Looking at the reports for a typical composite beam in RAM Structural System, I am seeing that RAM outputs I-effective (Ieff) and I-transformed (Itr) that are different from those listed in AISC Table 3-20 (Lower Bound Elastic Moment of Inertia for Plastic Composite Sections). I understand that this is because AISC presents lower-bound values and that this is due to a simplification made while producing an equivalent concrete area in their methodology.
RAM is clearly using a different method that produces a stiffer assembly. I'd like to know if their is a supporting calculation somewhere that details the exact methodology RAM is using to get numbers for Ieff and Itr. Also, can the methodology behind composite beam stiffness be changed somewhere per user preferences?
Thanks
Here's a verification sample to help: https://communities.bentley.com/products/ram-staad/m/structural_analysis_and_design_gallery/273520
Answer Verified By: Thomas Hill
Thanks, I will have to dig into this to understand the difference better.
Is there a way to specify the lower bound method within the program?
The only options (besides the design code) are under Criteria - Stud Criteria. The only lower bound that you can control is the min percentage of composite action.