Flat Slab
Flat Slab
(OP)
Is flat flat suitable for a building over 30 storeys (with core/shear walls)?
When was the last time you drove down the highway without seeing a commercial truck hauling goods?
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RE: Flat Slab
And in these areas it would quite often be bonded PT depending on spans.
RE: Flat Slab
RE: Flat Slab
RE: Flat Slab
No, Span/depth ratio would be in the order of 35 to 40 (not the stupid figures some people quote) and the resulting stresses would be less than in an RC slab if it was designed properly.
What spans are you talking about and how thin do you think the slab is going to be.
archeng59
This is a different question. We have gotten away for too long without considering vibrations correctly in building floors. And some people are making them far too thin, often because they do not know how to design properly and/or understand the problems.
In a hospital it is even more important.
But there is no reason why you cannot do a vibration analysis on a PT slab system to make sure the slab in in the correct response range for any type of building.
RE: Flat Slab
RE: Flat Slab
Dik
RE: Flat Slab
I have a piled ground floor slab, piles at spacings varying from 3.0mm to 3.75m depending on the loading (40N/mm2 to 60N/mm2) The RC slab designed is 300mm thick with top and bottom rebar of T16mm @ 200mm.
Typically would you expect that we could provide a saving on steel using PT. Would you recommend single strand bonded PT as a proposal to ask a designer to check?
RE: Flat Slab
They go a lot higher than 30 storeys.
Zambo,
Single strand bonded tendons are not economical. The smallest economical tendon size is normally 4 strands. VSL tried a 2 strand system in USA several years ago but it was very expensive and uneconomical (and they went broke). In normal slabs, bonded PT requires spans of about 7 metres to justify the use of 4 strand tendons and maintain reasonable tendon spacings. However with your very heavy loadings you could use 4 strand tendons in your slab.
With a slab this thick and with such short spans, I would use a mat of straight tendons top and bottom rather than draped tendons. Draped tendons would have too much losses.
You could save on concrete and steel but which would be most economical would depend on the local costs for RC versus PT.
You would also have to be wary of horizontal restraint effects in the slab from the piles.
RE: Flat Slab
Assuming normal costs for construction... where would you suggest the upper limit for RC construction would be?
Dik
RE: Flat Slab
I presume you mean RC frame rather than RC floors. I think 80 storeys has been done, possibly more.
Actually, Petronas Towers in Malaysia at 88 storeys and 452m is RC framed.
RE: Flat Slab
In Hongkong, a lot of buildings constructed in the 70's and onwards are over 30-40 storeys. They are all (nearly 88.5%) in the form of shear wall-beam-slab construction. I just wonder what the flat slab is not commonly adopted. In the UK, there is a lot of flat slab structures.....I just don't understand why....
RE: Flat Slab
I think you will find it is because the old time contractors and local consultants like their old methods so PT is not used much in high rise. When we talked to the contractors many years ago they could not see any advantage compared to the problems having another major sub-contractor on site and did not like the idea of change.
The majority of flat slabs being done in UK are bonded PT but this trend has only happened over the last five years.
There are some consultants looking at PT high rise in Hong Kong but they tend to be connected with Australian consultants where it has been done extensively for 30 years or more.