www.sefindia.org

[krishnapada_chanda]

Dear all,

The maximum Allowable deflection of steel stack at top for static wind load is h/200 as per Cl. 7.4 of IS 6533.

Can you please guide for Allowable deflection of steel stack at top for dynamic wind load?



Regards,

Krishnapada Chanda
Email: krishnapada.chanda@gmail.com

[psatya31]

Dear Krishnapada,

Steel stacks are susceptible to cross wind oscillations deflection which will in general be on higher side only it is very difficult to design for cross wind oscillations ehnec methods likes strakes or other methods are invariably adopted.


Coming to your quest this h/200 criteria should be followed for both static wind as well as gust wind.


thanks and regards
P. Sathyanarayana


On Sat, Sep 2, 2023 at 3:22 PM krishnapada_chanda <forum@sefindia.org (forum@sefindia.org)> wrote:

[Bhimaji Dashrath Kanawade]

Respected sir,

Allowable deflection of steel stack at top for dynamic wind load is H/500.



On Sat, 2 Sept 2023, 3:25 pm krishnapada_chanda, <forum@sefindia.org (forum@sefindia.org)> wrote:

[abhaygupta]

As per which reference?

=======
Regards,
Er Dr Abhay Gupta, Director
Skeleton consultants Pvt Ltd Noida
BE(C) ME(Struct) PhD FIE(I)
Chartered Engineer, Sr PE(ECI)
Res: 1883 Venezia, Mahagun Moderne, Sector 78, Noida
9871844932


On Sun, Sep 3, 2023, 10:14 Bhimaji Dashrath Kanawade <forum@sefindia.org (forum@sefindia.org)> wrote:

[quote]            Respected sir,

Allowable deflection of steel stack at top for dynamic wind load is H/500.



On Sat, 2 Sept 2023, 3:25 pm krishnapada_chanda, forum@sefindia.org (forum@sefindia.org))> wrote:

      --auto removed--

Posted via Email

[anandads]

Dear all,Generally permissible deflection at top should not be greater than H/500.
The deflection of Chimney will be maximum at top & deflection range during vortex shedding should be calculated  corresponding to bending stress at the chimney base.


 The effect of foundation settlement  also verified during computations.
Other considerations:


1. Loss of thickness  due to corrosion.


2. Temperature of shell


3. Vortex shedding of the wind 


4. ranges  for various weld classifications and design loads.


5.Material safety factor 1.1, applied to fatigue category,


 6.Modelling factor of 1.4 7


 7.Miner Number derived in fatigue calculations for temperatures up to 200°C 


8. Factor 1.5 for temperatures between 200°C and 400°C


9.Young's modulus shall be corresponding to maximum temperature of steel might attend.


10. Air density shall be ya=1.25 -(h1/8000) kg/m3


With regardsAnanda






On Sat, 2 Sept 2023, 15:24 krishnapada_chanda, <forum@sefindia.org (forum@sefindia.org)> wrote:

[psatya31]

H/500 for concrete stack which is more stringent

On Sun, Sep 3, 2023, 6:51 PM Bhimaji Dashrath Kanawade <forum@sefindia.org (forum@sefindia.org)> wrote:

[quote]            Respected sir,

Allowable deflection of steel stack at top for dynamic wind load is H/500.



On Sat, 2 Sept 2023, 3:25 pm krishnapada_chanda, forum@sefindia.org (forum@sefindia.org))> wrote:

      --auto removed--

Posted via Email

[abhaygupta]

This is not correct. Any deflection, vertical or horizontal, depends on serviceability requirements.What is ok for buildings is not same applicable for other structures.
For chimney n stacks it shud be referred from relevant IS code.
For communication towers, it depends on dish antenna mounted on it.
Please refer n use properly.
Thanks 

=======
Regards,
Er Dr Abhay Gupta, Director
Skeleton consultants Pvt Ltd Noida
BE(C) ME(Struct) PhD FIE(I)
Chartered Engineer, Sr PE(ECI)
Res: 1883 Venezia, Mahagun Moderne, Sector 78, Noida
9871844932



On Mon, Sep 4, 2023, 11:06 anandads <forum@sefindia.org (forum@sefindia.org)> wrote:

[quote]            Dear all,Generally permissible deflection at top should not be greater than H/500.
The deflection of Chimney will be maximum at top & deflection range during vortex shedding should be calculated  corresponding to bending stress at the chimney base.


 The effect of foundation settlement  also verified during computations.
Other considerations:


1. Loss of thickness  due to corrosion.


2. Temperature of shell


3. Vortex shedding of the wind 


4. ranges  for various weld classifications and design loads.


5.Material safety factor 1.1, applied to fatigue category,


 6.Modelling factor of 1.4 7


 7.Miner Number derived in fatigue calculations for temperatures up to 200°C 


8. Factor 1.5 for temperatures between 200°C and 400°C


9.Young's modulus shall be corresponding to maximum temperature of steel might attend.


10. Air density shall be ya=1.25 -(h1/8000) kg/m3


With regardsAnanda






On Sat, 2 Sept 2023, 15:24 krishnapada_chanda, forum@sefindia.org (forum@sefindia.org))> wrote:

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Posted via Email

[anandads]

Dear friends,I have designed 270m high three chimneys. Two Single flue for (for 500MW,700MW) one twin flue 270m,(for 2x800MW),  in addition 140m steel chimney (for 2x135MW) .
Three for coal fired & one for  gas thermal plants
Please note that don't relay on IS alone, you will get derailed. These are important structure which is to be looked upon in all angles. Many chimneys have failed because inadequate analysis & shallow knowledge on the behaviour of structure.
We had even gone for one the rare combination of interference of adjacent tall chimneys & cooling towers on the new one. 
Finally wind tunnel test conducted at IIT Kanapur proved interference was  one of the critical loading condition.
 
It is better to refer following widely accepted reference for analysis


CICIND Model Code for Steel Chimneys (Revision 1) Amendment A.


For these tall & slender structure, experienced designers (on the structure) advise matters a lot. 
The above reference throws lot of light on the analysis & design. Mere structural background is inadequate.
Regards
Ananda



On Mon, 4 Sept 2023, 12:52 abhaygupta, <forum@sefindia.org (forum@sefindia.org)> wrote:

[abhaygupta]

Yes. True that interference is one of the critical parameter. During my PhD at IIT Roorkee, I have worked on few wind tunnel studies of chimneys.U r correct in saying that only IS code shud not be the source of information. But at the same time, applying H/500 of buildings on chimneys is also not ok.
CICIND is no doubt a good reference.
Hence, international resources with experience and wind tunnel testing together shall form proper rationale.
Thanks 

=======
Regards,
Er Dr Abhay Gupta, Director
Skeleton consultants Pvt Ltd Noida
BE(C) ME(Struct) PhD FIE(I)
Chartered Engineer, Sr PE(ECI)
Res: 1883 Venezia, Mahagun Moderne, Sector 78, Noida
9871844932


On Mon, Sep 4, 2023, 17:52 anandads <forum@sefindia.org (forum@sefindia.org)> wrote:

[quote]            Dear friends,I have designed 270m high three chimneys. Two Single flue for (for 500MW,700MW) one twin flue 270m,(for 2x800MW),  in addition 140m steel chimney (for 2x135MW) .
Three for coal fired & one for  gas thermal plants
Please note that don't relay on IS alone, you will get derailed. These are important structure which is to be looked upon in all angles. Many chimneys have failed because inadequate analysis & shallow knowledge on the behaviour of structure.
We had even gone for one the rare combination of interference of adjacent tall chimneys & cooling towers on the new one. 
Finally wind tunnel test conducted at IIT Kanapur proved interference was  one of the critical loading condition.
 
It is better to refer following widely accepted reference for analysis


CICIND Model Code for Steel Chimneys (Revision 1) Amendment A.


For these tall & slender structure, experienced designers (on the structure) advise matters a lot. 
The above reference throws lot of light on the analysis & design. Mere structural background is inadequate.
Regards
Ananda



On Mon, 4 Sept 2023, 12:52 abhaygupta, forum@sefindia.org (forum@sefindia.org))> wrote:

      --auto removed--

Posted via Email

[srinivasarao3]

Dear All,

Mivan wall supporting Transfer girder in high rise Building we can release Torsion?

Please suggest

Warm Regards,

Er.Srinivasa Rao Bollimuntha
Associate Director - Structure
B.E Andhra University Vizag
M.Tech Structure
NIT-Warangal

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From: anandads [mailto:forum@sefindia.org]
Sent: 04 September 2023 11:06
To: general@sefindia.org
Subject: [SEFI] Re: Allowable deflection of steel stack at top for dynamic wind load



Dear all,Generally permissible deflection at top should not be greater than H/500.
The deflection of Chimney will be maximum at top & deflection range during vortex shedding should be calculated corresponding to bending stress at the chimney base.


The effect of foundation settlement also verified during computations.
Other considerations:


1. Loss of thickness due to corrosion.


2. Temperature of shell


3. Vortex shedding of the wind


4. ranges for various weld classifications and design loads.


5.Material safety factor 1.1, applied to fatigue category,


6.Modelling factor of 1.4 7


7.Miner Number derived in fatigue calculations for temperatures up to 200°C


8. Factor 1.5 for temperatures between 200°C and 400°C


9.Young's modulus shall be corresponding to maximum temperature of steel might attend.


10. Air density shall be ya=1.25 -(h1/8000) kg/m3


With regardsAnanda






On Sat, 2 Sept 2023, 15:24 krishnapada_chanda, forum@sefindia.org (forum@sefindia.org))> wrote:
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Posted via Email