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The aim of the project was to develop probability based design methods for use by the engineering profession in the offshore industry. The project has dealt with the development of methods and software for calculating the probability of failure of jacket type structures for a variety of member failure modes (plasticity, buckling, fatigue). The effect of redundancy of the structures can be investigated by calculating the combined probability of sequences of member (end) failures, either automatically or user specified. For plasticity limit states advanced Monte Carlo options are available. Particular aspects of the probabilistic analysis of offshore structures included: probabilistic modelling of environmental loads, pile foundations, tubular member behaviour and fatigue/fracture behaviour of tubular joints; development of efficient methods for performing global structural analysis; development of improved methods for structural system reliability analysis and development of methods for structural optimization under reliability constraints; and application of probabilistic methods in the fields of inspection, maintenance and repair. These objectives have been largely fulfilled and in some areas the developments have been more significant than was originally considered possible. In the case of inspection, maintenance and repair, a database system has been developed which can be used for compiling and analyzing inspection data. All the models and methods have been incorporated into a computer based reliability analysis system for offshore structures (RASOS). This is supported by extensive documentation comprising users' manuals, programmers' manuals and theoretical manuals. For use with RASOS a recommended set of models for random variables has been set up.
The RASOS software provides a comprehensive capability for the safety assessment of jacket type offshore structures which includes structural and load modelling, deterministic linear and nonlinear analysis, fatigue and fracture assessment, system reliability analysis using failure tree and simulation approaches and reliability based optimization. The probability of structural collapse can be assessed under conditions of extreme storm, fatigue, ship collision and fire and blast. Typical applications include reassessment of existing structures, design of repair and strengthening measures following accidental damage, in service inspection and maintenance planning and the preparation of safety cases. The benefits include rational inputs for decision making on issues of platform safety resulting in the reduction of costs and improvement of safety.

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