A case study on how SACS reports the UC ratio of individual bending components of a tubular section.

 

R:

For this, we are using a test model shared by one of our users. The following is reported in SACS. The probable confusions are marked in RED in the snap.

It seems the UC ratio of bending Y and Z calculations is not in line with the conventional method.

Let us focus on the combined UC which is is reported as 0.41. To begin, we will validate this value.

Referring to API RP 2A, 21st Edition, Equation 3.3.1-3, the combined UC is calculated as ([84.08^2+37.64^2] ^0.5)/225, which results in 0.41. Therefore, this calculation aligns at this stage.

Now, if we analyze the API code, it does not mention individual bending UC ratios, as reported by SACS in the Redesign window. Since the allowable bending stress is distributed along the Y and Z axes, the component UC can be interpreted as the proportion of stress contributing to the UC. SACS employs an algorithm for calculating individual UC components based on the projected length of a triangle.

 

Here, d and e represent components derived from contributions of a and b respectively, with d = a^2/c and e = b^2/c therefore ucy = 84.08^2/92.12/225 = 0.34 and ucz = 37.64^2/92.12/225 = 0.07.