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Seismic / Earthquake Load Combinations for structures/Buildings
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rojanmathewtsy
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PostPosted: Sat Jun 22, 2019 9:23 am    Post subject: Reply with quote

sukanta.adhikari wrote:
Dear sir

As per IS 875 Part 5:1987(Reaffirmed 2013),clause 8.1,reduction in live load is permitted both while generating seismic mass as well as during combination.The code is still active

Clause 8.1  Load combination

Note 3 - Whenever imposed load (IL) it combined with earthquake load (EL), the appropriate part of imposed load as specified in IS: 1893-1984 should be used both for evaluating, earthquake effect and for  combined load effects used in such combination.


Regards
S Adhikari



Dear Sir,

Please find the review if IS 1893 2002 by sk jain. It is clearly mentioned that the reduction of LL in load combination is not acceptable.

Rojan Mathew



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hemalmistry
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PostPosted: Sat Jun 22, 2019 5:30 pm    Post subject: Seismic / Earthquake Load Combinations for structures/Buildings Reply with quote

ASCE 7-16 (US code) does not even require to apply load factor on LL, when it is combined with seismic load. Also, unfactored live load can be reduced to half if it is less than 4.8 KN/m2 except for garages and storage area.

1.2DL+0.5LL+EQ.   ( for LL<4.8 kn/m2)


EQ loads as per ASCE are factored and does not require load factor to be applied.


Regards,
Hemal Mistry

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sakumar79
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PostPosted: Sun Jun 23, 2019 2:58 pm    Post subject: Reply with quote

Dear Sirs,
    As the IS 1893 code is newer, the usage of reduced LL in load combination is not allowed any more. This is consistent with the new NBC code also.

Yours sincerely
S Arunkumar
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rojanmathewtsy
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PostPosted: Mon Jun 24, 2019 10:22 am    Post subject: Reply with quote

Yogesh.Pisal wrote:
Your first question is already answered by Arunkumar. Provision for reduction of LL factor in load combination is not suggested by revised code IS1893 Part 1 2016.

Second Question: Whenever you are carrying out dynamic analysis with or without shear enhancement, you shall use dynamic analysis load case (response spectrum load case) for combination.

Best Regards,
Yogesh Pisal


I have doubt regarding this. Are you recommending to completely disregard  
the static eq analysis if we are considering response spectrum?

Rojan Mathew
mathew.rojan@gmail.com
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sukanta.adhikari
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PostPosted: Tue Jun 25, 2019 7:17 am    Post subject: Reply with quote

Dear Arun sir,


IS 875 Part 5 is also a part of NBC.

If reduction in live load is not to be considered in combination...IS 875 Part 5 also has to be revised parallelly...and the clause that LL reduction is allowed in combination also has to be deleted...to avoid any confusion among  user.


Regards
S Adhikari



sakumar79 wrote:
Dear Sirs,
    As the IS 1893 code is newer, the usage of reduced LL in load combination is not allowed any more. This is consistent with the new NBC code also.

Yours sincerely
S Arunkumar
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sakumar79
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PostPosted: Wed Jun 26, 2019 12:29 pm    Post subject: Reply with quote

Dear Er Sukanta Adikari,
    You are correct. While on the one hand BIS has removed the clause in IS 1893 Part 1 regarding reduced LL in Load combination, it has failed to remove the equivalent clause (Section 8.2 note 3 of Part 6) in NBC 2016. Theoretically, this gives a "loophole" for designers to "exploit". My understanding is that the clause was deliberately dropped in IS 1893 and hence, the equivalent clause under Load combinations in NBC 2016 is an oversight. However, until the same is rectified, it is technically acceptable to adopt reduced LL in the load combinations.

   The discrepancy needs to be forwarded to BIS so that suitable amendment can be issued to resolve the issue.

Yours sincerely
S Arunkumar
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