Local Strain Estimation of Under-Matched Welded Joints made of 800MPa Class Steel

An application of high performance steel (such as high strength steel) on steel bridges has globally been investigated. It is clear that a hybrid steel girder is one of the effective usages of high performance steel for steel bridges, but adoptions of hybrid steel girders might result in under- matched joints and significant on fatigue strength of under-matched welded joints made of over 700MPa class steel is not clear yet. In authors' previous studies, fatigue tests of welded joints made of 800MPa class steels were carried out. Test results indicate that the fatigue strength in higher stress range region is less than that made of mild strength steels, and showed that the cause of reduction of fatigue strength is that under-matching welded joints caused strain concentration at around weld roots. The objective of this study is to estimate local strain at weld root. Applicability of local strain estimation method was verified using the test results, and a unique curve was obtained from a relationship between local strain and the test results.