30 FATIGUE ANALYSIS

1 Make a copy of the inplace sacinp file Rename the file as sacinpfatigue

2 Make following changes to this file

a) In the LDOPT card change the Water Depth as per bid to account for absence of Storm Surge

b) Change the Cd and Cm values

c) Delete all loads except wave loads

d) Change the Kinematic factor to 10(see bid) in the WAVE card

e) In the Wave Height field change the wave height to Average wave height of the specific wave

f) Enter MS for obtaining maximumbase shear value

g) Delete all Load combinations from this file

h) Advance the wave in steps of 4degrees

i) The number of static steps will therefore be 3604 = 90

3 Run this file in Static 1048774 Linear static analysis 1048774 Select sacinpfatigue

4 In the output listing a saclst file is obtained from which the crest positions for minimum and maximum shear can be found for different wave heights and different wave directions

5 Obtain three angles between angle1(X) and angle 2(Y) as (Y-X)4 and remaining three angles as ((360-Y)+X)4

6 Enter the 6+2 angles in the sacinp file and change the number of steps to1 in increments of 1degree

7 Run the sacinp file in Linear Static Analysis

8 A saccsf file is obtained which will be used for the fatigue analysis

9 Create a ftginp file

10 In the FTOPT card enter design life(see bid) and factor(see bid usually 20) Also enter the fatigue time period as the Wave Period (generally 1 year)

11 Initially apply API X Prime for source of S-N curve ie APP

12 For SCFrsquos use Kuang amp Wordsworth for all joints initially

13 In the FTOPT2 card give PT Export Fatigue data Tubular Inline Check Inline Tubular SCF-AWS and Effective Thickness Ratio-2WAL

14 Specify the SCF limits in the SCFLM card as a maximum of 60 and a minimum of 16

15 For Grouted Joints enter Joint Override with SCF Option as Marshalls Method

16 In the GRPSEL RM card specify dummy structures appurtenances Risers and conductors which are not part of the main structural Member but attract Wave Load

17 In the EXTRAC HEAD AE card enter a cut off of 05 to extract joints which have a fatigue life of less than 50 years

18 Now in the Runfile Wizard go to Post 1048774 Fatigue Damage and Run the ftginp file with the saccsf file and note down the joints which have service life of less than 50 years

19 Now Extract these joints individually by using the EXTRAC card in the ftginp file

20 On running the file again as in step no18 a ftgext file is created automatically

21 In the ftgext file we can make changes in the Chord Thickness or S-N curve to be used etc to find the optimum change that has to be made to a chordbrace Note down the specific changes that need to be made for a specific joint

22 Now in the ftginp file enter the JNTOVR cards for the joint overrides that need to be specified as noted from the ftgext fileNOTE In the case of grouted joints if the S-N curve needs to be changed use the API X curve with effective thickness option ie AXP option

23 Run the Final ftginp file with the saccsf file till no joint have a service lifeless than 50years

24 The output files that are obtained from the run are the ftglst and the ftgext files

15 For Grouted Joints enter Joint Override with SCF Option as Marshalls Method

16 In the GRPSEL RM card specify dummy structures appurtenances Risers and conductors which are not part of the main structural Member but attract Wave Load

17 In the EXTRAC HEAD AE card enter a cut off of 05 to extract joints which have a fatigue life of less than 50 years

18 Now in the Runfile Wizard go to Post 1048774 Fatigue Damage and Run the ftginp file with the saccsf file and note down the joints which have service life of less than 50 years

19 Now Extract these joints individually by using the EXTRAC card in the ftginp file

20 On running the file again as in step no18 a ftgext file is created automatically

21 In the ftgext file we can make changes in the Chord Thickness or S-N curve to be used etc to find the optimum change that has to be made to a chordbrace Note down the specific changes that need to be made for a specific joint

22 Now in the ftginp file enter the JNTOVR cards for the joint overrides that need to be specified as noted from the ftgext fileNOTE In the case of grouted joints if the S-N curve needs to be changed use the API X curve with effective thickness option ie AXP option

23 Run the Final ftginp file with the saccsf file till no joint have a service lifeless than 50years

24 The output files that are obtained from the run are the ftglst and the ftgext files