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How to design building with soft story in etabs?
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saikiran gone
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PostPosted: Wed Dec 14, 2016 7:38 am    Post subject: Reply with quote

rahul.leslie wrote:
I am afraid, the above needs correction, I feel. What Er. ArunKumar said ...
Quote:
For example, in place of 1.5 DL+1.5 EL, use 1.5 DL + 3.75 EL.
... is what is to be done. Somebody please clarify my opinion.

Rahul Leslie


Hi Rahul Sir,


In my opinion, it should be 1.5DL+2.5 EL.

With Best,
Saikiran.
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vegad
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PostPosted: Wed Dec 14, 2016 7:49 am    Post subject: Reply with quote

This reply valid only on the basis of Ref: IS 1893 (Part 1) : 2002

Cl. 7.10.3 reads . .

" . . after carrying out earthquake analysis, neglecting the effect of infill walls in other storeys:

a) columns and beams of the soft storey are to be designed for 2.5 times the storey shears and moments calculated under seismic loads specified in the other relevant clauses: or . .  "

Please find the underlined.

I hope its clear enough in the referred revision.

Thank you.
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PostPosted: Fri Dec 16, 2016 12:15 pm    Post subject: Reply with quote

rahul.leslie wrote:
I am afraid, the above needs correction, I feel. What Er. ArunKumar said ...
Quote:
For example, in place of 1.5 DL+1.5 EL, use 1.5 DL + 3.75 EL.
... is what is to be done. Somebody please clarify my opinion.

Rahul Leslie




Hi Rahul Sir,

From IS 1893 draft code:

All the columns of the soft/weak storey should be designed for 2.5 times the seismic demand.From this statement, it is clear that it should be 1.5DL+2.5*EQ in lieu of 1.5DL+3.47*EQ. Correct me if I am wrong.


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Abishek_Siingh
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PostPosted: Fri Dec 16, 2016 1:14 pm    Post subject: Reply with quote

I think Er. Rahul is correct.

Basic case is DL+EQ in general situation.
With soft storey it becomes DL+2.5EQ.
With factor of 1.5 it becomes, 1.5(DL+2.5EQ) = 1.5DL+3.75EQ.


Abhishek
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PostPosted: Tue Dec 20, 2016 12:03 pm    Post subject: Reply with quote

Kumar_Abhishek_Singh wrote:
I think Er. Rahul is correct.

Basic case is DL+EQ in general situation.
With soft storey it becomes DL+2.5EQ.
With factor of 1.5 it becomes, 1.5(DL+2.5EQ) = 1.5DL+3.75EQ.


Abhishek



Dear Engineer's

Experts need to comment on this query.

In case of soft story.

Combination shall be
1.5DL+2.5 EQ

Or

1.5DL+3.75 EQ  (1.5*2.5=3.75)

Regards,
Saikiran.
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syed_A
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PostPosted: Tue Dec 20, 2016 6:07 pm    Post subject: Reply with quote

The soft storey columns/beams are to be designed by multiplying with factor 2.5 times of end forces which we obtain from analysis.....hope it is correct method
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sakumar79
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PostPosted: Wed Dec 21, 2016 1:47 pm    Post subject: Reply with quote

Dear Sirs,
     As far as I could search, there is no direct indication whether the 2.5 factor is to be taken as 1.5 x 2.5 or only 2.5.

    However, the next paragraph in the code (7.10.3 (b)) says "besides the columns designed and detailed for the calculated storey shears and moments, shear walls placed symmetrically in both directions of the building as far away from the centre of the building as feasible; to be designed exclusively for 1.5 times the lateral storey shear force calculated as before".

    Please note the factor for shear walls is 1.5. Now, logically, code would not put this clause to indicate 1.5 (DL+/-EL) should be designed for the same load factor for soft storey also.

   Further, normal load combinations include 1.5 (DL+/-EL), 0.9 DL +/- 1.5 EL and 1.2 (DL+LL+/-EL). Code has not indicated in the above factor (2.5 for columns, 1.5 for shear walls) any different factor for load cases involving LL also.

   Considering the above two points, I feel confident that the load factor for 1.5 (DL+/-EL) should be revised as 1.5 DL+/-3.75 EL only (and similarly for all other load combinations involving EQ load). Logically, it is the correct interpretation.

Yours sincerely
Arunkumar
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Abishek_Siingh
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PostPosted: Thu Dec 22, 2016 4:27 am    Post subject: Reply with quote

Absolutely agree with Arun.
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