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Prestressed members in seismic zone 4

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Would appreciate any comments/suggestions.
Seismic zone 4. Structural system consists of flat slab on 30 ft by 30
ft
column grids with concrete shear walls. Flat slab is PRESTRESSED.
1. ACI code does not allow steel fy greater than 60 ksi in seismic zone
4.
2. There is no definite yield point for prestressing steel. In fact,
beyond 
   its elastic range, it has a very short range of plastic yielding and
   fails in brittle mode. Therefore, no ductile behavior and no
development
   of plastic hinges so necessary when designing for Code-specified
forces 
   in Zone 4.
3. There is a proposal for providing two-way RC band beams between
columns
   with two-way PRESTRESSED slab spanning between these beams. What is
the
   behavior of prestressed slab under cyclic loading of earthquake ?
   Thanks in advance,
      M. A. Mufti