The method of design for the given equivalent moments is adopted in the Dutch code NEN 6720 (section 7.3.2).
The following algorithm is a simplification of the Wood& Armer algorithm.
When calculating reinforcement of a slab structure or activating the option of panel design for simple bending in a shell structure, design moments are calculated according to the NEN code (formulas are given below).
Determination of the moments M xd *, M yd * with a greater impact on top reinforcement ( + ).
M xd * = M x + |M xy |
M yd * = M y + |M xy |
Determination of the moments M xg *, M yg * with a greater impact on bottom reinforcement ( - ).
M xg * = M x - |M xy |
M yg * = M y - |M xy |
Analogously, design forces are calculated from the formulas given below for a plane stress structure or for the activated option of panel design for compression/ tension in a shell structure.
Calculation of tensile forces N xr *, N yr *.
N xr * = N x + |N xy |
N yr * = N y + |N xy |
Calculation of compressive forces N xs *, N ys *.
N xs * = N x - |N xy |
N ys * = N y - |N xy |
For complex stresses (shells with the activated option of panel design for bending + compression/ tension), with bending moments (M xx , M xy , M yy ) and membrane forces (N xx N xy , N yy ) acting simultaneously, there is no simplified algorithm devised. Since it is often the case that the modeled shells work almost as slabs (with slight membrane forces acting), therefore the possibility to calculate moments M xd *, M yd * according to the method presented still remains and these design moments are superimposed with longitudinal forces N xx , N yy .