SRSS load combo in RAM Structure

[zeemas]

Bentley help for repsonse spectrum specify following:
"Experts have recommended using a SRSS combination of two orthogonal response spectra analyses to determine the critical forces in a dynamic analysis (see reference ****). This method is not implemented in the current version of RAM Structural System. You will need to use load combinations to account for this code requirement."

My question is that how can we define SRSS load combo in RAM?

Thanks,
Z

 

[JoshPlumSE]

I have never used RAM. But, I do teach a class on dynamic analysis using the RISA software. One of the points that frequently comes up in that class is that you can use the SRSS combination method in RISA.... But, that the newer codes seem to prefer the 100% + 30% alternative.

Both are merely just statistical combination methods that are roughly equivalent. Personally I prefer the SRSS method. But, I think the reason for the code no longer referencing the SRSS method is that some folks had been applying it incorrectly resulting in non-conservative designs.