Static and Cyclic P- Y curves

Hello folks,

Exactly, for which loadings do you use Cyclic P-Ys and where do you use the Static P-Ys, say, in the case of a production platform?
The thing that confuses me is that an offshore platform or any other structure in marine environment, for that matter, is constantly exposed to cyclic loading of some sort, waves, winds...ect. and that being the case why does the API code have provisions for static P-Ys??
Is it only to be consistant?? (I kind o' doubt that).

In the case of using the program SACS(or other tools)to derive a Pilestub (equivalent linear pile length) for use linear analysis tools for earthquake analyses or farigue which curves are used??

I hope you take the time to clarify the subject for me
I really "want to learn"
Thank you ,

 

[Gourile]

The dynamic curves, allways have special conditions like frequency and relative dynamic displacement to the statics ones. It is not on top of my head, but there were two very important papers related on 1979 or so which became basics for API code. If you look at them carefully, you will find out about their valid range of each curve. For instance, you have to compare your static loads contraining all gravity loads with the dynamic ones in the case you are specifically studing. If the sum of the dynamic ones is less than 10% of the total loading, you may use the static ones, with care. Other wise you should use dynamic curves.

 

[teasip]

Static p-y curves are generally used for solving for the effects of monotonic loading to failure, such as ultimate strength or collapse analysis. They can also represent progressively increased cyclic or repeated loading wherein deflections are not controlled.

Cyclic p-y curves (not dynamic) represent the quasi-static lower-bound of the lateral resistance under repeated deflections. The curve is not a loading path, but represents the end-points of a large number of cycles wherein the deflection is controlled by elastic compliance of the structure.

The development of the formulation and examples of experimental static and cyclic p-y data are given in a paper by Hudson Matlock entitled "Correlations for Design of Laterally Loaded Piles in Soft Clay," Proceedings, 1970 Offshore Technology Conference, Houston, Texas, Paper Number OTC 1204.

 

[Focht3]

I just found this thread - hence the late posting.

teasip: Hook'em!
Varsity 50 - Farmers 20. Bliss & braggin' rights for another year...

Hmmm, back to the subject at hand.

Also be aware that the cyclic criteria in Matlock's 1970 OTC paper is not "definitive"; results from Harvey, LA Shell site show 0.29*p[sub]u[/sub], not 0.72*p[sub]u[/sub]. Matlock, Bogard, et al published a paper on this in the early/mid 1980's about this; I can't remember whether it was OTC or ASCE. Soft clay did a really good job of modelling static (after tweaking the e[sub]50[/sub] values), but lousy at predicting the cyclic field results.