Suspended Concrete Slabs – Everything You Should Know

Concrete slabs that do not come into contact with the ground can be differentiated into two types and Sephaku Cement is here to explain how suspended concrete slabs vary from ground concrete slabs.

Ideally used in roofing or floors that are suspended above ground level, while these are the two most common uses of suspended concrete slabs, these floating concrete fittings have also been used to create some of the more striking suspended or cantilevered concrete staircases and other decorative features.

Suspended concrete slabs are differentiated into two types of fittings, namely:

  • Suspended concrete slabs supported on two sides known as one-way slabs
  • Suspended concrete slabs supported on all four sides referred to as two-way slabs

Much in the same way that ground concrete slabs are made using a reinforced steel framework, suspended concrete slabs can be pre-cast or poured to fit the suspended structure. What’s more, both ground and suspended concrete slabs share very similar benefits and advantages including:

  • Energy-efficacies through their favourable thermal properties
  • They offer an excellent sound barrier between different levels and floors
  • Affordable, low maintenance, and lasting durability

Differentiating between a One-way Slab and A Two-way Slab

In order to determine the difference between a one-way slab and a two-way slab we must examine the span of the slab by dividing the length of the longer span by the length of the shorter span of the slab.

A one-way slab span will be determined by a span that is greater than or equal to two (2).

For example:

Longer Span / Shorter Span
10 meters / 4 metres = 2.5

A two-way slab span is determined by a span that is less than two (2)

For example:

Longer Span / Shorter span
5 meters/ 5 meters =1

So, what does this mean?

Because of the difference in span ratios between a one-way slab and a two-way slab these suspended concrete slabs’ load-bearing ability will differ and result in varying main reinforcements.

One-way Slab

The load placed on a one-way slab will run predominantly along the shorter span of this suspended concrete slab while pressure is still placed along the longer span of the slab, the load magnitude is therefore much less compared to the load pressure placed on the shorter span. As a result, the main reinforcement of a one-way slab is provided for in only one direction, running in the same direction as the shorter span, which helps to resist the moment demand. To prevent shrinkage stress experienced on this suspended slab, temperature reinforcements are placed in the opposite direction, running along the longer span of the one-way suspended slab.

Two-way Slab

The load placed on a two-way suspended concrete slab is carried equally, running in both directions of the short and longer span (where the ratio between the two is 2 or less), as a result, in order to adequately reinforce a two-way suspended slab, the main reinforcements run along both directions of the two-way slab both short and long, equally disbursing the load-bearing capacity throughout the slab.

Outside of incorporating steel reinforcements to the above two suspended concrete slabs, there are also a handful of different design options that enhance the strength to weight ratios of concrete slabs which we will explore in a future post.

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