10.2.1 Dutch Code NEN 6770

To indicate a predefined steel class according to the NEN 6770 code [77] you must choose $\blacktriangleright$ Steel $\blacktriangleright$ NEN 6770 and one of the steel classes S235 , S275 , or S355 . For each class NEN 6770 gives properties for three material models [Fig.10.3] of which you may choose one via a subconcept: Linear elasticity , Ideal plasticity , or Hardening plasticity .

Figure 10.3: Steel properties according to NEN 6770

The NEN 6770 gives the design value of the Young's modulus E_d , the Poisson's ratio $\nu$ , and the representative values of the yield stress f_y;rep and the tensile strength f_t;rep [Table 10.3]. Note that for the latter two properties the values depend on a range of thickness t . Additionally for all steel classes iDIANA presets a value for the mass density $\rho$ = 7850 kg/m³ .

Table 10.3: PROPERTIES FOR STEEL IN NEN 6770

		Thickness	Steel class
		[mm]	S235	S275	S355
Young's modulus	Ed		210000	210000	210000	N/mm2
Poisson's ratio	$\nu$		0.3	0.3	0.3
Yield stress	fy;rep	t$\le$40	235	275	355	N/mm2
		40 < t$\le$100	215	255	335	N/mm2
		100 < t$\le$250	175	205	275	N/mm2
Tensile strength	ft;rep	t$\le$40	360	430	510	N/mm2
		40 < t$\le$100	340	410	490	N/mm2
		100 < t$\le$250	320	380	450	N/mm2

10.2.1.1 Linear Elasticity

To indicate a linear elastic material model for steel according to the NEN 6770 code [Fig.10.3a] you must choose the Linear elasticity subconcept.

Stored input data    (file.dat)

     YOUNG  e
     POISON nu
     DENSIT rho

This describes linear elastic behavior via the Young's modulus e = E and the Poisson's ratio nu = $\nu$ . Additionally the mass density is defined as rho = $\rho$ .

10.2.1.2 Ideal Plasticity

To indicate an ideally plastic material model for steel according to the NEN 6770 code [Fig.10.3b] you must choose the Ideal plasticity subconcept. iDIANA presets the yield stress f_y;d with the material factor $\gamma_{{\mathrm{m}}}^{}$ = 1 :

$${\frac{{ f_{\mathrm{y;rep}} }}{{ \gamma_{\mathrm{m}} }}}$$ (10.6)

Stored input data    (file.dat)

     YOUNG  e
     POISON nu
     DENSIT rho
     YIELD  VMISES
     YLDVAL sy

This specifies the Von Mises plasticity model with a yield stress sy = f_y;d .

10.2.1.3 Hardening Plasticity

To indicate a plasticity material model with hardening for steel according to the NEN 6770 code [Fig.10.3c] you must choose the Hardening plasticity subconcept. iDIANA presets the hardening diagram as

$$\begin{split}f_{\mathrm{y;d}} & = \frac{ f_{\mathrm{y;rep}} }... ...thrm{t;rep}} - \varepsilon _{\mathrm{vl;d}} \right) \end{split}$$ (10.7)

With the material factor $\gamma_{{\mathrm{m}}}^{}$ = 1 and the representative tensile strain $\varepsilon_{{\mathrm{t;rep}}}^{}$ = 8 % .

Stored input data    (file.dat)

     YOUNG  e
     POISON nu
     DENSIT rho
     YIELD  VMISES
     HARDIA sy1 ky1 sy2 k2 sy3 ky3

This specifies the Von Mises plasticity model with a yield stress sy1 = f_y;d . The values sy1 to ky3 are the six terms to define the points in the hardening diagram: sy1 = f_y;d , ky1 = 0 , sy2 = sy1 or sy2 = E_d ^. 6 $\varepsilon_{{\mathrm{y;d}}}^{}$/10000 , ky2 = $\varepsilon_{{\mathrm{vl;d}}}^{}$ - sy2/E_d , sy3 = f_t;d , and ky3 = $\varepsilon_{{\mathrm{t;d}}}^{}$ - sy3/E_d .