Hello,
I have a bridge model that is consistently telling me there are fatigue stress issues with my plate girder section.
I have exported the live load range that the model has created for a given girder and while comparing it to the section modulus at the locations reported to have issues I am coming up with a stress that is significantly less that what is reported.
When I use just the bottom fiber Sx for the areas, I compute the stress for point 42.18 as follows:
When I add in the load factor of 1.75 x 2 ksi I get the stress to be 3.52 ksi at point 42.18 for example. The fatigue report is telling me this stress is being computed for the 12 ksi allowed is 1.75 x 6.089 = 10.66 ksi. This leads to the the report of 88% of capacity being returned.
I am not sure how to reconcile these stresses, the model I have is a bridge that is skewed in excess of 20 degrees, so perhaps there is a deflection base later flange stress being considered, but the reports for this in the analysis do not return a lateral bending moment in the flange. If anyone can provide some direction it would be greatly appreciated, thank you in advance.
I am also having the same issue with a curved steel girder bridge. Hand calculations show much lower fatigue stresses than reported in the Fatigue Design Check Report. Is this a known issue with the program since it seems to not be an isolated issue?