[SEFI] Re: ( DL + EQ ) Load Combinations

[p_hkumar]

Dear sir,

I too have a question regarding Load combinations.

In the combinations of 1.5(DL+EQ) and 0.9DL+1.5EQ what should be the mass of the structure to be taken for finding out EQ force? Is it the mass consisting of DL + 50% LL or only DL??

Generally in building design for arriving at EQ force, mass on the structure is taken to be deadload and a portion of live load. By taking this same EQ force for the combinations 1.5(DL+EQ) and 0.9DL+1.5EQ are we not making a mistake ? Since EQ force with only Dead load as the mass of the structure will be different from the EQ force with Dead load+portion of live load as the mass.

Also, while combining only DL and EQ it does not make sense for me to take an EQ force which is due to dead mass and live mass. May be my understanding of load combinations is not clear...

Please Help....


Hemanth Kumar
Design Engineer,
NTPC Limited




On Mon, 04 Aug 2008 skjain.iitk wrote :

Quote:

Dear Colleagues: I may mention that besides the load combinations listed below by Mr Varyani, the IS456 also requires that the structure should also be designed for 0.9DL + 1.5 EQ. This clarification is needed just so that someone does not get the false impression that the load combination 0.9DL + 1.5 EQ is not of consequence. In fact, it does govern design of many elements in the typical building projects. With best regards, Sudhir k Jain IIT Kanpur

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[jiwajidesai]

Yes, Hemanth, you are quite right. One has to consider that mass which contributes to the inertial effects during a particular EQ combination. If LL is not part of the combination, question of reducing it (by taking a portion of it) does not arise, as it is already equated to zero in this combination.
This is a problem, when some engineers use identical lumped joint weights in primary EQ cases in STAAD, calculated using DL and LL, uniformly for all EQ combinations even not involving LL.
Regards

Jiwaji Desai
Sr. GM (C & S[b])
WSP Engineering Services Ltd.[/b]

From: p_hkumar [mailto:fo...@sefindia.org]
Sent: Tuesday, August 05, 2008 12:47 PM
To: gen...@sefindia.org
Subject: [SEFI] Re: ( DL + EQ ) Load Combinations


Dear sir,

I too have a question regarding Load combinations.

In the combinations of 1.5(DL+EQ) and 0.9DL+1.5EQ what should be the mass of the structure to be taken for finding out EQ force? Is it the mass consisting of DL + 50% LL or only DL??

Generally in building design for arriving at EQ force, mass on the structure is taken to be deadload and a portion of live load. By taking this same EQ force for the combinations 1.5(DL+EQ) and 0.9DL+1.5EQ are we not making a mistake ? Since EQ force with only Dead load as the mass of the structure will be different from the EQ force with Dead load+portion of live load as the mass.

Also, while combining only DL and EQ it does not make sense for me to take an EQ force which is due to dead mass and live mass. May be my understanding of load combinations is not clear...

Please Help....


Hemanth Kumar
Design Engineer,
NTPC Limited




On Mon, 04 Aug 2008 skjain.iitk wrote :

[b]--auto removed--

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[sdec.in]

Dear hemant
Pl go thru the Part-V of IS-875 which clearly states that the portion of live load to be considered for EQ Load Combinations, will also be considered while working out the seismic weights.
i.e. if 50% LL is being considered for Combinations of EQ, it shall also be 50% LL and DL while working out the seismic weights.In fact DL and LL both will be existing while the EQ may strike, and that's why LL(or a part of it) is considered as well, while calculating Joint weights. The proportions for combinations during EQ are based on extensive research and only then are adopted by BIS Committees; maybe Dr Jain may like to give some more explanation about it.

Best regards
Sangeeta Wij
[quote] ----- Original Message -----
From: p_hkumar (fo...@sefindia.org)
To: gen...@sefindia.org (gen...@sefindia.org)

Sent: Tuesday, August 05, 2008 12:47 PM

Subject: [SEFI] Re: ( DL + EQ ) Load Combinations

Dear sir,

I too have a question regarding Load combinations.

In the combinations of 1.5(DL+EQ) and 0.9DL+1.5EQ what should be the mass of the structure to be taken for finding out EQ force? Is it the mass consisting of DL + 50% LL or only DL??

Generally in building design for arriving at EQ force, mass on the structure is taken to be deadload and a portion of live load. By taking this same EQ force for the combinations 1.5(DL+EQ) and 0.9DL+1.5EQ are we not making a mistake ? Since EQ force with only Dead load as the mass of the structure will be different from the EQ force with Dead load+portion of live load as the mass.

Also, while combining only DL and EQ it does not make sense for me to take an EQ force which is due to dead mass and live mass. May be my understanding of load combinations is not clear...

Please Help....


Hemanth Kumar
Design Engineer,
NTPC Limited




On Mon, 04 Aug 2008 skjain.iitk wrote :

[b]--auto removed--

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[u.mukesh]

Hello
He is talking about the combination involving Dead Load and Earthquake only.
This may be the case when building is complete but not occupied.

So the calculation of Earthquake loads should be done with Dead load only for
these combinations (1.5 or 0.9 DL+ 1.5EQ).

Regards
Mukesh Upadhyay
SNC-Lavalin

On Tue, Aug 5, 2008 at 2:40 PM, fo...@sefindia.org (fo...@sefindia.org)> wrote:
[quote] Dear hemant

Pl go thru the Part-V of IS-875 which clearly states that the portion of live load to be considered for EQ Load Combinations, will also be considered while working out the seismic weights.
i.e. if 50% LL is being considered for Combinations of EQ, it shall also be 50% LL and DL while working out the seismic weights.In fact DL and LL both will be existing while the EQ may strike, and that's why LL(or a part of it) is considered as well, while calculating Joint weights. The proportions for combinations during EQ are based on extensive research and only then are adopted by BIS Committees; maybe Dr Jain may like to give some more explanation about it.

Best regards
Sangeeta Wij
[quote] ----- Original Message -----

From: p_hkumar (fo...@sefindia.org (fo...@sefindia.org))
To: gen...@sefindia.org (gen...@sefindia.org) (gen...@sefindia.org (gen...@sefindia.org))

Sent: Tuesday, August 05, 2008 12:47 PM

Subject: [SEFI] Re: ( DL + EQ ) Load Combinations

Dear sir,

I too have a question regarding Load combinations.

In the combinations of 1.5(DL+EQ) and 0.9DL+1.5EQ what should be the mass of the structure to be taken for finding out EQ force? Is it the mass consisting of DL + 50% LL or only DL??

Generally in building design for arriving at EQ force, mass on the structure is taken to be deadload and a portion of live load. By taking this same EQ force for the combinations 1.5(DL+EQ) and 0.9DL+1.5EQ are we not making a mistake ? Since EQ force with only Dead load as the mass of the structure will be different from the EQ force with Dead load+portion of live load as the mass.

Also, while combining only DL and EQ it does not make sense for me to take an EQ force which is due to dead mass and live mass. May be my understanding of load combinations is not clear...

Please Help....


Hemanth Kumar
Design Engineer,
NTPC Limited

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[pankaj.virmani]

Dear All,

This was a hot topic of conversation in SEFI, sometimes in 2003, and if you search the archives you will find there was a lot of debate generated. But the net consensus (which is also the most logical and most obvious) reached after consultation with Prof Arya by Alpa, was that LL is NOT to be considered for calculating the joint weights for the load combinations in which LL was not considered, namely 1.5(DL+EL) and 0.9DL+1.5EL. For the combination DL+LL+EL, obviously the joint weights should include the required percentage of LL.


Regards

Pankaj Gupta

Roark Consulting
C 56A/27, Sector 62, NOIDA, UP, India
Phone (India) +91-120-426-2166 , +91-120-240-0356
(USA VOIP) +1-408-465-5245 (CA), +1-408-465-5246 (CA)
Fax (India) +91-120-240-0355
(US toll free) +1-888-791-0181
(UK) +44207-900-2964
Mobile +91-98114-37987
Web: http://www.roarkconsultants.com

From: sdec.in (fo...@sefindia.org)
Sent: Tuesday, August 05, 2008 2:40 PM
To: gen...@sefindia.org (gen...@sefindia.org)
Subject: [SEFI] Re: ( DL + EQ ) Load Combinations

Dear hemant
Pl go thru the Part-V of IS-875 which clearly states that the portion of live load to be considered for EQ Load Combinations, will also be considered while working out the seismic weights.
i.e. if 50% LL is being considered for Combinations of EQ, it shall also be 50% LL and DL while working out the seismic weights.In fact DL and LL both will be existing while the EQ may strike, and that's why LL(or a part of it) is considered as well, while calculating Joint weights. The proportions for combinations during EQ are based on extensive research and only then are adopted by BIS Committees; maybe Dr Jain may like to give some more explanation about it.

Best regards
Sangeeta Wij

Quote:

----- Original Message ----- From: p_hkumar (fo...@sefindia.org (fo...@sefindia.org)) To: gen...@sefindia.org (gen...@sefindia.org) (gen...@sefindia.org (gen...@sefindia.org)) Sent: Tuesday, August 05, 2008 12:47 PM Subject: [SEFI] Re: ( DL + EQ ) Load Combinations

Dear sir, I too have a question regarding Load combinations. In the combinations of 1.5(DL+EQ) and 0.9DL+1.5EQ what should be the mass of the structure to be taken for finding out EQ force? Is it the mass consisting of DL + 50% LL or only DL?? Generally in building design for arriving at EQ force, mass on the structure is taken to be deadload and a portion of live load. By taking this same EQ force for the combinations 1.5(DL+EQ) and 0.9DL+1.5EQ are we not making a mistake ? Since EQ force with only Dead load as the mass of the structure will be different from the EQ force with Dead load+portion of live load as the mass. Also, while combining only DL and EQ it does not make sense for me to take an EQ force which is due to dead mass and live mass. May be my understanding of load combinations is not clear... Please Help.... Hemanth Kumar Design Engineer, NTPC Limited On Mon, 04 Aug 2008 skjain.iitk wrote :

[b]--auto removed--

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[ishacon]

Dear All,

I think some things are being quoted out of context on this topic
and I am compelled to react.

To the best of my recollection, when CEAI organised a workshop
in 2003 ,on provisions of IS 1893-2002 and Prof Arya was invited
with some other members of the IS 1893 Committee, this issue was
discussed threadbare.
At no point in the workshop, did Prof Arya ever talk about
neglecting the LL components for computing the Seismic dead
weight, because the code is explicit in this regard.

As a matter of fact even the UBC 1997, vide Cl 1630.1.1, talks about
seismic dead load W being the total dead load and applicable portions
of other loads listed under 4 different categories.
The EQ loads are always calculated based on this seismic dead load W,
irrespective of its being used as DL + EQ or DL + LL+ EQ combination.

And all those who took the E course from IIT Kanpur may pls refer to the notes
given then for add'l explanation or to the Commentary / proposed revisions to
IS 1893by IITKanpur for GSDMA.

I can not accept that our knowledgeable writers of the CODE ,who have referenced
even UBC 1994, could ignore this important issue clearly spelled out in UBC.

With this I request Mr. S.C. Mehrotra and Dr. Jain , to clarify this point
after reviewing the proceedings of the Workshop organised by CEAI in 2003.

Regards,

V.P. Agarwal
ISHA CONSULTANTS (P) LTD
NEW DELHI

PH : 011- 2630 1158
(M) 93 1345 2180
(M) 98 6826 2759
ish...@bol.net.in (ish...@bol.net.in)
ish...@rediffmail.com (ish...@rediffmail.com)

[quote] ----- Original Message -----
From: pankaj.virmani (fo...@sefindia.org)
To: gen...@sefindia.org (gen...@sefindia.org)
Sent: Tuesday, August 05, 2008 4:52 PM

Subject: [SEFI] Re: ( DL + EQ ) Load Combinations

Dear All,

This was a hot topic of conversation in SEFI, sometimes in 2003, and if you search the archives you will find there was a lot of debate generated. But the net consensus (which is also the most logical and most obvious) reached after consultation with Prof Arya by Alpa, was that LL is NOT to be considered for calculating the joint weights for the load combinations in which LL was not considered, namely 1.5(DL+EL) and 0.9DL+1.5EL. For the combination DL+LL+EL, obviously the joint weights should include the required percentage of LL.


Regards

Pankaj Gupta

Roark Consulting
C 56A/27, Sector 62, NOIDA, UP, India
Phone (India) +91-120-426-2166 , +91-120-240-0356
(USA VOIP) +1-408-465-5245 (CA), +1-408-465-5246 (CA)
Fax (India) +91-120-240-0355
(US toll free) +1-888-791-0181
(UK) +44207-900-2964
Mobile +91-98114-37987
Web: http://www.roarkconsultants.com

From: sdec.in (fo...@sefindia.org (fo...@sefindia.org))
Sent: Tuesday, August 05, 2008 2:40 PM
To: gen...@sefindia.org (gen...@sefindia.org) (gen...@sefindia.org (gen...@sefindia.org))
Subject: [SEFI] Re: ( DL + EQ ) Load Combinations




Dear hemant
Pl go thru the Part-V of IS-875 which clearly states that the portion of live load to be considered for EQ Load Combinations, will also be considered while working out the seismic weights.
i.e. if 50% LL is being considered for Combinations of EQ, it shall also be 50% LL and DL while working out the seismic weights.In fact DL and LL both will be existing while the EQ may strike, and that's why LL(or a part of it) is considered as well, while calculating Joint weights. The proportions for combinations during EQ are based on extensive research and only then are adopted by BIS Committees; maybe Dr Jain may like to give some more explanation about it.

Best regards
Sangeeta Wij

[b]--auto removed--

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[JVCSNL]

Dear All,

Intensity of earthquake load EQ is calculated only one time based on applicable seismic weight as defined in the code you refer.

The EQ load calculated based on this seismic weight is used in any combination, whether with DL only or with DL+LL. Under no circumstances, the seismic weight change and thus seismic mass.

Since, live loads are not likely to be present 100% during seismic event, some reduced LL is suggested by almost all codes of practice. However, when you design your building, you never know in which portion of building the LL is present.

In lateral load resisting system, especially columns and bracing, DL contribution is known based on tributary area and it does not change. The vertical component is going to be same through out the life of the structure due to DL. However, if the same column is also part of lateral load resisting system, it will definitely share the EQ force based on the stiffness of column vs overall stiffness of lateral load resisting system. It shall be noted here that this column may not have contribution of vertical component of LL, as % of live load considered in seismic weight may be in other portion of the floor. Hence, if you see the system in global perspective, you would agree that 0.9DL+1.5EQ is logical combination to verify the uplift or minimum vertical load with maximum lateral load condition.

Hope this clarifies the reason behind unique EQ load based on only one seismic weight.

Regards,

Jignesh Chokshi

Quote:

Quote: Quote: fo...@sefindia.org 05-08-2008 >>>

ish...@bol.net.in (ish...@bol.net.in) (ish...@bol.net.in (ish...@bol.net.in))
ish...@rediffmail.com (ish...@rediffmail.com) (ish...@rediffmail.com (ish...@rediffmail.com))

Quote:

----- Original Message ----- From: pankaj.virmani (fo...@sefindia.org (fo...@sefindia.org)) To: gen...@sefindia.org (gen...@sefindia.org) (gen...@sefindia.org (gen...@sefindia.org)) Sent: Tuesday, August 05, 2008 4:52 PM Subject: [SEFI] Re: ( DL + EQ ) Load Combinations Dear All, This was a hot topic of conversation in SEFI, sometimes in 2003, and if you search the archives you will find there was a lot of debate generated. But the net consensus (which is also the most logical and most obvious) reached after consultation with Prof Arya by Alpa, was that LL is NOT to be considered for calculating the joint weights for the load combinations in which LL was not considered, namely 1.5(DL+EL) and 0.9DL+1.5EL. For the combination DL+LL+EL, obviously the joint weights should include the required percentage of LL. Regards Pankaj Gupta Roark Consulting C 56A/27, Sector 62, NOIDA, UP, India Phone (India) +91-120-426-2166 , +91-120-240-0356 (USA VOIP) +1-408-465-5245 (CA), +1-408-465-5246 (CA) Fax (India) +91-120-240-0355 (US toll free) +1-888-791-0181 (UK) +44207-900-2964 Mobile +91-98114-37987 Web: http://www.roarkconsultants.com

From: sdec.in (fo...@sefindia.org (fo...@sefindia.org (fo...@sefindia.org))) Sent: Tuesday, August 05, 2008 2:40 PM To: gen...@sefindia.org (gen...@sefindia.org) (gen...@sefindia.org (gen...@sefindia.org)) (gen...@sefindia.org (gen...@sefindia.org (gen...@sefindia.org))) Subject: [SEFI] Re: ( DL + EQ ) Load Combinations Dear hemant Pl go thru the Part-V of IS-875 which clearly states that the portion of live load to be considered for EQ Load Combinations, will also be considered while working out the seismic weights. i.e. if 50% LL is being considered for Combinations of EQ, it shall also be 50% LL and DL while working out the seismic weights.In fact DL and LL both will be existing while the EQ may strike, and that's why LL(or a part of it) is considered as well, while calculating Joint weights. The proportions for combinations during EQ are based on extensive research and only then are adopted by BIS Committees; maybe Dr Jain may like to give some more explanation about it. Best regards Sangeeta Wij [b]--auto removed--

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[sdec.in]

Dear Mr VP Aggarwal
You are right in your interpretation and I recall having personally clarified this point again, during a tea break, at the same event.I have no doubt that we use the same seismic weights calculated with %of LL applicable for the Project, for all EQ combinations being considered for design.Dear Dr jain, it's time your expert comments are required to conclude this discussion.
regards
Sangeeta

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[jlakhlani]

Dear Sefians,

I also agree with Mr. V P Agarwal. As per IS : 1893, we need to carry out following steps for seismic analysis of any building.

1) Calculation of design lateral force. (As per cl. 7.3, 7.4 and 7.5)

2) Analysis for different load combinations. (As per cl. 6.3.1.1 and 6.3.1.2)

For calculation of seismic weight of different floors, as per cl. 7.4.1, full dead load plus appropriate amount of imposed load is to be considered.

There is no specific distinction given in the code that calculation of seismic weight will depend on the load case being considered. So, irrespective of the load case, seismic weight and hence the design lateral force will remain same for all the load cases.

The only relaxation in imposed load, while considering the load cases for analysis, is as per cl. 7.3.3, wherein it is specified that the appropriate amount of imposed load considered for calculation of seismic weight is also to be used while considering the load cases containing earthquake load and imposed load together.

Regards.

Jayant Lakhlani
For
Lakhlani Associates
www.lakhlani.com


--- On Tue, 5/8/08, ishacon wrote:

Quote:

From: ishacon

Subject: [SEFI] Re: ( DL + EQ ) Load Combinations

To: gen...@sefindia.org Date: Tuesday, 5 August, 2008, 5:42 PM

Add more friends to your messenger and enjoy! [url=http://in.rd.yahoo.com/tagline_messenger_6/*http://in.messenger.yahoo.com/invite/]Invite them now.[/url]

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[jiwajidesai]

Two questions arise, with regard to the inclusion of same joint-weights in all combinations:-

a) When the combination (DL + EQ) explicitly excludes presence of LL in its definition, what is the logic behind including “applicable % of LL” in the seismic weights used to evaluate EQ forces in this combination?
b) If LL contributes in some fashion to seismic forces, why are we excluding it in the combination itself?

Codes stipulations are amended and improved in time. We all know that. Just because an old Code says it, may not be a sufficient ground for insisting on “same seismic weights” in all combinations.

Jiwaji Desai
Sr. GM (C & S[b])
WSP Engineering Services Ltd.[/b]

From: sdec.in [mailto:fo...@sefindia.org]
Sent: Wednesday, August 06, 2008 10:41 AM
To: gen...@sefindia.org
Subject: [SEFI] Re: ( DL + EQ ) Load Combinations

Dear Mr VP Aggarwal
You are right in your interpretation and I recall having personally clarified this point again, during a tea break, at the same event.I have no doubt that we use the same seismic weights calculated with %of LL applicable for the Project, for all EQ combinations being considered for design.Dear Dr jain, it's time your expert comments are required to conclude this discussion.
regards
Sangeeta

[b]--auto removed--

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[pankaj.gupta]

Dear Mr. Agarwal,

Nothing is being quoted out of context. If you read my email, I was not talking about CEAI workshop but about postings in SEFI somewhere around 2003. And whatever I have said can simply be verified if anybody cares to search the SEFI archives and further corroborated by Alpa Seth.

Regards

Pankaj Gupta

Roark Consulting
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From: ishacon (fo...@sefindia.org)
Sent: Tuesday, August 05, 2008 11:12 PM
To: gen...@sefindia.org (gen...@sefindia.org)
Subject: [SEFI] Re: ( DL + EQ ) Load Combinations

Quote:

Subject: [SEFI] Re: ( DL + EQ ) Load Combinations

Dear All, This was a hot topic of conversation in SEFI, sometimes in 2003, and if you search the archives you will find there was a lot of debate generated. But the net consensus (which is also the most logical and most obvious) reached after consultation with Prof Arya by Alpa, was that LL is NOT to be considered for calculating the joint weights for the load combinations in which LL was not considered, namely 1.5(DL+EL) and 0.9DL+1.5EL. For the combination DL+LL+EL, obviously the joint weights should include the required percentage of LL. Regards Pankaj Gupta Roark Consulting C 56A/27, Sector 62, NOIDA, UP, India Phone (India) +91-120-426-2166 , +91-120-240-0356 (USA VOIP) +1-408-465-5245 (CA), +1-408-465-5246 (CA) Fax (India) +91-120-240-0355 (US toll free) +1-888-791-0181 (UK) +44207-900-2964 Mobile +91-98114-37987 Web: http://www.roarkconsultants.com From: sdec.in (fo...@sefindia.org (fo...@sefindia.org (fo...@sefindia.org))) Sent: Tuesday, August 05, 2008 2:40 PM To: gen...@sefindia.org (gen...@sefindia.org) (gen...@sefindia.org (gen...@sefindia.org)) (gen...@sefindia.org (gen...@sefindia.org (gen...@sefindia.org)))

Subject: [SEFI] Re: ( DL + EQ ) Load Combinations

Dear hemant Pl go thru the Part-V of IS-875 which clearly states that the portion of live load to be considered for EQ Load Combinations, will also be considered while working out the seismic weights. i.e. if 50% LL is being considered for Combinations of EQ, it shall also be 50% LL and DL while working out the seismic weights.In fact DL and LL both will be existing while the EQ may strike, and that's why LL(or a part of it) is considered as well, while calculating Joint weights. The proportions for combinations during EQ are based on extensive research and only then are adopted by BIS Committees; maybe Dr Jain may like to give some more explanation about it. Best regards Sangeeta Wij [b]--auto removed--

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[vikram.jeet]

1.5(DL+EQ) case

I think the case 1.5(DL +EQ) is a case of( DL + EQ on DL) using
1.5 factor as load factor
This combination in ,my opnion, may not be more relevant to the buildings but may
be relevant to the structures such as chimneys etc( however low rise buildings
if checked by this( DL + EQ on DL)*1.5 governs the design


May please see SP-24 explanatory handbook on IS 456 wherein explanation
is provided for keeping this load case clearly for structures having predominant
lateral loading as wind/EQ

regards

vikramjeet

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