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irc6 Ultimate load combinations
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Engineer
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PostPosted: Mon Apr 18, 2011 4:21 pm    Post subject: irc6 Ultimate load combinations Reply with quote

I have old IRC 6. I am looking for Ultimate load combination factors for different loads. I am working on comparison of Composite Steel Concrete Girder bridge between AASHTO and Limit State Code IRC 24/22.

thanks in advance
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k.gangadharan
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PostPosted: Tue Apr 19, 2011 6:46 am    Post subject: irc6 Ultimate load combinations Reply with quote

dear sefians (bridge designers)

Please make clear whether Limit state design for design of bridges ( IRC 24 /22 as mentioned in one of the postings in SEFI)) is released now and it is to be followed inplace of working stress method for bridges

regards
K,Gangadharan
Structural consultant


On Mon, Apr 18, 2011 at 9:51 PM, Engineer <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
  I have old IRC 6. I am looking for Ultimate load combination factors for different loads. I am working on comparison of Composite Steel Concrete Girder bridge between AASHTO and Limit State Code IRC 24/22.

thanks in advance







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PostPosted: Tue Apr 19, 2011 11:56 am    Post subject: Limit state for bridghes Reply with quote

Sir,

As far as i know  for bridge designs ,IRC codes still advocates the use of working stress philosophy  only. Dear member may enlighten us whether IRC  has released new codal  provision for LIMIIT STATE Design.

Er.Balaji venkateswaran
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gauravmaroo
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PostPosted: Wed Apr 20, 2011 5:07 am    Post subject: Reply with quote

Dear SEFI members
kindly check IRC NOTIFICATION NO 53 DATES 28-05-2009 for IRC 6 ,which has given the Limit State design provisions for bridges...further explanatory documents may be underway....

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vikram.jeet
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PostPosted: Wed Apr 20, 2011 7:11 am    Post subject: irc6 Ultimate load combinations Reply with quote

Bridges are subjected to cyclic loading , all the time during their service life
The extent of live load(vis-a-vis DL) and frequency of ( live - - loading and
unloading ) on the structure needs design within elastic range .
Design beyond elastic limit may affect the design life of structure.
Some bridge design expert may kindly guide .

best regards  

vikramjeet


dear sefians (bridge designers)
Please make clear whether Limit state design for design of bridges ( IRC 24 /22 as mentioned in one of the postings in SEFI
)) is released now and it is to be followed in place of working stress method for bridges
regards
K,Gangadharan
Structural consultant

--

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ibarua
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PostPosted: Wed Apr 20, 2011 9:29 am    Post subject: irc6 Ultimate load combinations Reply with quote

20th April 2011

IRC has issued an amendment to IRC:6 in July 2010 by which it is nnow permissible to design bridges by LSM.

Indrajit Barua.

On Tue, 19 Apr 2011 13:28:25 +0530 "k.gangadharan" <forum@sefindia.org> wrote
[quote]     dear sefians (bridge designers)

Please make clear whether Limit state design for design of bridges ( IRC 24 /22 as mentioned in one of the postings in SEFI)) is released now and it is to be followed inplace of working stress method for bridges

regards
K,Gangadharan
Structural consultant


On Mon, Apr 18, 2011 at 9:51 PM, Engineer <forum@sefindia.org (forum@sefindia.org)> wrote:
      --auto removed--

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PostPosted: Wed Apr 20, 2011 9:35 am    Post subject: irc6 Ultimate load combinations Reply with quote

20th April 2011

I really don't think that the life of bridges designed by LSM will be shortened. Try to understand the philosophy behind LSM, and I'm sure you'lll agree with me.

Indrajit Barua.

On Wed, 20 Apr 2011 14:04:53 , "vikram.jeet" <forum@sefindia.org> wrote
     Bridges are subjected to cyclic loading , all the time during their service life
The extent of live load(vis-a-vis DL) and frequency of ( live - - loading and
unloading ) on the structure needs design within elastic range .
Design beyond elastic limit may affect the design life of structure.
Some bridge design expert may kindly guide .

best regards

vikramjeet


dear sefians (bridge designers)
Please make clear whether Limit state design for design of bridges ( IRC 24 /22 as mentioned in one of the postings in SEFI)) is released now and it is to be followed in place of working stress method for bridges
regards
K,Gangadharan
Structural consultant
-- ­­

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PostPosted: Wed Apr 20, 2011 11:53 am    Post subject: irc6 Ultimate load combinations Reply with quote

Dear All,

IRC:24-2010 has been published, which is the limit state version of the code. This means that all steel bridges henceforth are to be designed based on limit state method. IRC:6-2010 is already published which gives the load factors.

IRC : 22 – pertaining to composite construction (I,e steel-concrete composite) is also a limit state code now. Therefore the composite bridges are also supposedly to be designed as per limit state code. However the limit state version of the concrete code is yet to be published (the new IRC code on concrete will be replacing IRC:18 and IRC:21). The concrete limit state code is presently with the printers for final publication and it is expected to hit the shelf latest by July 2011

In absence of the concrete limit state code, there will be limited use of the IRC:22, since only the steel component can be designed based on limit state approach, which I do not think is a pragmatic approach.

Hope this clarifies the situation

With best wishes

Alok Bhowmick

From: vikram.jeet [mailto:forum@sefindia.org]
Sent: Wednesday, April 20, 2011 2:03 PM
To: general@sefindia.org
Subject: [SEFI] Re: irc6 Ultimate load combinations



Bridges are subjected to cyclic loading , all the time during their service life
The extent of live load(vis-a-vis DL) and frequency of ( live - - loading and
unloading ) on the structure needs design within elastic range .
Design beyond elastic limit may affect the design life of structure.
Some bridge design expert may kindly guide .

best regards

vikramjeet


dear sefians (bridge designers)
Please make clear whether Limit state design for design of bridges ( IRC 24 /22 as mentioned in one of the postings in SEFI)) is released now and it is to be followed in place of working stress method for bridges
regards
K,Gangadharan
Structural consultant

--

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vikram.jeet
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PostPosted: Thu Apr 21, 2011 6:29 am    Post subject: irc6 Ultimate load combinations Reply with quote

Respected sir,

I am at peace with your statement on LSM.

Also , now IRC standards have allowed LSM as per the posting from Mr Bhowmick

Just a vague comparison of two approaches:

LSM-- -
Load factor on DL - -1.5
Load factor on LL - -1.5 (say, but donot know the IRC stipulation,needs to be higher)
Partial safety factor in conc - -1.5
Partial safety factor in steel - -1.15

Net effect: Max allowed conc stress - - 30/(1.5*1.5) =13.33N/mm2
(M30 mix)
Net effect :Max allowed steel stress - - 500/(1.5*1.15) =289 N/mm2
(Fe 500 grade)*

WSM - -  
Load factor on DL - -1.0 (working loads)
Load factor on LL - -1.0 (working loads)
Safety factor in conc - -3.0
Safety factor in steel - -1.818 ( i.e. =1/0.55)

Net effect: Max allowed conc stress - - 30/(1.0*3) =10.0N/mm2
(M30 mix)
Net effect :Max allowed steel stress - - 500/(1.0*1.818) =275 N/mm2
(Fe 500 grade)*

From the above comparison, it seems that whereas net effect on steel  
reinf will be same but net effect on concrete is appreciable if a load
factor of 1.5 is used with LL. Maximum stress ( LSM) in concrete may touch
13.33 N/mm2 for mix M-30 whereas WSM permits 10.0 N/mm2

* For comparision sake ,Permitted Stresses in steel have been based on  
IS 456 ,though IRC -21permits lesser(may be to account for cyclic loading)

LSM may require extra vigilant quality control on concrete work as per
the above comparision
Longevity of structure is not affected as per the statement from respected  
Barua sahab and he is very right but for EVQC aspect.

with due regards

vikramjeet



20th April 2011
I really don't think that the life of bridges designed by LSM will be shortened. Try to understand the philosophy behind LSM, and I'm sure you'lll agree with me
Indrajit Barua.
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PostPosted: Thu Apr 21, 2011 11:52 am    Post subject: irc6 Ultimate load combinations Reply with quote

Dear Mr Vikramjeet  

I beg to differ with you Sir, when you say that “LSM may require extra vigilant quality control on concrete work as per
the above comparison”.

In my opinion one should not attempt to compare the two methods. They are two entirely different concepts, representing different times in the design development process. In fact the BS:5400 load factors for limit state design was evolved only based on worked out examples which ensured that the results from WSM and LSM matches. Therefore, it is not the results that matters but the approach. In LSM, there is always a scope for improvement by the code makers in changing the partial load factors, based on statistical approach.

LSM represents realistic and rational approach, safety being conceptually based on statistical and probabilistic approach, that caters for both overloads (or underloads), overstrength (or understrength) and degree of quality control at site.  

WSM method on the other hand, though has served the humanity for so many years and is still serving, the method does not cover the following :  

<![if !supportLists]>1. <![endif]>Consequence of material non-linearity and behavior in post-buckling stage.
<![if !supportLists]>2. <![endif]>Variability in the material specification w.r.t strength & other physical properties.
<![if !supportLists]>3. <![endif]>Uncertainities in the expected loads
<![if !supportLists]>4. <![endif]>Secondary Stresses.  

Coming to real comparative study based on LSM and WSM for Bridges, I find that the LSM approach gives economical design for routine concrete structures. However I am not sure whether the same can be said with authority for steel structures, where the Live Load / Dead Load ration is high.

With best wishes

Alok Bhowmick

From: vikram.jeet [mailto:forum@sefindia.org]
Sent: Thursday, April 21, 2011 2:04 PM
To: general@sefindia.org
Subject: [SEFI] Re: irc6 Ultimate load combinations



Respected sir,

I am at peace with your statement on LSM.

Also , now IRC standards have allowed LSM as per the posting from Mr Bhowmick

Just a vague comparison of two approaches:

LSM-- -
Load factor on DL - -1.5
Load factor on LL - -1.5 (say, but donot know the IRC stipulation,needs to be higher)
Partial safety factor in conc - -1.5
Partial safety factor in steel - -1.15

Net effect: Max allowed conc stress - - 30/(1.5*1.5) =13.33N/mm2
(M30 mix)
Net effect :Max allowed steel stress - - 500/(1.5*1.15) =289 N/mm2
(Fe 500 grade)*

WSM - -
Load factor on DL - -1.0 (working loads)
Load factor on LL - -1.0 (working loads)
Safety factor in conc - -3.0
Safety factor in steel - -1.818 ( i.e. =1/0.55)

Net effect: Max allowed conc stress - - 30/(1.0*3) =10.0N/mm2
(M30 mix)
Net effect :Max allowed steel stress - - 500/(1.0*1.818) =275 N/mm2
(Fe 500 grade)*

From the above comparison, it seems that whereas net effect on steel
reinf will be same but net effect on concrete is appreciable if a load
factor of 1.5 is used with LL. Maximum stress ( LSM) in concrete may touch
13.33 N/mm2 for mix M-30 whereas WSM permits 10.0 N/mm2

* For comparision sake ,Permitted Stresses in steel have been based on
IS 456 ,though IRC -21permits lesser(may be to account for cyclic loading)

LSM may require extra vigilant quality control on concrete work as per
the above comparision
Longevity of structure is not affected as per the statement from respected
Barua sahab and he is very right but for EVQC aspect.

with due regards

vikramjeet



20th April 2011
I really don't think that the life of bridges designed by LSM will be shortened. Try to understand the philosophy behind LSM, and I'm sure you'lll agree with me
Indrajit Barua.
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