Slabs are constructed to provide flat surfaces, usually horizontal, in building floors, roofs, bridges, and other types of structures. The slab may be supported by walls, by reinforced concrete beams usually cast monolithically with the slab, by structural steel beams, by columns, or by the ground.
Slabs are classified into two types:
- One Way Slab
- Two Way Slab
#1 One Way Slab:
One way slab is a slab which is supported by beams on the two opposite sides to carry the load along one direction. The ratio of longer span (l) to shorter span (b) is equal or greater than 2, considered as One way slab because this slab will bend in one direction i.e in the direction along its shorter span
Due to the huge difference in lengths, the load is not transferred to the shorter beams. Main reinforcement is provided in shorter span and distribution reinforcement in a longer span.
Example: Generally all the Cantilever slabs are one Way slab. Chajjas and verandahs are a practical example of one way slab.
#2 Two Way Slab:
Two way slab is a slab supported by beams on all the four sides and the loads are carried by the supports along with both directions, it is known as two way slab. In two way slab, the ratio of longer span (l) to shorter span (b) is less than 2.
In two way slabs, the load will be carried in both the directions. So, the main reinforcement is provided in both directions for two way slabs.
Example: These types of slabs are used in constructing floors of a multi-storeyed building.
Difference between One Way Slab and Two way slab:
|One Way Slab||Two Way Slab|
|Slabs are supported by the beams on the two opposite sides||Slabs are supported by beams on all the four sides.|
|Main reinforcement is provided on shorter span due to bending||Main reinforcement is provided in both sides due to bending occurs on both sides|
|Main Reinforcement is provided in only direction for one way slabs||Main Reinforcement is provided along both the directions in two way slabs.|
|Loads are carried along one direction in one way slab.||Loads are carried along both the directions in two way slabs.|
One way Slab reinforcement details:-
From fig, it is clear that Ly/Lx = 8/3 =1 ≥ 2.66
Hence, One-way slab is adopted where Cranked bars (main bars) are provided on the shorter side of the slab due to bending. Distribution bars(straight bars) provided on the longer side as shown in fig.
Two way Slab reinforcement details:-
As per below fig, it is clear that Ly/Lx = 5/5 =1 < 2.
Hence, two way slab is adopted where cranked bars (main bars) are provided on both sides of the slab.
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