Bai / Jin Marine Structural Design

2. Auflage 2015
ISBN: 978-0-08-100007-6
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, 1008 Seiten

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 holds the position of Chair Professor at Zhejiang University (China) and is also an academician at the Norwegian Academy of Technical Sciences. He is a fellow of the US Society of Naval Architects and Marine Engineers and the UK Royal Institution of Naval Architects. With an extensive background in offshore engineering structures and pipelines, Prof. Bai has held professorships at renowned universities, significantly contributing to the global offshore oil and gas industry through his publications and innovative achievements.

Autoren/Hrsg.

Bai, Yong

Jin, Wei-Liang

Inhaltsverzeichnis

1;Marine Structural Design;4
2;Copyright;5
3;Contents;6
4;Preface to First Edition;28
5;Preface to Second Edition;30
6;Part 1 Structural Design Principles;32
6.1;1 - Introduction;34
6.1.1;1.1 Structural Design Principles;34
6.1.1.1;1.1.1 Introduction;34
6.1.1.2;1.1.2 Limit-State Design;35
6.1.2;1.2 Strength and Fatigue Analysis;37
6.1.2.1;1.2.1 Ultimate Strength Criteria;37
6.1.2.2;1.2.2 Design for Accidental Loads;39
6.1.2.3;1.2.3 Design for Fatigue;40
6.1.3;1.3 Structural Reliability Applications;42
6.1.3.1;1.3.1 Structural Reliability Concepts;42
6.1.3.2;1.3.2 Reliability-Based Calibration of Design Factor;43
6.1.3.3;1.3.3 Requalification of Existing Structures;44
6.1.4;1.4 Risk Assessment;45
6.1.4.1;1.4.1 Application of Risk Assessment;45
6.1.4.2;1.4.2 Risk-Based Inspection;45
6.1.4.3;1.4.3 Human and Organization Factors;46
6.1.5;1.5 Layout of This Book;46
6.1.6;1.6 How to Use This Book;48
6.1.7;References;48
6.2;2 - Marine Composite Materials and Structure;50
6.2.1;2.1 Introduction;50
6.2.2;2.2 The Application of Composites in the Marine Industry;50
6.2.2.1;2.2.1 Ocean Environment;51
6.2.2.2;2.2.2 Application in the Shipbuilding Industry;53
6.2.2.2.1;Pleasure Boats Industry;53
6.2.2.2.2;Recreational Applications;54
6.2.2.2.3;Commercial Applications;54
6.2.2.2.4;Military Applications;54
6.2.2.3;2.2.3 Marine Aviation Vehicles and Off-Shore Structure;54
6.2.3;2.3 Composite Material Structure;56
6.2.3.1;2.3.1 Fiber Reinforcements;57
6.2.3.1.1;Glass Fibers;58
6.2.3.1.2;Aramid Fibers;58
6.2.3.1.3;Carbon Fibers;59
6.2.3.2;2.3.2 Resin Systems;59
6.2.4;2.4 Material Property;60
6.2.4.1;2.4.1 Orthotropic Properties;62
6.2.4.2;2.4.2 Orthotropic Properties in Plane Stress;65
6.2.5;2.5 Key Challenges for the Future of Marine Composite Materials;66
6.2.6;References;67
6.3;3 - Green Ship Concepts;70
6.3.1;3.1 General;70
6.3.2;3.2 Emissions;70
6.3.2.1;3.2.1 Regulations on Air Pollution;71
6.3.2.2;3.2.2 Regulations on GHGs;71
6.3.2.3;3.2.3 Effect of Design Variables on the EEDI;71
6.3.2.4;3.2.4 Influence of Speed on the EEDI;74
6.3.2.5;3.2.5 Influence of Hull Steel Weight on the EEDI;74
6.3.3;3.3 Ballast Water Treatment;75
6.3.4;3.4 Underwater Coatings;78
6.3.5;References;78
6.4;4 - LNG Carrier;80
6.4.1;4.1 Introduction;80
6.4.2;4.2 Development;81
6.4.3;4.3 Typical Cargo Cycle;82
6.4.3.1;4.3.1 Inert;83
6.4.3.2;4.3.2 Gas Up;83
6.4.3.3;4.3.3 Cool Down;83
6.4.3.4;4.3.4 Bulk Loading;83
6.4.3.5;4.3.5 Voyage;83
6.4.3.6;4.3.6 Discharge;84
6.4.3.7;4.3.7 Gas Free;84
6.4.4;4.4 Containment Systems;84
6.4.4.1;4.4.1 Self-Supporting Type;85
6.4.4.1.1;Moss Tanks (Spherical IMO-Type B LNG Tanks);85
6.4.4.1.2;IHI (Prismatic IMO-Type B LNG Tanks);87
6.4.4.2;4.4.2 Membrane Type;87
6.4.4.2.1;GT96;88
6.4.4.2.2;TGZ Mark III;89
6.4.4.2.3;CS1;90
6.4.5;4.5 Structural Design of the LNG Carrier;90
6.4.5.1;4.5.1 ULS (Ultimate Limit State) Design of the LNG Carrier;90
6.4.5.1.1;Design of the LNG Carrier Hull Girder;90
6.4.5.1.1.1;Design Principles;90
6.4.5.1.1.2;Design Wave;91
6.4.5.1.1.3;Global Load Conditions;92
6.4.5.1.1.3.1;Load Condition 1—Maximum Hogging;92
6.4.5.1.1.3.2;Load Condition 2—Maximum Sagging;93
6.4.5.1.1.4;Combination of Stresses;93
6.4.5.1.1.4.1;Longitudinal Stresses;94
6.4.5.1.1.4.2;Transverse Stresses;94
6.4.5.1.1.4.3;Shear Stresses;95
6.4.5.1.2;Capacity Checks;95
6.4.5.1.2.1;General Principles;95
6.4.5.1.2.2;Hull Girder Moment Capacity Checks;96
6.4.5.1.2.3;Hull Girder Shear Capacity Check;97
6.4.6;4.6 Fatigue Design of an LNG Carrier;97
6.4.6.1;4.6.1 Preliminary Design Phase;97
6.4.6.2;4.6.2 Fatigue Design Phase;98
6.4.7;References;101
6.5;5 - Wave Loads for Ship Design and Classification;104
6.5.1;5.1 Introduction;104
6.5.2;5.2 Ocean Waves and Wave Statistics;104
6.5.2.1;5.2.1 Basic Elements of Probability and Random Processes;104
6.5.2.2;5.2.2 Statistical Representation of the Sea Surface;107
6.5.2.3;5.2.3 Ocean Wave Spectra;107
6.5.2.4;5.2.4 Moments of Spectral Density Function;110
6.5.2.5;5.2.5 Statistical Determination of Wave Heights and Periods;111
6.5.3;5.3 Ship Response to a Random Sea;112
6.5.3.1;5.3.1 Introduction;112
6.5.3.2;5.3.2 Wave-Induced Forces;114
6.5.3.3;5.3.3 Structural Response;115
6.5.3.4;5.3.4 Slamming and Green Water on Deck;116
6.5.4;5.4 Ship Design for Classification;119
6.5.4.1;5.4.1 Design Value of Ship Response;119
6.5.4.2;5.4.2 Design Loads per Classification Rules;119
6.5.4.2.1;General;119
6.5.4.2.2;Load Components;120
6.5.4.2.3;Hull Girder Loads;120
6.5.4.2.4;External Pressure;121
6.5.4.2.5;Internal Tank Pressure;122
6.5.5;References;123
6.6;6 - Wind Loads for Offshore Structures;126
6.6.1;6.1 Introduction;126
6.6.2;6.2 Classification Rules for Design;126
6.6.2.1;6.2.1 Wind Data;126
6.6.2.2;6.2.2 Wind Conditions;127
6.6.2.2.1;General;127
6.6.2.2.2;Wind Profile;128
6.6.2.2.3;Turbulence;130
6.6.2.2.4;Wind Spectra;130
6.6.2.2.4.1;Hurricanes;131
6.6.2.3;6.2.3 Wind Loads;131
6.6.2.3.1;General;131
6.6.2.3.2;Wind Pressure;132
6.6.2.3.3;Wind Forces;133
6.6.2.3.3.1;Circular Cylinders;133
6.6.2.3.3.2;Rectangular Cross Sections;133
6.6.2.3.3.3;Finite Length Effects;135
6.6.2.3.3.4;Other Structures;135
6.6.2.3.4;Dynamic Wind Analysis;136
6.6.2.3.5;Model Wind Tunnel Tests;138
6.6.2.3.6;Computational Fluid Dynamics;138
6.6.3;6.3 Research of Wind Loads on Ships and Platforms;139
6.6.3.1;6.3.1 Wind Loads on Ships;139
6.6.3.2;6.3.2 Wind Loads on Platforms;144
6.6.4;References;147
6.7;7 - Loads and Dynamic Response for Offshore Structures;150
6.7.1;7.1 General;150
6.7.2;7.2 Environmental Conditions;150
6.7.2.1;7.2.1 Environmental Criteria;150
6.7.2.1.1;Wind;151
6.7.2.1.2;Waves;151
6.7.2.1.3;Current;152
6.7.2.2;7.2.2 Regular Waves;152
6.7.2.3;7.2.3 Irregular Waves;153
6.7.2.4;7.2.4 Wave Scatter Diagram;153
6.7.3;7.3 Environmental Loads and Floating Structure Dynamics;156
6.7.3.1;7.3.1 Environmental Loads;156
6.7.3.2;7.3.2 Sea Loads on Slender Structures;156
6.7.3.3;7.3.3 Sea Loads on Large-Volume Structures;157
6.7.3.4;7.3.4 Floating Structure Dynamics;158
6.7.4;7.4 Structural Response Analysis;159
6.7.4.1;7.4.1 Structural Analysis;159
6.7.4.2;7.4.2 Response Amplitude Operator;160
6.7.5;7.5 Extreme Values;164
6.7.5.1;7.5.1 General;164
6.7.5.2;7.5.2 Short-Term Extreme Approach;166
6.7.5.3;7.5.3 Long-Term Extreme Approach;170
6.7.5.4;7.5.4 Prediction of Most Probable Maximum Extreme for Non-Gaussian Process;172
6.7.5.4.1;Drag/Inertia Parameter Method;174
6.7.5.4.2;Weibull Fitting;175
6.7.5.4.3;Gumbel Fitting;175
6.7.5.4.4;Winterstein/Jensen method;177
6.7.6;7.6 Concluding Remarks;178
6.7.7;References;179
6.7.8;Appendix A: Elastic Vibrations of Beams;180
6.7.8.1;Vibration of a Spring/Mass System;180
6.7.8.2;Elastic Vibration of Beams;181
6.8;8 - Scantling of Ship's Hulls by Rules;184
6.8.1;8.1 General;184
6.8.2;8.2 Basic Concepts of Stability and Strength of Ships;185
6.8.2.1;8.2.1 Stability;185
6.8.2.2;8.2.2 Strength;186
6.8.2.3;8.2.3 Corrosion Allowance;189
6.8.3;8.3 Initial Scantling Criteria for Longitudinal Strength;189
6.8.3.1;8.3.1 Introduction;189
6.8.3.2;8.3.2 Hull Girder Strength;190
6.8.3.2.1;Longitudinal stress;191
6.8.3.2.2;Shear stress;192
6.8.4;8.4 Initial Scantling Criteria for Transverse Strength;192
6.8.4.1;8.4.1 Introduction;192
6.8.4.2;8.4.2 Transverse Strength;193
6.8.5;8.5 Initial Scantling Criteria for Local Strength;193
6.8.5.1;8.5.1 Local Bending of Beams;193
6.8.5.1.1;Stiffeners;194
6.8.5.1.2;Girders;195
6.8.5.2;8.5.2 Local Bending Strength of Plates;196
6.8.5.3;8.5.3 Structure Design of Bulkheads, Decks, and Bottom;197
6.8.5.4;8.5.4 Buckling of Platings;197
6.8.5.4.1;General;197
6.8.5.4.2;Elastic compressive buckling stress;197
6.8.5.4.3;Buckling evaluation;200
6.8.5.5;8.5.5 Buckling of Profiles;200
6.8.6;References;201
6.9;9 - Ship Hull Scantling Design by Analysis;202
6.9.1;9.1 General;202
6.9.2;9.2 Design Loads;202
6.9.3;9.3 Strength Analysis Using Finite Element Methods;204
6.9.3.1;9.3.1 Modeling;204
6.9.3.1.1;Global Analysis;204
6.9.3.1.2;Local Structural Models;204
6.9.3.1.3;Cargo Hold and Ballast Tank Model;204
6.9.3.1.4;Frame and Girder Model;205
6.9.3.1.5;Stress Concentration Area;205
6.9.3.1.6;Fatigue Model;207
6.9.3.2;9.3.2 Boundary Conditions;207
6.9.3.3;9.3.3 Types of Elements;208
6.9.3.4;9.3.4 Postprocessing;208
6.9.3.4.1;Yielding Check;209
6.9.3.4.2;Buckling Check;209
6.9.4;9.4 Fatigue Damage Evaluation;210
6.9.4.1;9.4.1 General;210
6.9.4.2;9.4.2 Fatigue Check;210
6.9.5;References;211
6.10;10 - Offshore Soil Geotechnics;212
6.10.1;10.1 Introduction;212
6.10.2;10.2 Subsea Soil Investigation;212
6.10.2.1;10.2.1 Offshore Soil Investigation Equipment Requirements;213
6.10.2.1.1;General;213
6.10.2.1.2;Seabed Corer Equipment;214
6.10.2.1.3;Piezocone Penetration Test;214
6.10.2.1.4;Drill Rig;215
6.10.2.1.5;Downhole Equipment;215
6.10.2.1.6;Laboratory Equipment;215
6.10.2.2;10.2.2 Subsea Survey Equipment Interfaces;217
6.10.2.2.1;Onboard Laboratory Test;217
6.10.2.2.2;Core Preparation;218
6.10.2.2.3;Onshore Laboratory Tests;218
6.10.2.2.4;Nearshore Geotechnical Investigations;218
6.10.3;10.3 Deepwater Foundation;219
6.10.3.1;10.3.1 Foundations for Mooring;219
6.10.3.2;10.3.2 Suction Caisson;219
6.10.3.3;10.3.3 Spudcan Footings;220
6.10.3.4;10.3.4 Pipe Piles;223
6.10.3.4.1;Axial Capacity;223
6.10.4;References;225
6.11;11 - Offshore Structural Analysis;228
6.11.1;11.1 Introduction;228
6.11.1.1;11.1.1 General;228
6.11.1.2;11.1.2 Design Codes;228
6.11.1.3;11.1.3 Government Requirements;229
6.11.1.4;11.1.4 Certification/Classification Authorities;229
6.11.1.5;11.1.5 Codes and Standards;230
6.11.1.6;11.1.6 Other Technical Documents;231
6.11.2;11.2 Project Planning;232
6.11.2.1;11.2.1 General;232
6.11.2.2;11.2.2 Design Basis;232
6.11.2.2.1;Unit Description and Main Dimensions;232
6.11.2.2.2;Rules, Regulations and Codes;233
6.11.2.2.3;Stability and Compartmentalization;233
6.11.2.2.4;Materials and Welding;233
6.11.2.2.5;Temporary Phases;233
6.11.2.2.6;Operational Design Criteria;234
6.11.2.2.7;In-service Inspection and Repair;234
6.11.2.2.8;Reassessment;234
6.11.2.3;11.2.3 Design Brief;234
6.11.2.3.1;Analysis Models;234
6.11.2.3.2;Analysis Procedures;235
6.11.2.3.3;Structural Evaluation;235
6.11.3;11.3 Use of Finite Element Analysis;235
6.11.3.1;11.3.1 Introduction;235
6.11.3.1.1;Basic Ideas behind FEM;235
6.11.3.1.2;Computation Based on FEM;236
6.11.3.1.3;Marine Applications of FEM;236
6.11.3.2;11.3.2 Stiffness Matrix for 2D Beam Elements;237
6.11.3.3;11.3.3 Stiffness Matrix for 3D Beam Elements;239
6.11.4;11.4 Design Loads and Load Application;243
6.11.4.1;Dead Loads;243
6.11.4.2;Variable Loads;243
6.11.4.3;Static Sea Pressure;243
6.11.4.4;Wave-Induced Loads;243
6.11.4.5;Wind Loads;244
6.11.5;11.5 Structural Modeling;245
6.11.5.1;11.5.1 General;245
6.11.5.2;11.5.2 Jacket Structures;245
6.11.5.2.1;Analysis Models;245
6.11.5.2.2;Modeling for Ultimate Strength Analysis;246
6.11.5.2.3;Modeling for Fatigue Analysis;247
6.11.5.2.4;Assessment of Existing Platforms;247
6.11.5.2.5;Fire, Blast, and Accidental Loading;247
6.11.5.3;11.5.3 Floating Production and Offloading Systems (FPSO);248
6.11.5.3.1;Structural Design General;248
6.11.5.3.2;Analysis Models;249
6.11.5.3.3;Modeling for Ultimate Strength Analysis;250
6.11.5.3.4;Modeling for Compartmentalization and Stability;252
6.11.5.3.5;Modeling for Fatigue Analysis;253
6.11.5.4;11.5.4 TLP, Spar, and Semisubmersible;255
6.11.6;References;258
6.12;12 - Development of Arctic Offshore Technology;260
6.12.1;12.1 Historical Background;260
6.12.2;12.2 The Research Incentive;263
6.12.3;12.3 Industrial Development in Cold Regions;264
6.12.3.1;12.3.1 Arctic Ships;264
6.12.3.2;12.3.2 Offshore Structures;265
6.12.4;12.4 The Arctic Offshore Technology Program;268
6.12.4.1;12.4.1 Three Areas of Focus;268
6.12.4.2;12.4.2 Environmental and Climatic Change;268
6.12.4.3;12.4.3 Materials for the Arctic;269
6.12.5;12.5 Highlights;270
6.12.5.1;12.5.1 Mechanical Resistance to Slip Movement in Level Ice;270
6.12.5.2;12.5.2 Ice Forces on Fixed Structures;271
6.12.5.3;12.5.3 Concrete Durability in Arctic Offshore Structures;273
6.12.6;12.6 Conclusion;273
6.12.7;References;274
6.13;13 - Limit-State Design of Offshore Structures;276
6.13.1;13.1 Limit-State Design;276
6.13.2;13.2 ULS Design;277
6.13.2.1;13.2.1 Ductility and Brittle Fracture Avoidance;277
6.13.2.2;13.2.2 Plated Structures;278
6.13.2.3;13.2.3 Shell Structures;279
6.13.3;13.3 FLS Design;284
6.13.3.1;13.3.1 Introduction;284
6.13.3.2;13.3.2 Fatigue Analysis;286
6.13.3.3;13.3.3 Fatigue Design;288
6.13.4;References;289
6.14;14 - Ship Vibrations and Noise Control;290
6.14.1;14.1 Introduction;290
6.14.2;14.2 Basic Beam Theory of Ship Vibration;291
6.14.3;14.3 Beam Theory of Steady-State Ship Vibration;292
6.14.4;14.4 Damping of Hull Vibration;293
6.14.5;14.5 Vibration and Noise Control;294
6.14.5.1;14.5.1 Propeller Radiated Signatures;294
6.14.5.2;14.5.2 Vortex Shedding Mechanisms;296
6.14.5.3;14.5.3 After-Body Slamming;298
6.14.6;14.6 Vibration Analysis;298
6.14.6.1;14.6.1 Procedure Outline of Ship Vibration Analysis;299
6.14.6.2;14.6.2 Finite Element Modeling;300
6.14.6.2.1;Lightship Weight Distribution;300
6.14.6.2.2;Loading Condition;301
6.14.6.2.3;Added Mass;301
6.14.6.2.4;Buoyancy Springs;302
6.14.6.3;14.6.3 Free Vibration;302
6.14.6.4;14.6.4 Forced Vibration;302
6.14.7;Further Reading;304
7;Part 2 Ultimate Strength;306
7.1;15 - Buckling/Collapse of Columns and Beam-Columns;308
7.1.1;15.1 Buckling Behavior and Ultimate Strength of Columns;308
7.1.1.1;15.1.1 Buckling Behavior;308
7.1.1.2;15.1.2 Perry–Robertson Formula;310
7.1.1.3;15.1.3 Johnson–Ostenfeld Formula;311
7.1.2;15.2 Buckling Behavior and Ultimate Strength of Beam-Columns;312
7.1.2.1;15.2.1 Beam-Column with Eccentric Load;312
7.1.2.2;15.2.2 Beam-Column with Initial Deflection and an Eccentric Load;313
7.1.2.3;15.2.3 Ultimate Strength of Beam-Columns;314
7.1.2.4;15.2.4 Alternative Ultimate Strength Equation—Initial Yielding;315
7.1.3;15.3 Plastic Design of Beam-Columns;316
7.1.3.1;15.3.1 Plastic Bending of Beam Cross Section;316
7.1.3.1.1;Rectangular Cross Section;316
7.1.3.1.2;Tubular Cross Section (t<

Leseproben

Chapter 1

Introduction

Abstract

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.

Keywords

Accidental loads; Applications; Calibration; Concepts; Fatigue assessment; Limit-state design; Risk assessment

1.1. Structural Design Principles

1.1.1. Introduction

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

d=Rd

(1.1)

where

Sd=?Sk·?f, design load effect

Rd=?Rk/?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...