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The AASHTO LRFD Bridge Specification, Section 10.5.3.3 says "shaft lateral resistance" should be checked at the strength limit state (i.e. factored loads). How is shaft lateral resistance determined using an LPile model? Is it the lateral load required to form a plastic hinge in the shaft?

If I'm dealing with a very short shaft (light pole foundation) am I likely to be governed by service limit state deflections & overall stability instead?

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Looking at the LPile website, it looks like they plot the strength of the pile in terms of a p-y curve. From the website,

Nonlinear lateral load-transfer from the foundation to the soil is modeled using p-y curves generated internally using published recommendations for various types of soils. Special procedures are programmed for computing p-y curves for layered soils and for rocks. Alternatively, the user can enter manually any other externally generated ip-y curves.

Thus, your lateral strength is based on the loading on the pile and the lateral deflection of the pile under load. I think this is analogous to a P-M curve one would generate for a concrete column.

The strength limit state then depends on your lateral soil support and the strength of the pile, so it's not really possible to say whether or not a plastic hinge forms in the pile without further information.

With a short pile length, I would agree that you're likely limited by deflection and stability since the pile doesn't have a lot of bite into the soil depth.

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  • $\begingroup$ I just want to clarify that LPile uses what is sometimes called "soil springs". The value of the springs can be plotted on a series of p-y curves, but it may help the questioner to think of them as springs that have a variable spring constant based on the deflection. $\endgroup$
    – hazzey
    Jul 31 '15 at 2:32

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