RC Shear Walls: 0.7*Ig vs. 1.0I*g

[hippo11]

Hello, does anyone understand why ACI 10.11.1 calls for UNcracked wall I to be 0.7Ig? Why not 1.0 Ig?

Would it be appropriate to use 1.0 Ig for the walls in an eigenvalue analysis?

Thanks!

 

[UcfSE]

Check the commentary on that section.

I wouldn't change the values ACI recommends unless you take into account everything that is stated in 10.11.1. The factors the code gives in that section are alternates to doing a much more in-depth analysis. So if you want to use 1.0Ig, you have a lot more work to do.

 

[hippo11]

Thanks for the help. I know the commentary gives background on code provisions, but I didn't see anything in it that explains the 0.7 term very well.

Doing more work is fine as long as I can justify using a higher Ig.

 

[UcfSE]

It said something about the coeeficients where 0.875 times those given in the reference material. You must really need that extra 0.3 to want to go through all the extra work to get it.

 

[hippo11]

Yes I do want the extra 0.3, because we're looking at a 40+ story shearwall/frame building with wind acceleration problems at the top, so every bit of stiffness helps.