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Horizontal Load capacity of pile foundation in Seismic case

 
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gauravmaroo
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PostPosted: Sat May 09, 2009 9:44 am    Post subject: Horizontal Load capacity of pile foundation in Seismic case Reply with quote

Respected SEFIans
I am working on a design of low height abutment retaning earth one side. It is part of a interchange elevated curve located in seismic Zone IV.
Pile foundation has been proposed due loose soil profile up to 5 m depth.So when i am applying dynamic increment of earth pressure the lateral force is increasing significantly and number of piles also.
Lateral load carrying capacity of pile corresponding to 5 mm deflection comes out to be 40 tons and vertical is 250 tons.
Now in seismic case which capacity i can increase by 25% as per Table 1 IS 1893(part 1-2002).
1)It is a practice to increase safe vertical load capacity but not in case of horizontal why?
2)In old IRC codes E=5700 SQRT(Fck) but in new versions it is E=5000 SQRT (Fck) .In computation of horizontal load capacity of pile it is making a difference of 2.5 tons.so if code has revised than all old design are unsafe?
3)If we increase vertical capacity in seismic case than should we take care of 12mm deflection criterion?

kindly guide me on this issue.

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ibarua
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PostPosted: Sun May 10, 2009 11:31 am    Post subject: Horizontal Load capacity of pile foundation in Seismic case Reply with quote

10th May 2009

A practical way of designing a pile group is given in 'Concrete Bridge Analysis & Design' by Dr V.K. Raina. However, there are some errors of computation in the numerical example in the book; so don't get frustrated if your results do not match those in the book.

It is usual to increase load carrying capacity, safe bearing capacity and similar parameters when eq. loads are applied. This is because eq. loads are transient and not permanent. However, when member responses are caused solely by horizontal actions due to earthquake /wind, no such increase may be allowed.

The change in the formula for Ec in IS:456 does not mean that structures designed by the older version of the code have sudenly become unsafe. It's only that the capacity of the section /member designed by the older version of the Code will stand reduced when it is checked by the formula in the present version.

Indrajit Barua.

On Sat, 09 May 2009 gauravmaroo wrote :
Quote:
Respected SEFIans
I am working on a design of low height abutment
retaning earth one side. It is part of a interchange
elevated curve located in seismic Zone IV.
Pile foundation has been proposed due loose soil
profile up to 5 m depth.So when i am applying dynamic
increment of earth pressure the lateral force is
increasing significantly and number of piles also.
Lateral load carrying capacity of pile corresponding to
5 mm deflection comes out to be 40 tons and vertical is
250 tons.
Now in seismic case which capacity i can increase by
25% as per Table 1 IS 1893(part 1-2002).
1)It is a practice to increase safe vertical load
capacity but not in case of horizontal why?
2)In old IRC codes E=5700 SQRT(Fck) but in new versions
it is E=5000 SQRT (Fck) .In computation of horizontal
load capacity of pile it is making a difference of 2.5
tons.so if code has revised than all old design are
unsafe?
3)If we increase vertical capacity in seismic case than
should we take care of 12mm deflection criterion?

kindly guide me on this issue.

------------------------
Gaurav Maroo
MTech(IITR),BE(MBMECJ)
+91-9015321215








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gauravmaroo
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PostPosted: Mon May 11, 2009 4:28 am    Post subject: Reply with quote

Respected Sir
Thanks for your valuable reply
But in case of Vertical load carrying capacity we have factor of safety of 2.5 while in case of horizontal load capacity we are computing our load capacity by 5mm deflection criterion so there is no extra factor of safety?
secondly the E value revision in IRC code comes very recently in june 2006 (IRC 18 ) so are these revision are going to affect any major bridge project which has been designed during this period like Delhi metro rail project.?

kindly correct me if i am missing any thing on this issue.

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knsheth123
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PostPosted: Wed May 13, 2009 1:21 am    Post subject: Horizontal Load capacity of pile foundation in Seismic case Reply with quote

Quote:
  
 

 
The IS Code formulae is valid only for homogeneous sand strata/NC Clay (Es vary linearly with depth), and for OC Clay strata with Es constant with depth. and is simplified version of Reese Matloack solution given in most of the books of Geotechnical Eng. ( J. E. Bowles, VNS Murthy etc. )
 

1. You may attempt using non dimensional solution by Reese and Matloack to get a representative solution.
 
2. In your case The upper 5m is loose strata, you might be disregarding resistance offered by this strata, this can be accounted by using any finite element software for lateral load analysis or a Geotechnical Engg. may consulted for this purpose.
 
3. The capacity of the pile estimated is based on estimate of Es from N-value, This is in a range varying about 100%.  If no. of piles are more in the project, a lateral load load may be performed.
 
K. N. Sheth
 
 
 
 
 

 

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