Without having access to ACI and just going by A23 and flexural crack control fundamentals, there should be an option to use service loads in determining the stress in the flexural zone that determines required crack control reinforcement. If not directly in the code then in the commentary. Based on what's in the Canadian code, if you don't have stress in the steel you're okay with only temp/shrinkage reinforcement.
Not always. If you do not mind the formation of significant cracks and the potential for corrosion won't affect the design life of the structure then you wouldn't have to follow this section.
Personally, I have never fully bought into this section of the code. If you're really concerned about cracking and corrosion and such, you might take a look at ACI 350 which has different provisions covering the same basic topic.
I'm not concerned at all. I have a spread footing and have not considered crack control spacing before.
Unfortunately, we have a new foundation software and it's giving warning that crack control spacing is not met.
I'm now trying to justify how to get away from this warning. Is there any documentation to justify not using this?
You could design it as an unreinforced footing. See chapter 22 in ACI 318. You could of course have to neglect the contribution of ANY flexural or shrinkage reinforcement.
I've gone MotorCity's route where I just designed it as plain concrete but included T&S rebar anyway. As Josh said, corrosion is a concern and cracking can result.
Maine Professional and Structural Engineer.
(Just passed the 16-hour SE exam, woohoo!)
One thing that is real "mumbo-jumbo" about this provision is the fs value (stress in reinforcement at service level loads). I know what it is at ultimate strength. I can calculate what an uncracked beam would have based on a transformed section. But, calculating it between initiation of cracking and ultimate strength is not something that is as straight forward.
The software probably assumes 2/3 fy which is permitted by the code. But, you could probably do some hand calculations to justify a lower value. And, therefore a larger maximum spacing.
Josh - I don't follow your point. After initiation of cracking the stress in the reinforcement at the cracks is easy to calculate at service load levels, assuming linear behaviour for steel and concrete in compression, and ignoring concrete in tension. The effect of the concrete between the neutral axis and the base of the cracks is very small, so this method gives a good approximation to the actual maximum stress in the bars.
