Abnormal Member UC on Cone Segment


I have run a topside in-place analysis using ISO code and the result of the analysis showed that the topside leg, especially on cone segment having UC>1.00. Based on the member review, i found out that the member actual stresses were less than allowable stresses in member details, but the UC generated is more than one. is it a bug? or SACS is not capable to design the cone section using ISO code? Appreciate if one can advice on it. Thanks.

  • This isn't a bug, but the reported allowable bending stress for LRFD code checks can be a bit difficult to report (See https://communities.bentley.com/products/offshore/w/wiki/40856/allowable-bending-stress for an example) because we are really using load capacity checks which don't have a definitive allowable stress in the calculations. The allowable stresses are "equivalent" allowable stresses which are supposed to be representative of the capacity for certain failure modes. For the particular case of cone sections, the reported axial allowable stress is based upon the equivalent tubular section checks (Equations 13.2 of ISO 19902). You can see this more clearly if you view the Detailed Report which gives the equivalent allowable stress calculations and the controlling failure mode. This cone is failing through a different mode, junction yielding, from section which is why the UC ratio doesn't match the actual/allowable ratio.



    Answer Verified By: Frans