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nurat
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 Posted: Thu Sep 07, 2023 8:30 am Post subject: Allowable deflection of steel stack at top for dynamic wind load |
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Dear Friends,In my opinion Deflection for Steel Chimney also depends a lot on these following factors too:
01. H/d Ratio ( Slenderness Ratio )
02. The property of Material Used. (Allowable Stress )
03. Whether Helical Strakes provided. ( If provided it will substantially reduce reduce the effect of Vortex Shedding)
04. Shape of Chimney.
Structural/ Experienced Engineers please have your comment on the above said.
Warm Regards,
T.K.RAMDAS, M.I.E., F.I.V., F.I.I.T. Arb.
Sarnath Consultants,
Flat No.6/13 "A" 1st floor, Sri Rama Prem Apartment,
Ramachandran Street, T.Nagar,
Chennai-600 017. Tamilnadu, India.
Ph. +91-44-28141454.
E-mail:sarnath.consultants@gmail.com (E-mail%3Asarnath.consultants@gmail.com)
Please visit us at: www.sarengg.com
On Thu, Sep 7, 2023 at 8:02 AM abhaygupta <forum@sefindia.org (forum@sefindia.org)> wrote:
| Quote: | 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) (forum@sefindia.org (forum@sefindia.org)))> wrote:
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ajay2612
SEFI Regulars
Joined: 14 Oct 2013
Posts: 30
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| Posted: Thu Sep 07, 2023 2:30 pm Post subject: Allowable deflection of steel stack at top for dynamic wind load |
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great.
From: "abhaygupta" <forum@sefindia.org>
Sent: Thu, 7 Sep 2023 18:18:13 GMT+0530
To: general@sefindia.org
Subject: [SEFI] Allowable deflection of steel stack at top for dynamic wind load
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:
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anandads
SEFI Regulars
Joined: 20 Oct 2015
Posts: 20
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| Posted: Sun Sep 10, 2023 4:30 pm Post subject: Allowable deflection of steel stack at top for dynamic wind load |
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Dear friends,There are many analysis which are to be carried out to doubly ensure to rule out deflection limit of h/500.
Please donot deviate any codal provisions nor limit oneself to one code only.
1. A 3D Staad or FEM model with foundation resting on soil or any strata ( use appropriate spring supports for subgrade modulus, refer Geotech Engg by Joseph Bowles) is most important for the chimney to study concentration of stresses at openings.
Bottom openings, duct openings ,etc will result in loss of cross sectional areas near base.
Also check deflection in the model.
2. For above model analyse for following separate load cases in addition to DL,LL,etc,
a) Dynamic wind +drag
b) Across wind
c) Vortex shedding
d) Interference if any
e) Seismic effect
f) Modal analysis for relevant load combinations
g) Most important second order analysis with relevant load combinations.
In all the cases check deflection.
Don't blindly ignore codal provisions, designer may face consequences if some failure or damage occurs as according to my experience these cushions in design save the structure due to unavoidable construction deviations & bad quality work at some portion bound to occur at site which generally will not come to designers notice. But designers will be made scape goat for the damaged.
With best wishes
Ananda
On Thu, 7 Sept 2023, 08:08 abhaygupta, <forum@sefindia.org (forum@sefindia.org)> wrote:
| Quote: | 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) (forum@sefindia.org (forum@sefindia.org)))> wrote:
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anandads
SEFI Regulars
Joined: 20 Oct 2015
Posts: 20
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| Posted: Sun Sep 10, 2023 5:30 pm Post subject: Allowable deflection of steel stack at top for dynamic wind load |
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As per IS 6533 Part 2 For Steel chimney.Clause 7.3.1 Chimney Shell
The minimum thickness of the structural chimney shell in single or multiple shell constructions, shall be the calculated thickness obtained from stress and deflection considerations plus the corrosion allowance ( see 7.5 ) but shall not be less than 6.0 mm nor less than l/500 of the outside diameter of the chimney at the considered height.
On Sun, 10 Sept 2023, 21:52 Ananda d s, <anandads14567@gmail.com (anandads14567@gmail.com)> wrote:
| Quote: | Dear friends,There are many analysis which are to be carried out to doubly ensure to rule out deflection limit of h/500.
Please donot deviate any codal provisions nor limit oneself to one code only.
1. A 3D Staad or FEM model with foundation resting on soil or any strata ( use appropriate spring supports for subgrade modulus, refer Geotech Engg by Joseph Bowles) is most important for the chimney to study concentration of stresses at openings.
Bottom openings, duct openings ,etc will result in loss of cross sectional areas near base.
Also check deflection in the model.
2. For above model analyse for following separate load cases in addition to DL,LL,etc,
a) Dynamic wind +drag
b) Across wind
c) Vortex shedding
d) Interference if any
e) Seismic effect
f) Modal analysis for relevant load combinations
g) Most important second order analysis with relevant load combinations.
In all the cases check deflection.
Don't blindly ignore codal provisions, designer may face consequences if some failure or damage occurs as according to my experience these cushions in design save the structure due to unavoidable construction deviations & bad quality work at some portion bound to occur at site which generally will not come to designers notice. But designers will be made scape goat for the damaged.
With best wishes
Ananda
On Thu, 7 Sept 2023, 08:08 abhaygupta, <forum@sefindia.org (forum@sefindia.org)> wrote:
| Quote: | 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) (forum@sefindia.org (forum@sefindia.org)))> wrote:
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Prasad Shankar Dayal
SEFI Member
Joined: 22 Dec 2011
Posts: 2
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| Posted: Mon Sep 11, 2023 4:30 am Post subject: Allowable deflection of steel stack at top for dynamic wind load |
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Iam agree with mr.abhay Gupta.
Thanks
P.S.Dayal
M.D
Dayal Infra Consultants.
99260-21888,
98266-21666,
Sent from RediffmailNG on Android
From: "abhaygupta" <forum@sefindia.org>
Sent: Thu, 7 Sep 2023 05:37:08 GMT+0530
To: general@sefindia.org
Subject: [SEFI] Allowable deflection of steel stack at top for dynamic wind load
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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abhio
...
Joined: 08 Mar 2010
Posts: 547
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| Posted: Mon Sep 11, 2023 6:10 am Post subject: |
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| We generally find that Indian codes are more conservative when compared with international ones. The limit of h/200 for deflection given in IS: 6533 part 2 is only checked for static wind load. However, even this is conservative when compared with the CICIND code, which does not put any limit on the deflection of the chimney. |
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