Brittle fracture estimation at ends of groove welded joints under cyclic loading

Abstract

To prevent brittle fracture in structural components during earthquakes, their cumulative ductility (plastic deformation capacity) should be determined beforehand and appropriate countermeasures applied accordingly. In this paper, a method for estimating the cumulative ductility of welded joints with defects based on the σW–Nf relationship and Miner's rule is proposed for steel structure components to facilitate brittle fracture estimation. To verify its effectiveness, it was applied to the testing of welded joints with defects and compared to experimental results. The experimental tests were conducted under cyclic loading conditions to reproduce brittle fractures starting from the ends of complete joint penetration groove welded joints. The joint models used in this study were part of beam-to-column connections between beam flanges and diaphragms. Defects were artificially introduced into the welded joints before the experimental tests; brittle fractures occurred at these preinstalled defects in the welded joint specimens. The calculated cumulative ductility was obtained from the fracture toughness and Weibull stress of the joint model measured using finite element analyses. The calculated cumulative ductility values corresponded well with the experimental results, albeit with some explicable errors. The results indicate that the proposed method can estimate the cumulative ductility for structural components with defects under cyclic loading independent of their materials, notch types, and connection details. Thus, the findings could contribute to the assessment of defects in welded joints in steel structures subjected to earthquake loadings.