It is apparent from viewing FIGS. 1 and 3 in combination that fold 18 acts as a beam to provide static resistance to bending. Specifically, depressed planar portion 44 acts as the lower flange of a beam. Major planar portions 15, 16 adjacent fold 18 act as the upper flanges of the beam. Inclined portions 45, 46 act as shear members connecting upper and lower flanges, and the fold thus provides stiffness to the floor slab. Thus, the fold plate construction defining an essentially upwardly concave interruption to the major supporting surface forms through its integrally connected portions a beam from the folded slab.