What is one way slab? its 6 Design Considerations
The slab is supported to the two opposite sides RCC beams responsible for carrying the slab load along one direction.
In one way, sab the beams length difference is vast, so the load will not transfer toward the shorter RCC beams. In these slabs in one direction, the primary reinforcements were provided.
According to Indian standard (IS 456:2000), the slab must have a,
- The longer span divided by
- To shorter span must
- Equal or greater than 2.
Formula:
One way slab = Longer span /Shorter span ≥ 2
In those slabs, the primary reinforcement was provided in a shorter span, and in the transverse direction, the distribution bars were provided.
Design consideration of one-way slabs:
The design consideration is essential in constructing this slab to get maximum strength and minimum deflection (In between limits). Therefore, the area of steel and the thickness of the slab is to be determined according to the conditions given below.
(a) Effective span (cl.22.2 of IS 456)
According to the slab boundary condition, the effective span of the slabs was determined. In the given below table (Table 1.0), the supports condition and the practical span guidelines are provided.
In this (Table 1.0), the Effective span of the slabs was to be determined according to (cl.22.2 of IS 456)
| Slr.No | Support condition | Effective span |
| 1 | With its supports the simply supported will not build integrally. | Lesser the (a) clear span of slab + the effective depth, and (b) the support of center to center. |
| 2 | If the clear span 1/12th is greater than the width of the support than continuous ( Width of supports < 1/12th of clear span) | same
|
| 3 | Continuous when If the support width is greater of the 1/12th of clear span or 600 mm.
(i) If one end continuous and the one end is for intermediate spans, (ii) If one end is continuous and the one end is free, (iii) Spans with rock bearings or may on the roller. | (i) Clear span of slab b/w the slab supports.
(ii) The clear span of sab + half of the slab effective depth. or (a) Slab clear span + half of the discontinuous support width. (iii) The distance b/w the centers of bearings
|
| 4 | The cantilever slab having an end continuous. | Up to the center of support length. |
| 5 | Cantilever span only | Up to the face of the support span length + half of the slab effective depth. |
| 6 | Frames | Centre to center distance |
(b)The slabs effective span to its effective depth ratio (cls.23.2.1a-e of IS 456)
The one-way slab deflections will always be under limits if the ratios of the effective span of the slabs to its adequate depth are to be chosen within the limits and provisions mentioned in (cl.23.2.1a-e of IS 456). Therefore, the beam’s stipulations are also applicable to these slabs, and they are considering it design them as the beam of unit width.
(c) Nominal cover (cl.26.4 of IS 456)
Mainly the nominal cover of the slabs is totally dependent upon the fire resistance requirements and durability. In the IS 456, Table 16 or 16A provides these values. According to the structure requirements, the proper nominal cover was provided.
(d) Minimum reinforcement (cl.26.5.2.1 of IS 456)
According to IS 456, the minimum reinforcement shall not be less than 0.12 and 0.15 % of the total mild steel (Fe250) cross-sectional area, and the deformed steel bar has high strength (Fe 415 and Fe 500)/welded fabric wire, respectively.
(e) The maximum diameter of reinforcing bars (cl.26.5.2.2)
The reinforcement diameter use in one-way slabs will not exceed 1/8 of the total slab depth.
(f) Maximum bars distance (cl.26.3.3 of IS 456)
The horizontal spacing between the parallel main steel bars is always less than three times the slab’s adequate depth, or a maximum of 300 mm.
The spacing shall be less than five times the slab’s adequate depth, or 450 mm in the distribution bars.
One Way Slab Reinforcement Detail
The diameter of the reinforcements and the spacing of bars are to be used according to the (cls.26.5.2.2 and 26.3.3 of IS 456).
The quantity of reinforcement along the large span of the slabs shall be as per (cl.26.5.2.1 of IS 456).
In the shorter span, the primary reinforcements were provided because the bending moment will be high in a shorter span.
In the longer span, the distribution bars will be provided for the purpose of load distribution purposes. We also have discussed the difference between main and distribution bars in a separate topic you can also check.
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