On SIF and SCF of Circumferential Welds on Steel Tubular Piles Under Bending Moments

Circumferential welds, also called splice welds, on steel piles installed in marine and offshore structures are potential fatigue hot spots, given harsh and cyclic loadings. This paper is devoted to linear elastic fracture mechanics (LEFM)-based fatigue assessment for pile splice welds under bending moments. Specifically, this paper studies two important factors for the LEFM analysis of surface crack at the circumferential welds, stress intensity factor (SIF) and stress concentration factor (SCF). So far, LEFM-based fatigue assessment has not been widely conducted for steel tubular piles. Particularly, the two factors have not been properly developed with regard to typical features of marine steel piles, i.e., small aspect ratio of crack shape, thin-walled condition, misalignments at splice, thickness transition, complicated loading effects including bending moments, etc. The determination of SIF heavily relies on a geometry function for the growth of a fatigue crack. Based on a literature review, this paper has identified a database of geometry functions that may be suitable in practice for the circumferential welds on tubular piles with a thickness ratio around 10 under bending moments. SCF is used to accommodate stress concentration effects due to assorted geometric misalignments at a pile splice, including diameter difference (or concentricity), center eccentricity, thickness difference, and out of roundness. Currently, SCFs for tubular connections are produced for axial forces. In this paper, a practical approximation to the SCF under bending moments is mathematically formulated on the basis of a flat-plate configuration. This paper presents practical information for LEFM-based fatigue assessment of steel piles installed in marine and offshore works.