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crack spacing for spread/mat footing

crack spacing for spread/mat footing

crack spacing for spread/mat footing

(OP)
do you consider crack spacing for spread/mat footing? staad foundation has that check.

RE: crack spacing for spread/mat footing

I haven't been considering it explicitly. I'll provide temperature and shrinkage level flexural steel at minimum on whichever face of the footing/mat has tensile stress.

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.

RE: crack spacing for spread/mat footing

I provide the steel required for strength or the minimum distributed according to the code. For a heavily loaded mat I would look at the affects of cracking, but not your typical spread footing.

RE: crack spacing for spread/mat footing

(OP)
where in the code can I see that crack rebar spacing is not required for typical spread footings?

RE: crack spacing for spread/mat footing

I think what these gents are trying to say is the steel they provide for T&S or strength requirements more than fulfills the crack control requirements so they don't specifically check for it.

I doubt there would be a code reference specifically omitting crack control checks for spread footings, but I could be wrong.

If you are looking for a specific code clause you may want to reference which code you are designing to.

RE: crack spacing for spread/mat footing

(OP)
Crack control spacing is a separate check and in many cases govern over T&S. should this be ignored on footing/mat, I would like to see any document where I can justify it. This has been discussed with my fellow engineers who use staad foundation and has crack control spacing check.

RE: crack spacing for spread/mat footing

Crack control is a serviceability state. If cracks greater than 0.2mm to 0.4mm are a problem then, yes, you need to check that. I could see this being applicable in this case if the water table was high or the matt slab was a finished surface where aesthetics were important. It is an engineering call if crack control is important or not. I do not think you will find an exact clause that states you need not check crack control for this specific case.

RE: crack spacing for spread/mat footing

For those of us who don't use staad, what limits on crack spacing does it use?

RE: crack spacing for spread/mat footing

(OP)
@hokie66, it checks per ACI-05 10.6.4

RE: crack spacing for spread/mat footing

Flexural crack control is assumed where As for flexure exceeds the minimum of As,min=0.02 Ag IN THE tension side of the section. (for 60 ksi rebar) (ACI 318-14 8.6.1.1)
This is required for two-way combined footings and mat foundations by ACI 318-14 13.3.4.4.

ACI 224 produces publications discussing how to estimate crack with and spacing.

RE: crack spacing for spread/mat footing

0.02 Ag is not anywhere near enough for big mat foundations which are heavily restrained by walls and the subgrade. Doesn't the ACI code address this situation? More like 0.05 or 0.06 is necessary.

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