# Response Modification Coef.



## MOOK (Apr 1, 2010)

If you have 3 story building, Response medication factor for the first floor is R = 5, the second floor R= 4, and the third floor R = 3.

What is the design value of the response modification factor for the first floor?

Some Reference used 4 and the other used 3.

What do you think?

Thanks


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## McEngr (Apr 2, 2010)

MOOK said:


> If you have 3 story building, Response medication factor for the first floor is R = 5, the second floor R= 4, and the third floor R = 3. What is the design value of the response modification factor for the first floor?
> 
> Some Reference used 4 and the other used 3.
> 
> ...


Hi Mook, ASCE 7 Section 12.2.3.2 states it pretty well. The least R value in that direction shall be used with a few exceptions. I would use 3, but if the 3 conditions are met, you may use the value for each line of resistance. Perhaps one example was a flexible diaphragm with 2 or less stories and the other was a rigid diaphragm? Just playing detective...


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## MOOK (Apr 2, 2010)

Hi McEngr

I hope you doing well

McEngr, actually the point here it is not flexible or rigid diaphragm. The point is if R for certain floor has to be less than any floor above or just less than the direct floor above.

Thanks


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## McEngr (Apr 2, 2010)

MOOK said:


> Hi McEngrI hope you doing well
> 
> McEngr, actually the point here it is not flexible or rigid diaphragm. The point is if R for certain floor has to be less than any floor above or just less than the direct floor above.
> 
> Thanks


I believe the answer lies in the section previous to the one I posted: 12.2.3.1 states that no story shall have an R-factor greater than any story above that story, therefore I interpret it as 3. Therefore, you may use 3 for the whole system.


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## Genuine_Opinion (Apr 12, 2010)

MOOK said:


> If you have 3 story building, Response medication factor for the first floor is R = 5, the second floor R= 4, and the third floor R = 3. What is the design value of the response modification factor for the first floor?
> 
> Some Reference used 4 and the other used 3.
> 
> ...


If upper stories posse more or less the same rigidity as the lower ones, 12.2.3.1 mentions to use the least of all R values we got. (which is 3 in our case).

However, if upper story/stories are flexible compared to the lower ones with two conditions for "two-stage procedure" are met; the portion of structure with upper flexible stories can be analyzed with its R value separately and the end results be amplified with appropriate ratio. These results then be added as reactions for the analysis of the lower portion with its own R value.

This is what I can think of based on the info we have, Mook. Let me know what you think.


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