Marine Structural Design, Second Edition, is a wide-ranging, practical guide to marine structural analysis and design, describing in detail the application of modern structural engineering principles to marine and offshore structures.
Organized in five parts, the book covers basic structural design principles, strength, fatigue and fracture, and reliability and risk assessment, providing all the knowledge needed for limit-state design and re-assessment of existing structures.
Updates to this edition include new chapters on structural health monitoring and risk-based decision-making, arctic marine structural development, and the addition of new LNG ship topics, including composite materials and structures, uncertainty analysis, and green ship concepts.
- Provides the structural design principles, background theory, and know-how needed for marine and offshore structural design by analysis
- Covers strength, fatigue and fracture, reliability, and risk assessment together in one resource, emphasizing practical considerations and applications
- Updates to this edition include new chapters on structural health monitoring and risk-based decision making, and new content on arctic marine structural design
Dr. Yong Bai obtained a Ph.D. in Offshore Structures at Hiroshima University, Japan in 1989. He is currently President of Offshore Pipelines and Risers (OPR Inc., a design/consulting firm in the field of subsea pipelines, risers and floating systems. In the 1990's, he had been a technical leader for several Asgard Transport pipeline and flowline projects at JP Kenny as Manager of the advanced engineering department. Yong was previously a lead riser engineer at Shell and assisted in offshore rules development at the American Bureau of Shipping (ABS) as Manager of the offshore technology department. While a professor, he wrote several books and served as a course leader on the design of subsea pipelines and irsers as well as design of floating systems. He also serves at Zhejiang University in China as professor.
This chapter discusses a modern theory for design and analysis of marine structures. The term "marine structures" refers to ship and offshore structures. The objective of this book is to summarize the latest developments of design codes, engineering practices, and research in the form of a book, focusing on applications of finite element analysis and risk/reliability methods. The purpose of this book is to summarize these technological developments in order to promote advanced structural design. The emphasis on finite element methods, dynamic response, risk/reliability, and information technology differentiates this book from existing ones. This chapter also illustrates the process of a structural design based on finite element analysis and risk/reliability methods. When this book was first drafted, the author's intention was to use it in teaching his course Marine Structural Design. The material presented in this book may be used for several MS or PhD courses, such as Ship Structural Design, Design of Floating Production Systems, Ultimate Strength of Marine Structures, Fatigue and Fracture, and Risk and Reliability in Marine Structures. This book addresses the marine and offshore applications of steel structures. In addition to the topics that are normally covered by civil engineering books on design of steel structures this book also covers hydrodynamics, ship impacts, and fatigue/fracture. In a comparison with books on design of spacecraft structures, this book describes applications of finite element methods and risk/reliability methods in greater detail. Hence, it should also be of interest to engineers and researchers working on civil engineering and spacecraft structures.
Accidental loads; Applications; Calibration; Concepts; Fatigue assessment; Limit-state design; Risk assessment
1.1. Structural Design Principles
This book is devoted to the modern theory for design and analysis of marine structures. The term "marine structures" refers to ships and offshore structures. The objective of this book is to summarize the latest developments of design codes, engineering practices, and research into the form of a book, focusing on applications of finite element analysis and risk/reliability methods. Calculating wave loads and load combinations is the first step in marine structural design. For structural design and analysis, a structural engineer needs to understand the basic concepts of waves, motions, and design loads. Extreme value analysis for dynamic systems is another area that has had substantial advances from 1995 to 2015. It is an important subject for the determination of the design values for motions and strength analysis of floating structures, risers, mooring systems, and tendons for tension leg platforms. Once the functional requirements and loads are determined, an initial scantling may be sized based on formulas and charts in classification rules and design codes. The basic scantling of the structural components is initially determined based on stress analysis of beams, plates, and shells under hydrostatic pressure, bending, and concentrated loads. Three levels of marine structural design have been developed: Level 1: Design by rules Level 2: Design by analysis Level 3: Design based on performance standards Until the 1970s, structural design rules were based on the design by rules approach, which used experiences expressed in tables and formulas. These formula-based rules were followed by direct calculations of hydrodynamic loads and finite element stress analysis. The finite element methods (FEM) have now been extensively developed and applied to the design of ships and offshore structures. Structural analysis based on FEM has provided results that enable designers to optimize structural designs. The design by analysis approach is now applied throughout the design process. The finite element analysis has been very popular for strength and fatigue analysis of marine structures. During the structural design process, the dimensions and sizing of the structure are optimized, and structural analysis is reconducted until the strength and fatigue requirements are met. The use of FEM technology has been supported both by the rapid development of computers and by information technologies. Information technology is widely used in structural analysis, data collection, processing, and interpretation, as well as in the design, operation, and maintenance of ships and offshore structures. The development of both computers and information technologies has made it possible to conduct complex structural analysis and process the results. To aid the FEM-based design, various types of computer-based tools have been developed, such as CAD (computer-aided design) for scantling, CAE (computer-aided engineering) for structural design and analysis, and CAM (computer-aided manufacturing) for fabrication. Structural design may also be conducted based on performance requirements such as designing for accidental loads, where managing risks is of importance.
1.1.2. Limit-State Design
In a limit-state design, the design of structures is checked for all groups of limit states to ensure that the safety margin between the maximum loads and the weakest possible resistance of the structure is large enough and that fatigue damage is tolerable. Based on the first principles, the limit-state design criteria cover various failure modes such as Serviceability limit state Ultimate limit state (including buckling/collapse and fracture) Fatigue limit state Accidental limit state (progressive collapse limit state). Each failure mode may be controlled by a set of design criteria. Limit-state design criteria are developed based on ultimate strength and fatigue analysis, as well as the use of the risk/reliability methods. The design criteria have traditionally been expressed in the format of working stress design (WSD) (or allowable stress design), where only one safety factor is used to define the allowable limit. However, in recent years, there is an increased use of the load and resistance factored design (LRFD) that comprises a number of load factors and resistance factors reflecting the uncertainties and the safety requirements. A general safety format for LRFD design may be expressed as
SSk·?f, design load effect Rd
SRk/?m, design resistance (capacity) Sk
Characteristic load effect Rk
Characteristic resistance ?f
Load factor, reflecting the uncertainty in load ?m
Material factor, the inverse of the resistance factor. Figure 1.1
illustrates the use of the load and resistance factors where only one load factor and one material factor are used, for the sake of simplicity. To account for the uncertainties in the strength parameters, the design resistance Rd is defined as characteristic resistance Rk divided by the material factor ?m. The characteristic load effect Sk is also scaled up by multiplying by the load factor ?f. The values of the load factor ?f and material factor ?m are defined in design codes. They have been calibrated against the WSD criteria and the inherent safety levels in the design codes. The calibration may be conducted using structural reliability methods that allow us to correlate the reliability levels in the LRFD criteria with the WSD criteria and to ensure the reliability levels will be greater than or equal to the target reliability. An advantage of the LRFD approach is its simplicity (in comparison with direct usage of the structural reliability methods) while it still accounts for the uncertainties in loads and structural capacities based on structural reliability methods. The LRFD is also called the partial safety factor design. Figure 1.1
Use of load and resistance factors for strength design. While the partial safety factors are calibrated using the structural reliability methods, the failure consequence may also be accounted for through the selection of the target reliability level. When the failure consequence is higher, the safety factors should also be higher. Use of the LRFD criteria may provide unified safety levels for the whole structures or a group of the structures that are designed according to the same code.
1.2. Strength and Fatigue Analysis
Major factors that should be considered in marine structural design include Still water and wave loads, and their possible combinations Ultimate strength of structural components and systems Fatigue/fracture in critical structural details. Knowledge of hydrodynamics, buckling/collapsing, and fatigue/fracture is the key to understanding structural engineering.
1.2.1. Ultimate Strength Criteria
Ultimate strength criteria are usually...