Minimum thickness of concrete slab

Least thickness of concrete slab, beam, column, foundation and other structural members is required to fulfill the design requirements with adherence to the standard codes. Least thickness of concrete structural components depends on ACI 318-14, IRC 2009, IS 456 2000, and UBC 1997.

The design process comprises of perfect guess of the sizes of structural components. After that, the recommended dimensions should be verified to ensure that it fulfills the requirements of the design.

When exact structural dimension is not taken, then lots of time and hard work are required for the design as considerable trials will be necessary unless agreeable dimensions are indicated.

As a result most of the codes offer minimum dimensions and specially thicknesses for almost all structural components.

a. Minimum Thickness of Slabs
b. Minimum thickness of One-way slab

As per ACI 318-14 recommended minimum thickness for one-way solid slab unless deflections are given below :-

Minimum thickness is denoted as h. - For Simply supported = I/20 One end continuous = I/24 Both end continuous = I/28 Cantilever = I/10

Notes: The values provided should be utilized directly for members with normal weight concrete and Grade 420 reinforcement. For other conditions, the values should be altered as follows:

a) For lightweight concrete with equilibrium density (wc) in the range of 1440 to 1840 kg/m3, the values should be multiplied with (1.65 – 0.0003wc) but not below 1.09.

b) For fy apart from 420 MPa, the values should be multiplied with (0.4 + fy/700).

Least thickness of Ribbed slab: As per ACI 318-14 code, the value of non-prestressed beams is equivalent as above. According to Unified Building Code (UBC), the least thickness of ribbed slab should be 1/12 distance among ribs or 51mm.

Slab thickness with implanted conduits and pipes

• As per UBC, least thickness of slabs with implanted conduits and pipes should be 25mm over and above entire overall depth of conduits or pipes.
• As per ACI 318-14 code, the conduits and pipes should not be greater in outside dimension than 1/3 the overall thickness of slab, wall, or beam in which they are implanted.

Least thickness of Slab on the ground: As per UBC, least thickness of Concrete floor slabs which rest directly on the ground should be 89mm, while BCGBC4010A employ structural principles to residential low-rise constructions that the minimum thickness should be 100mm.

Least thickness of Diaphragms: As per UBC, suggested concrete slab and composite topping slab which function as structural diaphragm for transferring earthquake forces should be 50mm.

Least thickness of Two-way slab: To obtain least thickness of slabs (along with slabs with beams, flat slabs, flat plates) with adherence to ACI 318-14 code, click on the following link theconstructor.org

Least thickness of Drop panel: Sometimes drop panels are utilized at top of columns to enhance the shear strength of slabs. The least thickness of drop panels should be quarter of slab thickness beyond the drop.

To get detail information on least thickness of Beam, Column and Foundation, go through the following link theconstructor.org