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Design of ground-supported floors

Traditionally ground-supported floor slabs have been designed by elastic methods, using equations developed by Westergaard in the 1920s that are still widely used. These design methods tend to be conservative and so the slabs produced are relatively thick and so assessment of deflections and other in-service requirements has not been necessary. As plastic methods of analysis have developed, so slabs have become thinner and factors such as deflections, load transfer across joints and crack control have to be considered as well as the load capacity of the slab.

The design approaches given in Technical Report 34, Concrete industrial ground floors consider both the ultimate and serviceability conditions.Equations are provided for:

• bending capacity under point loads,line loads and uniformly distributed loads
• load transfer across joints
• punching around concentrated loads
• deflections.

Slab design for bending is based on yield line theory. A principal requirement in the design of ground-supported slabs is the avoidance of cracks on the upper surface. Hence the moment capacity along the hogging yield lines is limited to the design cracking moment of the concrete. Punching is based on the approach for suspended slabs.

Acknowledgement: The Concrete Society

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Concrete for industrial floors
- guidance on specification and mix design - GCG1

TR34 Concrete industrial ground floors
a guide to design and construction - 4th Edition

Concrete industrial ground floors – user expectations