Backcheckrage
Structural
- Sep 23, 2012
- 84
Okay, all you smart people. In an effort to gain some sort of consistent understanding of a dynamic analysis / RSA procedure, I am pinging you. I seem to get differing responses from my peers. So here we go:
1. In ETABS, when you perform a dynamic analysis, should you ALWAYS perform this with a RSA? There is no benefit to just clicking the check box and having the black box go. The RSA (aka modal analysis?) will determine the dominating mode shapes and it is up to the user to RERUN the analysis considering 90% mass participation.
2 The base shear in each direction reported by an RSA will be some arbitrary value, and you have to take the ration of this with the STATIC analysis and then input that into the "SCALE FACTOR" box of the RSA spectrum definition window. The intent is to have the RSA loads in members and base shears report something more realistic. Correct?
3. How in the world can I determine my "new" structure period from the RSA? I can't seem to find it anywhere in the reporting options!
4. What is the benefit to running a RSA for buildings which have a dominant 1st mode? (i.e. a building with 90% mass participation at the 1st mode)
5. I was always under the assumption that a dynamic analysis will result in LOWER building demands if compared to the equivalent static analysis. It appears this is untrue (at least as far as my local code is concerned). So then what's the benefit?
6. Can one describe a generic step by step procedure to properly run a RSA with meaningful results?
Thanks guys, I have all the literature which the forum recommends but sometimes I need to have a discussion rather than just a lengthy textbook.
1. In ETABS, when you perform a dynamic analysis, should you ALWAYS perform this with a RSA? There is no benefit to just clicking the check box and having the black box go. The RSA (aka modal analysis?) will determine the dominating mode shapes and it is up to the user to RERUN the analysis considering 90% mass participation.
2 The base shear in each direction reported by an RSA will be some arbitrary value, and you have to take the ration of this with the STATIC analysis and then input that into the "SCALE FACTOR" box of the RSA spectrum definition window. The intent is to have the RSA loads in members and base shears report something more realistic. Correct?
3. How in the world can I determine my "new" structure period from the RSA? I can't seem to find it anywhere in the reporting options!
4. What is the benefit to running a RSA for buildings which have a dominant 1st mode? (i.e. a building with 90% mass participation at the 1st mode)
5. I was always under the assumption that a dynamic analysis will result in LOWER building demands if compared to the equivalent static analysis. It appears this is untrue (at least as far as my local code is concerned). So then what's the benefit?
6. Can one describe a generic step by step procedure to properly run a RSA with meaningful results?
Thanks guys, I have all the literature which the forum recommends but sometimes I need to have a discussion rather than just a lengthy textbook.
