Page 16 - Marine Structural Design

Contents xiii

17.1.3 Effect of Seawater and Corrosion Protection ................................................................... 331
17.1.4 Effect of Mean Stress ....................................................................................................... 331
17.1.5 Comparisons of S-N Curves in Design Standards ............................................................ 332
17.1.6 Fatigue Strength Improvement ......................................................................................... 335
17.1.7 Experimental S-N Curves ................................................................................................. 335
17.2 Estimation of the Stress Range ................................................................................................ 336
17.2.1 Nominal Stress Approach ................................................................................................. 336
17.2.2 Hotspot Stress Approach .................................................................................................. 337
17.2.3 Notch Stress Approach ..................................................................................................... 339
17.3 Stress Concentration Factors ................................................................................................... 339
17.3.1 Definition of Stress Concentration Factors ...................................................................... 339
17.3.2 Determination of SCF by Experimental Measurement .................................................... 340
17.3.3 Parametric Equations for Stress Concentration Factors ................................................... 340
17.3.4 Hot-Spot Stress Calculation Based on Finite Element Analysis ...................................... 341
17.4 Examples ................................................................................................................................. 343
17.4.1 Example 17.1: Fatigue Damage Calculation .................................................................... 343
17.5 References ............................................................................................................................... 344
CHAPTER 18 FATIGUE LOADING AND STRESSES ................................................................ 347
18.1 Introduction ............................................................................................................................. 347
18.2 Fatigue Loading for Ocean-Going Ships ................................................................................. 348
18.3 Fatigue Stresses ....................................................................................................................... 350
18.3.1 General ............................................................................................................................. 350
18.3.2 Long Term Fatigue Stress Based on Weibull Distribution .............................................. 350
18.3.3 Long Term Stress Distribution Based on Deterministic Approach .................................. 351
18.3.4 Long Term Stress Distribution - Spectral Approach ....................................................... 352
18.4 Fatigue Loading Defined Using Scatter Diagrams .................................................................. 354
18.4.1 General ............................................................................................................................. 354
18.4.2 Mooring and Riser Induced Damping in Fatigue Seastates ............................................. 354
18.5 Fatigue Load Combinations ..................................................................................................... 355
18.5.1 General ............................................................................................................................. 355
18.5.2 Fatigue Load Combinations for Ship Structures .............................................................. 355
18.5.3 Fatigue Load Combinations for Offshore Structures ....................................................... 356
18.6 Examples ................................................................................................................................. 357
18.7 Concluding Remarks ............................................................................................................... 361
18.8 References ............................................................................................................................... 361
CHAPTER 19 SIMPLIFIED FATIGUE ASSESSMENT .............................................................. 363

19.1 introduction ............................................................................................................................. 363
19.2 Deterministic Fatigue Analysis ................................................................................................ 364
19.3 Simplified Fatigue Assessment ................................................................................................ 365
19.3.1 Calculation of Accumulated Damage .............................................................................. 365
19.3.2 Weibull Stress Distribution Parameters ........................................................................... 366
19.4 Simplified Fatigue Assessment for Bilinear S-N Curves ........................................................ 366
19.5 Allowable Stress Range ........................................................................................................... 367
19.6 Design Criteria for Connections Around Cutout Openings ..................................................... 367
19.6.1 General ............................................................................................................................. 367
19.6.2 Stress Criteria for Collar Plate Design ............................................................................. 368
19.7 Examples ................................................................................................................................. 370
19.8 References ............................................................................................................................... 371
CHAPTER 20 SPECTRAL FATIGUE ANALYSIS AND DESIGN ............................................. 373
20.1 Introduction ............................................................................................................................. 373