When using shells in concrete design of a slab, should the absolute value of M13 be added to M11 and M33 when determining what moments to use for reinforcing design? I'm referring to the Wood and Armer method.
Wood and Armer method:
Determination of the 'lower' moments M xd *, M yd *.
M xd * = M x + |M xy
M yd * = M y + |M xy |
However, if M x < -|M xy | (i.e. the calculated M xd * < 0)
M xd * = 0
M yd * = M y + |M xy *M xy /M x |.
Similarly, when M y < -|M xy | (i.e. the calculated M yd * < 0) → (*)
M xd * = M x + |M xy *M xy /M y | → (*)
M yd * = 0 → (*)