Construction Cost Estimating


Details about proper thickness of a concrete slab

The loads and size of the slab are the two prime factors upon which the thickness of concrete slab relies. Normally, 6 inch (150mm) slab thickness is ideal for residential and commercial buildings with reinforcement details as stated in the design. Methods which determine the thickness of slab change for several types of slabs. As for instance, the computation process for finding out the thickness of one way slab varies from that of two-way slab.

The selection and calculation of slab thickness together with various types of slabs are considered as a crucial step in the design process. By pursuing the exact calculation method of a slab thickness, the design period is curtailed significantly, apart from maintaining consistent and inexpensive slab thickness.

Thickness of One-way Slab - The thickness of one-way slab is dependent on Deflection, Bending, Shear, and seldom fire resistance requirements.

1. Deflection Requirements

Except for slabs which are loaded intensely, as for example slabs bear numerous meters of soil, the slab thickness is chosen on the basis of deflection requirements. The restriction on slab thickness is set by the ACI code until deflections are measured and decided for being acceptable.

Conversely, thickness of one-way slabs should be minium L/20 for simply supported slabs; L/24 for slabs having one end continuous; L/28 for slabs having both ends continuous; and L/10 for cantilevers; where L stands for the span.

These values will be applicable on the condition that the slabs are not supporting or joined to partitions or other structures likely to be damaged with large deflections.

2. Bending and Shear Requirements

Determination of slab thickness depending on the bending and shear requirements is not recurrent. Though, these requirements should be verified in the design even when the thickness is chosen on the basis of deflection requirements.

Method for verifying slab thickness for bending requirements are provided below:

1. Work out trial factored loads depending on the slab thickness calculated on the basis of deflection requirements.

2. Calculate moments with appropriate methods like ACI Coefficient Method.

3. As the slabs seldom need reinforcement ratio more than 0.01, verity whether chosen slab thickness is sufficient for reinforcement ratio of 0.01.

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Details about proper thickness of a concrete slab