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design of pile reinforcement

 
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jagan0819
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PostPosted: Fri Apr 26, 2019 4:15 am    Post subject: design of pile reinforcement Reply with quote

hi sefians

i am designing a G+4 structure and while coming to foundation design, in soil report at 8mts depth the pile capacity is 195kN(bored pile) and undereamed pile capacity is 220kN and coming to point how can i design pile reinforcement (is design as same as column ) or any ??

please suggest

regards
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abhio
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PostPosted: Fri Apr 26, 2019 5:20 am    Post subject: Reply with quote

Dear Er Jagan,

Please refer to IS 2911 and any standard textbook for the procedure to design a pile. Reynolds' handbook also gives the procedure for finding reinforcement in a pile.

Briefly, in order to find the bending moment in the pile, we have to find the "depth of fixity". This gives us the effective height of the pile which, when multiplied by the lateral load, gives the maximum bending moment in the pile. The cross section is then designed for vertical load and moment as for a column (except that buckling is not considered unless the pile is exposed above ground level or there's a liquifiable soil stratum).

The depth of fixity method is rather simplistic, and you could use the Matlock-Reese method to improve your estimate of the bending moment in the pile and get a location for curtailing some of your reinforcement.

Regards,

Oundhakar
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sakumar79
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PostPosted: Wed May 01, 2019 5:06 pm    Post subject: Reply with quote

Dear Er Jagan,
    Er Abhio has rightly pointed out the method to design pile reinforcement. However, I am not sure the pile loading details given by you is practical.

    Normally, in a G+4 building, the loads will be quite high - may be around 1000 kN or even more. Pile capacity in the range of 200 kN will require large number of piles. Further, under-reamed piles rarely are used for such large depths as 8 m AFAIK and the spacing of such piles also will be 5 x pile dia. Normally, we do deep soil investigation (up to 30 m if required) to calculate suitable depth of pile and get higher pile capacity due to larger skin friction and better end bearing capacity. If you can get to hard rock strata, you will get good end bearing capacity especially if the piling contractor has the facility to core through and socket the pile in the rock.

    Please review with the soil investigation agency giving them the expected load details and request suitable solution.

Yours sincerely
S Arunkumar
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badamsundararao
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PostPosted: Sat May 04, 2019 4:43 pm    Post subject: PILE DESIGN Reply with quote

As per your narration,I feel that Under Reamed Pile foundations are not recommended. The Pile capacity of 8m is specified by you,but from Geo tech point of view,you should aware of Soil profile below 8m depth also. Some times you may have lower N values below that depth and hence I suggest to have Soil data up to a depth of not less than 12m for 8m pile. I suggest to increase the Pile length along with increased dia of Pile to reduce the number of Piles. Confirmation of Pile capacity by way of casting Test pile is a must.
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jagan0819
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PostPosted: Mon May 06, 2019 3:29 am    Post subject: thank u for ur valuable suggestion Reply with quote

dear

sundarrao, s arunkumar, abhio

thank u for your valuable suggestions
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mandeep_singh_kohli
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PostPosted: Wed May 29, 2019 12:34 pm    Post subject: Re: design of pile reinforcement Reply with quote

The design is same as column, but i dont think the depth of fixity will be  that easy to work out. You will have to perform lateral pile analysis using some software like L-pile etc, which will give you the pile deflection v/s pile load v/s Pile moment curves.

Based on the Maximum moment in the pile caused due to the loads, you will have to design the pile as a cantilever column under uniaxial bending and compression.





jagan0819 wrote:
hi sefians

i am designing a G+4 structure and while coming to foundation design, in soil report at 8mts depth the pile capacity is 195kN(bored pile) and undereamed pile capacity is 220kN and coming to point how can i design pile reinforcement (is design as same as column ) or any ??

please suggest

regards
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abhio
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PostPosted: Wed May 29, 2019 5:30 pm    Post subject: Reply with quote

Dear Er Kohli,

The depth of fixity charts given in IS: 2911 provide a reasonable solution. Of course, it can definitely be improved by means of a more detailed analysis. However, such an analysis is only as good as the data you put into it. For the most reliable estimates of lateral soil stiffness, you ought to have pressuremeter tests, rather than only SPT / CPT. In the absence of high quality data, I believe that high end analysis can give a dangerous, unjustified sense of extra high precision without underlying accuracy.

There's a joke that goes "measure with a micrometer, mark with chalk, and cut with an axe". Using SPT/ CPT data for estimates of lateral soil stiffness, and plugging these numbers into a high end software runs the risk of repeating the joke in the other direction.

Warm regards,

A S Oundhakar
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mandeep_singh_kohli
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PostPosted: Thu May 30, 2019 3:38 am    Post subject: Reply with quote

Dear Er Oundkar

I Beg to differ with you, and think that what you have mentioned is the excuse used by most engineers when they are not sure about what they are doing.

The software which i mentioned, u just needs the soil type profile, and the depths of the different layer and no SPT/CPT values. Its results are reliable, i have billions of dollars of projects relying on that.

The joke was valid when we were in the 18th century, now with advanced tools at our disposal, we can measure and check everything we have. In the age of FEM, and P-Delta analysis, i guess Today is the time "to Measure with a Micromemetr, mark with a stencil and cut with laser".

More so, since you will be hanged if the design that yuou have done is not safe. We have plenty of examples where engineers have been sentenced beacause of failures in structures, so its our job to use the data as effcectively as possible. The tables in IS code come with a clause that the engineer to ensure that they are valid and applicable, and you are very unlikely to find that exact profile, since the lateral stiffness of soil depends upon the different layers it encounters and their relative depths from top, wethher they are saturated or not etc. In this circustance its better to use data that we have got from the soil investigation consultant and know that he willbe held responsible for it and then use the best method available to get foundation properties.

Whats the use of soil investigation if we have to go back to IS code ? IS code have complete designs also in the SP-xx for almost all types of structures, foundations, roads, bridges, culverts shelters, why design then ??

With respect.

Mandeep S. Kohli


abhio wrote:
Dear Er Kohli,

The depth of fixity charts given in IS: 2911 provide a reasonable solution. Of course, it can definitely be improved by means of a more detailed analysis. However, such an analysis is only as good as the data you put into it. For the most reliable estimates of lateral soil stiffness, you ought to have pressuremeter tests, rather than only SPT / CPT. In the absence of high quality data, I believe that high end analysis can give a dangerous, unjustified sense of extra high precision without underlying accuracy.

There's a joke that goes "measure with a micrometer, mark with chalk, and cut with an axe". Using SPT/ CPT data for estimates of lateral soil stiffness, and plugging these numbers into a high end software runs the risk of repeating the joke in the other direction.

Warm regards,

A S Oundhakar
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