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cdeshpan SEFI Member
Joined: 26 Jan 2003 Posts: 6
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Posted: Thu Jul 22, 2004 7:06 pm Post subject: Daily Digest Thu Jul 22 23:00:03 2004 |
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Dear Sir,
I would appreciate if you can explain more regarding your recent post :"I have serious reservations on zoning in Peninsular India. During the past 40 years upgradation has taken place only in Peninsular India.Most of it is unjustified. " Why do you consider it unjustified?
Thanks in advance,
Chitra
Quote: | Message From for_prof_arc@hotmail.com Subject: Re: regarding reduction in live load Date: 22/07/04 Time: 17:05:55
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Quote: | Dear Mr. Joshi,
I agree with you that far too many combinations have been specified and no commentary is given explaining the reasons for the same. I would like that only effective live load (less than 100% of live load) be used when earthquake effects are considered.
You should realise that Code is always a compromise and can be illogical. But once it is published, we have no alternative but to adhere to it. Doubts regarding the various clauses should be formally cleared by BIS. In future editions, BIS should give due considerations to views of users.
I have serious reservations on zoning in Peninsular India. During the past 40 years upgradation has taken place only in Peninsular India.Most of it is unjustified.
I also have reservations on anchoring the base shear based on empirically determined fundamental period.
sincerely ARC
PS: Prof. Sudhir Jain is doing a wonderful work and more importantly, he is open to suggestions. He has an active role in formulations of the code and I hope he would react to your query either via SEFI or by direct mail and clarify what is meant by EQ and LL in 1.5(DL+EQ) & 1.2(LD+LL+EQ). I would also like to know whether EQ in the first case means EQ on DL only and in second case LL means LL considered for EQ or LL is full live load and EQ is for DL+effective LL
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ibarua General Sponsor
Joined: 26 Jan 2003 Posts: 1039
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Posted: Fri Jul 23, 2004 3:11 am Post subject: Daily Digest Thu Jul 22 23:00:03 2004 |
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LIVE LOAD COMBINED WITH EQ. FORCES ----------------------------------
1. Codes allow reduction in LL because the probabilty that the design eartquake will occur at the precise time when the structure is loaded with the maximum or design LL is remote (probably because of divine providence or intervention!). The codes, in my view are not illogical, at least in this case.
2. The Code prescribes design for 1.5*(DL+LL) [here LL is the design or maximum LL] and 1.2*(DL+LL+EQ) [here LL is the reduced LL]
3. Base shears may be computed using computer based methods. The base shear obtained by such computations is often much lower that what is found from the empirical formulae. The ACI Code prescribes that in such a case, the base shears obtained from the empirical formulae shall be used for design.
Indrajit Barua Consulting Engineer, Guwahati, Assam. (Seismic Zone V) On Thu, 22 Jul 2004 general@sefindia.org wrote : [quote]---------------------------------------------------------
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vandana_bimal SEFI Regulars
Joined: 26 Jan 2003 Posts: 21
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Posted: Fri Jul 23, 2004 6:03 am Post subject: Daily Digest Thu Jul 22 23:00:03 2004 |
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Dear Ashok
As far as the load combinations in the code are concerned, you should understand that there are four basic load cases 1. Dead loads (DL) 2. Live Loads (LL) 3. Wind Loads (WL) 4. Earthquake Loads (EQ)
There is no ambiguity in understanding these loads as they are always 100% at the time of calculating each one of them seperately.
Now it so happens that as EQ is not a force but an acceleration, the loads generated by ground motion are dependent on DL and LL because of inertia of the building. So while calculating EQ loads, full DL and a %age of LL (50 or 25) is to be considered and the EQ loads are generated. Now once the load case is ready, then we should go for load combinations at the design stage.
Thus for the load combination 1.5(DL + EQ) we do not have to consider LL (This combination is applicable when the building is ready but not occupied so the LL is zero)
Similarly, for the combination of 1.2(DL+LL+EQ) you have to consider the full LL only as it is a seperate load case.
I hope this clarifies your question regarding load combinations.
regards Bimal Shah MSU, Baroda
Respected sir, In your reply to Mahesh, you have said that the live load is reduced. i want to ask that suppose a building a subjected live load more than 5kN/m2 , now for calculating the earth quake forces whether we have to consider or not the live load for the load combination of 1.5(DL+EQ). If not why. The next question is for 1.2(LD+LL+EQ) combination the live load taken should be full or some % of live load as per the live load intensity on structure. I kept this question on sefi site also. a lot answers i replyed but not satisfactory for me. Please answer my questions in a detailed way.
Regards
ashok
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