In reality, sandwich-voided slabs are ribbed slabs with a slab placed both on their upper and lower surface.
Sandwich slabs may have the disadvantage of a larger weight compared to the ribbed ones but on the other hand, they have the advantage that their spans and supports behave in the same proper way. Their construction is more demanding than that of the common ribbed slabs but at the same time, they have the advantage of a uniform, solid lower surface.
As shown bellow, the only difference between the prior mentioned ribbed slab left as it is and the prior mentioned ribbed slab but calculated and constructed as a sandwich slab, is the differ-ent sections.
Generally, it is advised to use sandwich slabs only in cases of large slab thickness.
Reinforcement details of a sandwich-voided slab