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LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic Load
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sunilamkar
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PostPosted: Mon Jan 12, 2009 5:57 pm    Post subject: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic Load Reply with quote

Hello Everybody!

One of the load combinations mentioned in IS 456: 2000 is (0.9)Dead Load + (1.5)Seismic Load. The same is reflecting in IS 800: 2007 also. This load combination is generally taken into account to check uplift in the structure.

My query is as follows;

"The seismic load generated is fraction of total vertical load  which includes dead load as well as some part of live load (i.e. Seismic coefficient X Total vertical load).

If only 90% of dead load is present on the structure, the seismic load generated will be corresponding to only 90% of dead load. But in the load combination mentioned above, we consider the seismic load generated corresponding to 100% dead load + some part of live load.

How far it is practical ?"

Thanks in advance.

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Sunil J. Amkar
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kishku4u
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PostPosted: Tue Jan 13, 2009 5:57 am    Post subject: Reply with quote

Hi Sunil,

You may confused between the 'calculation of seismic forces' and 'generation of load combination'.

Load factors like 0.9, 1.5 etc will applicable only after arriving seismic forces.
However you have to apply certain factors to imposed load as per table 8 of IS 1893 and not for dead load.

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Krishna kumar
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ibarua
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PostPosted: Tue Jan 13, 2009 7:09 am    Post subject: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic Load Reply with quote

13th Jan 2009

The provision of 0.9*DL is because of the beneficial effect of axial load on a member that is subject to axial load and BM. Sometimes, design of shear walls is governed by this condition.

Indrajit Barua.


On Mon, 12 Jan 2009 sunilamkar wrote :
Quote:
Hello Everybody!

One of the load combinations mentioned in IS 456: 2000
is (0.9)Dead Load + (1.5)Seismic Load. The same is
reflecting in IS 800: 2007 also. This load combination
is generally taken into account to check uplift in the
structure.

My query is as follows;

"The seismic load generated is fraction of total
vertical load  which includes dead load as well as some
part of live load (i.e. Seismic coefficient X Total
vertical load).

If only 90% of dead load is present on the structure,
the seismic load generated will be corresponding to
only 90% of dead load. But in the load combination
mentioned above, we consider the seismic load generated
corresponding to 100% dead load + some part of live
load.

How far it is practical ?"

Thanks in advance.

------------------------
Sunil J. Amkar








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skjain.iitk
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PostPosted: Tue Jan 13, 2009 10:27 am    Post subject: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic Load Reply with quote

The combination involving 0.9D may also govern design of many footings, columns and beams (sagging moment at the ends).

Sudhir Jain


On 1/13/09, ibarua <forum@sefindia.org (forum@sefindia.org)> wrote: [quote]  13th Jan 2009

The provision of 0.9*DL is because of the beneficial effect of axial load on a member that is subject to axial load and BM. Sometimes, design of shear walls is governed by this condition.

Indrajit Barua.


On Mon, 12 Jan 2009 sunilamkar wrote :
--auto removed--

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aditya
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PostPosted: Tue Jan 13, 2009 3:35 pm    Post subject: confusion of drift check for buildings Reply with quote

Dear Respected S. K. Jain Sir,
Is it necessary to check the drift criteria as given under clause 7.11.1 of IS 1893:2002 for all load combinations? I could not get clear response from the forum. Should it be checked for lateral load case only? and why?
Please kindly clarify.
with regards,
aditya
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sunilamkar
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PostPosted: Tue Jan 13, 2009 5:40 pm    Post subject: Reply with quote

Dear Indrajit Sir and S.K. Jain Sir,

Thanks a lot for your reply.
I understood the requirement of this load combination.

Regards

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skjain.iitk
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PostPosted: Tue Jan 20, 2009 1:11 pm    Post subject: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic Load Reply with quote

Dear Aditya:

In my opinion, the drift is to be checked only for the seismic force (and without any partial load factor on the seismic force). When checking the drift requirement, one will not usually apply the dead and live loads.

Best regards,

Sudhir Jain
IIT Kanpur


On 1/13/09, aditya <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
  Dear Respected S. K. Jain Sir,
Is it necessary to check the drift criteria as given under clause 7.11.1 of IS 1893:2002 for all load combinations? I could not get clear response from the forum. Should it be checked for lateral load case only? and why?
Please kindly clarify.
with regards,
aditya







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Dr. N. Subramanian
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PostPosted: Wed Jan 21, 2009 2:58 am    Post subject: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic Load Reply with quote

Dear Prof. Jain,

Though the lateral load only produces lateral deformation in symmetric structures, D.L. and L.L. will always be present in any structure. Will not taking only lateral load for calculation of drift, represent a fictitious loading condition? Moreover, what harm will it produce if we consider DL + LL also. Moreover in unsymmetric structures will there not be some lateral deflection due to DL+LL also?

Regards,
Subramanian

--- On Tue, 1/20/09, skjain.iitk <forum@sefindia.org> wrote:
[quote]From: skjain.iitk <forum@sefindia.org>
Subject: [SEFI] Re: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic Load
To: general@sefindia.org
Date: Tuesday, January 20, 2009, 11:47 PM

Dear Aditya:

In my opinion, the drift is to be checked only for the seismic force (and without any partial load factor on the seismic force). When checking the drift requirement, one will not usually apply the dead and live loads.

Best regards,

Sudhir Jain
IIT Kanpur


On 1/13/09, aditya forum@sefindia.org)> wrote:        --auto removed--

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jiwajidesai
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PostPosted: Wed Jan 21, 2009 4:56 am    Post subject: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic Load Reply with quote

Dear Prof Jain

If you permit, I would like to add the following to what Dr Subramanian has stated in his mail below and seek your comments/guidance.

Seismic force would be generated from the masses actually present at the time of prevalent Load condition, ie if (design) IL is present in addition to (design) DL (which is permanently present as Dr Subramanian has pointed out), inertial lateral seismic force would also be accordingly higher, though vertical stabilizing force would also increase.  

Accordingly, in my thinking both the following combinations (at least) need to be checked respectively for all structural members:-
a)DL + EQd
b)DL + LL + EQi
with the proviso that  
<![if !supportLists]>a) <![endif]>relevant PSF’s would be applied as per SLS  
<![if !supportLists]>b) <![endif]>EQ is based upon the considered loading-masses EQd calculated using only designDL and EQi using DL and design proportion/occurrence of IL
Regards

Jiwaji Desai


From: drnsmani [mailto:forum@sefindia.org]
Sent: Wednesday, January 21, 2009 9:17 AM
To: general@sefindia.org
Subject: [SEFI] Re: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic Load


Dear Prof. Jain,

Though the lateral load only produces lateral deformation in symmetric structures, D.L. and L.L. will always be present in any structure. Will not taking only lateral load for calculation of drift, represent a fictitious loading condition? Moreover, what harm will it produce if we consider DL + LL also. Moreover in unsymmetric structures will there not be some lateral deflection due to DL+LL also?

Regards,
Subramanian

--- On Tue, 1/20/09, skjain.iitk wrote:
Quote:
From: skjain.iitk
Subject: [SEFI] Re: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic Load
To: general@sefindia.org (general@sefindia.org)
Date: Tuesday, January 20, 2009, 11:47 PM

Dear Aditya:

In my opinion, the drift is to be checked only for the seismic force (and without any partial load factor on the seismic force). When checking the drift requirement, one will not usually apply the dead and live loads.

Best regards,

Sudhir Jain
IIT Kanpur


On 1/13/09, aditya forum@sefindia.org (forum@sefindia.org))> wrote: --auto removed--  







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Jalil A. Sheikh
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Joined: 06 Dec 2008
Posts: 18

PostPosted: Wed Jan 21, 2009 11:31 am    Post subject: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic Load Reply with quote

Dear sefians,

I have to design a parking structure having basement + ground + three storied. EQ zone is III . There are no peripherial walls around whole building except in basement floor. Perapet walls at periphery at all upper stories are of m.s. sections i.e. no facade to resist wind load. Building is open @ all four sides. Now my question is should i consider wind load in load combinations or not? If yes then reason behind it.

JALIL SHEIKH

--- On Wed, 21/1/09, jiwajidesai <forum@sefindia.org> wrote:

[quote]From: jiwajidesai <forum@sefindia.org>
Subject: [SEFI] Re: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic Load
To: general@sefindia.org
Date: Wednesday, 21 January, 2009, 5:20 AM

Dear Prof Jain

If you permit, I would like to add the following to what Dr Subramanian has stated in his mail below and seek your comments/guidance.

Seismic force would be generated from the masses actually present at the time of prevalent Load condition, ie if (design) IL is present in addition to (design) DL (which is permanently present as Dr Subramanian has pointed out), inertial lateral seismic force would also be accordingly higher, though vertical stabilizing force would also increase.

Accordingly, in my thinking both the following combinations (at least) need to be checked respectively for all structural members:-
a)DL + EQd
b)DL + LL + EQi
with the proviso that
a) relevant PSF’s would be applied as per SLS
b) EQ is based upon the considered loading-masses EQd calculated using only designDL and EQi using DL and design proportion/occurrence of IL
Regards

Jiwaji Desai


From: drnsmani [mailto:forum@sefindia.org]
Sent: Wednesday, January 21, 2009 9:17 AM
To: general@sefindia.org (general@sefindia.org)
Subject: [SEFI] Re: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic Load


Dear Prof. Jain,

Though the lateral load only produces lateral deformation in symmetric structures, D.L. and L.L. will always be present in any structure. Will not taking only lateral load for calculation of drift, represent a fictitious loading condition? Moreover, what harm will it produce if we consider DL + LL also. Moreover in unsymmetric structures will there not be some lateral deflection due to DL+LL also?

Regards,
Subramanian

--- On Tue, 1/20/09, skjain.iitk wrote:
--auto removed--

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