Are voided slabs worth it ? 1

[Gus14]

Voided slabs are heavily marketed, and I really can't understand the hype, since most buildings are more so rectangular, biaxial bending is not really required. A famous voided slabs systems' Facebook page claims they used a 40 cm thick voided flat slab to support a 31 meter by 13 meters spaced column grid with an extra 15 cm drop over columns (residential building ). I also saw other crazy designs with crazy claims of money savings. When compared to flat slabs, they save reinforcement and concrete, but ribbed and waffle slabs are similarly reinforced, and polystyrene is far cheaper and could be removed later and reused. Voided slab installation is cheaper, but the savings figures I am seeing can't be real. What do you think? Did marketing engineers sell their souls for money? By the way non of this is post-tensioned.

 

[HTURKAK]

I agree with you ..

IMO , two advantages could be flat bottom face and better fire resistance than waffle and ribbed slabs..






Not to know is bad;
not to wish to know is worse.

NIGERIAN PROVERB

 

[BridgeSmith]

The advantage of voided slabs over solid slabs is they reduce the weight considerably, with very little loss in capacity. There's a trade-off between the simplicity of the solid slab and weight and material savings of the voided slab.

The choice of voided slabs over the waffle slabs or ribbed, has several factors. The labor for forming or casting is a big one; possibly local availability of precast sections, also. There's also the aesthetics and functionality of the slabs as a ceiling. The voided slab gives you a flat bottom face, which may be desirable or advantageous, depending or the use of the space.

 

[Gus14]

Thank you HTURKAK, and BridgeSmith for replying.

could be flat bottom face and better fire resistance

Yeah but the problem is they are not marketed for having high fire resistance, rather for being more economical.

I met with one of those companies engineers, and their design evaluation seems to be ( but the software said it was okay ).

The labor for forming or casting is a big one

Yes, this is the only thing I found that really saves money. Because they don't require stirrups and detailed as flat slabs. However, the money goes back into the plastic's price, with little left saved. I mean for large roof area good savings can be made, but how many of those mega project do we really see.

 

[Brad805]

In a seismic region I could see the reduction in your mass being beneficial. From a pure slab cost perspective I am not convinced. I have priced out some of those voids and they are not cheap. Each different version has its own problems to work with and your contractor would need to be on board.

 

[Gus14]

From a pure slab cost perspective I am not convinced. I have priced out some of those voids and they are not cheap. Each different version has its own problems to work with and your contractor would need to be on board.

Exactly that is why they are going for crazy designs and claims to lure in customers.