# Karamab Chi values and Nb_Rd

Dear Clemens @karamba3d

As your request i open a new topic about the NB_RD values.

01_SimpleBeam_cp-Jac.gh (41.3 KB)

On this example i applied a unique point load who generate uniform compression along the beam
My result below :

I dont find the same NB_RD values as yours

As you, i find χ yy = 0.9144 and χ zz = 0.7204
But for Nb.rd i find :
N b.rd.yy = 0,9144 * (45.25cm210^-4) * (235MPa10^6)/1000 ) / 1 (γM0) = 972 kN
N b.rd.zz = 0,7204 * (45.25cm210^-4) * (235MPa10^6)/1000 ) / 1 (γM0) = 766 kN

When Karamba give me NB_RD = 1063 kN

I misunderstood something ?

Also, the Az values in cross section components was 9.69cm2, i find 14.47 cm2 (Avz = A - 2.btf + (tw+2.r)*tf)

Regards
Jacques

Also related to this, are the Cmy, Cmz, CmLT values. I find mostly 1 for these, whereas in the manual it is explained that Annex B 1993-1-1 is used. Could we see how these values are being calculated? And why use a minimum of 0.9 (as in the manual) and not 0.4 as in the code right?

I assume you would like to calculate these values based on a linear two point approach right?

Hello

See

You can find the EC3 procedure implemented in Karamba

Hello,
The master thesis of Jukka Mäenpää (see https://www.grasshopper3d.com/group/karamba3d/forum/topics/master-of-science-thesis-algorithm-aided-structural-engineering?commentId=2985220%3AComment%3A1890178&groupId=2985220%3AGroup%3A251211) contains the simplifications used in the EC3 design procedure of Karamba3D (see page 13 f.).
Best,
Clemens

Dear Jacques (@keuj.84),
the chi-values are not applied to to NB_Rd but are used to calculate the utilization. The NB_RD value of 1063kN derives from yield strength times cross section area (23.5*45.25 = 1063.4kN).
The Ay and Az values in Karamba3D are those traditionally used for calculating the deformations. At the moment (Karamba 1.3.2.) these are also used for calculating the plastic shear resistance. In case of I-profiles these values lie on the conservative side as compared to those recommended in EN 1993-1-1.
This is one of the simplifications used in the design procedure of Karamba3D.
Best,
Clemens

Good evening Clemens @karamba3d

The misunderstanding comes from the term NB_RD, for me B says Buckling.

I checked, it’s perfect, the utilization ratio take account the minimum chi values.

Thanks