Reliability-based design of panels and fatigue details of ship structures.

摘要

The main objective of structural design is to insure safety, functional, and performance requirements of an engineering system for target reliability levels and a specified time period. As this must be accomplished under conditions of uncertainty, probabilistic analyses are needed in the development of such reliability-based design of panels and fatigue details of ship structures. The reliability-based structural design formats are more flexible and rational than their counterparts, the working stress formats, because they provide consistent levels of safety over various types of structural components. Such a design procedure takes into account more information than the deterministic methods in the design of ship structural components. This information includes uncertainties in the strength of various ship structural elements, in loads, and modeling errors in analysis procedures.; Load and Resistance Factor Design (LRFD) methods were developed in this dissertation for unstiffened panels, stiffened panels, and fatigue details of ship structures. The LRFD development presented herein was built on previous practices in the design of ship structures as well as on LRFD rules and specifications adopted by other related classification societies. In the LRFD development, commonly used strength models for ship panels and ship fatigue details were collected from many sources to evaluate their limitations and applicability, and to study their biases and uncertainties. Monte Carlo simulation was utilized to assess the probabilistic characteristics of strength models by generating basic random variables for a strength model and substituting the generated values in the model. The probabilistic characteristics of basic random variables of both the strength and the load were quantified based on statistical analyses of data that were collected for this purpose, on values recommended in other studies, and occasionally on sound engineering judgment.; The dissertation also presents detailed calculations of partial safety factors for the design variables in the performance function equations based on target reliability levels and on the probabilistic characteristics of the basic random variables. Ranges for the target reliability levels were carefully selected to include implied reliability levels in exiting marine design codes and recommended values by other studies in the field. Strength factors were computed for recommended sets of load factors. Calculations of partial safety factors were performed using the First-order Reliability Method (FORM).