# D5.D.6.5 Clause 6.3.2.3(2) – Modification factor, f, for LTB checks

The French NA specifies that the modification factor is to be obtained as per the default method given in EC-3. Hence this implementation will use the existing functionality to evaluate the correction factor kc to be used in the modification factor f.

The program uses a default value of 1.0 for kc. However the user can also input a custom value of kc by setting the design parameter KC to the desired value. You may instruct the program to calculate the value of kc automatically by setting the value of the KC parameter in the design input to 0. This will cause the program to evaluate kc from Table 6.6 of NF EN 1993-1-1:2005. This will correspond to the end conditions and the bending moment of the member (i.e., the value of CMM parameter specified).

For CMM = 7, the program will choose the value of kc to be either 0.90 or 0.91 based on the end moment ratio.

For CMM = 8, the program will choose the value of kc to be either 0.77 or 0.82 based on the end moment ratio.

An additional check will also be performed as given below:

$χ L T , mod ⁡ ≤ 1 λ ¯ L T 2$

The French Annex specifies that the modification factor is applicable only to members that are free to rotate on plan (i.e., CMN 1.0). Hence for all other values of CMN, this implementation will ignore "f" and hence will use χLT,mod =  χLT.