Calculation without Slippage
If no BBR is specified for the outermost coating then no slippage is assumed to occur and the algorithm for calculating bending moments from given curvatures and tension is the same as that described already for bare pipes, with the exception of the following adaptions:
i.In the case of Steps 2a to 2d, each slice now has a series of individual stresses for the different layers contained within the slice, see typical slice example in the figure below. These individual stresses inevitably vary depending on the material properties of the layers and so this results in different force values across the slice that need to be summed together to get overall representative forces (both bending and total axial) for the slice.
ii.If some of the coatings have anisotropic stress-strain behaviour, as is the case for concrete, then the neutral axis is to shift even without the specification of an input tension value and so some level of neutral axis iteration is generally needed.
Typical Slice across a Mulit-Coated Pipe Section
The points above are based on the assumption that the coatings have been assigned their own mechanical properties. If no such properties are defined then the contribution of the coatings to moment-curvature is ignored.