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CONTENTS
Volume 21, Number 2, August 2015
 

Abstract
The characteristics of the coherence functions of X axial, Y axial, and RZ axial (i.e., body axis) wind forces on the Shanghai World Trade Centre - a 492 m super-tall building with section varying along height are studied via a synchronous multi-pressure measurement of the rigid model in wind tunnel simulating of the turbulent, and the corresponding mathematical expressions are proposed there from. The investigations show that the mathematical expressions of coherence functions in across-wind and torsional-wind directions can be constructed by superimposition of a modified exponential decay function and a peak function caused by turbulent flow and vortex shedding respectively, while that in along-wind direction need only be constructed by the former, similar to that of wind speed. Moreover, an inductive analysis method is proposed to summarize the fitted parameters of the wind force coherence functions of every two measurement levels of altitudes. The comparisons of the first three order generalized force spectra show that the proposed mathematical expressions accord with the experimental results well. Later, the influences of coherence functions on wind-induced dynamic responses are analyzed in detail based on the proposed mathematical expressions and the frequency-domain method of random vibration theory.

Key Words
high-rise building; wind tunnel test for pressure measurement; coherence function; mathematical expressions; parameter fitting; peak function; inductive analysis method

Address
D.M. Huang: School of Civil Engineering, Central South University, Changsha 410075, China;
National Engineering Laboratory for High Speed Railway Construction, Central South University,
Changsha 410075, China
L.D. Zhu, W. Chen and Q.S. Ding:State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China


Abstract
This study focuses on the amplitude dependency of damping of tall structures by the random decrement technique (RDT). Many researchers have adopted RDT to establish the amplitude dependency of damping ratios in super-tall buildings under strong wind loads. In this study, a series of simulated examples were analyzed to examine the reliability of this method. Results show that damping ratios increase as vibration amplitudes increase in several cases; however, the damping ratios in the simulated signals were preset as constants. This finding reveals that this method and the derived amplitude-dependent damping ratio characteristics are unreliable. Moreover, this method would obviously yield misleading results if the simulated signals contain Gaussian white noise. Full-scale measurements on a super-tall building were conducted during four typhoons, and the recorded data were analyzed to observe the amplitude dependency of damping ratio. Relatively wide scatter is observed in the resulting damping ratios, and the damping ratios do not appear to have an obvious nonlinear relationship with vibration amplitude. Numerical simulation and field measurement results indicate that the widely-used method for establishing the amplitude-dependent damping characteristics of super-tall buildings and the conclusions derived from it might be questionable at the least. More field-measured data must be collected under strong wind loads, and the damping characteristics of super-tall buildings should be investigated further.

Key Words
tall building; wind effect; damping ratio; full-scale measurement; wind-induced vibration; random decrement technique

Address
An Xu: State Key Laboratory of Subtropical Building Science, South China University of Technology,
Guangzhou, 510641, China;
Engineering Technology Research and Development Center for Structural Wind Resistance and Health Monitoring in Guangdong Province, Guangzhou University, Guangzhou, 510006, China
Zhuangning Xie:State Key Laboratory of Subtropical Building Science, South China University of Technology, Guangzhou, 510641, China
Ming Gu: State Key Laboratory of Subtropical Building Science, South China University of Technology,
Guangzhou, 510641, China;
State Key laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, 200092, China
Jiurong Wu: State Key laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, 200092, China



Abstract
Experiments on two-dimensional rectangular prisms with various side ratios (B/D=2, 3, and 4, where B is the along-wind dimension, and D is the across-wind dimension) and rounded corners (R/D=0%, 5%, 10%, and 15%, where R is the corner radius) are reported in this study. The tests were conducted in low-turbulence uniform flow to measure the wind pressures on the surfaces of 12 models for Reynolds numbers ranging from 1.1x105 to 6.8x105. The aerodynamic force coefficients were obtained by integrating the wind pressure coefficients around the model surface. Experimental results of wind pressure distributions, aerodynamic force coefficients, and Strouhal numbers are presented for the 12 models. The mechanisms of the Reynolds number effects are revealed by analyzing the variations of wind pressure distributions. The sensitivity of aerodynamic behavior to the Reynolds number increases with increasing side ratio or rounded corner ratio for rectangular prisms. In addition, the variations of the mean pressure distributions and the pressure correlations on the side surfaces of rectangular prisms with the rounded corner ratio are analyzed at Re=3.4x105.

Key Words
wind tunnel test; Reynolds number effects; 2D rectangular prism; rounded corner; side ratio

Address
Xinrong Wang and Ming Gu: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China

Abstract
Wind speed is the most important parameter in the design and study of wind energy conversion systems. The weibull distribution is commonly used for wind energy analysis as it can represent the wind variations with an acceptable level of accuracy. In this study, the wind data for 11 cities in Iran have been analysed over a period of one year. The Goodness of fit test is used for testing data fit to weibull distribution. The results show that this data fit to weibull function very well. The scale and shape factors are two parameters of the weibull distribution that depend on the area under study. The kinds of numerical methods commonly used for estimating weibull parameters are reviewed. Their performance for the cities under study was compared according to root mean square and wind energy errors. The result of the study reveals the empirical, modified maximum likelihood estimate of wind speed with minimum error. Also, that the moment and modified maximum likelihood are the best methods for estimating the energy production of wind turbines.

Key Words
weibull distribution; numerical methods; Iran

Address
Majid Sedghi: Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, Iran
Siamak K. Hannani: School of Mechanical Engineering, Sharif University of Technology, Tehran, Iran
Mehrdad Boroushaki: Department of Energy Engineering, Sharif University of Technology, Tehran, Iran

Abstract
Open decks are a widely used deck configuration in long-span cable-stayed bridges; however, incorporating aerodynamic countermeasures are advisable to achieve better aerodynamic performance than a bluff body deck alone. A sectional model of an open deck cable-stayed bridge with a main span of 400 m was selected to conduct a series of wind tunnel tests. The influences of five practical aerodynamic countermeasures on flutter and vortex-induced vibration (VIV) performance were investigated and are presented in this paper. The results show that an aerodynamic shape selection procedure can be used to evaluate the flutter stability of decks with respect to different terrain types and structural parameters. In addition, the VIV performance of -shaped girders for driving comfortableness and safety requirements were evaluated. Among these aerodynamic countermeasures, apron boards and wind fairings can improve the aerodynamic performance to some extent, while horizontal guide plates with 5% of the total deck width show a significant influence on the flutter stability and VIV. A wind fairing with an angle of 55 showed the best overall control effect but led to more lock-in regions of VIV. The combination of vertical stabilisers and airflow-depressing boards was found to be superior to other countermeasures and effectively boosted aerodynamic performance; specifically, vertical stabilisers significantly contribute to improving flutter stability and suppressing vertical VIV, while airflow-depressing boards are helpful in reducing torsional VIV.

Key Words
cable-stayed bridge; open deck; aerodynamic shape selection method; aerodynamic countermeasures; flutter stability; vortex-induced vibration performance

Address
Rui Zhou: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China;
Department of Infrastructure Engineering, The University of Melbourne, VIC 3010, Australia
Yongxin Yang and Yaojun Ge: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China
Priyan Mendis: Department of Infrastructure Engineering, The University of Melbourne, VIC 3010, Australia
Damith Mohotti: School of Civil Engineering, The University of Sydney, NSW, 2006, Australia

Abstract
In the current study, dynamic and quasi-static analyses were performed to investigate the response of multiple-spanned and single-spanned transmission line conductors under both downburst and synoptic winds considering different wind velocities and different length spans. Two critical downburst configurations, recommended in the literature and expected to cause maximum conductor reactions, were considered in the analyses. The objective of the study was to assess the importance of including the dynamic effect when predicting the conductor\'s reactions on the towers. This was achieved by calculating the mean, the background and the resonant reaction components, and evaluating the contribution of the resonant component to the peak reaction. The results show that the maximum contribution of the resonant component is generally low (in the order of 6%) for the multiple-spanned system at different wind velocities for both downburst and synoptic winds. For the single-spanned system, the result show a relatively high maximum contribution (in the order of 16%) at low wind velocity and a low maximum contribution (in the order of 6%) at high wind velocity for both downburst and synoptic winds. Such contributions may justify the usage of the quasi-static approach for analyzing transmission line conductors subjected to the high wind velocities typically used for the line design.

Key Words
downburst; synoptic winds; transmission line conductors; turbulence gust factor (GF)

Address
Haitham Aboshosha: Boundary Layer Wind Tunnel Laboratory (BLWTL), University of Western Ontario, London, Ontario, Canada;
Department of Civil and Environmental Engineering, University of Western Ontario, London, Ontario, Canada
Ashraf El Damatty: Department of Civil and Environmental Engineering, University of Western Ontario, London, Ontario, Canada


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