Response Modification Factor ( R ) via Pushover analysis using SAP2000/ETABS
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Author: paladin
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Response Modification Factor ( R ) via Pushover analysis using SAP2000/ETABS
Dear members of Civilea,
I need help.
I want to know whether R ( R=Response Modification Factor ) we calculate based on method in fema 273 always results value of R that "near" with value of R in the building code ?
Can the value of "R" much smaller or bigger than "R theory" as in the building code ?
As for as I know, the R value given in code based on the FEMA. The calculated value may not away from the code value.
[-] The following 1 user says Thank You to visu for this post:
  • paladin
Dear visu & other members,
The topic here is calculating R via pushover, or can be said as "refined seismic design process" using real/actual "R" where "R" calculated from pushover analysis.
Btw, based on your experience calculate "R" using pushover analysis, :
1) for RC SMRF ( R theory = 8.5 in ubc 1997 ), what "R" value you got ( averagely ) from pushover analysis ?
2) for Dual System ( RC Shear Wall + RC SMRF, R theory for this dual system = 8.5 in ubc 1997 ), what "R" value you got ( averagely ) from pushover analysis ?
I want to know & compare it with my own experience, to know whether the process of my calculation is correct or not.
Thanks for your time & your answer
Dear Paladin,

I am not a professional and i am student. But i did a heavy research relating this Subject.
First Thing: Which Code you are consulting. In UBC 'R' is over strength factor and not Response modification factor. But in IBC or ASCE or FEMA 'R' is Response modification factor. So you can Relate Fema's 'R' with that mentioned in IBC and ASCE.
Second Thing: I dont know what is your scale to be defined as smaller or bigger. But in my case i used 8.5 from IBC but when carried out a nonlinear analysis it came out to be 4-5. Which as by me a bigger difference. Thus you can end up with 'R' value more or less than Theory's 'R'.
[-] The following 1 user says Thank You to 88FeNIX for this post:
  • paladin
Dear 88FeNIX,
#01 About R=Response modification factor
I read it in a lecturer notes of a university from USA
I think R=over strength factor ( UBC 1997 ) & R=Response modification factor ( IBC ), it just different in "term", plz give correction if I'm wrong
My country seismic design code partially adopted from UBC 1997, simply, my country seismic design code = modified UBC 1997
#02 About R from pushover
I did pushover analysis based on FEMA 273 to get "R".
Yes you are perfectly right, R from pushover between 4 & 5 ... I found the same.
I want to know :
- Does your professor/lecturer accept/agree with the result of your research ( R pushover between 4 & 5 with R theory =8.5 ) ?
- Does your professor/lecturer give some comment/explanation/suggestion related to the value of R between 4 & 5 ?
#03 About Bilinear curve
I need your help/suggestion
In process to get R, we need to create "bilinear curve"
The problem raise, the condition is not the same as describe in FEMA 273
I think the condition I found ---> Ki = Ke, the curve of base shear vs roof displ is look very simple
I create the bilinear, both line meet & get Vy plus roof displ
- Do you think my procedure correct ?
- plz guide me to get Ki, Ke & alpha ... I never found such condition ( Ki different with Ke )
Thanks for your time & your help
I really appreciate your effort to help me.
Dear Paladin,
#01: Overstrength Factor ('Omega' or 'R in UBC' ) and Response Modification 'R' are not only different in terms. the following diagram explains the difference and their interrelationship.
#02: Yes, my professor did accepted the result because in our case structure was not to be modified. However, the suggestion was made that the structure should be proportioned in such a way that its inherent R should approach Theory's R. Understand, Research was accepted but for practice try to achieve an agreement b/w you R and Theory's R.
#03: I did my research on sap and it generated pushover curves and parameters of curve, as per FEMA like Ki, Ke, alpha and Dy etc. If you want verification use sap V14. Because what you are telling in words seems right but what could be better verification?

Btw Paladin here it is.
[Image: 30746874121966446778.jpg]
[-] The following 1 user says Thank You to 88FeNIX for this post:
  • paladin
Dear 88FeNIX & members of Civilea who interesting on pushover analysis
I think all procedures to calculate "R" in FEMA is for single tower only.
What if the building has 2 towers over the basement or the podium ?
What the different in pushover anslysis process ?
Can I do the pushover analysis with one single file of etabs/sap2000 ( all the building : basement, podium & the 2 tower being modeled in one model, not sepate/divide it ) ?
You should model them in one file.
[-] The following 1 user says Thank You to 88FeNIX for this post:
  • paladin
Dear 88FeNIX & other members who love pushover analysis,
For example tall building has basement + there 4 towers over the podium.
The tower named as Tower A, B, C & D ( the tower is different one to others )
I agree the building must model in one file ( if possible ), then how the procedure to calculate "R" via pushover analysis of each tower ?
What's the trick to do it ( the pushover for 4 tower over podium ) ?
What's the different with single tower's procedure ?

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