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Clarifier Slab Design Question

Clarifier Slab Design Question

Clarifier Slab Design Question

(OP)
We have been contracted third party to come up with a design solution to a problem with the original design. The clarifier is 70' x ~15' tall, steel walls, flat concrete base. The original design was to ACI 318 instead of 350. The question is whether or not we can change the existing concrete slab designation to be a slab on grade if we add a membrane (whether it be concrete or other material), so that the ACI requirement changes to 318 instead of 350?

RE: Clarifier Slab Design Question

But what is the actual problem?

RE: Clarifier Slab Design Question

(OP)
The slab design is adequate but the rebar is under-designed for ACI 350. If we pour a membrane slab on top of the existing slab, does the existing slab still need to meet ACI 350?

RE: Clarifier Slab Design Question

350 still refers to the use of membranes within 350 (see section (see the "General Commentary" section in the Introduction.

So I don't think that use of a membrane somehow deletes any requirement for using 350.

Using 350 is described in the introduction as:

ACI 350 has no legal status unless it is adopted by government
bodies having the power to regulate building design and
construction. Where the code has not been adopted, it may
serve as a reference to good practice.


I think this might be more a judgement call on the engineer to determine the ramifications of the smaller reinforcement on the long-term water tightness of the concrete and its lifetime performance.

RE: Clarifier Slab Design Question

(OP)
I agree with you JAE and so does the other engineer here I've spoken to. We would still design the membrane slab to ACI 350 and prevent the existing slab from contact with the water, but just trying to find something that says the existing (lower slab) doesn't need to meet ACI 350 still. We believe it is so but my manager is trying (I think to get something more 'concrete' to go to the customer with). I don't think he's going to find it though.

RE: Clarifier Slab Design Question

If anyone questions that the lower slab needs to be retroactively designed to ACI 350, if the upper slab is designed to it, they don't understand the intent of this code.

RE: Clarifier Slab Design Question

Zheitman:
Everyone wants a bldg. code paragraph which points to the exact same detail and conditions for anything and everything they are trying to do. And, the codes are quickly moving in that direction too, voluminously, and ever more prescriptively. Soon we won’t be able to do anything in the way of Structural Engineering, and that includes anything based on experience and good engineering judgement, if the detail isn’t explicitly shown in the codes. Of course, that does seem to be the way Structural Engineering is going these days anyway, as less and less of the experience and judgement needed are available; hell anyone should be able to do it if they can only read and understand the convoluted verbiage which is hoped to, intended to, cover every possible situation in the universe. Soon, we’ll be out of business, they can just say on the plans, “contractor to follow bldg. code and its tables, combine details 34, 278, 300683, etc., and start buildin, no engineering judgement or experience required.”

RE: Clarifier Slab Design Question

(OP)
You have all basically read my mind. Thanks guys/gals(?). I have told my manager and I think having some additional feedback has made him feel better. I agree with you Jed. If it is separated from the exposure, then it shouldn't need to meet the exposure requirements.

Thanks again

RE: Clarifier Slab Design Question

As a clarifier, does the slab need additional care? what is it containing? harmful to concrete?

Dik

RE: Clarifier Slab Design Question

(OP)
It has slurry water from wet dust collectors. Another hitch in the equation is this clarifier is assisting existing settling ponds and is located between the ponds, so any seepage will go into the existing settling ponds anyway. Like I said, I'm pretty sure what the answer, it is a matter of convincing others. For now, I think they are satisfied. Thank you all.

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