Structural Action of R.C.C Two-Way Slab

RCC Slabs comprise flat or floor surfaces of a building. It is very important as a civil engineer to know some of basic of working in every structural element. We will discuss concrete two-way slab today.

Irrespective of the code you follow and minimum reinforcement implemented, it is essential to know why is the reinforcement provided in so and so pattern & where you have to provide.

Two-way slabs are slabs that transfer loads along two directions; both X and Y direction of the slab. These are slabs that are supported continuously on its four sides. As these slabs, transfer loads in X and Y direction, they undergo bending in both the directions as shown in the figure-1 below.


Fig.1. Bending Action and Reinforcement Details of Two-Way R.C.C Slabs


The bending of the slabs in both the direction makes the bottom portion to be in tension and top portion in compression. As concrete is weak in tension, and the bottom fiber portion of the slabs takes more tension, we introduce reinforcement in the below portion to take tensile stress.

As a two-way slab undergoes bending in both the direction, we provide main steel or tension reinforcement along both the direction. This is also called as bottom reinforcement.

We also provide distribution reinforcement on the top portion of slab in order to take shear stresses if any originated in the slabs.

Fig.2. Load Transfer Pattern in a Two-Way Slab to the Beams


As shown in Figure-2 above, the loads coming over a two-way slab above is taken to the Beams A and Beams B in a triangular pattern towards beam A and in a trapezoidal pattern towards beams B.

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