Effect of SCFs on S–N based fatigue reliability of multi-planar tubular DKT-joints of offshore jacket-type structures

Abstract

Due to the inherent random nature of various inputs affecting the response of offshore platforms, fatigue reliability analysis assumes great importance in the design of these structures. In the present paper, firstly, a fatigue limit-state function is derived using the principles of the S–N based fatigue strength assessment. Afterwards, the effects of different variable characteristics on the results of reliability analysis are investigated. The stress concentration factor (SCF) is one of the most important parameters in the fatigue reliability analysis which exhibits considerable scatter. This calls for greater emphasis in accurately computing the parameters of probability density function assigned to the SCF in the reliability analysis of steel offshore structures. In the present research, the effect of SCFs on the reliability of the tubular joint is investigated. In order to do so, a central brace SCF sample database is constructed using the results of FE analyses carried out on the right-angle two-planar tubular DKT-joints. This type of joint is frequently adapted in the construction of offshore jacket-type structures. The prepared SCF sample database is used to verify that the SCF follows a log-normal probability distribution, as it was assumed in the previous research works. The parameters of the probability function governing the peripheral distribution of SCFs along the weld toe are computed using the maximum likelihood procedure, and the degree of fitness of the defined probability distribution is examined using the Kolmogorov–Smirnov test. Different values are assigned to parameters of the probability distribution describing the SCFs, in order to study the effect of these parameters on the results of reliability analysis.