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skjain.iitkGeneral Sponsor

Joined: 26 Jan 2003Posts: 104

Posted: Wed Jan 21, 2009 6:08 pm Post subject: LOAD COMBINATION : (0.9)Dead Load +(1.5)Seismic Loa d

Dear Dr Subramanian and Mr Desai:

With reference to your comments on my mail yesterday:

a) The drift check is meant to ensure that the building has adequate lateral stiffness. This can be

achieved by checking the displacements under the design seismic force. It does not mean that

under certain situations, dead or live loads do not cause lateral deflections. Trying to do the

stiffness check under different load combinations of dead, live and seismic does not add much

information but adds to the work of the structural engineer. Hence, traditionally the seismic codes

have asked this check on the code-specified seismic loads (separately, for force in x-direction and

for force in y-direction), without considering the gravity loads.

b) One could argue that we should obtain different seismic weights (and hence seismic loads) for

different loadcombinations. Forinstance, one could say: why to consider 25% or 50% of live load

(as the case may be) for computing the design earthquake load, that will then be used in the

load combination of 0.9DL+1.5LL, and for this load case let us compute the seismic load on the

basis that there are no live loadspresent and the seismic weight is 90% of the deadload. This

will mean that we use different se ismic loads for different load combinations. Again, earthquake

forces specified in the codes are gross simplification of a complex phenomenon and hence, such

finer details are usua lly not needed because o f the complexity that these will add to the design

process without commensurate advantage in safety/economy. Hence, the codes expect one to

calculate the design seismic load once (different in x- and y-directions) and use it for any of the

load combination.

Such simplifications enable the design engineer to spend more time on other aspects (e.g.,

deta iling) that have far more impact on safety of the structure.

With best regards,

Sudhir Jain

On 1/21/09,jiwajidesai wrote: [quote] Dear Prof

Jain

If you permit, I would like to add the following to what Dr Subramanian has sta ted 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:-

59kLi ke S ha r e
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2/11

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 us ing only designDL and EQi

using DL and design proportion/occurrence of IL

Regards

Jiwaji Desai

From: drnsmani [mailto:[email protected] ([email protected] )]

Sent: Wednesday, January 21, 2009 9:17 AM

To: [email protected]([email protected])

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 w ill there not be some lateral deflection due to

DL+LL also?

Regards,

Subramanian

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

--auto removed--

Posted via Email

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aditya...

Joined: 05 Apr 2008Posts: 108

Posted: Wed Jan 21, 2009 6:19 pm Post subject: drift checking still nagging me

Dear Respected Dr. S. K. Jain Sir and Dr. Subrahamaniam Sirs,Thanks a lot for your kind responses. It seems that this issue still needs further elaborations to

us from both of you so that we get more enlightened on this confusion. I would again request a ll

to go through examples given in the "International Handbook of Earthquake Engineering, editor

Mario Paz" and kindly explain WHY IS IT THAT only SEISMIC LOAD CASE is only to be considered

as shown in the examples though most of us believe that DRIFT CHECKING should be done for

LOAD COMBINATION with SEISMIC LOAD. ASCE 07 a lso seem to suggest taking only SEISMIC

LOAD CASE only and not LOAD COMBINATION. Why this paradox?

Please kindly help me to resolve this seemingly paradoxical situation.

with best regards to all sefians,

aditya

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Dr. N. SubramanianGeneral Sponsor

Joined: 21 Feb 2008Posts: 4753

Location: Gaithersburg,MD, U.S.A.

Posted: Wed Jan 21, 2009 8:35 pm Post subject: LOAD COMBINATION : (0.9)Dead Load +(1.5)Seismic Loa d

Dear Mr. Jalil,

From your description of the building being designed by you, I find that there are not many

elements on which wind will be impinging; Hence even if you calculate the wind load it may not be

high enough to affect your design.

Regards,

NS

Dr.N.Subramanian,Ph.D.,F.ASCE, M.ACI,

Consulting Structural Engineer

Maryland, USA

See my books at: www.multi-science.co.uk/subramanian-book.htm

www.oup.co.in/search_detail.php?id=144559
http://www.oup.co.in/search_detail.php?id=144559http://www.multi-science.co.uk/subramanian-book.htmhttp://www.sefindia.org/forum/posting.php?mode=quote&p=10525http://www.sefindia.org/forum/viewtopic.php?p=10525#10525http://www.sefindia.org/forum/privmsg.php?mode=post&u=1848http://www.sefindia.org/forum/profile.php?mode=viewprofile&u=1848http://-/?-http://www.sefindia.org/forum/posting.php?mode=quote&p=10523http://-/?-http://www.sefindia.org/forum/privmsg.php?mode=post&u=1541http://www.sefindia.org/forum/profile.php?mode=viewprofile&u=1541http://-/?-mailto:[email protected]:[email protected]:[email protected]


3/11

--- On Wed, 1/21/09, Jalil A. Sheikhwrote:

Quote:

From: Jalil A. Sheikh Subject: [SEFI] Re: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic LoadTo: [email protected]: Wednesday, January 21, 2009, 5:23 PM

Dear sefians,

I have to design a park ing structure having basement + ground + three storied. EQ zone is III. There are no peripherial walls around whole building except in basement floor. Perapet wallsat periphery at all upper stories are of m.s. sections i.e. no facade to resist wind load. Buildingis open @ all four sides. Now my question is should i consider wind load in load combinations ornot? If yes then reason behind it.

JALIL SHEIKH

--- On Wed, 21/1/09, jiwajidesai wrote:

Quote:

From: jiwajidesaiSubject: [SEFI] Re: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic LoadTo: [email protected]([email protected])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 statedin his mail below and seek your comments/guidance.

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

Accordingly, in my thinking both the following combinations (at least) need to bechecked respectively for all structural members:-a)DL + EQdb)DL + LL + EQiwith the proviso thata) relevant PSFs would be applied as per SLSb) EQ is based upon the considered loading-masses EQd calculated using onlydesignDL and EQi using DL and design proportion/occurrence of ILRegards

Jiwaji Desai

From: drnsmani [mailto:[email protected]]Sent: Wednesday, January 21, 2009 9:17 AMTo: [email protected]([email protected]) ([email protected]([email protected]))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 loadfor calculation of drift, represent a fictitious loading condition? Moreover, what harm

will it produce if we consider DL + LL also. Moreover in unsymmetric structures willthere not be some lateral deflection due to DL+LL also?

Regards,Subramanian

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

Posted via Email

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Posted: Thu Jan 22, 2009 12:23 am Post subject: LOAD COMBINATION : (0.9)Dead Load +(1.5)Seismic Loa d
http://www.sefindia.org/forum/posting.php?mode=quote&p=10533http://www.sefindia.org/forum/viewtopic.php?p=10533#10533http://www.sefindia.org/forum/privmsg.php?mode=post&u=473http://www.sefindia.org/forum/profile.php?mode=viewprofile&u=473http://-/?-mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]


4/11

Joined: 21 Feb 2008Posts: 4753Location: Gaithersburg,MD, U.S.A.

Dear Prof. Jain,

Many thanks for educating me.

Of course, drift is a serviceability criterion and hence has to be checked a t working loads ( with a

partial load factor of 1.0). It is well known that we are not designing normal structures for the full

EQ load. Even then, may be, the drift effect due to DL+LL will be small compared to the drift for

EQ load.

Though Clause 7.11.1 of IS 1893:2002 states that "the storey drift in any storey due to the

minimum specified des ign lateral force,with a partial load factor of 1.0, sha ll not exceed 0.004times the storey height", somehow it did not strike to me that the drift has to be computed only

for EQ load.

Best regards

Subramanian

--- On Wed, 1/21/09, skjain.iitk wrote:

Quote:

From: skjain.iitk Subject: [SEFI] Re: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic LoadTo: [email protected]: Wednesday, January 21, 2009, 6:29 PM



a) The drift check is meant to ensure that the building has adequate lateral stiffness. This canbe achieved by checking the displacements under the design seismic force. It does not meanthat under certain situations, dead or live loads do not cause lateral deflections. Trying to do

the stiffness check under different load combinations of dead, live and se ismic does not addmuch information but adds to the work of the structural engineer. Hence, traditionally theseismic codes have asked this check on the code-specified seismic loads (separately, for forcein x-direction and for force in y-direction), without considering the gravity loads.

b) One could argue that we should obtain different seismic weights (and hence seismic loads)for different load combinations. For instance, one could say: why to consider 25% or 50% oflive load (as the case may be) for computing the design earthquake load, that will then beused in the load combination of 0.9DL+1.5LL, and for this load case let us compute the seismicload on the basis that there are no live loads present and the seismic weight is 90% of thedeadload. This will mean that we use different seismic loads for different load combinations.Again, earthquake forces specified in the codes are gross simplification of a complexphenomenon and hence, such finer details are usually not needed because of the complexitythat these will add to the design process without commensurate advantage in sa fety/economy.Hence, the codes expect one to calculate the design seismic load once (different in x- and y-directions) and use it for any of the load combination.


detailing) that have far more impact on safety of the structure.

With best regards,

Sudhir Jain

On 1/21/09, jiwajidesai [email protected] )> wrote:

Quote:

Dear Prof Jain



Accordingly, in my thinking both the following combinations (at least) need to bechecked respectively for all structural members:-a)DL + EQdb)DL + LL + EQiwith the proviso thata) relevant PSF's would be applied as per SLSb) EQ is based upon the considered loading-masses EQd calculated using only
mailto:[email protected]:[email protected]


5/11

designDL and EQi using DL and design proportion/occurrence of ILRegards

Jiwaji Desai

From: drnsmani [mailto:[email protected] ([email protected]([email protected] ))]Sent: Wednesday, January 21, 2009 9:17 AMTo: [email protected]([email protected]) ([email protected]([email protected]))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 loadfor calculation of drift, represent a fictitious loading condition? Moreover, what harmwill it produce if we consider DL + LL also. Moreover in unsymmetric structures willthere not be some lateral deflection due to DL+LL also?

Regards,Subramanian


Posted via Email

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Joined: 21 Feb 2008Posts: 4753Location: Gaithersburg,MD, U.S.A.


Dear Mr. Aditya,

Prof. S.K. Jain has given clearly the following opinion:

"The drift is to be checked only for the se ismic force (and w ithout any partial load factor on the

seismic force). When checking the drift requirement, one will not usually apply the dead and live

loads". Even now you have confusion?!

With the above clarification, it may be clear why Dr Mario Paz 's book "International Handbook of

Earthquake Engineering, considers only SEISMIC LOAD CASE in the examples for drift checking.

Many of us may not have access to that book though I have gone through that book once.

Best wishes

NS

Dr.N.Subramanian,Ph.D.,F.ASCE, M.ACI,

Consulting Structural Engineer

Maryland, USA

See my books at: www.multi-science.co.uk/subramanian-book.htm

www.oup.co.in/search_detail.php?id=144559

--- On Wed, 1/21/09, aditya wrote:

Quote:

From: aditya Subject: [SEFI] Re: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic LoadTo: [email protected]: Wednesday, January 21, 2009, 6:19 PM

Dear Respected Dr. S. K. Jain Sir and Dr. Subrahamaniam Sirs,
mailto:[email protected]://www.oup.co.in/search_detail.php?id=144559http://www.multi-science.co.uk/subramanian-book.htmhttp://www.sefindia.org/forum/posting.php?mode=quote&p=10534http://www.sefindia.org/forum/viewtopic.php?p=10534#10534http://www.sefindia.org/forum/privmsg.php?mode=post&u=473http://www.sefindia.org/forum/profile.php?mode=viewprofile&u=473http://-/?-mailto:[email protected]:[email protected]:[email protected]:[email protected]


6/11

Thanks a lot for your kind responses. It seems that this issue still needs further elaborations tous from both of you so that we get more enlightened on this confusion. I would again requestall to go through examples given in the "International Handbook of Earthquake Engineering,editor Mario Paz" and kindly explain WHY IS IT THAT only SEISMIC LOAD CASE is only to beconsidered as shown in the examples though most of us believe that DRIFT CHECKING shouldbe done for LOAD COMBINATION with SEISMIC LOAD. ASCE 07 also seem to suggest takingonly SEISMIC LOAD CASE only and not LOAD COMBINATION. Why this paradox?Please kindly help me to resolve this seemingly paradoxical situation.with best regards to all sefians,aditya

Posted via Email

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ishaconSilver Sponsor



Thanks Dr. Jain, for the detailed explanation

which should put a lot of minds to rest.

Unfortunately in several design cases we find that for 1.2(DL+EQL+LL)

case also, there are misconceptios. I see no merit in using only 25%

of LL in above formulation as for des ign of beams on any particular floor

of a multi storeyed housing building tower,

the full live load should be applicable and not 25% as several designers

take as per IS 1893, since only 25% LL is used for se ismic weight calculations.

V.P. Agarwal

ISHA CONSULTANTS (P) LTD

NEW DELHI

PH : 011- 2630 1158

(M) 93 1345 2180

(M) 98 6826 2759

[email protected] ([email protected])

[email protected] ([email protected])

Quote:

----- Original Message -----From:skjain.iitk ([email protected] )To:[email protected]([email protected])Sent:Wednesday, January 21, 2009 6:29 PMSubject:[SEFI] Re: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic Load



a) The drift check is meant to ensure that the building has adequate lateral stiffness. This canbe achieved by checking the displacements under the design seismic force. It does not meanthat under certain situations, dead or live loads do not cause lateral deflections. Trying to dothe stiffness check under different load combinations of dead, live and se ismic does not addmuch information but adds to the work of the structural engineer. Hence, traditionally theseismic codes have asked this check on the code-specified seismic loads (separately, for forcein x-direction and for force in y-direction), without considering the gravity loads.

b) One could argue that we should obtain different seismic weights (and hence seismic loads)for different load combinations. For instance, one could say: why to consider 25% or 50% oflive load (as the case may be) for computing the design earthquake load, that will then beused in the load combination of 0.9DL+1.5LL, and for this load case let us compute the seismicload on the basis that there are no live loads present and the seismic weight is 90% of thedeadload. This will mean that we use different seismic loads for different load combinations.Again, earthquake forces specified in the codes are gross simplification of a complexphenomenon and hence, such finer details are usually not needed because of the complexitythat these will add to the design process without commensurate advantage in sa fety/economy.Hence, the codes expect one to calculate the design seismic load once (different in x- and y-directions) and use it for any of the load combination.

Such simplifications enable the design engineer to spend more time on other aspects (e.g.,detailing) that have far more impact on safety of the structure.

With best regards,

Sudhir Jain

On 1/21/09, jiwajidesai [email protected] )> wrote:
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]://www.sefindia.org/forum/posting.php?mode=quote&p=10537http://www.sefindia.org/forum/viewtopic.php?p=10537#10537http://www.sefindia.org/forum/privmsg.php?mode=post&u=473http://www.sefindia.org/forum/profile.php?mode=viewprofile&u=473http://-/?-


7/11

Quote:

Dear Prof Jain



Accordingly, in my thinking both the following combinations (at least) need to be

checked respectively for all structural members:-a)DL + EQdb)DL + LL + EQiwith the proviso thata) relevant PSF's would be applied as per SLSb) EQ is based upon the considered loading-masses EQd calculated using onlydesignDL and EQi using DL and design proportion/occurrence of ILRegards

Jiwaji Desai

From: drnsmani [mailto:[email protected] ([email protected]([email protected] ))]Sent: Wednesday, January 21, 2009 9:17 AMTo: [email protected]([email protected]) ([email protected]([email protected]))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 loadfor calculation of drift, represent a fictitious loading condition? Moreover, what harmwill it produce if we consider DL + LL also. Moreover in unsymmetric structures willthere not be some lateral deflection due to DL+LL also?

Regards,Subramanian


No virus found in this incoming message.Checked by AVG - http://www.avg.comVersion: 8.0.176 / Virus Database: 270.10.10/1905 - Release Date:1/20/2009 2:34 PM

Posted via Email

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aditya...


Posted: Thu Jan 22, 2009 9:03 am Post subject: Thank s a lot on Drift Issue discussion!

Dear Respected Dr. S. K. Jain & Dr. N. Subrahamaniam Sirs,

I would like to express my sincere gratitude to both of you for kindly enlightening me in this issue

of drift calculation. My latter mail was posted before I read the comment from Dr. Jain and hence

my query. But now, the case is clear and thanks to other sefians as well.

I would like to suggest that SEFINDIA should also s tart another section dedicated to software

discussion beacuse I find that many users have problems or queries regarding the use &

interpretation of so ftwares like ETABS, SAP2000, STAAD.Pro etc and starting separate section

would enable separate discussion section under this forum itself while limiting the discussion on

the software issue only and I think it would lessen the clutter in discussion forum.

with best regards to all,

aditya

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JVCSNL...

http://www.sefindia.org/forum/posting.php?mode=quote&p=10541http://www.sefindia.org/forum/viewtopic.php?p=10541#10541http://www.sefindia.org/forum/privmsg.php?mode=post&u=1848http://www.sefindia.org/forum/profile.php?mode=viewprofile&u=1848http://-/?-http://www.sefindia.org/forum/posting.php?mode=quote&p=10539http://www.sefindia.org/forum/viewtopic.php?p=10539#10539http://www.sefindia.org/forum/privmsg.php?mode=post&u=22http://www.sefindia.org/forum/profile.php?mode=viewprofile&u=22http://-/?-http://www.avg.com/mailto:[email protected]:[email protected]:[email protected]:[email protected]


8/11


Dear SEFI members,

Further to Prof. Jain's explanation on consideration of se ismic weight, I would like to add following

points:

1. The seismic load (say EQ) is calculated using seismic we ight comprising of Full Dead load and

appropriate portion of Live load as per applicable code. This phenomena is undoubtedly universal.

There are several reasons behind consideration of only part live loads. The live loads by definition

are not supposed to be present all the time and are movable. Anything other than selfweight of

structure is likely to be a pe rmanent load (like in racks in libraries, store rooms or any permanent

facilities), the same shall be considered as permanent load like DL and 100% weights of suchparts shall be included in seismic we ights.

Please note that this is now a primary load like DL, IL and WL.

2. The load combinations are derived to produce most severe effects on the structure. One of

such combinations is 0.9DL +/- 1.5EQ.

You may all agree that this will generally produce the uplift condition for foundation, columns and

column bases in case of steel structures.

Large portion of the se ismic masses (weight) is generally lumped a t the floor level and its

distribution to individual columns in case o f RC frame structure or to bracing system in case of

steel structure, is based on lateral stiffness of the lateral load (like EQ) resisting system. Hence,the lateral forces are resisted by overall structural system.

Since, live load is not permanent, it may so happen that a portion of live loads may be present

only in one portion of the floor. In such condition, the other portion of the floor may not be loaded

by live loads and some columns may not be carrying the downward effects of live loads. However,

the lateral load produced by full DL + part LL will be res isted by the whole system. Thus, those

columns which are not carrying the downward live loads will also be resisting the seismic loads.

Hence, though a particular column is not carrying component o f live loads , it carries effects of

seismic loads produced on overall system. The combination 0.9DL +/- 1.5EQ will take care of this

condition.

To summarize, please note that there can not be different earth quake loads for different

combinations.

In both combinations

1. 0.9DL +/- 1.5EQ and

2. 1.2(DL+LL+/- EQ)

the EQ is calculated using seismic weight = DL + (x%) LL , where X% is taken from relevant

codes.

Someone suggested in a later mail considering full LL in seismic we ight. This would generally be

very conservative and rather not a practical situation. This consideration will also not yield

economical structure and we all know everyone is behind structural engineer to reduce the cost

of structure.

Regards,

Jignesh V Chokshi

Quote:

Quote:

Quote:

[email protected] 21-01-2009 >>>



a) The drift check is meant to ensure that the building has adequate lateral stiffness. This can be

achieved by checking the displacements under the design seismic force. It does not mean that

under certain situations, dead or live loads do not cause lateral deflections. Trying to do the

stiffness check under different load combinations of dead, live and se ismic does not add much


9/11

information but adds to the work of the structural engineer. Hence, traditionally the seismic codes

have asked this check on the code-specified seismic loads (separately, for force in x-direction and

for force in y-direction), without considering the gravity loads .

b) One could argue that we should obtain different seismic weights (and hence seismic loads) for

different load combinations. For instance, one could say: why to consider 25% or 50% of live load

(as the case may be) for computing the design earthquake load, that will then be used in the

load combination of 0.9DL+1.5LL, and for this load case let us compute the seismic load on the

basis that there are no live loads present and the se ismic weight is 90% of the deadload. This

will mean that we use different se ismic loads for different load combinations. Again, earthquake

forces specified in the codes are gross simplification of a complex phenomenon and hence, suchfiner details are usua lly not needed because o f the complexity that these will add to the design

process without commensurate advantage in safety/economy. Hence, the codes expect one to

calculate the design seismic load once (different in x- and y-directions) and use it for any of the

load combination.


deta iling) that have far more impact on safety of the structure.

With best regards,

Sudhir Jain

On 1/21/09, jiwa jidesai [email protected] )> wrote:Quote:

Dear Prof Jain

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

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

Accordingly, in my thinking both the following combinations (at least) need to be checkedrespectively for all structural members:-a)DL + EQdb)DL + LL + EQiwith the proviso that

a) relevant PSF's would be applied as per SLSb) EQ is based upon the considered loading-masses EQd calculated using only designDL andEQi using DL and design proportion/occurrence of ILRegards

Jiwaji Desai

From: drnsmani [mailto:[email protected] ([email protected] ([email protected]))]Sent: Wednesday, January 21, 2009 9:17 AMTo: [email protected]([email protected]) ([email protected] ([email protected]))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. andL.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 weconsider DL + LL also. Moreover in unsymmetric structures will there not be some lateraldeflection due to DL+LL also?

Regards,Subramanian


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vikram.jeetGeneral Sponsor

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10/11


Dear Dr SK Jain & Mr VP Agarwaal

Thanks for the clarrifications on the forum

consensus on this aspect was due because lot many times

the designers differ in interpretation of load combination

to be adopted during EQ conditions and tend to err on

unsafer side

thus for load combination of 1.2(DL+LL)+1.2EQ

The right interpretation is:

1.2(DL +LL as per IS 875with reduction in vertival load for foundations & columns only)

+1.2EQ [computed on(DL+ 25%or 50%LL)]

WRONG Interpretation:

1.2[DL + (25%or 50%)LL] +1.2EQ [computed on(DL+ 25%or 50%LL)]

with regards

vikramjeet

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jiwajidesaiGeneral Sponsor

Joined: 23 May 2008Posts: 34

Posted: Thu Jan 22, 2009 12:16 pm Post subject: LOAD COMBINATION : (0.9)Dead Load +(1.5)Seismic Loa d

Dear Vikram Jeet

I refer to Clause 7.3 of BIS 1893-2002

The Code gives reduction in LL as full LL is not present during the seismic event. Then why is that

full Live load is combined in your wrong interpretation with EQ (which corresponds to the mass

that is present).

The Code also says that no further reduction as per BIS 875 (2) for loads on columns / foundation

is permissible as you have probably implied in your interpretation.

Regards

Jiwaji Desai

From:vikram.jeet [mailto:[email protected]]

Sent:Thursday, January 22, 2009 11:22 AM

To:[email protected]

Subject:[SEFI] Re: LOAD COMBINATION : (0.9)Dead Load + (1.5)Seismic Load

Dear Dr SK Jain & Mr VP Agarwaal

Thanks for the clarrifications on the forum

consensus on this aspect was due because lot many times

the designers differ in interpretation of load combination

to be adopted during EQ conditions and tend to err on

unsafer side

thus for load combination of 1.2(DL+LL)+1.2EQ

The right interpretation is:

1.2(DL +LL as per IS 875with reduction in vertival load for foundations & columns only)

+1.2EQ [computed on(DL+ 25%or 50%LL)]

WRONG Interpretation:

1.2[DL + (25%or 50%)LL] +1.2EQ [computed on(DL+ 25%or 50%LL)]
mailto:[email protected]://www.sefindia.org/forum/posting.php?mode=quote&p=10543http://www.sefindia.org/forum/viewtopic.php?p=10543#10543http://www.sefindia.org/forum/privmsg.php?mode=post&u=1752http://www.sefindia.org/forum/profile.php?mode=viewprofile&u=1752http://-/?-


11/11

with regards

vikramjeet

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