Slab reinforcement details should be prepared following relevant codes of practice and standard methods for reinforcement detailing.
There are mainly three types of in situ concrete slabs.
- Single track fixing plates
- Two-axis boards
- Cantilever plates
In general, similar requirements apply to one-way and two-way slabs when preparing detailed slab reinforcement drawings.
Let's discuss the requirements specified in the design code for the slab reinforcement details.
The following slab reinforcement arrangements are given in BS 8110 Part 01.
- Minimum percentage of reinforcements
Provides a reinforcement area of 0.13%. (100As/Ac = 0.13)
- Anchoring Rods to a Simply Supported End
If the maximum shear stress in front of the column is less than half the corresponding Vc value, a straight length of rod beyond the centerline of the column equal to one third of the column width or 30 mm (whichever is greater) should be used It is).
- Bar spacing
The free distance between the bars must not exceed the value of 3d or 750 mm, where d is the effective depth.
Detailing rules could also be applied according to Eurocode 2.
As stated above, lap spacing must be maintained and the distance between overlapping bars must not be less than 50 mm or 4∅, whichever is less. Where ∅ is the diameter of the rod.
- Crack control – if crack widths are not verified by calculations No further check is required
a) The depth of the plate does not exceed 250 mm if the steel grade is 250
b) Plate depth is maximum 200 mm with a steel grade of 460
c) Proportion of slab reinforcement less than 0.3% (100As/bd < 0.3%
If conditions a, b and c above do not apply, the bar spacing shall be limited in accordance with the following table (Table 28 of BS 8110 Part) if the reinforcement ratio exceeds 1% or the values given in Table 28 divided by the booster portion for smaller amounts.
- Spacing of shrinkage ribs
The details of the slab reinforcement are the same as those of the wall reinforcement as specified in clause 3.9.4.19 of BS 8110.
For grade 460 steel, 0.25% of the cross-sectional area of the concrete must be provided.
- Simplified rule for slab reinforcement details
Simplified rules can be applied when creating detailed drawings for slab reinforcement if the following condition is met.
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- The plate is designed for evenly distributed loads
- For continuous slabs, the design loads are approximately the same
The following figure is taken from BS 8110 for reference.
As stated in BS 8110 above, the reinforcement plate must be 0.3 x span (from the face of the column) to ensure continuous support. However, the steel surface must be continued 100% up to 0.15 x span.
This can be achieved using an alternative bar arrangement as shown in the following figure.
Otherwise, we could continue the upper reinforcement at an average of 0.25 x span (from the support surface). This is not specified in the guidelines, but we can consider it for simplicity.
- Slab reinforcement details at boundary edges
The reinforcement arrangement follows the standard IStructE structure detailing method.
The details below show the tension anchor lengths and additional reinforcing bars at the edge.
Additionally, the following details are relevant to Eurocode 2.
The Slab Sizing article could be used in relation to the design aspects of slab reinforcement.
