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IS 800:2007 Vs IS800:1984( Working stress)
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abhik_shar
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PostPosted: Tue Nov 17, 2009 11:30 am    Post subject: IS 800:2007 Vs IS800:1984( Working stress) Reply with quote

Hello Sefians

I have compare working stress method of IS800:2007 & 1984

Permissible stress of Compression member as per IS 800:1984  is more than the IS800:2007 , it means member design by old code for working stress methodology will fail , if design by new code ??? as its capacity is decreaesd

I am attaching the file as example for tension & compression member

same is the case for tension member



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Comparative_1984&2007(ASD).zip
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abhik_shar
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PostPosted: Mon Nov 23, 2009 3:38 am    Post subject: Reply with quote

Hello

I am expecting Dr. Subramanian to comment on this issue.

Once again , I hv done comparative analysis of IS:800- 1984 & IS:800-2007 for working stress method

latest findings , same result for beam also .

i mean structural element if design by old code will fail w.r.t. new code.

Abhishek Sharma



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Dr. N. Subramanian
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PostPosted: Tue Nov 24, 2009 1:19 am    Post subject: Reply with quote

Hi Er Abhishek Sharma,

I went through the calculations and wish to comment as below:

For Tension Member the strength as per LSM is  198.7 kN and as per WSM 118 kN Multiplying the WSD result by 1.5 we get 177kN. i.e. 12 % higher value. In this case, the block shear failure governs the LSM design, which is not included in WSD.

in compression member you should use curve b, hence you will get the LSM strength as 733.7kN, Similarly for L/r =105.63, the allowable stress is 75.5 MPa and hence allowable load is 504 kN, multiplying by 1.5 we get, 755 kN. It is due to the use of different buckling curve. However the difference is 3% only.

For the beam the Moment Capacity as per LSM is 31.12 kNm and WSD is 20.3 kNm. Multiplying by 1.5 we get 30.45kNm, which is close to LSM value

Best wishes
Subramanian

abhik_shar wrote:
Hello

I am expecting Dr. Subramanian to comment on this issue.

Once again , I hv done comparative analysis of IS:800- 1984 & IS:800-2007 for working stress method

latest findings , same result for beam also .

i mean structural element if design by old code will fail w.r.t. new code.

Abhishek Sharma
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abhik_shar
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PostPosted: Tue Nov 24, 2009 3:26 am    Post subject: Reply with quote

Hello Sir,

I am comparing IS800-1984 & IS-800-2007---

TENSION MEMBER:
Please refer to clause no 11.2.1 , a), b) ,c)  ,of IS 800:2007 - the permissible stresses after calculating Tdn( as per clause 6.3) & Tdb( as per clause6.4) , the permissible stress fat as per yielding is 0.15KN/m2 , as per rupture is 0.165KN/m2 & as per block shear 0.135KN/m2

but as per IS 800-1984 , permissible stress is 0.15KN/m2

so, the critical is the new code , as the limiting stress is 0.135KN/m2
so if the same member is designed by new code it will fail as per old code.

COMPRESSION MEMBER:

IS800--2007 , Since in my example the column is braced along minor axis , the slenderness ratio is 21 & therefore the buckling curve is "a" to be used , as per table 9a, for slenderness ratio 21 & fy =250MPa , the design compressive stress is fcd=226MPa , as per clause 11.3.1 for calculating permisible compressive stress , fac for WSD = 0.6 fcd
so, the permissible compressive stress fac = 0.6 *226 = 136MPa

while as per IS800-1984 ,
for slenderness ratio 21 & fy = 250MPa
the design compressive stress = 148Mpa

so , member designed as per old code will fail as per new code ,

similar results for beam

as per IS800-2007 , the permissible stress is 128MPa

while as per IS800-1984 , the permissible stress is 140MPa
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Dr. N. Subramanian
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PostPosted: Tue Nov 24, 2009 3:11 pm    Post subject: Reply with quote

Dear Er Abhishek  Sharma,

Sorry. I did not notice that in your example the column is braced along minor axis. In that case you are getting fcd as 226 MPa. and the strength is 1507.4 KN. As per WSD you are getting 987 KN, multiplying it with 1.5, we get 1480.5 kN. Thus it is 1.8% increase only. How you are getting 136 MPa in the case of LSM, are you dividing the fcd by 1.67? I am afraid it is not the correct way to compare.

Best wishes,
NS

abhik_shar wrote:
Hello Sir,

I am comparing IS800-1984 & IS-800-2007---

TENSION MEMBER:
Please refer to clause no 11.2.1 , a), b) ,c)  ,of IS 800:2007 - the permissible stresses after calculating Tdn( as per clause 6.3) & Tdb( as per clause6.4) , the permissible stress fat as per yielding is 0.15KN/m2 , as per rupture is 0.165KN/m2 & as per block shear 0.135KN/m2

but as per IS 800-1984 , permissible stress is 0.15KN/m2

so, the critical is the new code , as the limiting stress is 0.135KN/m2
so if the same member is designed by new code it will fail as per old code.

COMPRESSION MEMBER:

IS800--2007 , Since in my example the column is braced along minor axis , the slenderness ratio is 21 & therefore the buckling curve is "a" to be used , as per table 9a, for slenderness ratio 21 & fy =250MPa , the design compressive stress is fcd=226MPa , as per clause 11.3.1 for calculating permisible compressive stress , fac for WSD = 0.6 fcd
so, the permissible compressive stress fac = 0.6 *226 = 136MPa

while as per IS800-1984 ,
for slenderness ratio 21 & fy = 250MPa
the design compressive stress = 148Mpa

so , member designed as per old code will fail as per new code ,

similar results for beam

as per IS800-2007 , the permissible stress is 128MPa

while as per IS800-1984 , the permissible stress is 140MPa
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nitishbhardwaj2710
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PostPosted: Tue Nov 24, 2009 6:42 pm    Post subject: IS 800:2007 Vs IS800:1984( Working stress) Reply with quote

the code changes certain aspects  there is some correction which are
revise in new one so consult the new don't compare these two.

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arulsteel
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PostPosted: Wed Nov 25, 2009 4:30 am    Post subject: IS 800:2007 Vs IS800:1984( Working stress) Reply with quote

My dear friend
I dont know why you choose not to reveal your identity. May be you are well known in this forum but let me politely ask you if could let us know your background. This helps us in the "level of rigour" in the explanations. It gives an idea whether you are a student, designer, teacher etc. Learning is a joy and you can learn from anybody you need not feel bad about it.
Thank you for your question. Chapter 11 in IS:800(2007) is only to help a transition between Allowable stress design to Limit state design. The more important reason for chapter 11 - in my personal opinion is in the "techno legal problems". There are many open ended design provisions in the Limit state code IS:800(2007) which may be subjected various interpretations. For example design of plate girders in the new code has two methods of design one conservative and the other efficient. Hence you cant call the efficient method as "failing" when compared to the conservative method. In the past five decades we have been used to the design checking which runs like - "less than the permissble and hence OK". Hence, in case of techno legal implications I think recourse may me made to chapter 11 of IS:800(2007) to compare the actual stresses are less than the allowable stresses.
However if you have contractual necessacity for allowable stress design then better stick to IS:800(1984).
Coming back to the questions - I can only say that working stress design as per IS:800(2007) is "conservative". It does not mean an alarming bell that designs as per IS:800(1984) are in the "fail" category. This kind of discrepancies do exists in other codes as well.
If you are not satisfied with my answer please dont hesitate to be in touch again but this time please reveal your identity.
regards
arul(serc)

From: abhik_shar forum@sefindia.org (forum@sefindia.org)
To: general@sefindia.org
Sent: Tue, 24 November, 2009 8:56:19 AM
Subject: [SEFI] Re: IS 800:2007 Vs IS800:1984( Working stress)

Hello Sir,

I am comparing IS800-1984 & IS-800-2007---

TENSION MEMBER:
Please refer to clause no 11.2.1 , a), b) ,c) ,of IS 800:2007 - the permissible stresses after calculating Tdn( as per clause 6.3) & Tdb( as per clause6.4) , the permissible stress fat as per yielding is 0.15KN/m2 , as per rupture is 0.165KN/m2 & as per block shear 0.135KN/m2

but as per IS 800-1984 , permissible stress is 0.15KN/m2

so, the critical is the new code , as the limiting stress is 0.135KN/m2
so if the same member is designed by new code it will fail as per old code.

COMPRESSION MEMBER:

IS800--2007 , Since in my example the column is braced along minor axis , the slenderness ratio is 21 & therefore the buckling curve is "a" to be used , as per table 9a, for slenderness ratio 21 & fy =250MPa , the design compressive stress is fcd=226MPa , as per clause 11.3.1 for calculating permisible compressive stress , fac for WSD = 0.6 fcd
so, the permissible compressive stress fac = 0.6 *226 = 136MPa

while as per IS800-1984 ,
for slenderness ratio 21 & fy = 250MPa
the design compressive stress = 148Mpa

so , member designed as per old code will fail as per new code ,

similar results for beam

as per IS800-2007 , the permissible stress is 128MPa

while as per IS800-1984 , the permissible stress is 140MPa









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abhik_shar
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PostPosted: Wed Nov 25, 2009 5:22 am    Post subject: Reply with quote

Dear Sir,

I am comparing old code with new code :

IS;800-2007, Please refer to clause 11.3.1 for calculating permisible compressive stress , fac for WSD = 0.6 fcd ,
so, the permissible compressive stress fac = 0.6 *226 = 136MPa & strength of column= 136*6670/1000 = 907KN

IS800-1984 , while as per old code, permissible compressive stress is 148MPa , corresponding ,
load carrying capacity of column =148 *6670/1000=987KN


with regards

Abhishek Sharma
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revanwaghode
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PostPosted: Fri Nov 27, 2009 5:10 am    Post subject: IS 800:2007 Vs IS800:1984( Working stress) Reply with quote

Dear Sefians,
 
Is it now mandatory to  use IS-800-2007 . Or Still we can proceed design  with IS-800-1984.If so by what time we can use and from when IS-800-2007 will be enforced?
 
With Regards
Abhay Waghode


On Wed, Nov 25, 2009 at 8:53 AM, nitishbhardwaj2710 <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
  the code changes certain aspects there is some correction which are
revise in new one so consult the new don't compare these two.








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jiwaji
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PostPosted: Fri Nov 27, 2009 7:13 am    Post subject: IS 800:2007 Vs IS800:1984( Working stress) Reply with quote

Dear Abhay

Once even a normal revision of a Code takes place, it is an established practice to use as using the earlier one is an outdated and undesirable practice. Continuing to use the old Code, especially when the Design Philosophy has been significantly changed to keep in tune with the new international practice, will put us at a disadvantage where both economy and advncement of expertise with latest methods is concerned.

So even if it is not mandatory, we have to make a decision in favour of the new Code.

If there are any shortcomings we need to try and put them right as we have been doing thru this Forum.

Regards

Jiwaji Y Desai



"revanwaghode" <forum@sefindia.org>  
11/27/2009 10:48 AM    Please respond to
general@sefindia.org

To
general@sefindia.org   cc
Subject
[SEFI] Re: IS 800:2007 Vs IS800:1984( Working stress)




Dear Sefians,

Is it now mandatory to use IS-800-2007 . Or Still we can proceed design with IS-800-1984.If so by what time we can use and from when IS-800-2007 will be enforced?

With Regards
Abhay Waghode


On Wed, Nov 25, 2009 at 8:53 AM, nitishbhardwaj2710 <forum@sefindia.org (forum@sefindia.org)> wrote:

Quote:
the code changes certain aspects there is some correction which are
revise in new one so consult the new don't compare these two.







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