Direct analysis for concrete - ACI 318

[vishalselvan]

Hello everyone,

I am required to analyse a building that has both steel framing for the first few floors and is then continued upwards as a concrete structure. I was able to use AISC's direct analysis method to check the deflections in the steel framing and check the members using reduced EI properties.

When I get to checking concrete, the code doesn't give an explicit method on how to do something similar to that shown in AISC. My understanding is that I can use moment magnifiers or run the analysis with P-delta turned on. My goal is to analyse the entire model in one fashion, and I'm interested in finding out how to analyse the concrete structure with P-delta. 

1) Would sway/non sway not matter when P-delta analysis is done? In AISC, they mention that k doesn't matter in P-delta analysis.

2) Is the iterative method to find EI applicable for concrete as well?

I'm using RISA 3D to perform the analysis. I would appreciate any help as I do not have a lot of experience in dealing with concrete structures.

Thanks,

Vishal