Reliability Analysis Based Safety Factors for Designing the Tubular Members of Horizontal Braces in Offshore Jacket Structures

In the present paper, the reliability of tubular members used in the horizontal braces of an offshore jacket structure against the failure induced by the presence of stresses higher than the allowable values is evaluated. In order to define the failure criteria, equations proposed by the 21th edition of API RP 2A-WSD (2007) for the design of tubular members under the combined axial pressure and bending are used. In this study, internal forces of the tubular members and the parameters involved in the member strength are considered as random variables and the probability distribution functions governing these forces including the axial compressive force and in-plane and out-of-plane bending moments are derived for a typical jacket-type platform installed in the Persian Gulf. For the modeling of environmental loads, information available on the sea states in the South Pars region has been used and the results of three different methods of reliability analysis including MVFOSM, HL-RF, and MCS are compared. Finally, based on the results of reliability analysis, a set of equations are proposed for the determination of suitable safety factors for designing the tubular members in horizontal braces of a jacket structure as a function of target reliability index and target failure probability.