1,721,050 research outputs found
Simplified analytical "m-θ" curves for predicting nonlinear lateral pile response
No full textThe relationship between the distributed moment acting on a pile segment due to vertical shear tractions at the pile-soil interface and the corresponding pile rotation (known as an “m-θ” curve) is important when determining the response of offshore monopiles with low slenderness ratios. Two simplified approaches to derive nonlinear “m-θ” curves (for clay under undrained conditions) are considered. Firstly, the vertical shear tractions can be derived in closed-form using known “t-z” curves (power-law and quadratic forms are considered) and integrating with respect to the pile circumference. Secondly, similarity in shape between an “m-θ” and a “t-z” curve is investigated which would enable a linear-transformation between the abscissas of the two normalised curves. This paper derives analytical linear-transformation factors using power-law and quadratic “t-z” curves and compares these with solutions available for a linear-elastic soil material. Finally, the effect of slip at the pile-soil interface on the “m-θ” curve is considered
Insight on kinematic bending of flexible piles in layered soil
No full textThe behaviour of a kinematically stressed pile in layered soil under the passage of vertically propagating. seismic S waves is investigated by means of rigorous three-dimensional Finite-Element. (FE) analyses. Both pile and soil are idealized as linearly viscoelastic materials, modelled by solid. elements and pertinent interpolation functions in the realm of classical elastodynamic theory. The. system is analyzed by a time-Fourier approach in conjunction with a modal expansion in space.. Constant viscous damping is considered for each natural mode, and a FFT algorithm is employed to. switch from frequency to time domain and vice versa in natural or generalized coordinates. The. scope of the paper is to: (a) provide some rigorous elastodynamic results in both frequency and time. domains that can be used as reference cases; (b) elucidate the role of a number of key phenomena. and salient dimensionless parameters for the amplitude of pile bending at an interface separating. two soil layers of different stiffness; (c) propose a simplified semi-analytical formula for evaluating. such moments; (d) provide some remarks about the role of kinematic bending in seismic design of. pile foundations, with emphasis on the long-standing issue of establishing an optimal pile diameter. to resist such bending. The results of the study offer a new interpretation of kinematic pile bending. in terms of the interplay between pile and soil, expressed through dimensionless layer thickness,. pile-to-soil stiffness ratio and impedance contrast at the layer interface. A case study from Japan is. presented
The role of pile diameter on earthquake-induced bending
Full text linkPile foundations in seismic areas should be designed against two simultaneous actions arising from kinematic and inertial soil-structure interaction, which develop as a result of soil deformations in the vicinity of the pile and inertial loads imposed at the pile head. Due to the distinct nature of these phenomena, variable resistance patterns develop along the pile, which are affected in a different manner and extent by structural, seismological and geotechnical characteristics. A theoretical study is presented in this article, which aims at exploring the importance of pile diameter in resisting these actions. It is demonstrated that (a) for large diameter piles in soft soils, kinematic interaction dominates over inertial interaction; (b) a minimum and a maximum admissible diameter can be defined, beyond which a pile under a restraining cap will inevitably yield at the head i.e., even when highest material quality and/or amount of reinforcement are employed; (c) an optimal diameter can be defined that maximizes safety against bending failure. The role of diameter in seismically-induced bending is investigated for both steel and concrete piles in homogenous soils as well as soils with stiffness increasing proportionally with depth. A number of closed-form solutions are presented, by means of which a number of design issues are discussed
Kinematic bending moment at pile head in layered soil
No full textDuring seismic shaking soil movements force piles to deform, resulting in a complex interplay between the two systems commonly referred to as “kinematic interaction”. This interaction generates internal forces along piles even in the absence of a superstructure. Current design practice usually takes into account only forces transmitted to the pile from the superstructure, thus neglecting kinematic interaction. Despite intense research in the topic, few contributions focus on kinematic effects at the pile head in the presence of a stiff pile cap restraining its rotation. The subject may be of importance,for the pile head is subjected both to relevant kinematic and inertial moments, the latter attenuating rapidly with depth. The paper presents the results of an extensive parametric study leading to a simplified formula for evaluating kinematic moments at the pile head in a two-layer soil profile
Selection criteria for pile diameter in seismic areas
Full text linkAccording to modern seismic codes such as Eurocode 8, pile foundations in earthquake-prone areas must resist two different, yet simultaneous bending actions resulting from kinematic and inertial interaction. Due to the different nature of the two demands, pile must resist seismic actions following different patters, thus leading to different design requirements. In this work, analytical solutions are presented to define maximum and a minimum pile diameters required to resist kinematic and inertial effects in an essentially elastic manner, respectively. It is shown that the range of admissible diameters decreases with decreasing soil stiffness and with increasing design acceleration, collapsing into a single admissible diameter for certain problem configurations. Regions where no pile diameter can guarantee elastic response during strong seismic shaking are identified
Corrigendum to "Kinematic response of single piles for different boundary conditions: Analytical solutions and normalization schemes". [Soil Dynam. Earthquake Eng. 44 (2013) 183-195]
No full textAnalytical base shear reaction curves for predicting monopile response in undrained clay
No full textIncorporating soil reaction curves at the monopile tip when calculating the response at the monopile head reduces overprediction of deformations when compared with solely employing traditional p-y models. This is particularly important for squat monopile foundations that are often used for offshore wind turbines. However, published soil reaction curves at the pile tip are limited in number and are the subject of far less research than the commonly employed p-y curves. In this work, closed-form expressions for the shear response at the pile tip are developed using a cone model for the soil material under the pile base, combined with a number of simplified non-linear soil constitutive models. The solutions can be used in conjunction with available p-y curves to obtain the full displacement response of monopile foundations without the need for time-consuming 3D numerical analyses, which is particularly useful in the early stages of design. The resultant non-linear expressions are compared with available solutions using a two-part similarity approach
Winkler Model for Axially-Loaded Piles in Inhomogeneous Soil
Full text linkAnalytical closed-form solutions are developed for the elastic and elasto-plastic settlement of axially loaded piles in inhomogeneous soil. The soil is modelled by way of a bed of Winkler (‘t–z’) springs with stiffness varying as a power function of depth, described by two dimensionless inhomogeneity parameters. The associated governing differential equation is solved in an exact manner using Bessel functions, which reproduce the solution for homogeneous soil. Additional limiting cases are explored including: (a) infinitely long piles, (b) short piles, (c) perfectly floating piles and (d) perfectly end-bearing piles. The solution is extended to the non-linear range by employing elastic–perfectly plastic Winkler springs. A systematic approach for predicting the full load–settlement curve is presented and applied to tests from a site in London. Dimensionless charts are provided for routine design
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