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 …

I and i

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

System Identification I

Dynamics of structures

: 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)

/pdf/nonlinear-time-series-analysis-1j3a35n4y3.pdf

Nonlinear Time Series Analysis.

SUMMARY

A super-tall building with height of 420 m and 88 floors is located in central Hong Kong. Field monitoring of wind effects on the high-rise structure was conducted during the passage of several typhoons on the basis of a wind and movement monitoring system installed in the building. Field data such as wind speed, wind direction, pressures on cladding, acceleration and displacement responses were simultaneously recorded during the typhoons and then analyzed. Typhoon wind parameters including turbulence intensity, gust factor, peak factor, turbulence integral length scale and power spectral density were presented and discussed. The dynamic properties of the high-rise structure were determined from the field measurements and compared with those calculated at the design stage. The damping ratios of the super-tall building were evaluated by a random decrement technique, which demonstrates amplitude-dependent characteristics. The relationships between the structural dynamic responses and the approaching wind speed were analyzed. Wind tunnel tests were conducted to investigate the wind effects on the super-tall building. The field-measured acceleration responses were found to be consistent with the model test results. Finally, the serviceability performance of the super-tall building during the typhoons was assessed on the basis of the field measurement results. The findings of the paper are expected to be of considerable interest and practical use to professionals and researchers involved in wind-resistant designs of super-tall buildings. Copyright © 2013 John Wiley & Sons, Ltd.

Monitoring of typhoon effects on a super-tall building in Hong Kong

This note investigates the influence of shear lag for thin-walled curved box girders, including longitudinal warping. The longitudinal warping displacement functions of the flange slabs are approximated by a cubic parabolic curve instead of a quadratic curve of Reissner’s method. On the basis of the thin-walled curved bar theory and the potential variational principle, the equations of equilibrium considering the shear lag, bending, and torsion (St. Venant and warping) for a thin-walled curved box girder are established. The closed-form solutions of the equations are derived, and Vlasov’s equation is further developed. The obtained formulas are applied to calculate the shear lag effects for curved box girder bridges. Numerical examples are presented to verify the accuracy and applicability of the present method.

Shear Lag of Thin-Walled Curved Box Girder Bridges

Genetic evolutionary structural optimization

A finite-segment method for analyzing shear-lag effects in box girders is presented in this paper, with an assumption that the spanwise displacements of the flange plates are described by a third-power parabolic function. The governing differential equations for two generalized displacements are established according to the principle of minimum potential energy. In order to obtain the longitudinal stresses under the shear-lag effect, the element stiffness equations are developed based on the variational principle by taking the homogeneous solutions of the differential equations as the displacement functions of the finite segment. The effect of two major parameters on shear lag is investigated for cantilever and continuous box girders with varying depth under three kinds of loads. It is shown that the height ratio, in addition to the flange width to span length ratio, has a significant influence on the shear lag. The solutions based on the present method are compared with the results of model testing and the finite strip method. The accuracy of the present method is proved to be satisfactory.

Qiusheng Li

Papers

Monitoring of typhoon effects on a super-tall building in Hong Kong

Shear Lag of Thin-Walled Curved Box Girder Bridges

Genetic evolutionary structural optimization

Shear lag in box girder bridges

Coupled on-site measurement/CFD based approach for high-resolution wind resource assessment over complex terrains