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A model for the response of single timber fasteners and piles under cyclic and dynamic loading Allotey, Nii Kwashie

Abstract

A model is presented for the cyclic and dynamic analysis of timber fasteners and pile foundations. Both systems are, in that they are beam-like structures that are embedded in a flexible medium. In the past, many different numerical methods, ranging from very elaborate finite element models, to closed-form solutions for beams on elastic foundations have been used to analyze these systems. Among these, in the development of computer software, the use of a 1-D finite element implementation of beams on a nonlinear foundation has been shown to be the most promising, mainly due to the relative accuracy and simplicity of the model. In this thesis, such a model is developed for the analysis of both systems. The model is based on one previously developed, which used a beam element on a nonlinear flexible foundation that takes into account the formation of gaps between the fastener/pile and medium. In this thesis, the effect of interface friction, and the initial confining pressure surrounding the fastener/pile has been included in the model. Due to the inclusion of interface friction, the model allows, in the case of piles, the study of problems with horizontal and/or vertical acceleration inputs. The model is the basis for the development of a cyclic analysis code for single timber fasteners, and cyclic and dynamic analysis codes for single piles in cohesionless soil. Various numerical examples of timber fasteners and piles are used to show that the predicted results of the model are consistent with expected response behavior. Since previous models have not taken either friction or initial confining pressure into account, the effect of both of these on the predicted response of both systems has been investigated. It is seen from this study that the amount of initial confining pressure around a timber fastener does not significantly influence the hysteretic response under lateral cyclic loading, but rather influences the amount of withdrawal in the case of driven fasteners. For estimated practical values of the coefficient of friction and tangential stiffness of the interface, friction is seen to have a significant influence on the amount of withdrawal, and not much influence on the hysteretic response. In the case of piles, neither the initial confining pressure nor friction are observed to have any considerable effect on the hysteretic response under lateral cyclic loading

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