Fatigue and Fracture Mechanics of Offshore Structures

The tubular welded joints used in the construction of offshore structures can experience millions of variable amplitude load cycles during their service life. Such fatigue loading represents a main cause of degradation in these structures. As a result, fatigue is an important consideration in their design. Fatigue and Fracture Mechanisms of Offshore Structures present novel research and the results of wave-induced stress on the operational life of offshore structures.

Containing results of an investigation undertaken to assess the fatigue and fracture performance of steels used in the offshore industry, Fatigue and Fracture Mechanics of Offshore Structures includes,

• Stress analysis of tubular joints
• Fatigue design
• Fatigue loading in Jackup structures
• Jack-up dynamic response
• Modelling of wave loading
• Test specimen considerations
• The stress intensity factor concept
• Variable amplitude crack growth models
• Consideration of sequence effects
• Sea state probability model

The important research in this book will be of interest to those dealing with a wide range of engineering structures - from bridges and buildings to masts and pipelines, as well as fatigue and fracture specialists, and those concerned with materials technology.

Series Editor's

Foreword

Acknowledgements

Foreword Notation

Chapter 1 Literature Review

1.1 Introduction and background

1.2 Review

1.3 Stress analysis of tubular joints

1.3.1 Definition of stresses in welded connections

1.3.2 Definition of hot spot stress

1.3.3 Methods of stress analysis

1.4 Fatigue design

1.4.1 S-N approach

1.4.2 The Fracture Mechanics (FM) approach

1.5 Summary

Chapter 2 Service Load Simulation of Offshore Structures

2.1 Introduction

2.2 Fatigue loading in Jack-up structures

2.3 Review of previous loading models

2.3.1 COLOS/C 12-20 series

2.3.2 UKOSRP II double-peaked spectrum

2.3.3 Hart/Wischung algorithm

2.3.4 WASH sequence

2.4 The JOSH model

2.5 Generation of JOSH

2.5.1 The pseudo random binary sequence technique

2.5.2 The Morkov chain technique

2.6 Jack-up dynamic response

2.6.1 The transfer function approach

2.6.2 Modelling of structural parameters

2.6.3 Modelling of soil-structure interaction

2.7 Modelling of wave loading

2.8 Selection of sea states

2.9 Discussion

2.10 Summary

Chapter 3 Large-scale Fatigue Testing

3.1 Introduction

3.2 Test specimen consideration

3.2.1 Properties of SE 702

3.2.2 consideration of test specimen geometry

3.2.3 Fabrication of SE 702 specimens

3.3 Experimental set-up

3.3.1 Details of test rig

3.3.2 Test control and data acquisition

3.3.4 Simulation of environmental conditions

3.4 Stress analysis of Y joints

3.4.1 Experimental stress and analysis procedure

3.4.2 Use of parametric equations

3.5 Experimental fatigue testing

3.5.1 Test parameters and the JOSH sequence

3.6 Fatigue test results

3.6.1 Fatigue crack initiation

3.6.2 Crack growth curves

3.6.3 Crack aspect ratio evolution

3.6.4 S-N data

3.7 Discussion

3.8 Summary

Chapter 4 Fracture Mechanics Analysis of Results

4.1 Introduction

4.2 The stress intensity factor concept

4.3 Experimental results

4.4 Use of empirical SIF solutions

4.4.1 The average stress model

4.4.2 The two phase model (TPM)

4.4.3 The modified average stress model

4.5 Adapted plate solutions

4.5.1 Newman-Raju SIF solution for surface cracks

4.6 New semi-empirical Y factor solution

4.7 Variable amplitude crack growth models

4.7.1 Equivalent stress range approach

4.7.2 Equivalent crack growth concept

4.8 Consideration of sequence effects

4.9 Fast assessment of offshore structures

4.9.1 New normalised PSD equation

4.10 Sea state probability model

4.10.1 Use of sea state probability distribution model

4.10.2 Formulation of the sea state equivalent stress concept

4.11 Discussion

4.12 Summary

Chapter 5 Conclusion

5.1 Summary of book

5.2 Conclusions and recommendations

References

Index

Linus Etube is the author of Fatigue and Fracture Mechanics of Offshore Structures, published by Wiley.