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

[bdbd]

Hi!
Very short but hard question: When you have more than one layer of reinfoircement on tension face, which steel stress should be used for crack width calculation and can you provide a reference to your answer?
A) Outermost reinforcement's stress
B) Stress at the centroid of the tensile reinforcement

 

[BridgeSmith]

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.

 

[IDS]

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

http://newtonexcelbach.wordpress.com/

 

[BridgeSmith]

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.

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