Published: Jan 1984
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A method previously presented by the author (in ASTM STP 154) is generalized to encompass soils having nonlinear p-y characteristics. This results in a method that can handle, but is not restricted to, pile-soil systems having (1) piles greater than 9 m (30 ft) in length having free, fixed, or partially fixed heads, and any cross-sectional shape and length relationship, for example, constant, tapered, or stepped, and of any materials or combination of materials; (2) soils of any variation with depth, whether homogeneous, stratified, or combinations thereof, and having p-y characteristics of any nature; (3) ability to qualitatively and quantitatively predict behavior and stresses under static, fluctuating, and repetitive lateral loadings, or where larger emergency loads can be interspersed between normal loads. Ways are suggested for dealing with each of these factors. In addition, a method is proposed for obtaining the effective soil constant at a given site for a range of lateral loads, using empirical test data from free-head piles of the same characteristics subjected to lateral loads. The method is validated by use on previously published data of a comprehensive series of tests on free-head piles by Assadeh and Davison (Journal of the Soil Mechanics and Foundation Division, Proceedings of the American Society of Civil Engineers, Vol. 96, No. SM5, Sept. 1970, pp. 1583–1603). Using the soil constants resulted in computed load-deflection curves closely approximating actual data. These constants are used in turn to compute the expected deflections and pile stress of those same piles under fixed-head conditions.
A serendipitous finding of the analysis was that there is a significant shape factor affecting the ability of piles to mobilize soil resistance to lateral loads, for example, under any given lateral load applied to free-head piles having approximately equal moments of inertia, those having circular cross sections were substantially more resistant to lateral movement than square or H-beam cross sections. This in turn significantly altered the effective soil modulus.
To determine the usefulness of the method in economic as well as structural design, an analysis was made of a built-up pile consisting of a 360-mm (14-in.) H-beam cut diagonally along its length and rewelded to form a tapered I beam 500 mm (20 in.) at the butt and 200 mm (8 in.) at the tip, with constant flanges. Although having the same weight as the basic H beam, the tapered pile was computed to have a lateral deflection under a load of 13 000 kg (30 000 lb), which is half of that of the basic beam under free-head conditions and 0.6 of that under fixed-head conditions.
foundations, piling, lateral loads, soil mechanics, design, deflection, footings, loads (fluctuating), subsurface structures