ABSTRACT
Welded joints between circular tubular braces and rectangular girder chords are widely used in super-structures of offshore platforms. However, no information regarding stress concentration factors (SCFs) for these joints exists in the literature. This paper presents some of the results obtained from an extensive finite element (FE) study conducted to generate SCFs for the fatigue design of internally stiffened, vertical and horizontal circular-to-box tubular joints. The results show that the brace SCFs are consistently higher than those in the chord. The SCFs occur at the intersection of the brace footprint and the stiffeners. SCFs for joints at the web and the flange of the girder are given as a function of increasing web and flange plate thicknesses, when the joints are subjected to axial and bending load acting on the circular braces. The joints include generic K, N, X and Y configurations with various stiffening schemes. Achieving SCFs of 2.5 or less for these joints is difficult, without resorting to thickening the box chord or providing special stiffening arrangements.
