This is probably a stupid question but i couldn’t find the answer anywhere else in these forums.

I am a new user of CAESAR and to satisfy my own curiosity I ran some very simply models so that I could compare the results to hand calculations. All of the results were as expected, except for the maximum 3D stress intensity – I was unable to achieve the solution that CAESAR produced. The technical reference indicates:

3D Maximum Shear Stress Intensity (Default)
SI = Maximum of:
S1OT - S3OT
S1OB - S3OB
Max(S1IT,RPS) - Min(S3IT,RPS)
Max(S1IB,RPS) - Min(S3IB,RPS)

The model i used was a cantilever consisting of ten 100mm lengths of DN100 STD A106 B pipe. The fluid had an SG of 1. The case under which i performed the calculations was the sustained case (W+P1). The pressure was 200kPa.

The result that caesar lists appears to simply be the sum of the axial pressure stress and the maximum bending stress. However in this case i believe that the result should be determined at the bottom outer surface. In this situation the summation of the longitudinal stresses would be negative (thus becoming S3). So S1-S3 = hoop stress - (longitudinal stresses). I tried many different conditions and never managed to obtain the same results as Caesar.

Could someone please explain how caesar gets these results because then don't seem to agree with the formulas in the reference manual. Also please let me know if you can see some obvious misunderstanding on my part.

Thanks in advance

I dusted off a MathCAD check that I ran a while back. Here's a copy of the work. Hopefully it will address your issue. Let me know if not.