Shamsher Prakash and Sanjeev Kumar - ISOPE 1996/Abstract... · Shamsher Prakash and Sanjeev Kumar...

Proceedings of the Sixth (1996) - International Offshore and Polar Engineering Conference (1996)Los Angeles, USA May 26-31, 1996Copyright © 1996 by The International Society of Offshore and Polar EngineersISBN 1·880653-22·2 (Set); ISBN 1·880653·23·0 (Vol. I)

Shamsher Prakash and Sanjeev KumarUniversity of Missouri-Rolla, Rolla, MO, USA

V.K. PuriSouthern Illinois University, Carbondale, IL, USA

Pile foundations are extensively used to support on-shore andoff-shore structures. Under the action of wind and sea wavesarising due to sea storms, sea quakes, hurricanes, and tsunamis, pilefoundations for off-shore structures experience dynamic loads. Pile-soil-pile interaction and nonlinear soil behavior play an importantrole in the analysis. A step-by-step procedure for the analysis ofpile foundations supporting offshore structures and including thenonlinear behavior of soil are presented. A review of solutions forsingle piles, pile-soil-pile interaction are also included. However,Response of pile foundations under the influence of these loads isdifferent from that of earthquake loads.

Offshore structures consist of production platforms and otherstructures and structural components of systems such as offshorestorage facilities, combination of storage and production structuresand coastal research, and support facilities. Some nuclear powerplants may also be located offshore. These structures are oftensupported on pile foundations to resist dynamic loads arising fromwind or wave currents due to sea storms, hurricanes, sea quakesand/or tsunamis. Figure 1 shows a typical pile supported structure.The bulk of loads are static loads, which form the basis for fIxingthe section (size), embedded length and possibly confIguration(spacing and arrangement) of the piles in the group.

The super-structure forms an integral part of the pile-foundation system. Therefore, an analysis of the structure-pile-soilssystem and its proper understanding is desirable. Very littleinformation is available on the behavior and analysis of pilesupported offshore structures for use in everyday practice. Thenature of loading and associated strain levels and soil-pile and pilegroup responses under wave loading on offshore structures are quitedifferent from earthquake loadings on the similar onshore and

offshore structures. Earthquake loading for piles under buildingsmay cause large deformations and soil nonlinearity and considerabledegradation of soil modulus. Interactions of the super-structure withpiles is important. In offshore structures, the piles are especiallylong and slender with considerable free-standing lengths andtherefore, in addition to large displacements and soil nonlinearity,even pile material may behave in non-linear manner, and bucklingof piles may assume importance (Prakash, Sally 1985, 1987).

In this paper a step-by-step procedure for complete analysisof pile groups has been recommended. A simple procedure toinclude the effect of soil nonlinearity, under wave loadings has alsobeen presented.

NATURE OF DYNAMIC LOADING ON OFFSHORESTRUCTURES

A signifIcant portion of the load on offshore structuresconsists of load arising out of the action of wind, sea currents and

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