Min. temperature and shrinkage reinforcement - Composite Slabs

The Vulcraft areas are less than .0018 x (area above the flutes). Maybe they are basing those areas on experience?

Code minimum values are not always conservative. For any mass concrete structure with displacement prevented (e.g. foundation slab) on an edge, or for other structures with strong restraints to expansion along several surfaces, the tensile stress due to combined shrinkage effects and thermal gradients may govern the rebar design. Codes, including Eurocode (and "CIRIA C660 Early-age Thermal crack control in concrete") provide equations to estimate these effects, as do some software. Vulcraft has probably performed tests and calculations and considered worst-case boundary conditions to arrive at their recommended minimum values for rebar.