Crack Control parameter in footings

[puszka]

Hi y'all,

I am designing some residential footings and the Canadian code isn't abundantly clear as to whether the crack control parameter is necessary for footing design. I have some pad footings whose reinforcement will be universally governed by satisfying z if that is the case.

I was under the impression that z was more for aesthetic reasons in visible concrete members to distribute more hairline cracks rather than having a couple of honkers, though I also read in an ACI document that it is also required for corrosion protection. Since my footings are exposed to earth and moisture I second guessed myself and am wondering if I need to satisfy the z value for 'exposed concrete'. The Canadian and American codes are very similar and I think they will have the same rationale behind this, so input from either is welcome

 

[skeletron]

CSA A23.3-14 Commentary N10.6.1 does address that the cover, for purposes of calculating dc, may be capped at 50mm. The commentary goes on to acknowledge that it may be difficult to satisfy the requirements in footings because of dc.

I include the check in my designs. I also am willing to calculate the actual fs instead of relying on the 240MPa (60% fy) approximation. This can help you achieve the required z. I think if you were to ignore the crack control parameter, you would be more in line with designing the footing to meet Clause 22 (plain concrete) and need to calculate the maximum tensile stress regardless.

 

[puszka]

Ah, that's a good call with calculating fs. I'm new at this and still building my analysis/design tools, so every little bit helps. Thanks!