Which Steel Stress for Crack Width Calculation for Multi-Layer Reinforcement?

I would suppose it would depend on what you're using for the thickness of the concrete cover. I would use the concrete cover to the outermost layer, and so I'd use tension stress in the outermost layer of reinforcing. It seems to me the crack width is related to the strain in the reinforcing and the distance to the face of the concrete, so additional layers of reinforcing are irrelevant to the crack width.

I agree with BridgeSmith.

Since strain and stress are assumed to linear, I suspect that using the centroid values, which would reduce the stress but increase the cover, wouldn't make much difference, but I haven't checked.


Doug Jenkins
Interactive Design Services

I suspect that using the centroid values, which would reduce the stress but increase the cover, wouldn't make much difference, but I haven't checked.

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because the decrease in stress is minimal, but the increase in cover is substantial, it makes the required reinforcement spacing quite a bit smaller.