Ann: Second Quarter Activities Report, page-38

Really the rebar is designed to shear in a earthquake? The raft slab in severe earthquake design is normally designed to float and slide on a loose bed unless it is also piered into the underlying soil and it may well be the piers that at a certain amplitude are designed to fail and allow horizontal movement . I wouldn't have thought any steel in the raft would be designed to fail in a earthquake as result would not be predicatable especially with masonary building above slab. . The rib raft slab gains strength by depth of rib design with tension on top slab hence top steel and compression in ribs so little rebar but a complete ring beam and able to hold flat shape even if soil underneath it changes downwards. Along weight bearing internal walls it would probably be specified for thicker rig and steel in the bottom IMO but year there is a lot less steel in any of these engineered systems and it has to be places exactly and poured exactly by experienced crews to meet original specs. NZ has had a whole revamp with earthquake design and I am not up to date . I'll have a read.