Minimum spacing of bars for crack control in reinforced concrete

[allimuthug]

Hi ,

I have a sump pit to be desigend absed on ACI Code , I figured flextural reinforcement , also checked the minimum spacing for cracks based on the stress in felxtural bars .
The minimum spacing of flextural bars are given in ACI 318 cl 10.6.4 ...
But can anyone tell me did i miss any criteria for minimum spacing of bars other than given above . Earlier times when i designed sump pit the minimum spacing of bars where restricted to 150 mm . I dont know the reason still. can anybody clarify me regarding this .

 

[delagina]

there is another aci code for environmental structures, aci 350. it has different minimum rebar.
see this link as example, you may want to download pca concrete tank design. i think it's free.

http://civil.colorado.edu/~silverst/cven4830/Rectangular_Tank_Example_Latest.pdf

 

[KootK]

I've wondered about this myself. Sumps seem to be in a no man's land of sorts. Are they liquid retaining structures? Yes in the sense that they'll be full of water at times and they often have liners. No in the sense that a) that water is not potable and b) the whole point of a sump pit is for water to be able to pass in and out freely.

My standard sump detail shows the bars at 150 which I believe is an ACI350 thing. But then smaller pits use 6" walls which I believe is not compliant with ACI350. My take is that sump pits do not need to be waterproof. They just need to be durable in an often wet environment.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Signious]

The only case I would think the sump would need to be waterproofed is if it is a retrofit on a structure with an insufficient granular base & placed over expandable soils. Drainage mat would only be around the perimeter and significant water lost to the underlying soils is going to lead to slab damage.

This could be accomplished with a wrap / WP membrane thought.

 

[cvg]

it doesn't matter if the water is potable or passes in or out of a sump, or if it "retains" the water, ACI 350 still applies

see quote from ACI 350 below with highlights

The code portion of this document covers the structural design, materials selection, and construction of environmental engineering concrete structures. [highlight #FCE94F]Such structures are used for conveying, storing, or treating liquid or other materials such as solid waste. They include ancillary structures for dams, spill-ways, and channels.[/highlight]

They are subject to uniquely different loadings, more severe exposure conditions, and more restrictive serviceability requirements than non-environmental building structures.

Loadings include normal dead and live loads and vibrating equipment or hydrodynamic forces. Exposures include concentrated chemicals, alternate wetting and drying, and freezing and thawing of saturated concrete. Serviceability requirements include liquid-tightness or gas-tightness.

[highlight #FCE94F]Typical structures include conveyance, storage, and treatment structures.
[/highlight]
Proper design, materials, and construction of environmental engineering concrete structures are required to produce serviceable concrete that is dense, durable, nearly impermeable, and resistant to chemicals, with limited deflections and cracking. Leakage must be controlled to minimize contamination of ground water or the environment, to minimize loss of product or infiltration, and to promote durability.

 

[Archie264]

Just to be a pedantic jackass, I believe that's maximum spacing. Minimum spacing is listed in Section 7.6. Generally speaking, the minimum spacing is the larger of d_b, I believe, though subject to the qualifications of that section.

 

[Archie264]

Whoops, that should be "...the larger of d_b or 1"..."

 

[rapt]

Achhie,

I was thinking it should be "maximum" also but decided to not be as pedantic as usual and let it slide!