Are you talking about a braced frame or a simple steel brace that would brace a beam or column? I am assuming a braced frame and that you are trying to determine how much lateral load to put into each frame when I say this: apply a unit load to each frame and compare the relative displacements. This will be the ratio of distributing lateral loads.
JStephen -> a cross brace, instead of a concrete wall that will restraint the displacements, i need to use a steel cross brace for a steel frame.
StructuralEIT -> yes, a braced frame.
I don't know if you already had a problem like this. Here where i am most of the structures are made in concrete, but now an arq. wants a building made with steel frames and to control the displacements i need braces. And my problem is how to calculate (in my EXCEL sheet) the center on rigidity with steel braces?
You will have do as I said above. Apply the same unit load to the top of each frame. Find the displacement of each frame. Once you have the displacement of each frame, you can calculate the relative rigidities. After all, you don't need the actual rigidity of each frame, just the relative. I don't know exactly how you have your spreadsheet set up, but that will get you what you need.
