OS-C501

Recommendations

Info

Offshore Standard DNV-OS-C501, November 2013 Sec.3 Design input – Page 34 As an alternative to the representation in Table 3-3, the fatigue loads can be represented on matrix form with one row for each mean strain, one column for each strain amplitude, and number of cycles as the entry of each matrix element as shown in the matrix representation of rain-flow counted strain amplitude distribution in Figure 3-3. Figure 3-3 Presentation of fatigue loads Guidance note: - The history of mean and amplitude of stress shall be established on discretised form by a rainflow analysis. - A minimum resolution of the discretisation of stresses has to be defined before the stress history is established. - Note that for the fatigue analysis the history of mean stress/strain and amplitude is needed. In a non-linear analysis, the mean may shift relative to the amplitude during the transfer from applied load to load response. - If the time duration of some cycles is long or if the mean value is applied over a long time, these loads may have to be considered for sustained load cases (stress rupture) as well. - Degradation is a non-linear, history-dependent process. If different load and environmental conditions can cause different degradation histories, all relevant load combinations shall be considered. ---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e--- 9.6.5 Based on the material properties, in particular the S-N curve and the magnitude of its slope parameter, it shall be assessed whether the bulk of the fatigue damage will be caused by several thousand or more stress cycles from the characteristic stress distribution, or if it will be caused by only one or a very few extreme stress amplitudes from this distribution. In the former case, the natural variability in the individual stress amplitudes can be disregarded as its effect on the cumulative damage will average out, and the partial load factor can be set equal to 1.0. In the latter case, the natural variability in the few governing extreme stress amplitudes cannot be disregarded and needs to be accounted for by a partial load factor greater than 1.0. If no detailed analysis of the load factor can be made, the same factors as those given in Sec.9 for static loads shall be used. 10 Environment 10.1 General 10.1.1 The term environment designates in this standard the surroundings that impose no direct load on the product, e.g. ambient temperature, moisture or chemicals. 10.1.2 The environment may impose indirect loads on the structure, e.g. thermal stresses or swelling due to moisture uptake. This should be considered as a load effect and should be calculated according to the relevant parts of Sec.9. However, the environment is generally considered for its effect on the degradation of material strength or change of elastic properties. 10.1.3 The following aspects shall be considered when evaluating the effect of the environment on local volume elements in a structure: — direct exposure — possible exposure if protective system fails — exposure after time — exposure after diffusion through a protective layer — exposure after accident — exposure after degradation of a barrier material, or any material. Guidance note: A non-exhaustive list of the most common environments to be considered in the design is given for guidance in the App.A. ---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e--- DET NORSKE VERITAS AS
Offshore Standard DNV-OS-C501, November 2013 Sec.3 Design input – Page 35 10.1.4 The time history of all quantities that characterise environmental conditions (e.g. temperature, humidity) shall be documented for each phase during the design life of the structure. 10.1.5 The time history of all environments has to be documented for the entire life of the product. Time histories and characteristic values shall be established according to the same principles as described for load in Sec.1. 10.1.6 Different environmental values are defined in this standard: — the characteristic value — the sustained value. Guidance note: The definition of the different load values is summarised in Table 3-4. The detailed definition presented in the relevant chapters shall be used. Table 3-4 Definition of the different load values Designation Definition To be used for Characteristic value Extreme value with return period of 100 years Check of Ultimate Limit States Sustained value Average value over a long period Long-term degradation of material properties Fatigue value Only for loads Accidental value Same as characteristic value For example: when considering temperature as an environment, the following values can be defined: - Sustained environmental value corresponding to the average temperature - Extreme environmental value corresponding to the maximum temperature - Accidental environmental value corresponding to a fire situation - Fatigue environmental values corresponding temperature fluctuations imposing thermal stress fluctuations in the material ---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e--- 10.1.7 The notion of fatigue value for the environment is not considered in this chapter. If the environment impose indirect fatigue loads on the structure, e.g. cyclic thermal stresses, these loads should be considered according to [9]. 10.1.8 The notion of accidental value is not used in this standard. It shall be decided whether the product should be designed for a given accidental event (e.g. fire, chemicals leakage) or whether it should not de designed for it and protected against it by other means (e.g. chemical protection structure around the product). 10.1.9 Different types of loads and environment shall be combined. Depending on which load and environment values are combined, different load and environmental conditions are defined. These different load and environmental conditions define the different design cases to be considered. These design cases are described in Sec.3 [11]. 10.2 Effects of the environment on the material properties 10.2.1 All possible changes of material properties due to the effect of the environment shall be considered. Guidance note: The following interactions should be considered: - temperature: variation of the mechanical properties (stiffness, strength…) - exposure to water (salinity / corrosion, marine fouling…) - exposure to humidity - exposure to chemicals - exposure to UV - exposure to other radiation - erosion. ---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e--- 10.2.2 The degradation of material properties caused by the environmental conditions is described in Sec.4 [5] (laminate) and Sec.5 [5] (sandwich structures). 10.2.3 The environmental conditions that shall be used for the determination of time-dependent material properties are described in Sec.3 [11.3]. DET NORSKE VERITAS AS
Page 1 and 2: OFFSHORE STANDARD DNV-OS-C501 Compo
Page 3 and 4: Offshore Standard DNV-OS-C501, Nove
Page 33: Offshore Standard DNV-OS-C501, Nove
Page 85 and 86:
Offshore Standard DNV-OS-C501, Nove
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Page 163 and 164:
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Page 179 and 180:
Page 181 and 182:
Page 183 and 184:
Page 185 and 186:
Page 187 and 188:
Page 189 and 190:
Page 191 and 192:
Page 193 and 194:
Page 195 and 196:
Page 197 and 198:
Page 199 and 200:
Page 201 and 202:
Page 203 and 204:
Page 205 and 206:
Page 207 and 208:
Page 209 and 210:
Page 211 and 212:
Page 213 and 214:
Page 215 and 216:
Page 217 and 218:
Page 219 and 220:
Page 221 and 222:
Page 223 and 224:
Page 225 and 226:
Page 227 and 228:
Page 229 and 230:
Page 231 and 232:
Page 233 and 234:
Page 235 and 236:
Page 237 and 238:
Page 239 and 240:
Page 241 and 242:
Page 243 and 244:
Page 245 and 246:
Page 247 and 248:
Page 249 and 250:
show all

OS-C501

Create successful ePaper yourself

Delete template?

Save as template?