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CONTENTS
Volume 12, Number 6, November 2009
 

Abstract
Structural health monitoring (SHM) systems have been recently embraced in long span cable-supported bridges, in which buffeting-induced stress monitoring is one of the tasks to ensure the safety of the bridge under strong winds. In line with this task, this paper presents a SHM-oriented finite element model (FEM) for the Tsing Ma suspension bridge in Hong Kong so that stresses/strains in important bridge components can be directly computed and compared with measured ones. A numerical procedure for buffeting induced stress analysis of the bridge based on the established FEM is then presented. Significant improvements of the present procedure are that the effects of the spatial distribution of both buffeting forces and self-excited forces on the bridge deck structure are taken into account and the local structural behaviour linked to strain/stress, which is prone to cause local damage, are estimated directly. The field measurement data including wind, acceleration and stress recorded by the wind and structural health monitoring system (WASHMS) installed on the bridge during Typhoon York are analyzed and compared with the numerical results. The results show that the proposed procedure has advantages over the typical equivalent beam finite element models.

Key Words
suspension bridge; finite element model; buffeting; stress analysis; structural health monitoring; comparison.

Address
T.T. Liu;Department of Engineering Mechanics, Dalian University of Technology, Dalian, China, Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
Y.L. Xu; Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
W.S. Zhang; Department of Engineering Mechanics, Dalian University of Technology, Dalian, China, Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
K.Y. Wong; Bridges and Structures Division, Highways Department, The Government of Hong Kong Special Administrative Region, Hong Kong
H.J. Zhou; Department of Civil and Structural Engineering,
The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
K.W.Y. Chan; Bridges and Structures Division, Highways Department, The Government of Hong Kong Special Administrative Region, Hong Kong

Abstract
Synchronous wind-induced pressures, measured in wind-tunnel tests on model buildings instrumented with hundreds of pressure taps, are an invaluable resource for designing safe buildings efficiently. They enable a much more detailed, accurate representation of the forces and moments that drive engineering design than conventional tables and graphs do. However, the very large volumes of data that such tests typically generate pose a challenge to their widespread use in practice. This paper explains how a wavelet representation for the time series of pressure measurements acquired at each tap can be used to compress the data drastically while preserving those features that are most influential for design, and also how it enables incremental data transmission, adaptable to the accuracy needs of each particular application. The loss incurred in such compression is tunable and known. Compression rates as high as 90% induce distortions that are statistically indistinguishable from the intrinsic variability of wind-tunnel testing, which we gauge based on an unusually large collection of replicated tests done under the same wind-tunnel conditions.

Key Words
wind tunnel testing; data compression; pressure taps; wind loads; bending moments; wavelet representation; wavelet thresholding; extreme values.

Address
Antonio Possolo; Statistical Engineering Division, Information Technology Laboratory, National Institute of Standards and Technology, U.S. Department of Commerce, Gaithersburg, Maryland, USA
Michael Kasperski; Department of Civil and Environmental Engineering Sciences, Ruhr-Universit?t Bochum, Bochum, Germany
Emil Simiu; Materials and Construction Research Division, Building & Fire Research Laboratory, National Institute of Standards and Technology, U.S. Department of Commerce, Gaithersburg, Maryland, USA

Abstract
This paper presents the results of a study into experimental and numerical methods for the identification of bridge deck flutter derivatives. Nine bridge deck sections were investigated in a water tunnel in order to create an empirical reference set for numerical investigations. The same sections, plus a wide range of further sections, were studied numerically using a commercially available CFD code. The experimental and numerical results were compared with respect to accuracy, sensitivity, and practical suitability. Furthermore, the relevance of the effective angle of attack, the possible assessment of non-critical vibrations, and the formulation of lateral vibrations were studied. Selected results are presented in this paper. The full set of raw data is available online to provide researchers and engineers with a comprehensive benchmarking tool.

Key Words
bridge flutter; flutter derivatives; water tunnel; CFD; numerical simulation; effective angle of attack; non-critical vibration; lateral vibration.

Address
Uwe Starossek and Hasan Aslan; Hamburg University of Technology, 21073 Hamburg, Germany
Lydia Thiesemann; WTM Engineers, Ballindamm 17, 20095 Hamburg, Germany

Abstract
This paper explains how to correctly measure the drag coefficient of a circular cylinder in wind tunnels with large blockage ratios and for the sub-critical to the super-critical flow regimes. When dealing with large blockage ratios, the drag has to be corrected for wall constraints. Different formulations for correcting blockage effect are compared for each flow regime based on drag measurements of smooth circular cylinders performed in a wind tunnel for three different blockage ratios. None of the correction model known in the literature is valid for all the flow regimes. To optimize the correction and reduce the scatter of the results, different correction models should be combined depending on the flow regime. In the sub-critical regime, the best results are obtained using Allen and Vincenti\'s formula or Maskell\'s theory with ?=0.96. In the super-critical regime, one should prefer using Glauert\'s formula with G=0.6 or the model of Modi and El-Sherbiny. The change in the formulations appears at the flow transition with a variation of the wake pattern when passing from sub-critical to super-critical flow regimes. This parameter being not considered in the known blockage corrections, these theories are not valid for all the flow regimes.

Key Words
drag coefficient; blockage effect; wind tunnel measurement; bluff body; circular cylinder; flow transition.

Address
J. Anthoine; Von Karman Institute for Fluid Dynamics - Chauss?e de Waterloo, 72 - B-1640 Rhode-St-Gen?se, Belgium
D. Olivari; AirSR, Belgium and von Karman Institute for Fluid Dynamics - Chauss?e de Waterloo, 72 - B-1640 Rhode-St-Gen?se, Belgium
D. Portugaels; Service Public de Wallonie, Namur, Belgium

Abstract
This paper presents statistical analysis results of wind speed and atmospheric turbulence data measured from more than 30 anemometers installed at 15 different height levels on 325 m high Beijing Meteorological Tower and is primarily intended to provide useful information on boundary layer wind characteristics for wind-resistant design of tall buildings and high-rise structures. Profiles of mean wind speed are presented based on the field measurements and are compared with empirical models\' predictions. Relevant parameters of atmospheric boundary layer at urban terrain are determined from the measured wind speed profiles. Furthermore, wind velocity data in longitudinal, lateral and vertical directions, which were recorded from an ultrasonic anemometer during windstorms, are analyzed and discussed. Atmospheric turbulence information such as turbulence intensity, gust factor, turbulence integral length scale and power spectral densities of the three-dimensional fluctuating wind velocity are presented and used to evaluate the adequacy of existing theoretical and empirical models. The objective of this study is to investigate the profiles of mean wind speed and atmospheric turbulence characteristics over a typical urban area.

Key Words
field measurement; boundary layer wind characteristic; wind speed profile; atmospheric turbulence; tall building design.

Address
Q.S. Li; Department of Building and Construction, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong
Lunhai Zhi; Department of Building and Construction, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong
, College of Civil Engineering, Hunan University, Changsha, Hunan 410082, PR China
Fei Hu; Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, PR China


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