PSI - Issue 38

Antti Ahola et al. / Procedia Structural Integrity 38 (2022) 457–465 Ahola et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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1. Introduction Fatigue strength is amongst the most important design criteria in dynamically and cyclically loaded steel structures – particularly in the case of welded joints and components. Welding can produce high tensile residual stresses at the critical details, notches and crack-like geometrical imperfections at the weld toe and weld root. From the manufacturing viewpoints, fillet welding is usually applied in corner joints to assemble intersecting plate components. On the other hand, poor accessibility or even inaccessibility inevitably leads to fillet welding from one side, as exemplified in Fig. 1. Such single-sided fillet welds and their fatigue behavior have been widely studied in the context of rib-to-deck joints in the orthotropic steel decks (OSDs), see e.g. (Luo et al., 2020, 2018). However, in those components, the fatigue load actions are mainly induced by the wheel loads and the findings are thus specific to the OSD bridges. Sundermeyer et al. (2015) investigated the fatigue behavior of single-sided load-carrying fillet welds with partial and full penetration. However, further knowledge is essentially needed from the fatigue behavior of single sided fillet weld joints loaded transversely, perpendicular to the weld, and longitudinally, parallel to the weld, as exemplified in Fig. 1.

(a)

(b)

Fig. 1. Structural details with continuous and intermediate single-sided fillet welds: (a) transverse non-load-carrying SSFW joints and (b) longitudinal load-carrying fillet weld joints.

In respect to the fatigue design, current fatigue design codes and guidelines, see e.g. the IIW Recommendations (Hobbacher, 2016) and Eurocode 3 (EN 1993-1-9, 2005), the design categories for transverse NLC attachments do not differentiate between single-sided and double-sided fillet welds (SSFWs/DSFWs). In the fatigue design code of cranes, two different categories have been provided for SSFW (FAT80) and DSFW (FAT90) details (EN 13001-3-1, 2018). A recent work of the authors (Ahola et al., 2021) showed that the fatigue failure from the weld root to base plate was the critical failure mechanism in NLC joints with SSFWs, albeit the category FAT80, similar to weld toe failures, was found suitable for fatigue design purposes in these joints. The aim of present work is to conduct an overview on the fatigue strength of longitudinal load-carrying (LC) and transverse non-load-carrying (NLC) fillet single-sided weld joints, and compare their fatigue performance SSFW and DSFW joints based on the existing experimental fatigue test data, supplemented with new experimental findings for DSFW joints and intermediate SSFW joints.

Nomenclature Symbols FAT 50% mean fatigue strength at two million cycles K t,m stress concentration factor for membrane stress K t,b stress concentration factor for bending stress l w weld length m slope parameter of S - N curve N f , N cycles to failure, fatigue life P s survival probability R applied stress ratio (S min /S max ) r ref reference radius, see ENS S stress T σ

scatter range index (corresponding to P s = 10%: P s = 90%)

plate thickness

t