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Effects of local (point) load on large tube
5

Effects of local (point) load on large tube

Effects of local (point) load on large tube

(OP)
Hi, all.

One of my clients has asked me how he should calculate the local stresses in a large diameter pile while it is cantilevering down from the piling gates, subject to current and wave load, before the toe is resting on the sea bed.

He has all that he need to calculate the actual current and wave loads on the pile, and the local reactions on the rollers at the gates.  For his own purposes, that is just about all he needs, since he is designing the piling rig. The question arises - what do those loads do to the pile tube itself?.  

I seem to recall that in the fairly distant past Roark used to have some useful formulae related to local loads on pipes or cylindrical shells.  However, I can find no such help in my edition of Roark (6th., dated 1989).

The best I can get from my copy relates to pipes supported at intervals where he states: "For a pipe...supported at intervals...the stress analysis is difficult and the results are rendered uncertain by doubtful boundary conditions".  (Not the most helpful thing he has written?)

Can anyone suggest any other source which might help (short of doing FE analysis - the software we have available to us is not really up to that)?

RE: Effects of local (point) load on large tube

austim,

1. i guess the loading from the pile gates results in radial loading and i guess it is probably only distributed around say 1/3 or so of the pile  circumference? maybe it is much more direct loading - like pipe-on-pipe?

2. what is the spacing of the pile gate supports?

i am thinking Timoshenko, or maybe treat the problem as a stress concentration or bodies under direct bearing - ie pile bearing on a roller.

not sure if i am even close!


RE: Effects of local (point) load on large tube

(OP)
Hi, ingenuity,

Small solid circular cylinder contacting large pipe (with axes perpendicular) is what we are talking of.  Note, NOT contact stress between two solid cylinders.

Gate rollers probably 200mm OD, basically solid steel cylinder with polyurethane surface coating (perhaps 25 thick) to protect the coating on the piles.

Piles 1200 mm OD * 16 wall.

Gates far enough apart to have no interaction (about 5 pile diameters).  I would be quite happy to consider the problem as being one isolated local load on the pile.

The loads on the pile are reacted by opposing (but unequal) roller loads at the bottom and top gates.  It is possible for all loads to act on only one roller at each level (depends on direction of resultant load on pile).

I will look at my Timoshenko's Elasticity plus Den Hartog and any other texts that I can quickly lay my hands on.  Thanks for the prompting.

RE: Effects of local (point) load on large tube

2
austim...
I would look at two considerations...bending of the section as a beam and localized crushing.  The bending issue is easy to check.  The localized crushing a bit more difficult!

Since your pipe is 1200mm in diameter, it will act as a plate, so plate/shell elastic approach would be appropriate.  The following is a reference/link to a paper that gives a pretty good treatment of the subject..
ssml.naoe.pusan.ac.kr/publication/1995/1995-7.pdf

It is a paper by Paik and Pedersen on crushing strength of plated structures

Will it ultimately be concrete filled?

RE: Effects of local (point) load on large tube

2
The local stresses around the point load can be calculated using WRC 107 / WRC 297.  WRC is the Welding Research Council, and the papers can be ordered at http://www.forengineers.org/wrc/index.htm.  However, these methods, while giving local stresses, will not give you deflection or buckling analysis.

It would seem that if the local stresses and the global buckling effects due to bending moment are both considered, then you will have things covered.

RE: Effects of local (point) load on large tube

(OP)
Ron, butelja.

Thanks for your input.  I don't read Korean very well () but as you say, those papers look like just what I need.

No, the piles will not be concreted, but I am only interested in the very short period while they are being supported by the piling gates (which could possibly include storm conditions with up to 10 metre waves).

RE: Effects of local (point) load on large tube

Hi, Tim

Analysis of local loads on cylinders is included in the British pressure vessel standards. I have BS.5500 Appendix G. I can fax to you the extracts. By coincidence, the first time I used this was on a problem with lateral loads on piles.

Russell Keays

RE: Effects of local (point) load on large tube

I would use Roark formulae for simple calculation.  Assume the pile is an ideal ring with a effective length of Le.  Le = 1.1 Sqrt(Dt)as suggested by API, or Le =2*95 t /sqrt(Fy)if using AISC non-compact flange requirements.  Then using Roark equations to calculate the hoop stress (primarily due to moment) under a point load.

You can download the RING.EXE from http:www.lanxun.com/pce to do the calc.

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