RCC stands for Reinforced Cement Concrete, hence RCC stairs are the stairs in which RCC is used as the material. Nowadays, RCC stairs are used almost everywhere, be it a house (domestic), hospitals (public), or office buildings (commercial). Given the properties of RCC, these stairs are strong as well as fire-resistant. This fulfills the requirements of a good stair.
Most RCC stairs are cast-in-situ, which means the shape of the RCC is given at the site itself pouring the fresh concrete onto the formwork.
Now based on the direction of the RCC slab, which supports the steps within a flight, the stair is categorized into two main categories.
- Stair with slab spanning horizontally
- Stair with slab spanning longitudinally
Let’s discuss few more details about each category.
Stair with slab spanning horizontally
As we know, stairs are sloped along their length, while the width of the stair lies in the horizontal plane. When the slab of the stair spans along this horizontal width the stair must be supported at one side by a wall or a stringer beam and with a stringer beam on the other side. Few points to be noted about slab spanning horizontally are as follows.
- Effective span L of the slab is the horizontal distance between centre to centre of the supports (wall or stringer beam).
- Each step is designed as spanning horizontally with length L, and width b of the step measured along the pitch/slope of stringer.
- The design moment for the slab is WL2/8, where W is the uniformly distributed load(udl), per unit area, on the step, inclusive of the self weight of the RCC.
- The effective depth d of the slab equal D/2, where D is the D is measured from the corner of a step, as shown in the image below.
- The main reinforcement is provided along the span length L, while the ditribution steel is provided along parallel to stringer beam.
Stair with slab spanning longitudinally
In this category, the slab is not supported on sides, but at the top and bottom of each flight, or at landings. Hence, here the span of the slab becomes quite long. The beams are provided as support to the slab, at the top or bottom of the flight, or landings. In case, the support is provided at the landings, then the landing also becomes a part of the slab. Dog Legged stairs are the typical example of such supports at landings. Few things to be noted about this category of RCC stair are as follows.
- Effective span L of such a RCC is to be measured along the flight length.
- The main reinforcement is provided along the flight.
- Distribution reinforcement is procided along the width of the stair.
Other Category
Sometimes, in rare cases, when the stair width is quite large, a central stringer beam is provided on which the stairs slab is supported. The stringer beam acts as a T beam and the waist slab is designed as a cantilever on both sides of the stinger beam.
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