Minimum Thickness of Concrete Beams and Slabs

One of the common mistakes being committed by some builders, who rely on experience and not on structural calculations, is not observing the minimum thickness or depth of concrete beams and slabs specified in the code.

The code specified minimum thicknesses for different types of support in order to prevent excessive deflection or sagging on site.

NSCP 2010 states the following...

...where L is the length of beam or one way slab and the denominator is the dividing factor. Length in beams is obvious. It is simply the center to center distance of the columns that support the beam. In one way slabs, however, the design length is not the longer side of the slab. It is wiser to design one way slabs considering the shorter side. For example, if you have a 2m x 4m slab, we take the 2m as the length of the slab and design it as a 1m-wide strip beam.

Example: Calculate the minimum thickness of 6m long beam with both ends continuous.

Given:

     Type of Structure:    Beam
     Type of Support:      Both ends continuous
     Length of beam:      6m

Solution:

     Based on the table, the minimum thickness for a beam with both ends continuous is L/21.

Therefore:

     T = L/21
        = 6m / 21
        = 0.286 m or 286 mm

Here is the program that automatically calculates minimum thickness of concrete beams and slabs:
Click here and download the file -> Concrete Beam and Slab Thickness Calculator