Slab thickness is a crucial factor in the design and construction of a building and is directly related to the cost of the structural system.
For example, in a tall building, increasing the slab thickness by 5 mm leads to a significant increase in the axial loads of the columns. So we need to increase the sizes of pillars, reinforcements, foundation sizes, etc.
Finally, it affects construction costs.
Therefore, in any project, we must limit the thickness to the limits required by the project (utility and ultimate limit state).
The main factors that affect the minimum board thickness can be listed below.
- Applied loads
- Concrete durability
- Fire safety requirements
- Usability requirements such as: B. Deflections
- Usability requirements such as: B. Ground vibrations
- Structural requirements
Different standards may specify different thickness requirements. However, taking into account the above factors, we can calculate the basic minimum thickness requirements.
The calculation is based solely on the design and detailing requirements of BS 8110 Part 01.
- The armor coverage is 20 mm, which is the minimum specified in the standard for light load conditions with a one-hour fire resistance.
- Reinforcement bar diameter = 10mm, the beam is composed of four bars with upper reinforcements.
- The minimum distance between bars is based on the aggregate particle size + 5. Generally, we use 20mm aggregate for concrete work.
Therefore, the minimum concrete thickness can be calculated as follows.
Concrete slab thickness = 20 x 2 + 10 x 4 + 20+5 = 105 mm
This is the theoretical requirement for board thickness. However, reinforcement cannot be placed with the precision calculated to maintain the distance between bars with a total size of +5.
Furthermore, the slab reinforcement is undermined by the beam reinforcement and cannot be placed as considered in the calculation.
So it's very, very difficult to meet these requirements. Limiting the thickness to 105 mm is therefore a difficult task in practice.
With this in mind, the commonly used concrete slab thickness is 125 mm.
Standards like ACI 318 define the minimum slab thickness based on the slab span.
- Simply supported plate = span / 20
- One-sided continuous plate = span / 24
- Continuous plate at both ends = span / 28
- Cantilever arm = span/10
However, in most other standards, the minimum panel thickness is not clearly specified.
