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Failure of overhead water tank,at BANKURA,WEST BENGAL
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diproghosh
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PostPosted: Fri Jan 24, 2020 12:30 pm    Post subject: Failure of overhead water tank,at BANKURA,WEST BENGAL Reply with quote

Hello everyone,I watched the video multiple times and noted 3 points mainly
1. According to local people they heard a very loud humming sound which was coming from the water tank which made them gather and prepare to record the video
2. The horizontal crack developed at the circumference of the supporting tube structure at almost mid height.
3. In last 8seconds or so before collapse, many vertical cracks were propagating downwards generating from the original horizontal crack.. which resulted in the final collapse inclining at that direction where these vertical cracks were propagated.


My own opinion, may be I am not right due to lack of thorough knowledge, but my interpretation is basically that the structure failed due to compression failure of the supporting tube and most probably due to less quality material. Have no idea what generated the sounds but the seperation of walls into the form of vertical strips at the final time may be a sign of compression failure of that tubular member. May be I am wrong, just thought in own way. Discussion and corrections are expected.


Thanking you
Dipro


On Fri, 24 Jan, 2020, 5:19 PM mohd_arastu, <forum@sefindia.org (forum@sefindia.org)> wrote:

Quote:
           Hi 


In my opinion it is a planned collapse of the tank. The concrete at the mid height of the tank was cut when the tank was empty  and then filling  of water have started to increase the axial load on shaft.  As the load increased, the rebars exceeded their axial capacity which results into the collapsed of tank.



On Thu, Jan 23, 2020, 10:56 PM indutridibesh forum@sefindia.org (forum@sefindia.org))> wrote:

Quote:
           Here is a link to the complete videohttps://youtu.be/vUEhqlBTCqo





The circumferential crack in the shaft is clearly visible from some time ahead of collapse. The crack might be due to inadequate reinforcement and/or weak joint in concrete as well.



If the shaft wall is thin enough in proportion to its diameter, then the wall would wobble and it may fail when there is bending of the shaft.





On Thu, 23 Jan, 2020, 14:27 uhvaryani, forum@sefindia.org (forum@sefindia.org) (forum@sefindia.org (forum@sefindia.org)))> wrote:

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Rudra Nevatia
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PostPosted: Fri Jan 24, 2020 1:30 pm    Post subject: Failure of overhead water tank,at BANKURA,WEST BENGAL Reply with quote

We observe that :

1. Failure occurs at a construction joint near mid-height of the shaft
2. Failure is gradual due to crushing of concrete in circumferencial direction
3. The tank topples over in the direction of crushed concrete


Possible cause of failure could be :


1. All vertical bars were inadequately lapped at the construction joint
2. Foundation tilted ever so slightly towards the visible front direction triggering P-Delta moments
3. Lapped bars started failing resulting in bending failure of the shaft.


My two paisa worth.


Regards,
Rudra Nevatia














On Fri, Jan 24, 2020 at 5:25 PM aknargotra <forum@sefindia.org (forum@sefindia.org)> wrote:

Quote:
Dear Sefians
Height appears to be much more than 7.5 m. Compare with building height. This was waiting to happen since there was a big circumferential crack. Exact reasons can be analysed once full particulars of structure including history of crack is known.With regards,
Ajay Kumar


On Thu 23 Jan, 2020, 10:56 PM indutridibesh, <forum@sefindia.org (forum@sefindia.org) (forum@sefindia.org (forum@sefindia.org))> wrote:

Quote:
                 Here is a link to the complete videohttps://youtu.be/vUEhqlBTCqo (https://youtu.be/vUEhqlBTCqo)





The circumferential crack in the shaft is clearly visible from some time ahead of collapse. The crack might be due to inadequate reinforcement and/or weak joint in concrete as well.



If the shaft wall is thin enough in proportion to its diameter, then the wall would wobble and it may fail when there is bending of the shaft.





On Thu, 23 Jan, 2020, 14:27 uhvaryani, forum@sefindia.org (forum@sefindia.org) (forum@sefindia.org (forum@sefindia.org)))> wrote:

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rkmallik
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PostPosted: Fri Jan 24, 2020 6:30 pm    Post subject: Failure of overhead water tank,at BANKURA,WEST BENGAL Reply with quote



https://youtube.com/watch?v=99DY-qxNfsA&feature=share&fbclid=IwAR0fK4bVqHSV9xGcfB9LwAmm9Eq8nQIBAkVt8m-w4A95ypHItNT0BVfNUMo


Best Regards
R.K.Mallik
Structural Engineer

R.N.D. Centre Pvt. Ltd.
Koupandole, Lalitpur
Kathmandu
Nepal














On Fri, Jan 24, 2020 at 11:42 PM aknargotra <forum@sefindia.org (forum@sefindia.org)> wrote:

Quote:
           Dear Sefians
Height appears to be much more than 7.5 m. Compare with building height. This was waiting to happen since there was a big circumferential crack. Exact reasons can be analysed once full particulars of structure including history of crack is known.With regards,
Ajay Kumar


On Thu 23 Jan, 2020, 10:56 PM indutridibesh, forum@sefindia.org (forum@sefindia.org))> wrote:

Quote:
           Here is a link to the complete videohttps://youtu.be/vUEhqlBTCqo





The circumferential crack in the shaft is clearly visible from some time ahead of collapse. The crack might be due to inadequate reinforcement and/or weak joint in concrete as well.



If the shaft wall is thin enough in proportion to its diameter, then the wall would wobble and it may fail when there is bending of the shaft.





On Thu, 23 Jan, 2020, 14:27 uhvaryani, forum@sefindia.org (forum@sefindia.org) (forum@sefindia.org (forum@sefindia.org)))> wrote:

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satyavijet
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PostPosted: Sat Jan 25, 2020 5:30 am    Post subject: Failure of overhead water tank,at BANKURA,WEST BENGAL Reply with quote

Hi,

I think all the opinions shared stating circumferential cracks, local buckling etc are not correct. It seems a planned collapse bcos the video shared in the forum shows it has been captured in a mobile. How come they know that the tank is failing. There might be a problem during construction and wanted it to dismantle.

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satyabhanuangirash
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PostPosted: Sat Jan 25, 2020 5:30 am    Post subject: Failure of overhead water tank,at BANKURA,WEST BENGAL Reply with quote

Dear Sefians,


There is a maximum possibility of:-
1. Overlapping of vertical Bars at failure section was not appropriate.

2. Also the all verticals bars were overlapped at same locations due to which the maximum percentage of vertical reinforcement may be achieved.

You may first council the Labour and Site incharge as I am sure that they were not familiar with these structural considerations.








Best Regards


Satyabhanu Angirash

BE Civil (Hons), M Tech (Struct Engg), FIV, MIE, C Engg
Director
DHARA ENG CONSULTANTS (P) LTD
D-35, JLN Marg, Above SBI Bank, Near Kanha Restaurant,
Malviya Nagar, Jaipur (Rajasthan), INDIA - 302017

E-mail: dhaaraassociates@gmail.com (dhaaraassociates@gmail.com)
www.dharaeng.com
(M) +91-7727096633






















On Fri, Jan 24, 2020 at 8:25 PM diproghosh <forum@sefindia.org (forum@sefindia.org)> wrote:

[quote]            Hello everyone,I watched the video multiple times and noted 3 points mainly
1. According to local people they heard a very loud humming sound which was coming from the water tank which made them gather and prepare to record the video
2. The horizontal crack developed at the circumference of the supporting tube structure at almost mid height.
3. In last 8seconds or so before collapse, many vertical cracks were propagating downwards generating from the original horizontal crack.. which resulted in the final collapse inclining at that direction where these vertical cracks were propagated.


My own opinion, may be I am not right due to lack of thorough knowledge, but my interpretation is basically that the structure failed due to compression failure of the supporting tube and most probably due to less quality material. Have no idea what generated the sounds but the seperation of walls into the form of vertical strips at the final time may be a sign of compression failure of that tubular member. May be I am wrong, just thought in own way. Discussion and corrections are expected.


Thanking you
Dipro


On Fri, 24 Jan, 2020, 5:19 PM mohd_arastu, forum@sefindia.org (forum@sefindia.org))> wrote:

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Ragothaman.s
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PostPosted: Sat Jan 25, 2020 6:30 am    Post subject: Failure of overhead water tank,at BANKURA,WEST BENGAL Reply with quote

Dear all

In my openion,  local buckling is not a reasin,  if so it should hv collapsed even immediately after commisioning. The OT looks like old and might hv been serving for quite long time.


Thus reason could be sudden increase in p-delta moment due to WL or SL only.

Regards, 


Raghu.

CEO, GRA.



On Fri, 24 Jan 2020, 8:19 pm Rudra Nevatia, <forum@sefindia.org (forum@sefindia.org)> wrote:

[quote]            We observe that :

1. Failure occurs at a construction joint near mid-height of the shaft
2. Failure is gradual due to crushing of concrete in circumferencial direction
3. The tank topples over in the direction of crushed concrete


Possible cause of failure could be :


1. All vertical bars were inadequately lapped at the construction joint
2. Foundation tilted ever so slightly towards the visible front direction triggering P-Delta moments
3. Lapped bars started failing resulting in bending failure of the shaft.


My two paisa worth.


Regards,
Rudra Nevatia














On Fri, Jan 24, 2020 at 5:25 PM aknargotra forum@sefindia.org (forum@sefindia.org))> wrote:

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N. Prabhakar
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PostPosted: Sat Jan 25, 2020 6:53 am    Post subject: Reply with quote

Dear Sefians,

To me, this collapse of water tank is in fact a planned demolition, and not a natural collapse on its own for whatever reasons that have been discussed in this Forum.

From Google search it is known that the tank had been the subject of numerous complaints by locals who had noticed cracks in its structure. They were forced to ensure that nobody goes near the tank, for fear that it may collapse.  

Against the fear, the local authorities may have done the demolition themselves, not  by using explosives or chemicals, but  making a horizontal cut (seen as a horizontal crack from a long distance) in the circular shaft for an appreciable depth and filling the tank full with water or by filling one half full creating eccentric load on the shaft.  This suspicion arises as 5 news channels were there near the location of tanks, waiting  to make  videos (seen in YouTube) of the planned demolition.  Had it been a natural collapse, those five news channels wouldn't be there waiting  to make the videos.  Hence, the reason for a planned demolition.

It is not worth discussing in this Forum about the reasons for the collapse when it is actually a planned demolition.

With best wishes,

N. Prabhakar
Chartered Structural Engineer
Vasai (E)
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uhvaryani
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PostPosted: Sat Jan 25, 2020 8:30 am    Post subject: Failure of overhead water tank at BANKURA,WEST BENGAL Reply with quote

Dear Sefians,I wish to offer many thanks to our engineer-friends who have given opinion on the above subject.This failure just disturbed me ,so I have written about it.I have no knowledge,who is the designer and who is the contractor.
The diameter of the shaft is 6.0m and thickness is 150mm and the capacity of the tank is 700cu.m.and the shaft was slip-formed.
I expect some engineers from West Bengal may throw more light on this subject.I wrote a paper on this subject,
"Structural Design of Reinforced Concrete Circular Staging Shafts for Overhead Tanks Under Direct Compression-Some Vital Aspects"
Civil Engineering and Construction Review,October 1999.pp.19-25
with best wishes and regards,
uhvaryani

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anandads
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PostPosted: Sat Jan 25, 2020 8:30 am    Post subject: Failure of overhead water tank,at BANKURA,WEST BENGAL Reply with quote

Dear sir 1)what is the capacity of the tank?
2) Grade of concrete for tank?
3) If there is photograph it will throw lot lnformation.
I have designed intz tanks of capacities 50000 liters,75000lutres & 100000 lakh litres. The minimum thickness of shaft ranged from 350mm for 50000litres & for 100000lakh litres it was 450mm
Shaft diameter kept around 2/3 of the dome. The tank was 45m above ground & designed seismic zone III, considering dynamic force due to water splashing  at that height causing large moments in addition horizontal seismic   force due to dead load. It is founded on soft rock with SBC 500kN/sq.m.  constructed during 2012.
Well on prima-facie study following could be cause of failure.
1) If grade of concrete based on core samples <25MPa , 150mm thick in adequate
2) Disasters aggravate when cover is increased more than 50mm. 
3) Possibility of high cover as applied for water tank might have been applied to this.
4) Crushing for pure vertical load occurs at base due to bearing failure but here at the middle indicating poor concrete or may not have been cured.
5) Buckling is ruled out due to large L/r for shafts. 
6)Moment  effect is also ruled out if it is resting on  sound foundation & resting on solid raft.
7) No chance of seismic force as there was no seismic activity during recent past.
Cool Dynamic wind or Gust wind depends on structural parameter h/b ratio & time period. I dont see it can cause such disasters.
9)Some tines we provide bifurcation in large tank for maintenance purpose  in which case there will be water in one chamber & empty in other chamber. (In case if thermal plants) . Then there will be moments. I hope it is not so.
10) Finally settlement which could provide p-delta effect with large mass though delta bit less but large moment due to water weight & structural weight.


But i feel it is certainly because less thickness , more cover, poor quality of work & in adequate curing.
 
Designers play important role here by way introducing statutory note on raising the shaft, treating joints, stressing on cover, minimum core thickness,spacing of hoops, dowels, I
n other words a review from experts is must as from my experience  i suggest one can make 3D models with brick elements , play with model varying design parameters analyse structure static & dynamic analysis you will see unanticipated failures , then you would know how to strengthen it.
Numerical calculations do not depict stress concentrations. May not be able to do complex analysis like modal analysis, p-delta etc.












3) 





On Thu, 23 Jan 2020, 14:28 uhvaryani, <forum@sefindia.org (forum@sefindia.org)> wrote:

Quote:
           Dear Sefians,   Recently,a failure of an overhead water tank,supported on a reinforced concrete shaft of 150 mm thickness and of height 7.5 m has been reported in the media.
The shaft broke at about mid-height.What could be the reason of this failure?
Earlier cases of failure of these structures showed sinking of the shaft in the ground.In the present case soil is reported to be good, so the shaft has broken into two parts.I request our senior members to consider this case and give us the reason of this failure.My view is that the shaft thickness of 150mm is in sufficient and this has caused local buckling of the shaft.
with best wishes and regards,
uhvaryani
     



     



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anandads
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PostPosted: Sat Jan 25, 2020 8:30 am    Post subject: Failure of overhead water tank,at BANKURA,WEST BENGAL Reply with quote

With best regardsAnanda


On Sat, 25 Jan 2020, 13:40 Ananda d s, <anandads14567@gmail.com (anandads14567@gmail.com)> wrote:

Quote:
Dear sir 1)what is the capacity of the tank?
2) Grade of concrete for tank?
3) If there is photograph it will throw lot lnformation.
I have designed intz tanks of capacities 50000 liters,75000lutres & 100000 lakh litres. The minimum thickness of shaft ranged from 350mm for 50000litres & for 100000lakh litres it was 450mm
Shaft diameter kept around 2/3 of the dome. The tank was 45m above ground & designed seismic zone III, considering dynamic force due to water splashing  at that height causing large moments in addition horizontal seismic   force due to dead load. It is founded on soft rock with SBC 500kN/sq.m.  constructed during 2012.
Well on prima-facie study following could be cause of failure.
1) If grade of concrete based on core samples <25MPa , 150mm thick in adequate
2) Disasters aggravate when cover is increased more than 50mm. 
3) Possibility of high cover as applied for water tank might have been applied to this.
4) Crushing for pure vertical load occurs at base due to bearing failure but here at the middle indicating poor concrete or may not have been cured.
5) Buckling is ruled out due to large L/r for shafts. 
6)Moment  effect is also ruled out if it is resting on  sound foundation & resting on solid raft.
7) No chance of seismic force as there was no seismic activity during recent past.
Cool Dynamic wind or Gust wind depends on structural parameter h/b ratio & time period. I dont see it can cause such disasters.
9)Some tines we provide bifurcation in large tank for maintenance purpose  in which case there will be water in one chamber & empty in other chamber. (In case if thermal plants) . Then there will be moments. I hope it is not so.
10) Finally settlement which could provide p-delta effect with large mass though delta bit less but large moment due to water weight & structural weight.


But i feel it is certainly because less thickness , more cover, poor quality of work & in adequate curing.
 
Designers play important role here by way introducing statutory note on raising the shaft, treating joints, stressing on cover, minimum core thickness,spacing of hoops, dowels, I
n other words a review from experts is must as from my experience  i suggest one can make 3D models with brick elements , play with model varying design parameters analyse structure static & dynamic analysis you will see unanticipated failures , then you would know how to strengthen it.
Numerical calculations do not depict stress concentrations. May not be able to do complex analysis like modal analysis, p-delta etc.












3) 





On Thu, 23 Jan 2020, 14:28 uhvaryani, <forum@sefindia.org (forum@sefindia.org)> wrote:

Quote:
           Dear Sefians,   Recently,a failure of an overhead water tank,supported on a reinforced concrete shaft of 150 mm thickness and of height 7.5 m has been reported in the media.
The shaft broke at about mid-height.What could be the reason of this failure?
Earlier cases of failure of these structures showed sinking of the shaft in the ground.In the present case soil is reported to be good, so the shaft has broken into two parts.I request our senior members to consider this case and give us the reason of this failure.My view is that the shaft thickness of 150mm is in sufficient and this has caused local buckling of the shaft.
with best wishes and regards,
uhvaryani
     



     




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