[SEFI] why 1.5in equation U= 1.5 ( DL + EQ )
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uhvaryani
Aug 4, 2008, 7:56:12 AM8/4/08
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DEAR SEFIANS,
i request all to kindly consider this aspect of the code IS:456-2000,table 18.table 18 gives for design of structures,
U= 1.5 ( DL + LL )............(1)
U= 1.2 ( DL + LL + EQ )...(2)
U =1.5 (DL + EQ )............(3)
my question is when a building is unoccupied i.e with no LL and with no risk, why should the load factor be 1.5 ?when the building is occupied and the risk is more, why should the load factor be 1.2 ( less than 1.5 ) ?
equation (3) governs the design and about 10% more steel is consumed in buildings on this account.we should not use eq. (3) for design of buildings as suggested by SP:24 explanatory handbook of IS:456-1978 and thereby save steel.
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i request all to kindly consider this aspect of the code IS:456-2000,table 18.table 18 gives for design of structures,
U= 1.5 ( DL + LL )............(1)
U= 1.2 ( DL + LL + EQ )...(2)
U =1.5 (DL + EQ )............(3)
my question is when a building is unoccupied i.e with no LL and with no risk, why should the load factor be 1.5 ?when the building is occupied and the risk is more, why should the load factor be 1.2 ( less than 1.5 ) ?
equation (3) governs the design and about 10% more steel is consumed in buildings on this account.we should not use eq. (3) for design of buildings as suggested by SP:24 explanatory handbook of IS:456-1978 and thereby save steel.
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skjain.iitk
Aug 4, 2008, 9:39:03 AM8/4/08
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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
On 8/4/08, uhvaryani fo...@sefindia.org)> wrote:
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
On 8/4/08, uhvaryani fo...@sefindia.org)> wrote:
| Quote: |
kunal
Aug 5, 2008, 1:57:49 AM8/5/08
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Dear
Different load combination are specified by code which gives critical forces for particular structural element. i.e. for corner column load combination 0.9DL+1.5EQ is generally cirtical. for central column it may be 1.5 DL +1.5 LL .
It depends upon geometry of structures.
Building is design for particular life say 50 yrs. for that period it is subjected to different load. Considering critical combination to design of elements we use different load combination.
Regards & wishes
Kunal Jain
Different load combination are specified by code which gives critical forces for particular structural element. i.e. for corner column load combination 0.9DL+1.5EQ is generally cirtical. for central column it may be 1.5 DL +1.5 LL .
It depends upon geometry of structures.
Building is design for particular life say 50 yrs. for that period it is subjected to different load. Considering critical combination to design of elements we use different load combination.
Regards & wishes
Kunal Jain
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ibarua
Aug 8, 2008, 10:37:58 PM8/8/08
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5th August 2008
This refers to the mail from my classmate U.H. Varyani (IIT-KGP-CE-1958).
The issue is one of probability and of saving lives, and not one of saving steel. Safety & security are far important than money -- at least that's how I, who has to live and work in seismic zone V, look at life.
What is the probability that a building will have no LL when an earthquake hits?
Is it likely to have the full design LL or something less than that?
When the probability of an occurrence is high, the LF is also high. Conversely, when the probability of the occurrence is low, the LF may be set at a lower value.
Lastly, will Mr Varyani let me have his e-mail and telephone number at: iba...@deguild.com or iba...@yahoo.com, please?
Indrajit Barua.
On Mon, 04 Aug 2008 uhvaryani wrote :
This refers to the mail from my classmate U.H. Varyani (IIT-KGP-CE-1958).
The issue is one of probability and of saving lives, and not one of saving steel. Safety & security are far important than money -- at least that's how I, who has to live and work in seismic zone V, look at life.
What is the probability that a building will have no LL when an earthquake hits?
Is it likely to have the full design LL or something less than that?
When the probability of an occurrence is high, the LF is also high. Conversely, when the probability of the occurrence is low, the LF may be set at a lower value.
Lastly, will Mr Varyani let me have his e-mail and telephone number at: iba...@deguild.com or iba...@yahoo.com, please?
Indrajit Barua.
On Mon, 04 Aug 2008 uhvaryani wrote :
| Quote: |
sher khan
Aug 9, 2008, 12:57:37 AM8/9/08
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Respected sir,
many aspects in the codes are not clear.A keen observation shows that IS codes more are less are just copies of British or U.S codes rather than depending on sound mathematical principles.
congratulations for pointing out one such clause.I hope the so called team of experts who spends crores of rupees in elite institutions/research labs should stand up and speak on the subject.
A.H.KHAN
structural consultant
afzalk...@yahoo.co.in
09440349148
many aspects in the codes are not clear.A keen observation shows that IS codes more are less are just copies of British or U.S codes rather than depending on sound mathematical principles.
congratulations for pointing out one such clause.I hope the so called team of experts who spends crores of rupees in elite institutions/research labs should stand up and speak on the subject.
A.H.KHAN
structural consultant
afzalk...@yahoo.co.in
09440349148
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uhvaryani
Aug 10, 2008, 2:58:56 AM8/10/08
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dear all,
this is to thank dr. s. k. jain for his comments.the eq. U=0.9 DL + 1.5 EQ isalso to be considered in design.SP:24 states that this condition is relevant for checking
overturning in tall, slender structures. further,there are flaws in this equation.load factor for the term 0.9 DL is missing and load factor for EQ should be 1.2 in place
of 1.5.the correct form of this equation is U=1.2(0.9 DL + EQ ).i have explained this matter in detail in my article which was listed in the forum's list of articles for some period of time,but now it has been dropped.dr. jain has not expressed his opinion on the validity of load factor 1.5 in equation U=1.5(DL+EQ).I WOULD APPRECIATE HIS GUIDANCE IN THIS MATTER.
with many thanks and regards,
uhvaryani
this is to thank dr. s. k. jain for his comments.the eq. U=0.9 DL + 1.5 EQ isalso to be considered in design.SP:24 states that this condition is relevant for checking
overturning in tall, slender structures. further,there are flaws in this equation.load factor for the term 0.9 DL is missing and load factor for EQ should be 1.2 in place
of 1.5.the correct form of this equation is U=1.2(0.9 DL + EQ ).i have explained this matter in detail in my article which was listed in the forum's list of articles for some period of time,but now it has been dropped.dr. jain has not expressed his opinion on the validity of load factor 1.5 in equation U=1.5(DL+EQ).I WOULD APPRECIATE HIS GUIDANCE IN THIS MATTER.
with many thanks and regards,
uhvaryani
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rahul.leslie
Aug 10, 2008, 3:53:34 AM8/10/08
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Yes, I do believe that the combination of 0.9DL+1.5EQ is for cases with risk of upliftment of supports only. I would suggest checking whether any case of negative values of support reactions exist, and ignore these cases for which there isn't any. That's what I understand from footnote "1)", Table 18, IS:456-2000... Please correct me if I'm wrong.
Rahul Leslie
rahul....@gmail.com
Rahul Leslie
rahul....@gmail.com
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manoj_en
Aug 19, 2008, 2:48:26 AM8/19/08
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Dear Sefians
The reason behind inclusion of 1.5 (DL + LL) have not been explaned.I would appreciate if any experts can elaborate the matter in detail.
Regards
manoj Chakraborty
The reason behind inclusion of 1.5 (DL + LL) have not been explaned.I would appreciate if any experts can elaborate the matter in detail.
Regards
manoj Chakraborty
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akbar.civil
Aug 19, 2008, 10:37:59 AM8/19/08
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Dear Mr. Manoj Chakraborty,
In my opinion the combination 1.5*(DL+LL) is the basic combination which is present atleast 90% of any structure's life time especially when there is no earthquake and the winds are too mild. If I am correct, many designers consider this load combination for preliminary sizing of their columns in the early stages of any project.
Although I must admit that I am not an expert in this field :). Seniors, please supplement my answer.
Regards,
*******************************
M. A. Akbar
M-Tech: Structural Engg.
Calicut, Kerala
India
*******************************
In my opinion the combination 1.5*(DL+LL) is the basic combination which is present atleast 90% of any structure's life time especially when there is no earthquake and the winds are too mild. If I am correct, many designers consider this load combination for preliminary sizing of their columns in the early stages of any project.
Although I must admit that I am not an expert in this field :). Seniors, please supplement my answer.
Regards,
*******************************
M. A. Akbar
M-Tech: Structural Engg.
Calicut, Kerala
India
*******************************
----- Original Message ----
From: manoj_en
To: gen...@sefindia.org
Sent: Monday, August 18, 2008 11:48:26 PM
Subject: [SEFI] Re: why 1.5in equation U= 1.5 ( DL + EQ )
Dear Sefians
The reason behind inclusion of 1.5 (DL + LL) have not been explaned.I would appreciate if any experts can elaborate the matter in detail.
Regards
manoj Chakraborty
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prof.arc
Aug 20, 2008, 8:24:44 PM8/20/08
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I see a lot of postings trying to explain various factors, one such being "1.5"
One has to remember that codes represent compromise among the members of the committee recommending the numbers and most codes follow a leader [US codes in particular, as there is most vigorous debate only in that country before adoption of the clauses]. However, it is a fact all such formulae are empirical.
We should assume that only DL can be estimated with reasonable accuracy. Even in DL, special effort is necessary to estimate that of ,say, infills if the modelling adopts bare frame only. It will be interesting for you to estimate what is the live load in an actual building and then compare what code has recommended. In the case of earthquake, the entire live load as given for static conditions will not be effective [the incidence if live load at the time of event would always be less and further live loads are friction mounted]
In earlier versions of IS:1893 we gave the option to designer to estimate live load under earthquake conditions, if he has the ability and take the risk !!
With the advent of easy access to commercial software and anyone (including persons without advanced knowledge of the theory) can design, it is better that every structure is designed for the same condition of empirical loading.
Adopting the code no doubt kills innovation and risk taking ability of some -
code is a sort of socialism. However much a person dresses up explanation, it is that person's dress only !!
ARC
On 8/19/08, manoj_en fo...@sefindia.org)> wrote:
One has to remember that codes represent compromise among the members of the committee recommending the numbers and most codes follow a leader [US codes in particular, as there is most vigorous debate only in that country before adoption of the clauses]. However, it is a fact all such formulae are empirical.
We should assume that only DL can be estimated with reasonable accuracy. Even in DL, special effort is necessary to estimate that of ,say, infills if the modelling adopts bare frame only. It will be interesting for you to estimate what is the live load in an actual building and then compare what code has recommended. In the case of earthquake, the entire live load as given for static conditions will not be effective [the incidence if live load at the time of event would always be less and further live loads are friction mounted]
In earlier versions of IS:1893 we gave the option to designer to estimate live load under earthquake conditions, if he has the ability and take the risk !!
With the advent of easy access to commercial software and anyone (including persons without advanced knowledge of the theory) can design, it is better that every structure is designed for the same condition of empirical loading.
Adopting the code no doubt kills innovation and risk taking ability of some -
code is a sort of socialism. However much a person dresses up explanation, it is that person's dress only !!
ARC
On 8/19/08, manoj_en fo...@sefindia.org)> wrote:
| Quote: |
| Dear Sefians The reason behind inclusion of 1.5 (DL + LL) have not been explaned.I would appreciate if any experts can elaborate the matter in detail. Regards manoj Chakraborty |
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