Rib offset of ribbed-waffle slabs cannot be more than 70cm (T.S. 500 11.3.2)
According to TS500 11.3.2 for rib and waffle slabs, the free space between Rib can be maximum 70 cm in Ribbed slabs. Warning is given when this range is more than 70 cm.
Possible solutions:
Entering rib spacing less than 70 cm for ribbed or waffle flooring.
Changing the slab type.