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Daily Digest Thu Jul 22 23:00:03 2004

 
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cdeshpan
SEFI Member
SEFI Member


Joined: 26 Jan 2003
Posts: 6

PostPosted: Thu Jul 22, 2004 7:06 pm    Post subject: Daily Digest Thu Jul 22 23:00:03 2004 Reply with quote

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

----------------------------------------------------------
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
General Sponsor


Joined: 26 Jan 2003
Posts: 1039

PostPosted: Fri Jul 23, 2004 3:11 am    Post subject: Daily Digest Thu Jul 22 23:00:03 2004 Reply with quote

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
SEFI Regulars


Joined: 26 Jan 2003
Posts: 21

PostPosted: Fri Jul 23, 2004 6:03 am    Post subject: Daily Digest Thu Jul 22 23:00:03 2004 Reply with quote

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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