Embedments in concrete
Embedments in concrete
(OP)
Hi To All
I have a client that is asking to run his round HVAC in the flat concrete slab... the issue is that the pipes are 150mm in diameter and the flat slab thickness is 230mm ... I am trying to find a provision in the Canadian code or a paper... I found in the ACI318 clause 6.3.5.1 that the embedments shall not be larger than 1/3 of the thickness of the slab... but how is that calculated? is there a paper on that?
I have a client that is asking to run his round HVAC in the flat concrete slab... the issue is that the pipes are 150mm in diameter and the flat slab thickness is 230mm ... I am trying to find a provision in the Canadian code or a paper... I found in the ACI318 clause 6.3.5.1 that the embedments shall not be larger than 1/3 of the thickness of the slab... but how is that calculated? is there a paper on that?





RE: Embedments in concrete
RE: Embedments in concrete
RE: Embedments in concrete
As hokie66 noted....a ridiculous suggestion. Just reject it.
RE: Embedments in concrete
1. the slab thickness is 230mm one third of that is approx. 76.66mm therefore we are here 100mm (dia of HVAC) minus 76.66 equals to 23.4mm ... that is 23.4mm more than the ratio stipulated in ACI318.
2. Based on item # 1 I chased the equivalent stress block for rectangular section to find the neutral axis and I found it at 23mm from the top of slab.
Now does the neutral axis get affected (in other words shifts) if there is an opening?
RE: Embedments in concrete
This all depends upon where in the slab the ducts will be run. It is common practice is some slab systems to void certain areas of a slab to remove dead weight, but we would never consider this at supports or areas of high shear without computations. Is this a one-way or two-way slab? Will ducts run randomly throughout the slab, or can they be confined in "good regions"? As far as allowing random voids of this size, in general, I'd be skeptical about crack performance, but doubt you would fail a reinforced slab in any meaningful way because of a duct here or there.
RE: Embedments in concrete
If that were so then the client should even better understand the problem of what he/she is asking you to do. "Pulling rank" as having some engineering background tends to belie the true ability of such individuals.
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: Embedments in concrete
Mike McCann
MMC Engineering
RE: Embedments in concrete
Dik
RE: Embedments in concrete
We aren't talking about a SOG here.
RE: Embedments in concrete
Mike McCann
MMC Engineering
RE: Embedments in concrete
The phrase “as the limit does NOT apply to engineered solutions” this is an excellent phrase… to answer your question, the slab is a two way flat slab… the duct as I mentioned earlier is now 100mm after a good discussion with the client… now I took your advise and started with what you called "good regions"…. see below my side of the solution
ornerynorsk
Well we all had people that try to push the limits of engineering… but as I mentioned before to many clients a simple answer of “no” or “it can not be done” is not enough… you need to give them proofs or in other words you need to support your claim in an engineering way… and at the end of the day we are liable to what we say or what we claim and responsible to what we design.
The solution in my opinion…
Now… my opinion is as follow … I went back to the basic principles of the equivalent stress block for rectangular section and found that the neutral axis is at 23mm below the top of slab (reinforcement is accounted for in calculating the equivalent stress block) , and correct me if I am wrong here, the neutral axis will not be affected by the circular whole in the section then the stresses are above the duct… therefore by avoiding the high shear area and concentrating in areas that has reasonably low moments.. (coincidentally it is at 1/3 of the span between columns) the slab should be fine … again correct me if I am wrong here…
Finally for the chosen locations I checked the shear capacity and the factored shear at that location…and I made sure that there will won't be any concentration of other sleeves from other services.
RE: Embedments in concrete