Qiusheng Li

Bio: Qiusheng Li is an academic researcher from City University of Hong Kong. The author has contributed to research in topics: Wind speed & Wind tunnel. The author has an hindex of 47, co-authored 429 publications receiving 8830 citations. Previous affiliations of Qiusheng Li include Chinese Ministry of Education & Guangzhou University.

Numerical studies on the effects of the lateral boundary on soil-structure interaction in homogeneous soil foundations

Abstract: In this paper, the finite element method is applied to investigate the effect of the lateral boundary in homogenous soil on the seismic response of a superstructure. Some influencing factors are presented and discussed, and several parameters are identified to be important for conducting soil-structure interaction experiments on shaking tables. Numerical results show that the cross-section width L, thickness H, wave propagation velocity and lateral boundaries of soil layer have certain influences on the computational accuracy. The dimensionless parameter L/H is the most significant one among the influencing factors. In other words, a greater depth of soil layer near the foundation should be considered in shaking table tests as the thickness of the soil layer increases, which can be regarded as a linear relationship approximately. It is also found that the wave propagation velocity in soil layer affects the numerical accuracy and it is suggested to consider a greater depth of the soil layer as the wave propagation velocity increases. A numerical study on a soil-structure experimental model with a rubber ring surrounding the soil on a shaking table is also conducted. It is found the rubber ring has great effect on the soil-structure interaction experiments on shaking table. The experimental precision can be improved by reasonably choosing the elastic parameter and width of the rubber ring.

Modal Identification Technologies for High-Rise Buildings Under Non-Stationary Excitations

Abstract: For high-rise buildings subjected to typhoon or earthquake actions, the excitations are likely non-stationary, which inevitably violates the stationary assumption that is generally adopted by conventional modal identification methods. Under such a condition, conventional modal identification methods may not be applicable, and their performances need to be evaluated. To this end, the performances of seven widely used modal identification algorithms for structural modal estimation under non-stationary excitations are evaluated via a numerical simulation study. Then, three methods with good performance are selected to evaluate their applicability and accuracy for field measurements involving non-stationary excitations. From the comparative study, a time–frequency domain method with the best performance among these seven methods is employed to investigate the structural dynamic properties of a 509-m-tall skyscraper under typhoon and earthquake excitations. Based on the reliable modal estimates, the relationships between the modal properties with response amplitude and environmental temperature are presented and discussed. This paper aims to identify the effective methods for accurate estimation of structural modal parameters based on non-stationary structural responses and investigate the structural dynamic properties of high-rise buildings under typhoon and earthquake excitations.

Free vibration analysis of flexural-shear plates under the action of axial forces

Abstract: The governing differential equations for vibration of flexural-shear plates considering the effects of flexural, shear deformation and axial forces are established. The general solutions of a one-step flexural-shear plate are derived and used to obtain the eigenvalue equations of a multi-step flexural-shear plate with various boundary conditions. The new exact approach which combines the transfer matrix method and closed form solutions of a uniform flexural-shear plate with various boundary conditions is presented. A numerical example demonstrates that the calculated natural frequencies and mode shapes of a tall building that is treated as a two-step flexural-shear plate are in good agreement with the experimentally measured data. It is also shown that the effect of shear deformation on the fundamental natural frequency can be ignored, but its effect on the higher natural frequencies should be considered. On the contrary, the effect of axial force (N) on the higher natural frequencies is not significant, ...

An Exact Approach For Free Vibration Analysis of Multi-Step Nonuniform Shear Plates

Abstract: In this paper multi-story frame buildings are treated as shear plates with variably distributed mass and stiffness for free vibration analysis. An analytical model of a shear plate is proposed and an exact approach for determining natural frequencies and mode shapes of such shear plates is presented. The function for describing the distribution of mass of a shear plate along the plate height is an arbitrary one and the distribution of shear stiffness is expressed as a functional relation with the distribution of mass and vice versa. The exact solutions of one-step shear plates are obtained first for seven cases. Then the derived exact solutions of one-step shear plates are used to establish the frequency equations of multi-step shear plates by using the transfer matrix method. The numerical example shows that the natural frequencies and mode shapes of a shear plate calculated by the proposed methods are in good agreement with the measured data and those determined by the Ritz method and the finite element method, verifying the accuracy and applicability of the proposed methods.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Nonlinear Time Series Analysis.

Abstract: : This thesis applies neural network feature selection techniques to multivariate time series data to improve prediction of a target time series. Two approaches to feature selection are used. First, a subset enumeration method is used to determine which financial indicators are most useful for aiding in prediction of the S&P 500 futures daily price. The candidate indicators evaluated include RSI, Stochastics and several moving averages. Results indicate that the Stochastics and RSI indicators result in better prediction results than the moving averages. The second approach to feature selection is calculation of individual saliency metrics. A new decision boundary-based individual saliency metric, and a classifier independent saliency metric are developed and tested. Ruck's saliency metric, the decision boundary based saliency metric, and the classifier independent saliency metric are compared for a data set consisting of the RSI and Stochastics indicators as well as delayed closing price values. The decision based metric and the Ruck metric results are similar, but the classifier independent metric agrees with neither of the other metrics. The nine most salient features, determined by the decision boundary based metric, are used to train a neural network and the results are presented and compared to other published results. (AN)