1: Real stress and strain values of steel. To modeling concrete in plastic region and investigation of destruction in it, concrete plastic damage model has been used. The values of stress, strain, and plastic destruction of concrete are represented in Tab. 2 and 3.

Tensile strength (MPa)

Fraction strain

Destruction parameter in tension

35

000000.0 000176.0 001539.0

00.0 25.0 99.0

31.5

58.0 Table 2: Values of stress, strain and plastic destruction of concrete in tension.

Tensile strength (MPa)

Fraction strain

Destruction parameter in compression

17.5 25.7 34.9

0.000000 0.00038 0.00189 0.00218 0.00456

0.000 0.112 0.429 0.466 0.701

35

38 Table 3: Values of stress, strain and plastic destruction of concrete in compression.

Yield criterion Von Mises and isotropic hardening law have been used for modeling behavior of steel.in this model, the problems relevant to geometric nonlinear analysis were considered too and great transformation method has been used and due to contact elements between steel and concrete and appropriation of contact surface friction, asymmetric Newton- Raphson method has been implemented. Concrete core is defined by an eight-node hexahedral element or three transferred

319