When performing fatigue analysis for offshore structures, stress concentration factors or SCF's are required to compute hotspot stresses from the nominal beam stresses. Tubular connection SCF's can be estimated using parametric equations like Efthimiu but non-tubular connections typically require a finite element analysis to determine the SCF.

How to set up a non-tubular SCF extraction using the SACS Joint Mesh program?

1. We first need to mesh the joint and generate the SCF extrapolation points when meshing the non-tubular connection.

I'm using Sample 23 for an example. Open the model in Precede, navigate to the Joint > Joint Mesher > select the joint you want to mesh, and supply the joint mesh input file (jtminp.) if you have one > OK

In the MESH TOOL window, select the brace that you would like to extrapolate the SCF, then select YES on 'Create Elements for Fatigue Analysis' > Apply > Mesh Joint

 

Precede will generate a meshed model file, a post input file for every extrapolated brace. Save the meshed model with a new name (sacinp.mesh).

2. We now need to calculate the stress concentration factor based upon the beam nominal loads.

In the Analysis Generator > Basic Static Analysis > Select the meshed input file as the model input > Select the Element code check option > Turn on the post input file option > Select the generated post input file as your input > Save > Run the analysis.

The SCFs will then be reported in the output listing file. 

The reported SCF's can now be used in the fatigue analysis to determine the connection hotspot stresses.