A two way slab is supported by beams on all four sides and has a ratio of longer to shorter span of less than 2. It has reinforcement in both directions. The design process involves preliminary sizing based on deflection criteria, analysis, sizing of reinforcement in the shorter direction as a singly reinforced section, checking for shear and deflection, and detailing of reinforcement including development length and torsion reinforcement.

1. Two way slab

2. Two way slab
 Two way slab is supported by beams in all four sides.
 The ratio of longer span to shorter span (Ly/Lx) <2
than it is call two way slab.
 Main reinforcement is provided in both direction
incase of two way slab.

3. Cont.
 Load distribution in slab

4. Types of two way slab

6. Design steps for two way slab
 Step 1: Preliminary Design.
 Find depth of slab using deflection control criteria.
 Take span/d = 28 for simply supported slab and 32 for
continuous slab.
 D ≥ Dmin = 100mm for normal design and 125mm for
earthquake resistant design.
 Step 2: Analysis of Slab.
 Slab is analyzed by IS code method. (Ref. Annex D-1
and Annex D-2).

7.  Step 3: Design of Slab.
 Verify depth of slab ‘D’.
 Determine ‘Ast’ and ‘Φ’ and number of bars in shorter direction of
slab.
 Slab section is normally designed as Singly Reinforced Under
Reinforced Rectangular Section.
 Ast = Mu/(0.87fy(d-0.416xu)) which should not be less than
Astmin.
 Check slab for shear in shorter direction.

8.  Step 4: Check slab at limit state of serviceability in
deflection in shorter direction.
 l/d ≤ αβγδγ
 Step 5: Detailing of reinforcement:
 Curtail/bend the surplus bars as per detailing rules of code. (Ref.
Annex)
 Check development length at support.
 Ld ≤ 1.3Ml / Vu + ld
 Provide torsion reinforcement at the discontinuous edge of slab
as per codal provision.