One way Slab – These types of slab are when twice the shorter span is less than the longer span, it is considered a one-way slab. It is called a one-way slab because it will bend in one direction only. (along a short span) The following figures represent the simple steps and rules for laying the reinforcement.
The figures below show the basic steps and rules for laying reinforcing bars in a one-way slab.
Put a concrete Spacer (25mm) and Lay bottom bars along the shorter span of the slab.Starting at a measured distance of L/4 on both sides, lay the bent-up bars along the shorter span. L is the slab’s clear span, measured from the support’s face to the other side.Distribute the bottom distribution bar throughout the slab’s longer span.Install top distribution bars at the L/4 distance or at the bent up bars.Install additional top bars near support of the slab. Because this is the zone where concrete is subjected to tension, the spacing of the primary reinforcing bars at the bottom midspan is the same as it is at the top near the support.Install top bars and distribution bars at the top of the midspan. The top bars must be on top of the distribution bar.
Two Way Slab – when twice the shorter span is greater than or equal to the longer span, it is called two way slab. Two way slab will carry load in both directions so the bending will be in both directions(two way bending) and the main reinforcements is provided in both directions.
The following figures are the simple steps and basic rules on how to lay reinforcing bars in a two-way slab.
Put a concrete Spacer (25mm) and Lay bottom bars along the shorter span of the slab.Lay the bottom bars along the longer span of the slab.Lay bent-up bars along the longer span of the slab from an L/4 distance from the edge. As it is seen in the figure, the main bottom reinforcing bars along the shorter span are always below the main bottom reinforcing bars along the longer span of the slab.Next to lay is the Distribution bars at the edge of the slab. Top distribution bars must be below the main bars(bent up bars).Install extra top bars(cut bars) at the edges of the slab. In the figure, the spacing of the main reinforcing bars at the bottom midspan is the same at the top near the edge or support because this is the region where concrete is subjected to tension.Lay top distribution bars at midspan. These bars are called temperature or shrinkage bars as they resist the expansion and contraction of concrete due to temperature change.
Difference between One Way Slab and Two Way Slab
One Way Slab
Supported by the beams on the two opposite sides.
Main reinforcement is provided on shorter span due to bending
Main reinforcement is provided in only direction.
Loads are carried along one direction.
Two Way Slab
Supported by beams on all the four sides.
Main reinforcement is provided in both sides due to bending occurs on both sides
Main Reinforcement is provided along both the directions.
