Abstract
This research has arisen from recent changes in attitudes to offshore safety. To help demonstrate structural safety to the Health and Safety Executive, operators are increasingly using structural system reliability assessments. While significant developments have been achieved in this area, there are still a number of uncertainties associated with such assessments. Unresolved technical issues also introduce significant variability in the results. The aim of this project is to develop a framework for system reliability, which will set a basis for moving towards more consistent reliability assessments. An extensive review study was undertaken first to establish the state of the art in the area of structure system reliability analysis of offshore structures. Based on the findings of this study, a generic system reliability framework was developed which was then developed further for specific application to fixed offshore platforms. These initial studies identified some of the key technical issues that required further investigation. The subsequent offshore application and sensitivity study, using a representative fixed platform model, concentrated on these issues and in particular on the effects of foundation parameters on ultimate strength and their interaction with other key parameters in determining the resistance function. The effect of foundation parameters and different modelling methods on system strength and reliability of fixed offshore platforms, which has largely been neglected in the past, was also investigated. The response surface methodology was developed for system reliability assessment of offshore structures incorporating the effect of foundation reliability. The findings were then used to revise the framework and provide more comprehensive account of key steps in the process of system reliability assessment. Some guidelines on the application of the response surface technique to fixed platform assessment were developed. In addition, an initial screening tool was also proposed for assessing the level of complexity required for the resistance model of the reliability assessment. The presentation of the reliability framework provides a comprehensive account of the various steps, methods and decisions associated with system reliability analysis. The framework, which can be used in both the design and reassessment of structures, can provide a basis for moving towards more consistent reliability assessments. Recommendations on areas that require further research are also presented.