Papers by Author: Ying Hai

Abstract: In this paper, the rotational invariance technique (ESPRIT) based on the cross-correlation matrix is used to estimate the power quality indices (PQI) . This method enables the alleviation of the effects of additive noise, and improves the computational efficiency. Computer simulation and experimental were performed on synthesized signals to assess the performance of the method.

Abstract:

Using constitutive modelling principle of thermodynamics with internal variables, the yield surfaces rotation of saturated sands subjected triaxial compression stress state are justified and explained. The explanation for the yield surfaces rotation of saturated sands prove the correctness and feasibility for the principle of thermodynamics with internal variables to construct elastoplastic constitutive relation of saturated soils.

Abstract: The coefficient of compressibility a_v and the coefficient of permeability k_v of clays decrease during the one dimention consolidation process, especially when the strain of clays in the process are large. This paper studies the effects of large strain, decreasing compressibility and decreasing permeability during the one dimention large strain consolidation process by analyzing results obtained from the nonlinear finite element method and comparing with results from the conventional consolidation theory. The research results of this paper shows that the compression index C_c and the permeability change index C_k are two important clay parameters which influence one dimention large strain consolidation process.When the instantaneous load increment remains unchanged, the larger the value of the C_{c ,} the larger the value of the final settlement and the slower the settlement development; the larger the value of the C_k, the faster the dissipation of excess pore water pressure in one dimention large strain consolidation process.

Abstract: According the theory of thermodynamics with internal variables, the relation between yield function and dissipation function and the condition of associated flow rule in stress space are presented; the elastoplastic matrix of the incremental form of the material constitutive equation is given out, this matrix is determined by the free energy function and the yield function. The Gibbs free energy function of solid phase of saturated soils subjected triaxial compression stress state is presented, and using the constitutive theory of thermodynamics with internal variables, yield function and stress-strain relation of the modified Cam-Clay model is obtained by the free energy function and the dissipation function. These results prove the correctness and feasibility for this constitutive theory to construct elastoplastic constitutive relation of saturated soils.

Abstract: Generally the shear strength of saturated soils has been predicted by the Mohr-Coulomb theory. However, field data accumulated in the past have evidently shown that saturated conditions are actually never reached in arid and semi-arid regions. An analytical model is developed to predict shear strength of an unsaturated soil with respect with matric suction. The formulation takes into account the influence of the mean stress on soil water retention curves. The results of the model developed for predicting the shear strength are compared with available experimental results. The good agreement between the estimates and the experimental data indicates that the proposed equation is promising and reliable for estimating preliminary unsaturated shear strength parameters.

Abstract: The shear strength value of unsaturated loess is required in the design in geotechnical engineering in the North and the North West of China. In 2004, a new method, that is the fractal model theory, was proposed for determining the shear strength of unsaturated soil. Based upon the fractal model theory, the surface fractal dimension DS and the air entry value of two unsaturated loess samples are obtained from their soil-water characteristic curve (SWCC), the shear strength contribution due to matric suction of the two loess samples is determined, a new approach for determination of the shear strength of unsaturated loess with its SWCC is presented. By comparing results of this paper with those of the laboratory tests, the relationship between the SWCC and the shear strength of unsaturated loess is discussed and the validity of the fractal model theory for unsaturated loess is explained.

Abstract: The use of steel tube confined concrete columns has been the interests of many structural engineers. For investigation of the axially loading capacity of short concrete filled double skin tubes (CFDST) columns, axial compression loading experiments were carried on 9 short CFDST column samples. According to experimental results and with numerical analysis, an ultimate load estimation equation of CFDST column with one correction parameter is presented, the linear relation between the parameter and the inner-to-outer diameters ratio Di/Do is given out. The ultimate load estimation equation is validated by the test results of short CFDST column samples.