The Experts below are selected from a list of 18729 Experts worldwide ranked by ideXlab platform
Kalya R Piratla - One of the best experts on this subject based on the ideXlab platform.
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robust design and optimization procedure for piled Raft Foundation to support tall wind turbine in clay and sand
Soils and Foundations, 2018Co-Authors: Nadarajah Ravichandra, Shweta Shrestha, Kalya R PiratlaAbstract:Abstract A geotechnical design and optimization procedure for piled-Raft Foundations to support tall wind turbines in clayey and sandy soil are presented in this paper. From the conventional geotechnical design, it was found that the differential settlement controlled the final design and was considered as the response of concern in the optimization procedure. A parametric study was subsequently conducted to examine the effect of the soil shear strength parameters and wind speed (random variables) on the design parameters (number and length of piles and radius of Raft). Finally, a robust design optimization procedure was conducted using a Genetic Algorithm coupled with a Monte Carlo simulation considering the total cost of the Foundation and the standard deviation of differential settlement as the objectives. This procedure resulted in a set of acceptable designs forming a Pareto front which can be readily used to select the best design for given performance requirements and cost limitations.
Hanlong Liu - One of the best experts on this subject based on the ideXlab platform.
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dynamic response of ballastless track xcc pile Raft Foundation under train axle loads
Journal of Testing and Evaluation, 2019Co-Authors: Gangqiang Kong, Hanlong LiuAbstract:In order to study the dynamic response of ballastless track X-section cast-in-place concrete (XCC) pile-Raft Foundations under different axle loads, this article presents an experimental study focusing on the dynamical soil stresses and velocity response of a ballastless track XCC pile-Raft Foundation under vertical cyclic loading. It was found that the dynamic soil stresses on the subgrade surface and the subsoil surface exhibit “ω” and “U” shapes, respectively. The gravel cushion has given an invaluable damping effect to the soil in transmitting velocity to the soil Foundation.
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vibration velocity of x section cast in place concrete xcc pile Raft Foundation model for a ballastless track
Canadian Geotechnical Journal, 2017Co-Authors: Gangqiang Kong, Hanlong Liu, Andrew Cudzo AmenuvoAbstract:This paper presents two case studies of the dynamic response of a ballastless track, X-section cast-in-place concrete (XCC) pile–Raft (referred to as BTXPR) Foundation embedded in sand subsoil. Model tests were conducted at a scale of 1/5 using a 7 m deep box with cross-sectional dimensions of 5 m × 4 m. In one case the box was filled with subsoil consisting of air-dried sand, whereas in the other case the box was filled with saturated sand. The tests involved measurement and analysis of the response in velocity under different applied cyclic load frequencies. It has been shown that the magnitude and variation of vibration velocity in the BTXPR Foundation are closely related to the degree of saturation of the subsoil. Due to the existence of pore water in the saturated sand subsoil, the first natural frequency of the BTXPR Foundation embedded in saturated sand is 5 Hz lower than that in air-dried sand. In addition, the amplitude of vibration velocity of the BTXPR Foundation embedded in the saturated sand ...
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numerical investigation of piled Raft Foundation in mitigating embankment vibrations induced by high speed trains
Journal of Central South University, 2015Co-Authors: Hanlong Liu, Xuanming Ding, Changjie ZhengAbstract:A three-dimensional dynamic finite element model of track-ballast-embankment and piled Raft Foundation system is established. Dynamic response of a railway embankment to a high-speed train is simulated for two cases: soft ground improved by piled Raft Foundation, and untreated soft ground. The obtained results are compared both in time domain and frequency domain to evaluate the effectiveness of the ground improvement in mitigating the embankment vibrations induced by high-speed trains. The results show that ground improving methods can significantly reduce the embankment vibrations at all considered train speeds (36- 432 km/h). The ground response to a moving load is dictated largely by the relationship between load speed and characteristic value of wave velocities of the ground medium. At low speeds, the ground response from a moving load is essentially quasi-static. That is, the displacements fields are essential the static fields under the load simply moving with it. For the soft ground, the displacement on the ballast surface is large at all observed train speeds. For the model case where the ground is improved by piled Raft Foundation, the peak displacement is reduced at all considered train speeds compared with the case without ground improvement. Based on the effect of energy-dissipating of ballast-embankment-ground system with damping, the train-induced vibration waves moving in ballast and embankment are trapped and dissipated, and thus the vibration amplitudes of dynamic displacement outside the embankment are significantly reduced. But for the vibration amplitude of dynamic velocity, the vibration waves in embankment are absorbed or reflected back, and the velocity amplitudes at the ballast and embankment surface are enhanced. For the change of the vibration character of embankment and ballast, the bearing capacity and dynamic character are improved. Therefore, both of the static and dynamic displacements are reduced by ground improvement; the dynamic velocity of ballast and embankment increases with the increase of train speed and its vibration noise is another issue of concern that should be carefully evaluated because it is associated with the running safety and comfort of high-speed trains.
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three dimensional numerical analysis of the stress transfer mechanism of xcc piled Raft Foundation
Computers and Geotechnics, 2014Co-Authors: Hanlong Liu, Xuanming Ding, Anthony GunawaAbstract:Abstract An X-section cast-in-place concrete (XCC) piled Raft is a new type of Foundation that uses piles with X-shaped cross-sections. Compared to a traditional circular cast-in-place concrete (CCC) pile, an XCC pile of the same cross-sectional area has a larger side resistance due to its larger cross-sectional perimeter. Although the pile capacity and load transfer mechanism of the XCC piled Raft have been studied, the influence of this X-shaped geometry on the stress transfer between pile and surrounding soil is still not fully understood. To investigate the effects of the cross-sectional geometry, three-dimensional numerical analyses are conducted on an XCC and a traditional CCC piled Rafts using the finite element method. The numerical results are verified by a field test of an XCC piled Raft. Computed results reveal that lateral soil arching develops to a distance of approximately twice pile diameter surrounding the XCC pile, which can be demonstrated by the rotation of the principal stresses, leading to a non-uniform effective normal stress across a given cross-section and along the pile depth. The magnitude of the unit side resistance that acts on the concave surfaces of the XCC pile is up to twice the magnitude of the unit side resistance that acts on the flat surfaces. For a given applied load, the total side resistance mobilised on the XCC pile is usually larger than the total side resistance of the CCC pile, by a factor that ranges from 0.5 to 10, depending on the pile depth. Therefore, approximately 66% and 46% of the applied load is carried by the XCC and CCC piles respectively, and simultaneously, approximately 45% and 24% of the applied load is taken by the side resistance of the XCC and CCC piles, respectively. The larger effect of the XCC piled Raft contributes to the cross-sectional geometry, which results in a larger perimeter and arching effects.
Nadarajah Ravichandra - One of the best experts on this subject based on the ideXlab platform.
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robust design and optimization procedure for piled Raft Foundation to support tall wind turbine in clay and sand
Soils and Foundations, 2018Co-Authors: Nadarajah Ravichandra, Shweta Shrestha, Kalya R PiratlaAbstract:Abstract A geotechnical design and optimization procedure for piled-Raft Foundations to support tall wind turbines in clayey and sandy soil are presented in this paper. From the conventional geotechnical design, it was found that the differential settlement controlled the final design and was considered as the response of concern in the optimization procedure. A parametric study was subsequently conducted to examine the effect of the soil shear strength parameters and wind speed (random variables) on the design parameters (number and length of piles and radius of Raft). Finally, a robust design optimization procedure was conducted using a Genetic Algorithm coupled with a Monte Carlo simulation considering the total cost of the Foundation and the standard deviation of differential settlement as the objectives. This procedure resulted in a set of acceptable designs forming a Pareto front which can be readily used to select the best design for given performance requirements and cost limitations.
Tarek M A Alazrak - One of the best experts on this subject based on the ideXlab platform.
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evaluation of soil Foundation structure interaction effects on seismic response demands of multi story mrf buildings on Raft Foundations
International Journal of Advanced Structural Engineering, 2015Co-Authors: Shehata Abdel E Raheem, Mohamed M Ahmed, Tarek M A AlazrakAbstract:Soil conditions have a great deal to do with damage to structures during earthquakes. Hence the investigation on the energy transfer mechanism from soils to buildings during earthquakes is critical for the seismic design of multi-story buildings and for upgrading existing structures. Thus, the need for research into soil–structure interaction (SSI) problems is greater than ever. Moreover, recent studies show that the effects of SSI may be detrimental to the seismic response of structure and neglecting SSI in analysis may lead to un-conservative design. Despite this, the conventional design procedure usually involves assumption of fixity at the base of Foundation neglecting the flexibility of the Foundation, the compressibility of the underneath soil and, consequently, the effect of Foundation settlement on further redistribution of bending moment and shear force demands. Hence the SSI analysis of multi-story buildings is the main focus of this research; the effects of SSI are analyzed for typical multi-story building resting on Raft Foundation. Three methods of analysis are used for seismic demands evaluation of the target moment-resistant frame buildings: equivalent static load; response spectrum methods and nonlinear time history analysis with suit of nine time history records. Three-dimensional FE model is constructed to investigate the effects of different soil conditions and number of stories on the vibration characteristics and seismic response demands of building structures. Numerical results obtained using SSI model with different soil conditions are compared to those corresponding to fixed-base support modeling assumption. The peak responses of story shear, story moment, story displacement, story drift, moments at beam ends, as well as force of inner columns are analyzed. The results of different analysis approaches are used to evaluate the advantages, limitations, and ease of application of each approach for seismic analysis.
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soil Raft Foundation structure interaction effects on seismic performance of multi story mrf buildings
Engineering Structures and Technologies, 2014Co-Authors: Shehata Abdel E Raheem, Mohamed M Ahmed, Tarek M A AlazrakAbstract:Recent studies show that the effects of Soil Structure Interaction (SSI) may be detrimental to the seismic response of structure and neglecting SSI in analysis may lead to un-conservative design. Despite this, the conventional design procedure usually involves assumption of fixity at the base of Foundation ne- glecting the flexibility of the Foundation, the compressibility of soil mass and consequently the effect of foun- dation settlement on further redistribution of bending moment and shear force demands. The effects of SSI are analyzed for typical multi-story building resting on Raft Foundation. Three methods of analysis are used for seismic demands evaluation of the target moment resistant frame buildings: equivalent static load (ESL); response spectrum (RS) methods and nonlinear time history (TH) analysis with suit of nine time history records. Three-dimensional Finite Element (FE) model is constructed to analyze the effects of different soil conditions and number of stories on the vibration characteristics and seismic response demands of build- ing structures. Numerical results obtained using soil structure interaction model conditions are compared to those corresponding to fixed-base support conditions. The peak responses of story shear, story moment, story displacement, story drift, moments at beam ends, as well as force of inner columns are analyzed.
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soil structure interaction effects on seismic response of multi story buildings on Raft Foundation
JES. Journal of Engineering Sciences, 2014Co-Authors: Shehata Abdel E Raheem, Mohamed M Ahmed, Tarek M A AlazrakAbstract:The investigation on the energy transfer mechanism from soils to buildings during earthquakes is critical for the design of earthquake resistant structures and for upgrading existing structures. Thus the need for research into Soil-Structure Interaction (SSI) problems is greater than ever. Moreover, recent studies show that the effects of SSI may be detrimental to the seismic response of structure and neglecting SSI in analysis may lead to un-conservative design. Despite this, the conventional design procedure usually involves assumption of fixity at the base of Foundation neglecting the flexibility of the Foundation, the compressibility of soil mass and consequently the effect of Foundation settlement on further redistribution of bending moment and shear force demands. Hence the soil-structure interaction analysis of multi-story buildings is the main focus of this study; the effects of SSI are analyzed for typical multi-story building resting on Raft Foundation. Three methods of analysis are used for seismic demands evaluation of the target moment resistant frame buildings: equivalent static load (ESL); response spectrum (RS) methods and nonlinear time history (TH) analysis with suit of nine time history records. Three-dimensional FEM model is constructed to analyze the effects of different soil conditions and number of stories on the vibration characteristics and seismic response demands of building structures. Numerical results obtained using soil structure interaction model conditions are compared to those corresponding to fixed-base support conditions. The peak responses of story shear, story moment, story displacement, story drift, moments at beam ends, as well as force of inner columns are analyzed. The analysis results of different approaches are used to evaluate the advantages, limitations, and ease of application of each approach for seismic analysis.
Erol Tutumlue - One of the best experts on this subject based on the ideXlab platform.
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dynamic response modeling of high speed railroad ballastless track over pile Raft Foundation
GeoShanghai International Conference, 2018Co-Authors: Yuanjie Xiao, Liuxi Che, Kunye Zhou, Erol TutumlueAbstract:Ballastless tracks have been extensively used in newly built high-speed railroads in China. Most of their Foundations are constructed without pile improvement; however, the pile-Raft design concept has been increasingly used as a rapid yet effective construction technique to reinforce the Foundations. Limited attention has been paid to the behavior of this Foundation system under dynamic loads either in the laboratory trials or field applications. This study presented the results of displacement responses obtained from three-dimensional (3D) dynamic finite element simulations of a typical high-speed railroad ballastless track over the pile-Raft Foundation. Both the soft ground improved by the pile-Raft technique and the unreinforced ground, as control, were modeled and compared to quantify the effectiveness of the ground improvement in mitigating the detrimental effects of dynamic impact loads induced by high-speed trains. Other features of the 3D finite element models included the simulation of the moving train at different speed levels, the use of nonlinear constitutive models for track Foundation geomaterials, and the consideration of the pile-soil interaction. The results of this study could lead to further research in this area as guidelines to design piled Raft Foundations economically.
