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Journal ArticleDOI

Seismic Response Characteristics of a Piled Raft in Clay

17 Apr 2019-Journal of Earthquake and Tsunami (World Scientific Publishing Company)-Vol. 13, Iss: 01, pp 1950005
Abstract: This paper presents a study on three-dimensional seismic soil–structure interaction analysis of a piled-raft (PR) foundation in clay by the substructure approach. Two different pile modeling techni...
Topics: Foundation (engineering) (55%), Pile (52%)
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Journal ArticleDOI
Abstract: Evaluation of the impedance functions and internal forces in various modes of vibration form an important step in the design of pile supported structures subjected to dynamic loads. This study tries to assess the variation in impedance functions and load distribution characteristics when a ground contacting pile cap is introduced over single and group piles. A substructuring method-based soil structure interaction (SSI) analysis model is employed to study vertical and horizontal dynamic impedances of piled rafts (PR) in homogeneous and layered soil conditions. The amplitude and phase of the dynamic interaction factor, signifying the interaction between the raft and pile group for various PR area ratios and soil conditions are evaluated. For the 2 × 2 piled rafts analysed, the dynamic load sharing between pile and raft is found to be frequency dependent in the vertical mode and practically frequency independent in the horizontal mode.

8 citations

Journal ArticleDOI
01 Dec 2020-Structures
Abstract: Increasing demand for high-rise buildings and other important structures in urban areas and unfavorable land has resulted to opt for piled raft foundation by the designers. The present study is an attempt to investigate the seismic behavior of piled raft foundation supporting structural system embedded in very soft clay encompassing variations of different influential parameters. The piled raft system is modeled using three-dimensional (3D) finite element analysis. At first, the 3D numerical model is validated with past numerical studies. This is followed by a detailed parametric study on the effect of different influential parameters, such as flexibility of raft, pile spacing to diameter ratios, and asymmetry in pile length on dynamic characteristics and seismic response of the piled raft foundation system considering dynamic soil-structure interaction (DSSI). It is observed that the fundamental period of the structure gets significantly lengthened with increasing raft flexibility whereas pile head shear considerably reduced. Further, non-identical pile lengths attributing asymmetric group configuration results in a significant change in the fundamental period of the structure and pile head shear.

5 citations

Journal ArticleDOI
Abstract: Across the globe, rapid urbanization demands the construction of tunnels within the vicinity of high-rise buildings supported on piled raft foundations. As a consequence, ground movements ...

4 citations

Journal ArticleDOI
01 Oct 2021-Structures
Abstract: Ever-increasing scarcity of land and demand for high-rise structures has significantly contributed to the use of combined piled raft foundations (CPRF) in soft ground. However, utility, design constraints and aesthetic considerations bring asymmetry to superstructures, making structures more vulnerable during seismic excitations. Traditional design practices involve designing superstructure elements and foundation considering fixity at the base of the superstructure and ignoring soil-structure interaction (SSI) which may result in under-estimation of forces and displacement in the system. Hence, the present study aims at developing new seismic design guideline pertaining to asymmetric single and multi-storied structure supported on CPRF embedded in soft clay. Some important parameters, such as torsional coupling mode of vibration and multi-storey idealisation involving the effect of higher modes are investigated incorporating seismic SSI effect. The study broadly reveals that the torsional to lateral period ratio considerably influence the seismic response of asymmetric structural system on the piled raft foundation due to the incorporation of SSI. Furthermore, multi-storey building idealisation gives a higher estimation of response compared to single storey idealization in superstructure and pile head which may be due to the effect of higher modes of vibration and SSI

Journal ArticleDOI
01 Jun 2020-
Abstract: The foundation input motion (FIM) that a structure experiences during an earthquake, is known to be different from the free field ground motion due to soil structure interaction (SSI) effects. Kinematic interaction in a single pile can also introduce a rotational component to the FIM. Conventionally, soil structure interaction is performed by applying the free field ground motion to the structure ignoring the effects of kinematic interaction. Deep foundation elements such as piles are known to suppress certain frequencies of ground motion which in turn induces kinematic bending moments in them. In this study, kinematic soil pile interaction is simulated using 3D numerical models using a coupled finite element-boundary element method. Single pile, group pile and piled raft models in a homogeneous soil profile are analysed for vertically propagating shear waves. Three earthquake time histories with varying frequency content are considered in this study. Transfer functions are then plotted together to analyse the effects of pile induced filtering of ground motion. The ratio of response spectrum at the foundation level and free field ground, for the pile group considered, is found to closely follow the behaviour of a fixed headed single pile. It is found that embedment of the pile cap, as in the case of a piled raft can result in further filtering of ground motion.

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Journal ArticleDOI
Abstract: SUMMARY A substructuring method has been implemented for the seismic analysis of bridge piers founded on vertical piles and pile groups in multi-layered soil. The method reproduces semi-analytically both the kinematic and inertial soil—structure interaction, in a simple realistic way. Vertical S-wave propagation and the pile-to-pile interplay are treated with suƒcient rigor, within the realm of equivalent-linear soil behaviour, while a variety of support conditions of the bridge deck on the pier can be studied with the method. Analyses are performed in both frequency and time domains, with the excitation specified at the surface of the outcropping (‘elastic’) rock. A parameter study explores the role of soil—structure interaction by elucidating, for typical bridge piers founded on soft soil, the key phenomena and parameters associated with the interplay between seismic excitation, soil profile, pile—foundation, and superstructure. Results illustrate the potential errors from ignoring: (i) the radiation damping generated from the oscillating piles, and (ii) the rotational component of motion at the head of the single pile or the pile-group cap. Results are obtained for accelerations of bridge deck and foundation points, as well as for bending moments along the piles.

180 citations

Journal ArticleDOI
Abstract: This paper presents a comprehensive set of dimensionless graphs that could be readily utilized in practical applications A comparative study of these graphs leads to interesting conclusions that may contribute towards an improved appreciation of the nature of seismic pile-soil-pile interaction The graphs should be of practical value in determining the 'effective' seismic input motion at the base of structures, if the free-field motion is known The discussion of the study results focuses on elucidating the role of the key parameters, and aims at developing engineering insight into kinematic soil-pile and pile-pile interactions during earthquakes

149 citations

Journal ArticleDOI
Abstract: Presented here is a numerical investigation of the influence of non-uniform soil conditions on a prototype concrete bridge with three bents (four span) where soil beneath bridge bents are varied between stiff sands and soft clay. A series of high-fidelity models of the soil-foundation-structure system were developed and described in some details. Development of a series of high-fidelity models was required to properly simulate seismic wave propagation (frequency Lip to 10Hz) through highly nonlinear, elastic plastic soil, piles and bridge structure. Eight specific cases representing combinations of different soil conditions beneath each Of the bents are simulated. It is shown that variability of soil beneath bridge bents has significant influence on bridge system (soil-foundation-structure) seismic behavior. Results also indicate that free field motions differ quite a bit from what is observed (simulated) under at the base of the bridge columns indicating that use of free field motions as input for only structural models might not be appropriate. In addition to that, it is also shown that usually assumed beneficial effect Of Stiff soils underneath a Structure (bridge) cannot be,generalized and that such stiff soils do not necessarily help seismic performance of structures. Moreover, it is shown that dynamic characteristics of all three components of a triad made Lip of earthquake, soil and structure play crucial role in determining the seismic performance of the infrastructure (bridge) system. Copyright (C) 2009 John Wiley & Sons, Ltd.

88 citations

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