One Way and Two Way Slabs


                                        One-way Slab

  • One-way slabs, supported by parallel walls or beams, bend in only one direction and transfer their loads to the two opposite support walls or beams.

  • Even when a rectangular slab is supported on all the four edges, the slab may be considered as a one-way slab if the length-to-breadth (L/B) ratio of the slab is equal to or greater than two.

  • A one-way slab is designed for the spanning direction alone; the main tension reinforcing bars of such slabs run parallel to the span. For the transverse direction, a minimum amount of shrinkage reinforcement is provided.

  • One-way slab action is assumed in a ribbed floor (slab with joist beams) made of precast double-tee sections, in a ribbed floor with integral beams, and also in hollow-block or -cored slabs.

Plan view of one-way slab (a) Supported on two opposite edges
(b) Supported on all edges (L/B > 2)

Two-way Slab

  • When the ratio of long side to short side of a slab is less than two, it is called two-way slab.

  • The panel will deflect in a dish- or saucer-like form under the action of external load and its corners will lift if the slab is not monolithically cast with the supports.

  • Two-way slabs are designed to transfer their loads to all the four support walls. A slab supported on three edges or two adjacent edges may also be considered as a two-way slab. The load gets divided in the two directions, depending on the ratio of the sides.

  • Two-way slab behaviour is assumed in a waffle floor and in a waffle floor with integral beams. In waffle slabs, also called two-way ribbed slabs, ribs are provided in both directions of the span. The hollow block floor is constructed with blocks made of clay tile or lightweight concrete blocks.
Two-way slabs bend and deflect in double curvature