This document discusses two-way slabs, which are supported on all four sides or at column centerlines. It describes two main types - edge supported slabs and column supported slabs. Edge supported slabs are suitable for spans of 20-30 feet and live loads of 60-120 psf. They have increased stiffness and low deflection. Column supported slabs include flat slabs and two-way ribbed/waffle slabs. Flat slabs have no beams or column capitals and are suitable for spans of 20-30 feet. Ribbed and waffle slabs have reduced dead load and architectural beauty, with spans of 30-48 feet and live loads of 60-120 psf. The document also discusses minimum

1. Dhaka university of engineering and technology,
Gazipur
TWO WAY SLAB
Prepared by
MD. AMINUL ISLAM(CE-32
MD. ABUHENA BASHIR(CE-32)

2. TWO WAY SLAB
# Supported by beam in four side or coloumn centre line.
# deflection = Dish shape.
# L/B <2.
# load transfer in both short and long direction.
# carries more load than one way slab.

3. Types of two way slab
Two types :
1.Edge supported
2.Coloumn supported

4. Edge supported slab:
#suitable span 20 to 30 ft
& live load 60 to 120 psf.
#increase stifness
#low deflection

5. Coloumn supported slab.
Flat slab:
a.suitable for span 20 to 30 ft,
&load 80 to 150 psf

7. Coloumn supported slab
• Flat plate floors:
# flate ceiling.
#no beams,coloumn capital .
#low shear capacity ,low stifness.
#fails on punching shear.
#suitable for span 20 to 25 ft.
& live load 60 to 100 psf.

8. Coloumn supported slab.
Two way ribbed and waffle slab system:
# L/B < 2
#slab thickness about 2 to 4 inch
# rib spacing about 20 to 30 inch.
#reduce dead load.
#architectural beauty
#suitable span 30 to 48 ft
& live load 60 t0 120 psf.

10.  In fig let us assume , it is consist of 2 sets of parallel strips ,
in each of 2 direction , intersecting each other.

11. maximum deflection equation

12.  Equating the center deflection of the short & the long strips
gives
Consequently ,

13. Minimum thickness
• The equation of determinate thickness on the
basis on αfm , αf = (Stiffness of beam/Stiffness of slab)

14. Minimum thickness
(β= ln/ls )
• In Bangladesh usually used in 125mm slab thickness
• According to B.N.B.C the minimum thickness of slab is 100mm

15. Minimum reinforcement
• For two way slab rmin should not be less
than temperature and shrinkage bar

16. Corner reinforcement
 Corner reinforcement are used in exterior corner of two way edge supported slab only
 In slabs which are restrained along the edges and are not free to lift, cracks as shown
below get developed at the corners because of the high torsional moment. We need to
prevent such types of crack formations in the slab and thus reinforce these sections by
providing reinforcement.
 Spacing of corner reinforcement should be used same as minimum spacing of main bar.

17. Design methods of two way slab
I. ACI co-efficient method
II.Direct Shear design method
III.Equivalent frame method
IV.Strip method
V.Yield line analysis method