concrete building in sdc d

huangyhg

concrete building in sdc d
hi,
i am designing a building: 200ft tall and falls in sdc d.  asce 7-02 section 9.5.2.2.4.1 permits 240ft tall building with specially reinf. concrete shear walls resisting < 60% of total shear.  this would imply the use of other slrs, such as ordinary concrete moment frame, etc.
it has been my experience that the most economical structural system for this kind of structure is to utilize flat slab pt + shear walls.  however, due to seismic requirements as described above, we have to provide a secondary system for ductility, which means 'moment frames'; and since additional formwork will be required already for slab-beam forming already, it sounds like the way to go is with specially reinf. concrete shear walls + special moment frames = dual system, with higher r.  is this the right way to go?     
i am hoping to collect some professional opinions of how you have dealt with this situation in the past.  all inputs are greatly ppreciated.