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The seismic response of pile-supported offshore structures is strongly affected by the nonlinear behavior of the supporting piles. Nonlinear response of the pile foundation is the most important source of potential nonlinearity in the dynamic response of offshore platforms to earthquake excitations. It is often necessary to perform a dynamic analysis of offshore platforms that accounts for soil nonlinearity, discontinuity conditions at pile–soil interfaces, energy dissipation through soil radiation damping, and structural nonlinear behaviors of piles. In this paper, an attempt is made to develop an inexpensive and practical procedure, compatible with readily available structural analysis software, for estimating the lateral response of flexible piles embedded in layered soil deposits subjected to seismic loading. In the proposed model a beam on nonlinear Winkler foundation (BNWF) approach, consisting of simple nonlinear springs, dashpots, and contact elements, is used. This model was incorporated into a finite element program, ANSYS, which was used to compute the response of laterally excited piles. A nonlinear approach was used for seismic free-field ground motion analysis. The computed responses compared well with the centrifuge test results. This paper deals with the effects of free-field ground motion analysis on nonlinear seismic behavior of embedded piles. Different parts of a BNWF model, together with quantitative and qualitative findings and conclusions for dynamic nonlinear response of offshore piles, are discussed and addressed in detail.Key words: nonlinear, seismic response, offshore piles, seismic pile–soil interaction, BNWF models.

Tubular joints of offshore structures are prone to fatigue damage. Because of uncertainties involved in quantifying the fatigue process in this type of structure, a reliability approach may be adopted to assess the risks of failure. In-service inspections of structures produce additional information, which may be taken into consideration in order to update the reliability. The paper reviews the methods for carrying out such reliability analyses based on principles of linear elastic fracture mechanics and applies them to a sample tubular joint. The results of this type of analyses may be used for inspection, planning, and (or) decision making regarding repairs or modification of the service life of a structure.Key words: fatigue, reliability, tubular joints, offshore structures, condition assessment.

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