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Crack in precast pile
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mukeshkumar121in@gmail.co
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PostPosted: Sat Jun 30, 2018 5:30 pm    Post subject: Crack in precast pile Reply with quote

Hi Sefian,

We have encountered one problem in precast pile. The precast pile is 13 m long and is of size 400x400 mm. The reinforcement provided is 4 nos 16 dia main bar.
During lifting and shifting, the pile gets cracked. What could be the possible reason behind this cracks?


Thanks

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bkrajashekar
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PostPosted: Sun Jul 01, 2018 4:53 am    Post subject: Crack in Precast Pile Reply with quote

Mukesh Kumar,Are you a contractor or a consultant or the owner's engineer?Can you send us the photo of the cracked pile,calculations, drawing of the pile?What is the crack width noticed? In which location the crack is observed? One crack or more cracks?How many piles did you cast? and in how many piles the crack was observed?What is the pattern of the cracks?Who designed the pile? An experienced engineer?Has the calculations been made for handling stresses for the pile? At which location the pile was lifted from the mould? What type of provision is made for lifting the pile from the casting bed?How did you lift and shift the pile or piles?  Using Gantry? with spreader beams?Please check the calculations and ensure the  clear cover requirements including the tie details as shown in the drawings are matching with the as built pile.Has anyone checked the strength of concrete proposed and the strength of concrete attained with  cube tests?What type of curing was done? For how many days the curing was carried out?Was there any leakage of water through shuttering during concreting observed?Please answer all the above questions to find out the root cause of the cracks..Unless and until the root cause is known it would be difficult for anyone to solve the problem.To predict the root cause the above details are needed as a minimum if not more.Regards,Raja Shekar.
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Segzman
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PostPosted: Sun Jul 01, 2018 7:57 am    Post subject: Re: Reply with quote

The reinforcement seems inadequate. I doubt if 4Y16 is even up to the nominal reinforcement required for that section. I doubt if any design was done.
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TPS61
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PostPosted: Sun Jul 01, 2018 8:35 am    Post subject: CRACK IN PRECAST PILE Reply with quote

Mr. rajashekar has asked some very pertinent questions. A meaningful reply can be given only after having answers to those questions
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PostPosted: Mon Jul 02, 2018 4:34 pm    Post subject: Reply with quote

Posted: 01 Jul 2018 05:53    Post subject: Crack in Precast Pile
Dear Sir
Thanks for your response. I am site Engineer. I have attached the pics of cracks. The crack width is around 3 mm and is from top to bottom of the pile near centre of the pile.In few piles there are more than 4 to 5 cracks.Regarding calculation, I am not sure whether it has been designed for handling stress.Kindly throw light on this.The pile has been lifted at distance of 0.2L from both end using lifting hook.Crane has been used for lifting it. No spreader beam is used.Curing is done by pond methods and also by gunny bags.The cube test is around 35 MPA.There is no leakage in shuttering.

I hope I have answered most of the questions.
Looking for an expert view of root cause of cracks.

Regards
Mukesh








Mukesh Kumar,Are you a contractor or a consultant or the owner's engineer?Can you send us the photo of the cracked pile,calculations, drawing of the pile?What is the crack width noticed? In which location the crack is observed? One crack or more cracks?How many piles did you cast? and in how many piles the crack was observed?What is the pattern of the cracks?Who designed the pile? An experienced engineer?Has the calculations been made for handling stresses for the pile? At which location the pile was lifted from the mould? What type of provision is made for lifting the pile from the casting bed?How did you lift and shift the pile or piles?  Using Gantry? with spreader beams?Please check the calculations and ensure the  clear cover requirements including the tie details as shown in the drawings are matching with the as built pile.Has anyone checked the strength of concrete proposed and the strength of concrete attained with  cube tests?What type of curing was done? For how many days the curing was carried out?Was there any leakage of water through shuttering during concreting observed?Please answer all the above questions to find out the root cause of the cracks..Unless and until the root cause is known it would be difficult for anyone to solve the problem.To predict the root cause the above details are needed as a minimum if not more.Regards,Raja Shekar.



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bkrajashekar
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PostPosted: Tue Jul 03, 2018 11:20 am    Post subject: Crack in Precast Pile Reply with quote

Mukesh,


Thanks for the part information provided. Is this a driven pile? or going to be placed in prebored holes?

Please ask your design engineer to design or check all the provisions and requirements of the code IS2911 part1 sec 3  or IS2911 part 1 sec 4 including lifting and handling stresses etc.

The minimum reinforcement to be provided as per IS2911 part1 sec 3 is  24 sqcm. Whereas what is provided is 8 sqcm. ( 4 numbers 16mm dia)

The cube strength obtained was at the time of lifting? 7 days or 28 days?
What is the strength specified in the drawing issued for construction?

What is the clear cover for the main rebar specified in the drawing and provided in the cast pile?

The minimum clear cover to main bars shall be 50mm.

Was there any form work used for the base of the pile with friction free surface using shuttering oil/mould releasing oil etc? or it was directly cast on the ground?

It seems that the pile is cast directly on finished ground..??( as per the pictures sent by you).

What is the arrangement of the lifting hooks embedded in the piles?

The Pile was lifted simultaneously using two hooks? was the pile kept horizontal at the time of lifting?

Have you used two gantries?

The design has to match the site conditions and the  minimum requirements of the applicable standards and industry practice if not more.

All the best.

Regards,
Raja Shekar.
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PostPosted: Tue Jul 03, 2018 4:24 pm    Post subject: Re: Crack in Precast Pile Reply with quote

Dear Sir

Thanks again for such a prompt response.
The pile is driven pre cast pile. We asked the design engineer to provide minimum 1.5 percent as l/d ratio is greater than 30 and to follow IS code-2911 part 1 but he did not follow the suggestion. rather he gave this explanation that it is not driven by hammer rather it is driven by hydraulic push driving. I then told it is not a matter of driving as the pile is getting cracked during lifting and shifting.
I too feel the same that reinforcement is less and due to this pile is getting cracked. But during discussion he told that bending moment developed is around 32 KN-m and pile capacity of the section is 62 KN-m. Then it should not get cracked. The designer callculated the bending moment considering it as beam having udl of 4 KN/m(0.4*0.4*25=4). Then I suggested him not to calculate moment in that way rather it should be calculated as given in IS-2911.If there is 2 lift point then bending moment induced is 2.3 WL( where W-weight of pile and length 13m). As per code bending moment comes to be 149.5. Kindly correct me on this if I am wrong.
The cube strength was obtained for both 7 days and 28 days. 7 days strength is around 25 MPa and 28 days as 37 MPa. Design value is 30 MPa.
The clear cover is 50 mm.

Was there any form work used for the base of the pile with friction free surface using shuttering oil/mould releasing oil etc? or it was directly cast on the ground?
Ans:Yes. Brick bed is prepared.
The picture taken is after lifting and shifting.

What is the arrangement of the lifting hooks embedded in the piles?
Ans: The lifting hook is U type embedded in concrete

The Pile was lifted simultaneously using two hooks? was the pile kept horizontal at the time of lifting?
Ans: Yes Sir

Have you used two gantries?
Ans: No Sir

Thank you so much Sir.
Kindly provide your suggestion on reinforcement and bending moment induced and its capacity.

Regards
Mukesh

bkrajashekar wrote:
Mukesh,


Thanks for the part information provided. Is this a driven pile? or going to be placed in prebored holes?

Please ask your design engineer to design or check all the provisions and requirements of the code IS2911 part1 sec 3  or IS2911 part 1 sec 4 including lifting and handling stresses etc.

The minimum reinforcement to be provided as per IS2911 part1 sec 3 is  24 sqcm. Whereas what is provided is 8 sqcm. ( 4 numbers 16mm dia)

The cube strength obtained was at the time of lifting? 7 days or 28 days?
What is the strength specified in the drawing issued for construction?

What is the clear cover for the main rebar specified in the drawing and provided in the cast pile?

The minimum clear cover to main bars shall be 50mm.

Was there any form work used for the base of the pile with friction free surface using shuttering oil/mould releasing oil etc? or it was directly cast on the ground?

It seems that the pile is cast directly on finished ground..??( as per the pictures sent by you).

What is the arrangement of the lifting hooks embedded in the piles?

The Pile was lifted simultaneously using two hooks? was the pile kept horizontal at the time of lifting?

Have you used two gantries?

The design has to match the site conditions and the  minimum requirements of the applicable standards and industry practice if not more.

All the best.

Regards,
Raja Shekar.
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bkrajashekar
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PostPosted: Wed Jul 04, 2018 12:03 pm    Post subject: Crack in Precast Pile Reply with quote

Mukesh,

How many piles were cast so far?

How many piles have cracked after lifting?

Ask your designer to check the section for the two point lifting moment and single point lifting moment with appropriate load factors as per code.

Please note that at the time of driving the pile will be lifted at single point only to fix it to the piling frame guide.

The concrete strength shall be 25 MPa or the test cube strength at the time of lifting the pile from the bed, whichever is less.

The cube and the pile should have been cured under similar conditions for the same number of days.

It is also very important to select the lifting hooks type and place them at the correct location.

Either threaded steel eyes or tubes shall be embedded in the pile.

The embedded tube at the center of the pile through which a pin can be passed enables a bridle to be used. This will avoid the risk of diagonal lifting.


It is a good idea to use a lifting frame and thereby the  lifting force should be made vertical and not diagonal.

Please send the pic of the hooks and the gantry also including yard, rails etc,casting bed etc.

Please also improve the the curing methods and the quality of concrete.

Is it ready made concrete?
Did anyone check the slump consistently?

May be the lifting method followed is incorrect or the strength of concrete is less due to inadequate curing or the base is not free from friction or the clear cover is more or the rebar is less for the unforeseen stresses due to tilting,shifting and lifting of the pile.

You can cast two more Piles with the base resting on smooth friction free surface and taking due precautions as above  and one pile with with 4 nos 16 and the other pile with rebars as per the code requirements and lift to observe the result to arrive at a solution after finalized by your management. This is my opinion.

We need to adhere to the code requirements always. It is based on the previous lessons learnt in various projects throughout the world.

Please also follow the Subject matter experts' advice on this issue.

All the best.

Raja Shekar.
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PostPosted: Sun Jul 08, 2018 6:36 am    Post subject: Re: Crack in Precast Pile Reply with quote

bkrajashekar wrote:
Mukesh,

How many piles were cast so far?
Ans: Appx 50

How many piles have cracked after lifting?
Ans: around 40

Ask your designer to check the section for the two point lifting moment and single point lifting moment with appropriate load factors as per code.
Ans: The design moment as per IS code 2911 is 2.2 WL where W is the weight of pile(0.4x0.4x13x25=52 KN). Hence moment will be 2.2x52x13=1487.2 KN-m(too high).Kindly correct me if I am wrong.
As per our designer, the moment is WL^2/8 where W considered is UDL;ie;0.4x0.4x25=4 KN/m.WL^2/8=4x8^2/8=32 KN-m at centre and in canitever portion is WL^2/2=4x2.5^2/2=12.5 KN-m. So net hogging moment is 32-12.5=19.5 KN-m. Even if we multiply by factor 2.2 for 2 point lifting the value is 42.5 KN-m. The moment resisting capacity of the section is 62 KN-m.
Kindly tell the correct Bending moment developed in the section.

Please note that at the time of driving the pile will be lifted at single point only to fix it to the piling frame guide.
Ans: Noted Sir.In this case BM will be 4.3 WL which is too high.
The concrete strength shall be 25 MPa or the test cube strength at the time of lifting the pile from the bed, whichever is less.
Ans: Noted Sir

The cube and the pile should have been cured under similar conditions for the same number of days.
Ans: Noted Sir

It is also very important to select the lifting hooks type and place them at the correct location.
Either threaded steel eyes or tubes shall be embedded in the pile.
Ans: OK Sir

The embedded tube at the center of the pile through which a pin can be passed enables a bridle to be used. This will avoid the risk of diagonal lifting.


It is a good idea to use a lifting frame and thereby the  lifting force should be made vertical and not diagonal.
Ans: Thanks a lot for this suggestion and we will incorporate this.

Please send the pic of the hooks and the gantry also including yard, rails etc,casting bed etc.
Ans:

Please also improve the the curing methods and the quality of concrete.
Ans: Noted Sir

Is it ready made concrete?
And: No Sir.
Did anyone check the slump consistently?
Ans: Yes Sir. The slump is around 140 mm

May be the lifting method followed is incorrect or the strength of concrete is less due to inadequate curing or the base is not free from friction or the clear cover is more or the rebar is less for the unforeseen stresses due to tilting,shifting and lifting of the pile.
Ans: Kindly suggest some good practise for lifting the piles to avoid stress in pile.

You can cast two more Piles with the base resting on smooth friction free surface and taking due precautions as above  and one pile with with 4 nos 16 and the other pile with rebars as per the code requirements and lift to observe the result to arrive at a solution after finalized by your management. This is my opinion.
Ans: Thanks a lot sir for your valuable suggestion. We will implement this and check.

We need to adhere to the code requirements always. It is based on the previous lessons learnt in various projects throughout the world.
Ans: Right Sir.

Please also follow the Subject matter experts' advice on this issue.
Ans: Kindly share lesson learnt or any literature on this if you have. Thanks a lot Sir

All the best.

Raja Shekar.



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PostPosted: Mon Jul 09, 2018 2:13 am    Post subject: Re: Crack in Precast Pile Reply with quote

Dear Er.Mukeshkumar


[quote="mukeshkumar121in@gmail.co"][quote="bkrajashekar"]Mukesh,

Ask your designer to check the section for the two point lifting moment and single point lifting moment with appropriate load factors as per code.
Ans: The design moment as per IS code 2911 is 2.2 WL where W is the weight of pile(0.4x0.4x13x25=52 KN). Hence moment will be 2.2x52x13=1487.2 KN-m(too high).Kindly correct me if I am wrong.
As per our designer, the moment is WL^2/8 where W considered is UDL;ie;0.4x0.4x25=4 KN/m.WL^2/8=4x8^2/8=32 KN-m at centre and in canitever portion is WL^2/2=4x2.5^2/2=12.5 KN-m. So net hogging moment is 32-12.5=19.5 KN-m. Even if we multiply by factor 2.2 for 2 point lifting the value is 42.5 KN-m. The moment resisting capacity of the section is 62 KN-m.
Kindly tell the correct Bending moment developed in the section.

The formulae given in IS:2911 Part I Sec 3 - 2010 in Table 1 are not correct. The coefficients have to be divided by 100. The coefficients given in Clause 5.11.6 of the 1979 version of the code are correct

Please note that at the time of driving the pile will be lifted at single point only to fix it to the piling frame guide.
Ans: Noted Sir.In this case BM will be 4.3 WL which is too high.

When the correct formula for bending moment is applied, the pile is safe for this condition also.

In my opinion, since the piles are being hydraulically pushed down and not hammered down, the minimum reinforcement specified in the code is not really necessary.

However, it may be noted that at the start of pushing of the pile the effective length of the pile will be 13m. This efffecive length will progressively get reduced as we push down the pile. The force required to push the pile will be small initially. Since this force depends upon soil resistance, the force required will progressively increase as the pile is pushed down. I hope the axial strength of the pile has been checked at various stages of penetration.

It is a good idea to use a lifting frame and thereby the  lifting force should be made vertical and not diagonal.
Ans: Thanks a lot for this suggestion and we will incorporate this.

I agree.

Did anyone check the slump consistently?
Ans: Yes Sir. The slump is around 140 mm

A slump of 140 mm is needed for cast in situ piles only. For precast piles, a slump of 50 mm or so will be adequate.

The photographs of the cracks are inadequate to study the same

However, you can check whether these cracks are flexural cracks as follows

[1] Flexural cracks will be vertical
[2] At the lifting point, the crack will be wider at top and become narrower towards the bottom. Top surface will be cracked and bottom surface will be uncracked
[3] At midspan the crack will be wider at bottom and become narrower towards the top. Top surface will be uncracked and bottom surface will be cracked

If the cracks are not like this, it is likely that they are secondary cracks due to shrinkage etc. In this case the concrete mix may be reviewed by an expert in concrete technology

The various comments given by Er.Rajashekar are applicable not only to this particular case, but to civil engineering construction anywhere. I do hope the young engineers of this forum will study his comments deeply and enrich themselves

With best wishes
S.P.Srinivasan



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