Postprocessing of Bending Moments & Stresses in the Steel Layer
The previously discussed calculations for the moment-curvature response of a coated pipe section (accounting for the various factors etc.) directly affect the finite element solution in PipeLay due to the corresponding changes in the stiffness matrix for the model. Once the solution, whether it is static or dynamic, has completed the PipeLay postprocessing must then determine output bending moments and stresses for the elements, which in turn are used for a variety of purposes such a code checking and tabular output. From an engineering perspective the moments and stresses in the steel layer are of primary interest and so the postprocessing must determine these from the overall coated moment-curvature response of the solution. The steps taken to determine the bending moments and stresses in the steel layer are as follows:
i.A moment-curvature relationship is calculated for the steel layer only (all coatings ignored), with the relevant level of tension applied (see the Moment-Curvature Calculation with a Tension Input section of this Technical Note).
ii.The steel bending moments are determined by combing the overall element curvature response from the solution with the steel only moment-curvature relationship from above.
iii.The steel bending stresses are easier to determine as the overall element curvature response from the solution can be used to calculate strain values which are then directly converted to stresses using the input stress-strain curve.