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Point of fFixity in pile foundation design
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saikiran gone
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PostPosted: Tue Aug 30, 2016 6:48 am    Post subject: Point of fFixity in pile foundation design Reply with quote

Dear Sir,

As per IS 2911(Part I -Sec-2) CL-C4 ,Fig 3. In case of pile length is less than point of fixity , what we need to consider?

Ex: Provided length = 1500 mm , but as per point of fixity calculation based on the stiffness factor it is resulting L = 2200 mm . Kindly suggest me whether I need to L= 2200 mm (by increasing 1500 to 2200 mm) or what is the solution for above problem.


Thank you,
Regards,
Saikiran.



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abhio
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PostPosted: Wed Aug 31, 2016 4:40 am    Post subject: Reply with quote

Dear Er Saikiran,

It would be best if you model the pile as beam on elastic foundation following the recommendations of Matlock and Reese.
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PostPosted: Wed Aug 31, 2016 9:45 am    Post subject: Reply with quote

Dear Er Saikiran,
     Why would you have a pile of 1.5 m depth? If your clay soil is only 1.5 m deep, why not go for open foundation?

Yours sincerely
Arunkumar
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PostPosted: Wed Aug 31, 2016 12:34 pm    Post subject: Reply with quote

Dear Sir's

Thank you for your replay's . Actually this problem is getting in design of foundations to Solar panels legs/supports.

Thank you,

Regards,
Saikiran.
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PostPosted: Sun Sep 04, 2016 4:08 pm    Post subject: Reply with quote

Dear Engineers,

Kindly give me the solution to above pile length point of fixity problem.

Thank You,

Regards,
Saikiran.
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PostPosted: Mon Sep 05, 2016 1:50 am    Post subject: Reply with quote

Er. Saikiran,
You please post the details of your foundation with sketches. Then the members can easily comprehend it and think how to tackle the issue.

Regards,
E S Jayakumar
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PostPosted: Tue Sep 06, 2016 3:08 am    Post subject: Reply with quote

Er. Saikiran,
Nothing is heard from you in response to my query on the details and loading on your structure. Please explain why you are particular in providing  piles for a shallow foundation of only 1.50 m depth. You can consider isolated footings, preferably tied together at the top of the stub, like a grade beam, to provide stability in view of horizontal loads. By the way, will there be much wind load induced on the solar panels ?
     Depth of fixity in your case comes to 2.20 m means for less than this depth, it will not get fixed at some point at any depth. That means, your pile is short. Such piles will fail by way of shear failure of soil by causing either rotation ( free pile head) or translation/ sliding (restrained pile head) of the pile. Long laterally loaded piles will fail by deflection or strength failure of pile only.
     If you are particular to use pile only, you can bank on Broms method on laterally loaded short pile. You can work out the ultimate lateral load capacity using the formulas given, knowing Cu (un-drained shear) of the clayee soil and using the details of the pile proposed. See the attachment.

Regards,
E S Jayakumar



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PostPosted: Wed Sep 07, 2016 6:28 am    Post subject: Reply with quote

Sir,

Thanks for your valuable replay.
Kindly find the attachment of  sample calculation of one solar panel leg foundation design . Length provided = 1800 mm,but in deflection calculation point of fixity (Zf) resulting in 2420 mm .

Also find the attachment of the Tomilson textbook reference for calculation of stiffness factor (i.e 1.8 T)  . But I have chosen 1.9 T as per IS 2911.

Sir, My doubt is provided length(1800mm) is less than the length required for point of fixity (2420mm) . So do I need to increase the pile length to 2420 or what to do?

Thank You,
Regards,
Saikiran



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PostPosted: Wed Sep 07, 2016 8:19 am    Post subject: Reply with quote

Er. Saikiran,
How did you work out the lateral force of around 6 kN and the uplift force ?
Why cannot you provided a small square column footing with stub column of size 250mm x 250mm or so, which is more stable, instead of the "pile", which will be weak in uplift too ?

E S Jayakumar
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PostPosted: Wed Sep 07, 2016 10:57 am    Post subject: Reply with quote

Sir ,
Please give me the solution to  above point of fixity problem. I know many other piling/foundation options , but my query is what to do if provided length is < Point of fixity length (Zf) in deflection calculation obtained from  the graph of IS 2911.

Thank You,

Regards,
Saikiran.
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