Reliability Analysis of Continuous Structural Systems

Lee, Joo-Sung (1989) Reliability Analysis of Continuous Structural Systems. PhD thesis, University of Glasgow.

Abstract

This study mainly deals with developing another approximate method for system reliability analysis and its applications to the continuous structures such as an assembly of stiffened cylindrical and rectangular sections used in Tension Leg Platform (TLP). Various methods developed for the structural system reliability analysis are reviewed The developed system reliability method, called herein the "Extended Incremental Load Method", is an extended approach of the conventional incremental load method. It has been developed in order to extend its applicability to the system reliability analysis of a structure under multiple loadings. It directly uses existing component strength formulae in the system analysis and more realistically takes account of the post-ultimate (post-failure) behaviour of a failed component when assessing the system reliability and ultimate strength. This is an important merit of the method over other methods. The method allows for load re-distribution during the development of elasto-plastic moments in large cross-sections under the action of axial and bending forces and in the presence of lateral hydrostatic and hydrodynamic pressure. The effects of shearing actions are ignored. A search is made for the most important failure modes to give the lowest system safety index. In the method the modified safety margin equation, which has been proposed to use existing strength formulae for principle components of a floating offshore structure, is employed in which the strength modelling parameter is treated as a basic random variable in system reliability analysis as well as component reliability analysis and the concept of the first-order second moment method is adopted to obtain the resistance coefficients and the loading coefficients in the safety margin equation. Details about deriving the safety margin equation by the proposed reliability method, calculation of the total load factor, the procedure of identifying the most important failure modes and flow vectors of principle component are described in the Appendices. Applications to discrete structures are demonstrated to show the validity of the proposed method. The method has been applied to the Hutton TLP and two variants, TLP-A and TLP-B, which are modified models of the Hutton TLP and of the design using TLP Rule Case Committee type loading and improved strength models, under the design environmental loading conditions. Components and systems safety indices of the models, Hutton TLP, TLP-A and TLP-B, are illustrated with three dimensional collapse mechanisms figures. Reserve and reserve strength characteristics are derived for the design as built and for more economical and efficient variations of the design. The TLP form is shown to possess high redundancy and systems safety. Sensitivity studies to changes in stochastic parameters of resistance and loading variables have been carried out. For this purpose the strength modelling parameter, yield stress and certain member sizes are selected as resistance variables, and effects of their mean values and/or coefficients of variation on the system, as well as on the component reliability index, have been investigated. The effects of mean bias and coefficient of variation of load effects, namely, static, quasi-static and dynamic component, on the the system as well as on the component reliability index have also been investigated. The results are discussed with regard to effects of various parameters on safety, with illustrating figures, from which the relative importance of random variables can be seen. As an another important resistance variable, the post-ultimate behaviour of failed components has been taken account of in system reliability assessment, which should be the most important resistance variable affecting the system reliability and the effective residual strength of a structure. Some case studies have been carried out with the simplified non-linear model which has a form of piecewise multi-state (more than two states) and is characterised by the post-ultimate slope and the residual strength. The results are illustrated in figures and tables and discussion made about its effects on the system reliability level. (Abstract shortened by ProQuest.).

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Naval engineering, Ocean engineering
• Date of Award: 1989
• Depositing User: Enlighten Team
• Unique ID: glathesis:1989-77805
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jan 2020 11:53
• Last Modified: 14 Jan 2020 11:53
• URI: https://theses.gla.ac.uk/id/eprint/77805