Buckling Strength of Pile NAI C. YANG, Senior Design Engineer, The Port of New York Authority Previous solutions for the buckling strength of piles are based on the assumptions that the piles are fully embedded and subject to no horizontal loads. In common engineering practice, the buckling of a pile is constantly associated with its freestanding length above the mud line. The solution of such problems re- quires the extrapolation of the analysis and the accuracy of the result is correspondingly affected. In this paper, a review has been given of (a) the elastic sta- bility of partially embedded piles by assuming that the buckling deflection is ahalf-sine curve; (b) the general equation of hori- zontal subgrade reaction based on the interaction of pile and foundation soil; (c) the relation between pile deflection and soil reaction; and (d) the effect of horizontal translation on the crit- ical buckling strength of a pile. When the critical buckling strength of a pile is greater than its compressive yield strength of material, the pile will not fail by elastic buckling. In normal foundation condition, only a little soil confinement is required to prevent the buckling of a pile unless the freestanding length becomes excessively long. The reduction of elastic stability is more critical for a pile subject to a horizontal force than due to the increase of freestanding length. •THE PROBLEM of pile buckling usually does not exist when the piles are fully em- bedded. The early research on this subject was done in connection with the freestanding long piles used in waterfront construction where the piles are assumed to be fixed at a certain depth below the mud line, and Euler's formula is applied to determine the crit- ical buckling capacity. Such an empirical approach has served very well in the past. In recent years, however, high capacity piles have been widely adopted to serve both as structural columns and as load transfer media in the foundation soil. The common problems arising in the superstructure, such as rotation, translation and displacement of joints, become, then, inherent features of the pile design. While the buckling con- cept of piles is still in the development stage, some foundation difficulties would be anticipated. In this paper, the theory of the elastic stability of piles is reviewed. The introduc- tion of lateral soil resistance would be helpful in achieving a better understanding of the mechanics of the pile deflections. Four theoretical boundary conditions are separately discussed on the effect of pile fixities. For practical engineering applications, the de- gree of fixity of the pile head should be carefully studied. As demonstrated in this paper, a pile with its head fixed can withstand much greater load than one in which the head is free to rotate, and the horizontal translation of a pile head usually causes the worst condition of critical buckling. ELASTIC STABILITY OF PILE The previous solutions for the buckling strength of piles were based on the flexural equation Paper sponsored by Committee on Substructures, Retaining Walls and Foundations and presented at the 45th Annual Meeting. 35
Buckling Strength of Pile
May 16, 2023
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