August E. Niederhoff

Bio: August E. Niederhoff is an academic researcher from United States Department of the Army. The author has contributed to research in topics: Pile. The author has an hindex of 1, co-authored 1 publications receiving 17 citations.

A Study of Piles during Earthquakes: Issues of Design and Analysis

Abstract: The seismic response of pile foundations is a very complex process involving inertial interaction between structure and pile foundation, kinematic interaction between piles and soils, seismically induced pore-water pressures (PWP) and the non-linear response of soils to strong earthquake motions. In contrast, very simple pseudo-static methods are used in engineering practice to determine response parameters for design. These methods neglect several of the factors cited above that can strongly affect pile response. Also soil–pile interaction is modelled using either linear or non-linear springs in a Winkler computational model for pile response. The reliability of this constitutive model has been questioned. In the case of pile groups, the Winkler model for analysis of a single pile is adjusted in various ways by empirical factors to yield a computational model for group response. Can the results of such a simplified analysis be adequate for design in all situations? The lecture will present a critical evaluation of general engineering practice for estimating the response of pile foundations in liquefiable and non-liquefiable soils during earthquakes. The evaluation is part of a major research study on the seismic design of pile foundations sponsored by a Japanese construction company with interests in performance based design and the seismic response of piles in reclaimed land. The evaluation of practice is based on results from field tests, centrifuge tests on model piles and comprehensive non-linear dynamic analyses of pile foundations consisting of both single piles and pile groups. Studies of particular aspects of pile–soil interaction were made. Piles in layered liquefiable soils were analysed in detail as case histories show that these conditions increase the seismic demand on pile foundations. These studies demonstrate the importance of kinematic interaction, usually neglected in simple pseudo-static methods. Recent developments in designing piles to resist lateral spreading of the ground after liquefaction are presented. A comprehensive study of the evaluation of pile cap stiffness coefficients was undertaken and a reliable method of selecting the single value stiffnesses demanded by mainstream commercial structural software was developed. Some other important findings from the study are: the relative effects of inertial and kinematic interactions between foundation and soil on acceleration and displacement spectra of the super-structure; a method for estimating whether inertial interaction is likely to be important or not in a given situation and so when a structure may be treated as a fixed based structure for estimating inertial loads; the occurrence of large kinematic moments when a liquefied layer or naturally occurring soft layer is sandwiched between two hard layers; and the role of rotational stiffness in controlling pile head displacements, especially in liquefiable soils. The lecture concludes with some recommendations for practice that recognize that design, especially preliminary design, will always be based on simplified procedures.

RC pile–soil interaction analysis using a 3D‐finite element method with fibre theory‐based beam elements

Abstract: To evaluate the overall response of a structural system including its foundation and surrounding soil, an equivalent finite element model with reduced degrees of freedom using fibre theory-based beam element was proposed. The proposed model was based on investigations of the subgrade soil reaction of a single-layer model, and was verified for the cyclic behaviour of a laterally loaded single RC pile in terms of the load–displacement relationship, pile deformation, and soil pressures on the pile surface. Also investigated was the effect of the interfacial element between pile and soil on the behaviour of the laterally loaded pile. Copyright © 2006 John Wiley & Sons, Ltd.

Lateral cyclic response of pile in viscoelastic winkler subgrade

Abstract: The lateral cyclic response of a pile foundation is formulated by treating the subgrade as a viscoelastic Winkler model for simplicity. Viscoelastic characterization of the model is convenient for the computation of a cyclic response exhibiting the hysteresis nature. The governing equation of a pile foundation is solved for a cyclic force applied at the pile head with the Laplace transformation. The inverse integration is evaluated on a complex plane using a contour integration. The residue of the integration around the pole is associated with the steady‐state response. With this solution, simple expressions are developed for the maximum responses along the depth and for the spring and dashpot parameters of a pile at its head. Applications of these simple expressions are demonstrated for the evaluation of pile responses observed in shake table tests, in which the soil was liquefied or semiliquefied during the shaking. The responses are evaluated both in a conservative way and in a straightforward manner. ...