One way slab and Two way slab

 

R.C.C. slabs are plane structural member which is used as floors and roof coverings in buildings. Slabs support mainly transverse loads and transfer these loads to supports by bending action in one or more directions.

CLASSIFICATION OF SLABS

On the basis of ratio of long span to short span. R.C.C. slabs are classified into following two types :

 

OneWay Slab

The slabs in which the l_y/l_x (ratio of larger span to shorter span) ratio is greater than or equal to 2 are called one way slab. These slabs are called edge supported slabs (i.e. slabs supported on two opposite parallel edge/walls).

Hence a slab will be called as one way slab in the following two situations :

(a) Slabs supported on two opposite parallel edges only shown in fig.

(b) Slab supported on all the four edges and l_y/l_x (is equal to 2 or greater than 2)

 

One Way Slab

reinforcements in one way slabs : There are two types of reinforcement provided in one way slabs.

      A.    Main reinforcement

      B.    Distribution reinforcement

 

(A) Main reinforcement : Main reinforcement is provided parallel to the shorter span. Main reinforcement is provided to resist the bending moments due to transverse loads coming on the main slab.

 

(B) Distribution reinforcement : Distribution reinforcement is provided in a direction perpendicular to the direction of main reinforcement (i.e. parallel to larger span). These bars are normally not provided with hooks (even if mild steel is used). The distribution steel bars should be tied above the main steel bars. Otherwise the lever arm (which is measured upto the center of main steel) shall be reduced resulting in the reduction of moment of resistance.

 

Distribution reinforcementis provided for the following purposes :

I.       To distribute the concentrated loads coming over the slab.

II.     To resist shrinkage and temperature stresses.

III.   To keep the main reinforcement in position.

 

Two Way Slab

The slabs which are supported on all the four edges and having l_y/l_x (ratio of larger span to shorter span) less than 2 are called two way slabs. Two way slabs are also called as slabs spanning in two direction because bending take place in both the directions. Therefore, the main reinforcement is provided along both the directions in a two way slab.

 

DIFFERENCE B/W ONE WAY SLAB OR TWO WAY SLAB

Sr. No.	ONE WAY SLAB	TWO WAY SLAB
1.	Longer span/Shorter span greater than 2 or equal to 2.	Longer span/shorter span is less than 2.
2.	Bending take place along shorter span only.	Bending take place along both the span.
3.	Main reinforcement is provided along shorter span.	Main reinforcement is provided along both the span.
4.	Distribution steel is provided along longer span.	No distribution steel is provided
5.	As thickness of slab and amount of steel required is more, therefore, less economical as compared to two way slab	As thickness of slab and amount of steel required is less, therefore, more economical as compared to one way slab