By Steve Maddox and Carol Johnston
The fatigue design curves in the current edition of BS7608:2014 include fatigue data and analysis that dates back to the 1960s. During the revision of the document in 2014, changes were made to the design curves in the light of more recent data, but the validity of the existing curves was not checked in detail.
This report describes statistical analysis carried out on the complete, new datasets, to confirm that they are still valid for the details included in each fatigue design Class.
- The original assumptions used to define the fatigue classes have been documented and new data have been added to the original databases.
- In some cases, the standard deviation of the larger database differed from that of the current design classes but in most cases it was an insignificant difference.
- Class B did not originally include test results from any parent material. Recent analysis of results from parent material show that the slope depends on the applied R ratio and so further analysis should be done in this area and Class B updated.
- Overall, the fatigue Classes assigned to the weld details in BS7608 were all found to be appropriate when the updated databases of test results were analysed statistically.