On strength criteria of fillet welds

A comparison between two widely used strength criteria (ISO and Eurocode 3) for welding design is carried out in this paper. Limit analysis theorems are applied for analysis of collapse load of a fillet weld using von Mises yield criterion, generalizing a previous methodology in which Tresca criterion was used. Using von Mises criterion, lower bounds of collapse load can be found by solving a quartic equation, thus avoiding the numerical sweep needed with Tresca criterion. The results of limit analysis fit much better with those of Eurocode 3 criterion, and this criterion also reasonably fits experimental results for side-fillets, but experimental results on end-fillets agree with ISO criterion and not with Eurocode 3 criterion and limit analysis. A numerical finite element analysis shows that this apparent contradiction is originated by the influence of overlapping between the welded plates, which gives rises to the transmission of part of the internal moment through contact forces between plates and not through the throat. The results support the use of Eurocode 3 criterion instead of ISO, and this is confirmed by the analysis of a varied set of welded layouts using the former in a general numerical method developed previously, which gives results that show a very reasonable agreement with experimental results found in the bibliography.