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CONTENTS
Volume 6, Number 3, May 2003
 

Abstract
A long suspension bridge is often located within a unique wind environment, and strong winds at the site seldom attack the bridge at a right angle to its long axis. This paper thus investigates the buffeting response of long suspension bridges to skew winds. The conventional buffeting analysis in the frequency domain is first improved to take into account skew winds based on the quasi-steady theory andrnthe oblique strip theory in conjunction with the finite element method and the pseudo-excitation method. The aerodynamic coefficients and flutter derivatives of the Tsing Ma suspension bridge deck under skew winds, which are required in the improved buffeting analysis, are then measured in a wind tunnel using specially designed test rigs. The field measurement data, which were recorded during Typhoon Sam in 1999 by the Wind And Structural Health Monitoring System (WASHMS) installed on the Tsing Ma Bridge, are analyzed to obtain both wind characteristics and buffeting responses. Finally, the field measured buffeting responses of the Tsing Ma Bridge are compared with those from the computer simulation using the improved method and the aerodynamic coefficients and flutter derivatives measured under skew winds. The comparison is found satisfactory in general.

Key Words
long suspension bridge, skew wind, buffeting analysis, wind tunnel test, aerodynamic coefficient, flutter derivative, field measurement, Typhoon Sam, comparison.

Address
Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, ChinarnDepartment of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, ChinarnState Key Laboratory for Disaster Reduction in Civil Engineering, Department of Bridge Engineering, Tongji University, Shanghai 200092, Chinarn

Abstract
Galloping instability of dry inclined cables of cable-stayed bridges has been reported by Japanese researchers. A suggested stability criterion based on some experimental studies in Japan implies that many of stay cables would be expected to suffer galloping instability, which, if alid, would cause serious difficulty in the design of cable-stayed bridges. However, this is not the case in reality. Thus, it isrnpractically urgent and necessary to confirm the validity of this criterion and possible restriction of it. In the present study, a 2D sectional cable model was tested in the wind tunnel, and effects of various physical parameters were investigated. It is found that the stability criterion suggested by Japanese researchers is more conservative than the results obtained from the current study.

Key Words
cable aerodynamics; inclined circular cylinder; high-speed vortex excitation; dry inclined cable instability; Reynolds number.

Address
Department of Civil Engineering, University of Ottawa, Ottawa, Ontario, CanadarnNational Research Council, Ottawa, Ontario, CanadarnNational Research Council, Ottawa, Ontario, CanadarnDepartment of Civil Engineering, University of Ottawa, Ottawa, Ontario, Canadarn

Abstract
A tornado changes its wind speed and direction rapidly; therefore, it is difficult to study the effects of a tornado on buildings in a wind tunnel. In this work, the status of the tornado-structure interaction is surveyed by numerical simulation. Various models of the tornado wind field found in literature are surveyed. Three-dimensional computer modeling work using the turbulence model based onrnlarge eddy simulation is presented. The effect of tornado on a cubic building is considered for this study. The Navier-Stokes (NS) equations are approximated by finite difference method, and solved by a semi-implicit procedure. The force coefficients are plotted in time to study the effect of the Rankine-CombinedrnVortex Model. Some flow visualizations are also reported to understand the flow behavior around the cube.

Key Words
tornado; building; tornado-structure interaction; computational fluid dynamics; wind engineering.

Address
Department of Civil Engineering, University of Arkansas, Fayetteville, AR, 72701, USA

Abstract
The design of high-rise building is often influenced by wind-induced motions such as accelerations and lateral deflections. Consequently, the building's structural stiffness and dynamic (vibration periods and damping) properties become important parameters in the determination of such motions. The approximate methods and empirical expressions used to quantify these parameters at the design phase tend to yield values significantly different from each other. In view of this, there is a need to examine how actual buildings in the field respond to dynamic wind loading in order to ascertain a more realistic model for the dynamic behavior of buildings. This paper describes the findings from full-scale measurements of the wind-induced response of typical high-rise buildings in Singapore, and recommends an empirical forecast model for periods of vibration of typical buildings in Singapore, an appropriate computer model for determining the periods of vibration, and appropriate expressions which relate the wind speed to accelerations in buildings based on wind tunnel force balance model test and field results.

Key Words
field measurements; tall buildings; wind induced acceleration; wind loads; force balance test.

Address
Department of Civil Engineering, National University of Singapore, Block E1A, #07-03, Engineering Drive 2, Singapore 117576, SingaporernDepartment of Civil Engineering, National University of Singapore, Block E1A, #07-03, Engineering Drive 2, Singapore 117576, SingaporernStructural Engineering Department, Housing & Development Board, 480 Lorong 6 Toa Payoh, Singapore 310480, Singapore


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