Buckling Capacity of a Partially Embedded Pile
Buckling Capacity of a Partially Embedded Pile
(OP)
Hi all, Happy New Year
I am designing a pile supported off-shore structure. The structure is supported on timber bearing piles. The piles are embedded in a 40+ ft of dense sand and extends 10+ ft above mudline. As such, the piles are in fact unsupported laterally throughout the length above the mudline. I am trying to determine the allowable axial capacity for this pile. To be more specific, what is the unsupported length of this pile/column and what bottom end condition should be considered. Any suggestions!!
Thanks
I am designing a pile supported off-shore structure. The structure is supported on timber bearing piles. The piles are embedded in a 40+ ft of dense sand and extends 10+ ft above mudline. As such, the piles are in fact unsupported laterally throughout the length above the mudline. I am trying to determine the allowable axial capacity for this pile. To be more specific, what is the unsupported length of this pile/column and what bottom end condition should be considered. Any suggestions!!
Thanks





RE: Buckling Capacity of a Partially Embedded Pile
For sand, if you deem it to remain stable, the stiffer assumptions for the modulus of subgrade reaction (and its lateral counterpart to derive supporting springs' stiffnesses) would be best, and the contrary if you see it unreliable, mainly if you see that your would love go even deeper for stability. This is critical, for if scour occurs nothing of we are talking is of relevance.
However your problem most surely is tabulated somewhere. Have not looked deeply nor my books nor the web but if I find something will post.
RE: Buckling Capacity of a Partially Embedded Pile
http://www.tdi.state.tx.us/general/pdf/wscgsec400.pdf
RE: Buckling Capacity of a Partially Embedded Pile
RE: Buckling Capacity of a Partially Embedded Pile
In my younger days, my standard reference was a paper presented to a Symposium on Bearing Capacity of Piles. If you can get hold of a copy, it may be some help to you.
Authors :A.J. Francis, L.K.Stevens and D.H. Trollope,
Title :"Flexure and Load-carrying Capacity of Slender Piles in Soft Soil"
Regrettably, my ancient dog-eared copy does not specify the date, which I believe would have been about 1965 or so (the most recent reference quoted in the paper was 1964).
Similarly there is some doubt as to precise location of the symposiom. My copy of the paper is annotated in hand-writing "Symposium on Bearing Capacity of Piles - India" (Originally it said Hong Kong, but that was over-written).
I hope this may help you.
RE: Buckling Capacity of a Partially Embedded Pile
The "unsupported length" is actually longer than the ten feet above the mudline. The condition you have is a cantilever beam of length y, with "y" being determined by the fixity of the pile. If you do an analysis of the soil-pile interaction (L-Pile or similar) you can find the inflection point for the moment, thus its fixity. You can do this by hand analysis, finding the minimum depth to handle the lateral load moment (use iteration to find).
Once this is done, the problem is just a simple cantilever beam bending problem.
RE: Buckling Capacity of a Partially Embedded Pile
Sorry...I didn't read your question correctly. Disregard my prior post (unless you have lateral loading, which then you will need to add to the compressive axial loading).
For buckling, the effective length considered is, just as in the lateral bending, the point of fixity of the pile. Typically, for dense sand, you can assume an additional depth of 1x the height above the mudline, in this case, your unsupported length would be 20 feet. From that, compute the critical load (Pcr) from Euler's equation with k=2.0.