Title Page
ABSTRACT
국문 초록
PREFACE
Contents
NOMENCLATURE 23
PART 1 23
PART 2 26
PART 1. FLANGE LOCAL BUCKLING FOR HORIZONTALLY CURVED I-GIRDER 30
Chapter 1. Introduction 30
Chapter 2. Background 33
Chapter 3. Literature review 37
3.1. Design specification and guideline 37
3.2. Previous studies 48
3.3. Implications 58
Chapter 4. Analytical study 63
4.1. Finite Element Analysis modeling 67
4.2. Parametric study 104
4.3. Result 125
Chapter 5. Conclusion 147
PART 2. STIFFENING THE CYLINDRICAL STEELWIND TURBINE TOWERS WITH OPENINGS AGAINST LOCAL BUCKLING 154
Chapter 1. Introduction 154
Chapter 2. Background 157
Chapter 3. Literature review 160
3.1. Design specification and guideline 161
3.2. Previous studies 169
3.3. Implications 175
Chapter 4. Analytical study 181
4.1. Finite element analysis modeling 182
4.2. Parametric study 189
4.3. Result 211
Chapter 5. Conclusion 217
REFERENCES 224
PART 1 224
PART 2 228
Table 1. Boundary conditions in curved plate shell models to similar arch 75
Table 2. Boundary conditions in modified curved plate shell model 78
Table 3. Boundary conditions in curved I-shaped beam models to similar arch 86
Table 4. Boundary conditions in modified curved I-shaped beam model 91
Table 5. Model parameters 105
Table 6. Boundary conditions in curved plate for elastic buckling analysis 107
Table 7. Critical buckling stress according to curvature and stress gradient in the plate model (web line - simply B.C) 110
Table 8. Critical buckling stress according to curvature and stress gradient in the plate model (web line - Fixed B.C) 113
Table 9. Critical buckling stress according to curvature and stress gradient in the curved I-shaped beam model (tƒ:tw = 1:1)[이미지참조] 121
Table 10. Critical buckling stress according to curvature and stress gradient in the curved I-shaped beam model (tƒ:tw = 1:2)[이미지참조] 122
Table 11. Stresses of the outer flange element by curvature 135
Table 12. Stresses of the inner flange element by curvature 135
Table 13. Specifications of wind turbines over MW 158
Table 14. Classification of cylinders and factor by length type-EN1993-1-6 163
Table 15. Values of fabrication quality parameter Q 164
Table 16. Buckling coefficients for unstiffened cylindrical shells 165
Table 17. Coefficients A₁ and B₁ for reduction factor C₁ 168
Table 18. Types of shell analysis provided by EN 1993-1-6 (2007) 182
Table 19. Material properties for S355 188
Table 20. Boundary conditions in analytical models 190
Table 21. Parametric model for convergence analysis of perfect cylindrical shell 191
Table 22. Comparison of elastic buckling stress (L = 9m) 194
Table 23. Analysis parameters for cylindrical shell with openings 195
Table 24. Comparison of LBA results by parameters 200
Table 25. Comparison of GMNA results by parameter 206
Table 26. Comparison of FEM results based on the design strength and the opening angle 212
Table 27. Maximum displacement and ultimate strength according to collar stiffener thickness (U1, Lateral-1) 215
Figure 1. Torsional shape by curvature 33
Figure 2. Stress gradient in curved I-shaped beam 34
Figure 3. Flange local buckling due to stress gradient 36
Figure 4. Compression elements members subject to flexure 39
Figure 5. Basic form of all I-section compression flange flexural resistance equations 43
Figure 6. Warping-torsional behavior 45
Figure 7. Longitudinal variation of bending and warping stress 49
Figure 8. Internal forces and stresses for flange 50
Figure 9. Warping torsion shape 51
Figure 10. Stress distribution for flanges of compact sections 52
Figure 11. Longitudinal flange stresses due to bending and warping 53
Figure 12. Finite element model for verification - multi girder system 54
Figure 13. Analytical model: plate with rotational stiffness at the center subjected to stress gradient 55
Figure 14. Uniformly distributed radial loading 64
Figure 15. Direction definition of stress gradient in plate 68
Figure 16. Hoop loading and symbols for thin-cylinder sections 70
Figure 17. Plate shell validation model under uniform compression 71
Figure 18. Stress distribution in plate shell using FEA results 71
Figure 19. Curved plate convergence analysis results 72
Figure 20. Analytical cross-section symbol and modeling shape in curved plate 74
Figure 21. Modeling boundary conditions and loading conditions in curved plate shell models to similar arch 74
Figure 22. Deformation shape and reaction force analysis result of curved plate shell models to similar arch 75
Figure 23. Deformation shape and stress distribution analysis result of curved plate shell models to similar arch 76
Figure 24. Modeling boundary conditions and loading conditions in modified curved plate shell model 77
Figure 25. Deformation shape and reaction force analysis result of modified curved plate shell model 79
Figure 26. Deformation shape and stress distribution analysis result of modified curved plate shell model 79
Figure 27. Modeling boundary conditions and loading conditions in curved plate shell model with stress gradient 80
Figure 28. Deformation shape and reaction force analysis result of curved plate shell model with stress gradient 81
Figure 29. Deformation shape and stress distribution analysis result of curved plate shell model with stress gradient (R=500 cm) 82
Figure 30. Deformation shape and stress distribution analysis result of curved plate shell model with stress gradient (R=2000 cm) 82
Figure 31. Deformation shape and stress distribution analysis result of curved plate shell model with stress gradient (R=5000 cm) 83
Figure 32. Analytical cross-section symbol and modeling shape in curved I-shaped beam 84
Figure 33. Modeling boundary conditions and loading conditions in curved I-shaped beam models to similar arch 86
Figure 34. Deformation shape and reaction force analysis result of curved I-shaped beam models to similar arch (R=500 cm) 87
Figure 35. Deformation shape and reaction force analysis result of curved I-shaped beam models to similar arch (R=2000 cm) 87
Figure 36. Deformation shape and reaction force analysis result of curved I-shaped beam models to similar arch (R=5000 cm) 88
Figure 37. Deformation shape and stress distribution analysis result of curved I-shaped beam models to similar arch (R=500 cm) 88
Figure 38. Deformation shape and stress distribution analysis result of curved I-shaped beam models to similar arch (R=2000 cm) 89
Figure 39. Deformation shape and stress distribution analysis result of curved I-shaped beam models to similar arch (R=5000 cm) 89
Figure 40. Modeling boundary conditions and loading conditions in modified curved I-shaped beam model 90
Figure 41. Deformation shape and reaction force analysis result of modified curved I-shaped beam models (R=500 cm) 92
Figure 42. Deformation shape and reaction force analysis result of modified curved I-shaped beam models (R=2000 cm) 93
Figure 43. Deformation shape and reaction force analysis result of modified curved I-shaped beam models (R=5000 cm) 93
Figure 44. Deformation shape and stress distribution analysis result of modified curved I-shaped beam models (R=500 cm) 94
Figure 45. Deformation shape and stress distribution analysis result of modified curved I-shaped beam models (R=2000 cm) 94
Figure 46. Deformation shape and stress distribution analysis result of modified curved I-shaped beam models (R=5000 cm) 95
Figure 47. Direction definition of stress gradient in curved I-shaped beam 96
Figure 48. Modeling boundary conditions and loading conditions in curved I-shaped beam model with stress gradient 96
Figure 49. Deformation shape and reaction force analysis result of curved I-shaped beam models with stress gradient (R=500 cm) 97
Figure 50. Deformation shape and reaction force analysis result of curved I-shaped beam models with stress gradient (R=2000 cm) 98
Figure 51. Deformation shape and reaction force analysis result of curved I-shaped beam models with stress gradient (R=5000 cm) 99
Figure 52. Deformation shape and stress distribution analysis result of curved I-shaped beam models with stress gradient (R=500 cm) 100
Figure 53. Deformation shape and stress distribution analysis result of curved I-shaped beam models with stress gradient (R=2000 cm) 101
Figure 54. Deformation shape and stress distribution analysis result of curved I-shaped beam models with stress gradient (R=5000 cm) 102
Figure 55. Eigenmode shape of curved plate model and deformation shape factor of section (web line - simply B.C) 109
Figure 56. Critical buckling stress by curvature according to stress gradient (web line - simply B.C) 110
Figure 57. Eigenmode shape of curved plate model and deformation shape factor of section (web line - fixed B.C) 112
Figure 58. Critical buckling stress by curvature according to stress gradient (web line - fixed B.C) 114
Figure 59. Buckling coefficient to the radius of curvature by stress gradient 114
Figure 60. Buckling coefficient to stress gradient by the radius of curvature 115
Figure 61. Comparison of buckling coefficients of straight and curved plates by stress gradient 115
Figure 62. Eigenmode shape of curved I-shaped beam model (tƒ:tw = 1:1)[이미지참조] 119
Figure 63. Critical buckling stress by curvature according to stress gradient in the curved I-shaped beam model (tƒ:tw = 1:1)[이미지참조] 121
Figure 64. Critical buckling stress by curvature according to stress gradient in the curved I-shaped beam model (tƒ:tw = 1:2)[이미지참조] 123
Figure 65. Buckling mode shape according to the thickness ratio of the flange and the web (Re = 500cm, ƒw/ƒb = 0)[이미지참조] 126
Figure 66. Buckling mode shape according to the thickness ratio of the flange and the web (R = 2000cm, ƒw/ƒb = 0)[이미지참조] 127
Figure 67. Buckling mode shape according to the thickness ratio of the flange and the web (R = 10000cm, ƒw/ƒb = 0)[이미지참조] 128
Figure 68. Buckling mode shape according to the thickness ratio of the flange and the web (R = ∞, ƒw/ƒb = 0)[이미지참조] 128
Figure 69. Comparison of buckling coefficients for curved plates and I-shaped beams based on curvature and stress gradient (tƒ = 0.5cm, tw = 0.5cm)[이미지참조] 130
Figure 70. Comparison of the buckling coefficient for the I-shaped beam by FEA results according to the thickness and curvature (tƒ : tw = 1: 1,λƒ/λw = 0.5)[이미지참조] 133
Figure 71. Stress of an element in a curved I-shaped beam under uniform compression 134
Figure 72. Normal stress and critical buckling stress according to the position of the flange partial element 136
Figure 73. Comparison of buckling coefficient and proposed formula for I-shaped beams FEA results by the thickness 140
Figure 74. Comparison of the buckling coefficient and the proposed formula for the I-shaped beam by FEA results according to the thickness and stress gradient 142
Figure 75. Slenderness ratio when reaching yield strength considering residual stress by parameter 144
Figure 76. comparison of non-compact section slenderness ratio limit 145
Figure 77. Composition of wind power generation system (IEC 61400-3) 157
Figure 78. Comparison of turbine capacity and tower bottom diameter 158
Figure 79. Circumferentially edge-stiffened openings installation shape and symbol (collar stiffener type, DNVGL-ST-0126) 167
Figure 80. Finite element analysis model types and result contours 170
Figure 81. Trend of the strength reduction factor (C₁) based on the opening angle (𝛿) 176
Figure 82. Stress-strain curve (S355 Steel, 16 〈t ≤ 40) 188
Figure 83. Loads and boundary conditions applied to the analytical models 190
Figure 84. Comparison of elastic buckling stress FEA and theoretical results 192
Figure 85. Buckling mode shape according to r/t (1st mode, L = 9m) 194
Figure 86. Drawings and dimensions of collar stiffeners and openings 196
Figure 87. Detail of the opening sketch on ABAQUS (2023) 197
Figure 88. FEA Modeling of a cylindrical shell with openings 198
Figure 89. Comparison of LBA results according to collar stiffener thickness 199
Figure 90. Eigenmode shape of LBA results by collar stiffener thickness 202
Figure 91. Comparison of GMNA results according to collar stiffener thickness 205
Figure 92. Deformation shape and stress distribution in the ultimate load of GMNA results by collar stiffener thickness 208
Figure 93. Comparison of FEM results based on the design strength and the opening angle 212
Figure 94. Displacement distribution according to collar stiffener thickness on the cylindrical shell with openings (U1, Lateral-1) 215