The resulting equivalent stress (HMH, von Mises) and plastic strain are calculated on plates. When the yield strength (multiplied by resistance factor for structural steel ϕ = 0.9, which is editable in Code setup) on the bilinear material diagram is reached, the check of the equivalent plastic strain is performed. The limit value of 5 % is suggested in Eurocode (EN1993-1-5 App. C, Par. C8, Note 1), this value can be modified in Code setup but verifications were done for the recommended value.
Plate element is divided into 5 layers and elastic/plastic behavior is investigated in each of them. The program shows the worst result from all of them. The CBFEM method can provide stress a little bit higher than yield strength. The reason is the slight inclination of the plastic branch of the stress-strain diagram, which is used in the analysis to improve the stability of the interaction calculation. This is not a problem for practical design. The equivalent plastic strain is exceeded at higher stress and the joint does not satisfy anyway.