Crack and Uncracked Walls ACI

[drasticxx]

Hey

In ACI cracked and un-cracked Ie (Walls) are different 0.7 and o,35 respectively,so when when i design how can i predict which one to pick??

 

[KootK]

Two paths to take:

1) if you know which value will produce conservative results for your purpose, and you're comfortable with that conservatism, run with that value.

2) Guess whether your walls are cracked and confirm your guess after you run your analysis. Walls where axial loads dominate over flexural demands tend to 0.7. When the reverse is true, 0.35.

The Canadian code has a formula for estimating stiffness based on axial load. It's just for seismic considerations however.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[drasticxx]

Thank you

 

[chekre]

This is how i do it.
I Run my analysis with 0.7 for all the walls.
The walls which will be usually cracked are the ones at the top of your building since they will carry moment and the axial force is not that much to equilibrate the tension stresses.
using P/A - Mv/I (M : moment in absolute value) and comparing it to 0.62 (f'c)^0.5, i usually check which walls are cracked and which are not and apply the appropriate modifiers.