What are Waffle Pod Slabs and Should You Cut Them
We all like waffles, don’t we? The distinct shape of a waffle is what gives the waffle pod slab its name, because it pretty much looks like a waffle. It is a special type of slab used where large, long spans are given to support the superstructure. In this article, we will learn about what are waffle pod slabs and should you cut them.
What are Waffle Pod Slabs
Waffle pod slabs, also known simply as waffle slabs, are a special kind of slab used for constructing the floor or roof of a portion of a building where large, long spans are used.
This slab looks like a waffle from the bottom side, with holes spread over the surface – hence the name.
Why do we need waffle slabs
When you need to have a clear area in a large room, that is, you cannot use columns in the middle of the room (like in a theater), there you have to use long, strong slabs to hold up the roof (or the upper floor). Therefore, you need to use thick but light slabs running between wide beams. This is essentially why waffle pod slabs are used.
How waffle pod slabs are made
Waffle slabs are used mainly for their reduced weight at the same strength. To reduce the self-weight of the slab, unnecessary part of the concrete, which forms heaviest mass in any structure, is removed. This reduces the effective self-weight of the slab.
What is the unnecessary concrete in a slab? Well, since the tensile strength in any RCC member is satisfied by the steel reinforcement but not the concrete (the tensile strength of the steel being ten times greater than common concrete), any concrete that’s below the neutral axis of stress in the member is unnecessary.
In a waffle slab, this is done by placing clay pots (or other light removable material) inside the formwork where the concrete isn’t needed, at the time of casting the slab. The result is a slab whose effective bottom side (it is cast upside down when casting, though) will look like there are lots of big holes in the slab, in-between the reinforcements. It may look half-done and weak, but due to the steel, it is just as much strong.
Advantages of Waffle Pod Slabs
1. Stiffer and lighter than an equal size and quality flat slab/raft
2. Faster construction than flat slab of same size
3. Economic – uses 30% less concrete and 20% less steel
4. Provides low floor deflections
5. Robust floor strength and good finish
6. Results in slimmer floor depth
7. Greater vibration control than standard RCC members
Can You Cut Waffle Pod Slabs
The short answer is yes, but it is a bit complicated. Since waffle pod slabs are cast specially, you need to know what you can or cannot do with waffle slabs. The good thing here is that waffle pod slabs are quite versatile and can be placed in many kinds of architecture.
When you are casting a waffle slab, you have to provide void formers (like in regular concreting) for utilities connections. However, they are not installed with trenches in them, like normal slabs do. So, if you want to cut a waffle pod slab, you have to cut through the void former. This in effect will compromise the integrity of the slab – so you will end up plugging them up with more concrete. Which, in turn, defeats the purpose of using the waffle slab in the first place.
Therefore, pay very close attention to how the stress will be distributed before cutting a waffle pod slab. Make sure you consider the architectural and engineering drawings minutely to know exactly what the results of your cut on the slab will be.
How concrete is made
As long as you have estimated the effect of the cut and applied the necessary patch-ups if any, you shouldn’t have any problem cutting a waffle slab. However, it is still best to plan long ahead and not get into the situation at all where you have to cut a waffle pod slab – better safe than sorry, right?
Image Courtesy: neumannsteel.com.au