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Seismic / Earthquake Load Combinations for structures/Buildings
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haridevender
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PostPosted: Tue Jun 04, 2019 6:41 am    Post subject: Seismic / Earthquake Load Combinations for structures/Buildings Reply with quote

1.     DL+LL+EQ Combinations

1. In EQ load: it is a function of DL+ Partial LL, when considering in the above combination, LL shall be Part LL or full LL? Suppose EQ load is Ah x (DL+0.25 LL), then in the combination, LL shall be 0.25 LL or 100 percent LL?

2.     DL+EQ or DL+LL+EQ Combinations

As we are doing response spectrum analysis after enhancing the base shear, is it be necessary to consider static EQ or Dynamic EQ (Spec) in load combinations or both? Why?

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Hari Devender
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sakumar79
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PostPosted: Tue Jun 04, 2019 7:36 am    Post subject: Reply with quote

Dear Sir,
    For Q1, IS 1893 2002 code allowed usage of reduced LL in the load combination. This has been removed (disallowed) in 2016 revision.

   Not sure I understand Q2. Please explain.

Yours sincerely
Arunkumar
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haridevender
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PostPosted: Tue Jun 04, 2019 8:19 am    Post subject: Reply with quote

Dear Sir
My Question number 2 is in  DL+EQ or DL+LL+EQ Combinations, whether we need to consider static EQ or Dynamic EQ (Spec) ? Why?

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rojanmathewtsy
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PostPosted: Thu Jun 06, 2019 7:12 am    Post subject: Re: Seismic / Earthquake Load Combinations for structures/Buildings Reply with quote

haridevender wrote:
1.     DL+LL+EQ Combinations

1. In EQ load: it is a function of DL+ Partial LL, when considering in the above combination, LL shall be Part LL or full LL? Suppose EQ load is Ah x (DL+0.25 LL), then in the combination, LL shall be 0.25 LL or 100 percent LL?

2.     DL+EQ or DL+LL+EQ Combinations

As we are doing response spectrum analysis after enhancing the base shear, is it be necessary to consider static EQ or Dynamic EQ (Spec) in load combinations or both? Why?


As per IS code, Reduction is live load is applicable to Eq load calculation, not in the load combination.

For your second question, you have to consider both static and dynamic cases and take out the critical out of that for individual members.
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rahul.leslie
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PostPosted: Tue Jun 11, 2019 7:45 am    Post subject: Reply with quote

Quote:
For your second question, you have to consider both static and dynamic cases and take out the critical out of that for individual members.


There are criteria in IS:1893 for deciding on which method to use: very limited ones for static cases. However, there is a confusion under certain peculiar conditions, as posted in https://www.sefindia.org/forum/viewtopic.php?t=19813

however, generally for multi storied buildings, I presume that Response spectrum be followed for buildings not falling under "regular buildings with height less than 15 m in seismic zone II", I presume. But the forces need to be scaled for Base-shear correction if required, and that's where criticality of the static method vs dynamic method is incorporated in the procedure.
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Yogesh.Pisal
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PostPosted: Tue Jun 18, 2019 9:27 am    Post subject: Reply with quote

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.

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Yogesh Pisal
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FARA
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PostPosted: Thu Jun 20, 2019 12:17 pm    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 IS 1893 Part 1 2016.

Best Regards,
Yogesh Pisal



Yogesh Sir,

Can you share clause of 1893 from 2002 n 2016, where the LL shall be taken as reduced n 100% respectively .

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sakumar79
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PostPosted: Thu Jun 20, 2019 1:16 pm    Post subject: Reply with quote

Dear Sir,
   Clause 7.3.3 in IS 1893 Part 1 2002 code allowed the reduction of live load in load combinations. This clause has been removed in latest (2016) revision.

Hope that helps
Yours sincerely
S Arunkumar
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sukanta.adhikari
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PostPosted: Fri Jun 21, 2019 5:20 am    Post subject: Reply with quote

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.


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S Adhikari



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hemal
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PostPosted: Fri Jun 21, 2019 11:30 am    Post subject: Seismic / Earthquake Load Combinations for structures/Buildings Reply with quote

Dear Mr. Arunkumar,

Does it overrule clause 8.1, footnote 3 of IS 875 part 5?


Regards,
Hemal Mistry

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