STRUCTURAL ENGINEERING FORUM OF INDIA [SEFI]

Kins · SEFI Member Joined: 31 Jul 2010 Posts: 10

Dear Friends and Respected Sirs,
I’m a regular reader of SEFI posts. Most of the members till now have very well explored the code IS: 800-2007. I think I'm free to ask small doubts from code though it might be very simple for those who had done thorough study of same..I have one small query regarding Equation of Fcd for Compression member design in IS: 800-2007.I hope experts would help me for understanding of same.
I observed that in the code that imperfection factor arising due to initial bow of column, eccentric loading & residual stress in column is taken care in the equation by factor ‘Alpha’ which may tends to reduce the Axial capacity of Column. But at the same time we are increasing strength of column by increasing material strength going ahead of yield point.
Query: Like imperfection factor in equation of Fcd what factor in equation and its derivation which reflects the increase of strength of material? I request experts to correct me if I’m wrong in understanding.
Thanks & Regards ,
Kinjal Dave

Kins · SEFI Member Joined: 31 Jul 2010 Posts: 10

I was waiting for reply from dear SEFIANS.Please educate me on my query.

sspawar · SEFI Stars Joined: 05 Jun 2009 Posts: 550

Dear Er. KINS

Can you elaborate more on -

"But at the same time we are increasing strength of column by increasing material strength going ahead of yield point."

Regards

drnsmani · Posted: Wed Aug 04, 2010 9:59 pm Post subject:

Dear Er Dave,

I too do not understand your question. As per the equation given in Cl. 7.1.2.1 of the code, fcd will never exceed the yield stress. The non-dimensional Effective slenderness ratio Lamda takes into account several other factors that will affect the behaviour of column.

Best wishes,
Subramanian

Kins · SEFI Member Joined: 31 Jul 2010 Posts: 10

Thankyou Sir for your kind replies,.

I had just started to understand the new code so I might be wrong somewhere in asking my querry. I apologise for same.

What i was trying to ask is that when i check Axial capacity of standard IS channel section by old code and new code, always permissible stress found out by Fcd equation is greater than that what we were getting in old code. I was wondering the reason for same.
I thought because of invclusive of imperfection factor we might get less permissible stress compare to old. But in actual case this capacity gets increased using new code .Is it because we were on more conservative side in WSM method using the factor 0.6 ???

I hope you got my doubt. Please correct if I'm wrong which might be possible somewhere.

Thanks and regards,

Kinjal Dave

drnsmani · Posted: Thu Aug 05, 2010 7:16 pm Post subject:

Dear Er Dave,

What you are getting using LSM expression, i.e., fcd, is not allowable stress. Hence you can not compare it with that of all. stress of WSM. Note that the loads actions in LSM are those of WSM multiplied by 1.5!

Best wishes
NS

Kins · SEFI Member Joined: 31 Jul 2010 Posts: 10

Thankyou Sir,I got your point!!!!!