I have to analyze soft story RC-moment resisting building. I calculate the gross stiffness initially adding stiffness of all the column i.e. Kcol=12EI/L3, and added all the column stiffness and shear wall stiffness. Increasing the height of any story to 4.5m (all other story are 3.5m height). than the stiffness of the 4.5m story is about the 0.5 times of other story. But after analysis in ETABS the story stiffness is dependent upon the story lateral force and the story displacement. in same case the stiffness of the story is varying for static analysis and response spectrum analysis.
how can we say that the specific story is either soft or not before the analysis ? i have to make soft story for analysis how can i make that story soft/weak initially before analysis in ETABS?
Thank you!
Hello Mahesh
I guess you are after the lateral stiffness?
If so, the following article is really great and may answer your question:
http://www.iitk.ac.in/nicee/wcee/article/8_vol5_597.pdf
Best wishes
Hello Messaoud
thank you for your contribution, I am going through.
thank you!
Dear Mahesh,
I would suggest you to refer to ASCE 7-16 where two different vertical irregularities are defined:
Type 1a: Stiffness - Soft Story Irregularity: this situation is defined to exist where there is a story in which the lateral stiffness is less than 70% of that in the story above or less than 80% of the average stiffness of the three stories above.
Type 1b: Stiffness - Extreme Soft Story Irregularity: this situation is defined to exist where there is a story in which the lateral stiffness is less than 60% of that in the story above or less than 70% of the average stiffness of the three stories above.
You can refer to these types when determining the initial stiffness of the story to introduce the soft story situation prior to the analysis. Hope it helps.
Regards,
Andri
Please check reference below.. hope it will be helpful for you… Regards…
https://www.iitk.ac.in/nicee/wcee/article/14_05-03-0155.pdf
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