Two Layers of Tension Rebar

[ottles]

How often do you use two layers of tension rebars distance 1 inch apart (the 2 layers). The outer side would yield first before the inner ones. Usually how many percentage yielding of the outside side before the inner ones yield? and why is this allowed in structural books. I only want single layer in my design but I saw others doing 2 layers. What is your experience and say on this? Thank you.

 

[rapt]

Ottles,

You do not have to do it by that formula. Or you can use iteration for kd values to solve that formula if you want to.

You can follow the same procedure I have outlined above and iterate for neutral axis depth.

The straight line concrete stress diagram will only be close to correct for concrete strengths below .4F'c. Higher stress than that and the curve is non-linear.