Eurocode 3 part 1-8 gives stiffness boundaries for nominally pinned, semi-rigid and rigid beam-to-column joints and for semi-rigid and rigid column bases. The background for these limits has been investigated and analysed to see how they affect the resulting moment- and deflection distributions for a range of portal frames. The analyses show that for some types of frames the results are affected as much as 50 % in non – conservative direction. FE simula-tions performed for a commonly used column base which traditionally is assumed to be nominally pinned shows that the actual rotational stiffness is so high that the base should be classified as semi-rigid.