D5.D.8.7 Clause 6.3.3(5) – Interaction factors kyy, kyz, kzy, and kzz
The Polish NA recommends the equations in Annex B of PN-EN 1993-1-1 to calculate these interaction factors. The current implementation of EC3 BS in STAAD.pro uses the method in Annex B by default. The proposed implementation of the Polish NA will also use Annex B for Cl.6.3.3 checks.
The Polish NA also gives two additional simplified checks. This implementation will provide for these additional checks as well. However as they are intended as optional checks, by default, the program will not perform these checks. However, the user can invoke these checks by using the PLG parameter. Refer to D5.C.6 Design Parameters
If the value of the PLG parameter is set to 1, the following two checks will be performed as per Cl. NA.20.(2) and NA.20(3) respectively:
Cl. NA.20.(2): The following condition will be checked
n/ χ and + Cmy my/ χLT + C mz m with ≤ 1- Δ0 (I = y or z)where
- max My,Ed (+ Δ My, Ed)/My, Rd; mz = max M,Z Ed (+ Δ M , Ed)/MZ Rd,
- χ and
- buckling factor
- LTB factor
- moment factor from table B 3 of PN EN 1993-1-1
- correction factor (estimation of maximum reduction) and will be worked out as:
- Δ0 = 0,1 + 0,2 (wi – 1), przy czym wi = Wpl,i/Wel,i , or
- Δ0 = 0,1 – in case of class 3 and 4 sections.
Cl. NA.20.(3): This condition will only be checked for circular hollow sections.
n/χi + [(kii mi)2 + (Cmj mj)2] 1/2 ≤ 1 (i,j =y,z)where
- the interaction factor from table B.1 of PN-EN 1993-1-1
- n, m, and Cmj
- as previously described
If the PLG parameter has been set to 1, the maximum among the following ratios will be taken as being critical for Cl 6.3.3:
- 6.3.3: Eqn6.61
- 6.3.3: Eqn6.62
- NA.20(2) and
If however PLG has been set to 0 (or not specified at all), the program will ignore the last two checks in the list above.