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CONTENTS
Volume 19, Number 4, October 2014
 

Abstract
A new method is proposed in this study for estimating the damping ratio of a super tall building under strong wind loads with short-time measured acceleration signals. This method incorporates two main steps. Firstly, the power spectral density of wind-induced acceleration response is obtained by the wavelet transform, then the dynamic characteristics including the natural frequency and damping ratio for the first vibration mode are estimated by a nonlinear regression analysis on the power spectral density. A numerical simulation illustrated that the damping ratios identified by the wavelet spectrum are superior in precision and stability to those values obtained from WWelch\'s periodogram spectrum. To verify the efficiency of the proposed method, wind-induced acceleration responses of the Guangzhou West Tower (GZWT) measured in the field during Typhoon Usagi, which affected this building on September 22, 2013, were used. The damping ratios identified varied from 0.38% to 0.61% in direction 1 and from 0.22% to 0.59% in direction 2. This information is expected to be of considerable interest and practical use for engineers and researchers involved in the wind-resistant design of super-tall buildings.

Key Words
wind effect; tall building; field measurement; damping ratio

Address
An Xu:Engineering Technology Research and Development Center for Structural Wind Resistance and Health
Monitoring in Guangdong Province, Guangzhou University, Guangzhou, 510006, China;
Research Center for Structural Safety and Health Monitoring of Guangdong Education Department ,Guangzhou University, Guangzhou, 510006,China;
Guangzhou Municipal Key Laboratory for Structural Safety and Health Monitoring, Guangzhou University,Guangzhou, 510006, China;
Key Laboratory of Structure and Wind Tunnel of Guangdong Higher Education Institutes, Shantou 515063,China
Jiurong Wu and Ruohong Zhao:Engineering Technology Research and Development Center for Structural Wind Resistance and Health
Monitoring in Guangdong Province, Guangzhou University, Guangzhou, 510006, China;
Research Center for Structural Safety and Health Monitoring of Guangdong Education Department ,Guangzhou University, Guangzhou, 510006,China;
Guangzhou Municipal Key Laboratory for Structural Safety and Health Monitoring, Guangzhou University,Guangzhou, 510006, China

Abstract
Probability plotting positions are popular and used as the basis for distribution fitting and for inspecting the quality of the fit because of its simplicity. The plotting positions that lead to excellent approximation to the mean of the order statistics should be used if the objective of the fitting is to estimate quantiles. Since the mean depends on the sample size and is not amenable for simple to use closed form solution, many plotting positions have been presented in the literature, including a new plotting position that is derived based on the weighted least-squares method. In this study, the accuracy of using the new plotting position to fit the Gumbel distribution for estimating quantiles is assessed. Also, plotting positions derived by fitting the mean of the order statistics for all ranks is proposed, and an approximation to the covariance of the order statistics for the Gumbel (and Weibull) variate is given. Relative bias and root-mean-square-error of the estimated quantiles by using the proposed plotting position are shown. The use of the proposed plotting position to estimate the quantiles of annual maximum wind speed is illustrated.

Key Words
Gumbel distribution; Weibull distribution; least-squares methods; plotting positions

Address
H.P. Hong and S.H. Li: Department of Civil and Environmental Engineering, University of Western Ontario, Canada N6A 5B9

Abstract
The flow characteristics of a circular cylinder surrounded by an outer permeable cylinder were experimentally investigated using Particle Image Velocimetry Technique in deep water flow. In order to consider the effects of diameter and porosity of the outer cylinder on flow structures of the inner cylinder, five different outer cylinder diameters (D=37.5, 52.5, 60, 75 and 90 mm) and eight different porosities (B= 0.4, 0.5, 0.6, 0.65, 0.7, 0.75, 0.8 and 0.85) were selected. During the experiments, the diameter of inner cylinder was kept constant as d=30 mm. The depth-averaged free-stream velocity was adjusted as U=0.156 m/s, which corresponds to the Reynolds number of Re=5000 based on the inner cylinder diameter. It has been concluded that both the outer permeable cylinder diameter and the porosity have important influences on the attenuation of vortex shedding in the wake region. The presence of outer permeable cylinder decreases the magnitude of Reynolds shear stress and turbulent kinetic energy compared to the bare cylinder case. Moreover, the spectral analysis of vortex shedding frequency has revealed that the dominant frequency of vortex shedding downstream of the cylinder arrangement also reduces substantially due to the weakened Karman shear layer instability.

Key Words
passive control; PIV; circular cylinder; vortex shedding

Address
Bengi Gozmen: Department of Mechanical Engineering, Usak University, 1 Eylül Kampüsü, 64200, Usak, Turkey
Huseyin Akilli:Department of Mechanical Engineering, Cukurova University, 01330, Yüreğir, Adana, Turkey

Abstract
This paper examines the nonlinear behaviour of corrugated steel plate shear walls under lateral pushover load. One of the innovations in these types of walls which have used in recent years is the use of the corrugated steel shear walls rather un-stiffness plates. In the last decades many experimental studies have been done on the on the corrugated steel shear walls. A finite element analysis that includes both material and geometric nonlinearities is employed for the investigation. A comparison is made between the behaviour of steel shear walls with sinusoidal corrugated plate and trapezoidal corrugated plate. The effects of parameters such as the thickness of the corrugated plate, the corrugation depth in the corrugated plates and the corrugation length of the infill of the corrugated plates, are investigated. The results of this study have demonstrated that in the wall with constant dimensions, the trapezoidal plates have higher energy dissipation, ductility and ultimate bearing than sinusoidal waves, while decreasing the steel material consumption.

Key Words
steel shear wall; sinusoidal corrugated plate; trapezoidal corrugated plate; energy dissipation; ductility; ultimate bearing

Address
S.A. Edalati and A. Emadi: Department of Civil and Environmental Engineering, Tarbiat Modares University, Tehran, Iran
Y. Yadollahi: Department of Civil Engineering, Shomal University, Amol, Iran
I. Pakar: Young Researchers and Elites club, Mashhad Branch, Islamic Azad University, Mashhad, Iran
M. Bayat: Department of Civil Engineering, College of Engineering, Mashhad Branch, Islamic Azad University,
Mashhad, Iran

Abstract
With the assistance of typhoon field data at aerial elevation level observed by meteorological satellites and wind velocity and direction records nearby the ground gathered in Guangzhou Weather Station between 1985 and 2001, some key wind field parameters under typhoon climate in Guangzhou region were calibrated based on Monte-Carlo stochastic algorithm and Meng\'s typhoon numerical model. By using Peak Over Threshold method (POT) and Generalized Pareto Distribution (GPD), Wind field characteristics during typhoons for various return periods in several typical engineering fields were predicted, showing that some distribution rules in relation to gradient height of atmosphere boundary layer, power-law component of wind profile, gust factor and extreme wind velocity at 1-3s time interval are obviously different from corresponding items in Chinese wind load Codes. In order to evaluate the influence of typhoon field parameters on long-span flexible bridges, 1:100 reduced-scale wind field of type B terrain was re-illustrated under typhoon and normal conditions utilizing passive turbulence generators in TJ-3 wind tunnel, and wind-induced performance tests of aero-elastic model of long-span Guangzhou Xinguang arch bridge were carried out as well. Furthermore, aerodynamic admittance function about lattice cross section in mid-span arch lib under the condition of higher turbulence intensity of typhoon field was identified via using high-frequency force-measured balance. Based on identified aerodynamic admittance expressions, Wind-induced stochastic vibration of Xinguang arch bridge under typhoon and normal climates was calculated and compared, considering structural geometrical non-linearity, stochastic wind attack angle effects, etc. Thus, the aerodynamic response characteristics under typhoon and normal conditions can be illustrated and checked, which are of satisfactory response results for different oncoming wind velocities with resemblance to those wind tunnel testing data under the two types of climate modes.

Key Words
wind-induced vibration; long-span bridge; typhoon; wind tunnel test; numerical simulation

Address
Yaojun Ge and Lin Zhao: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, China

Abstract
Hyperbolic thin-shell cooling towers have complicated vibration modes, and are very sensitive to the effects of group towers and wind-induced vibrations. Traditional aero-elastic models of cooling towers are usually designed based on the method of stiffness simulation by continuous medium thin shell materials. However, the method has some shortages in actual engineering applications, so the so-called \"equivalent beam-net design method\" of aero-elastic models of cooling towers is proposed in the paper and an aero-elastic model with a proportion of 1: 200 based on the method above with integrated pressure measurements and vibration measurements has been designed and carried out in TJ-3 wind tunnel of Tongji university. According to the wind tunnel test, this paper discusses the impacts of self-excited force effect on the surface wind pressure of a large-scale cooling tower and the results show that the impact of self-excited force on the distribution characteristics of average surface wind pressure is very small, but the impact on the form of distribution and numerical value of fluctuating wind pressure is relatively large. Combing with the Complete Quadratic Combination method (hereafter referred to as CQC method), the paper further studies the numerical sizes and distribution characteristics of background components, resonant components, cross-term components and total fluctuating wind-induced vibration responses of some typical nodes which indicate that the resonance response is dominant in the fluctuating wind-induced vibration response and cross-term components are not negligible for wind-induced vibration responses of super-large cooling towers.

Key Words
cooling tower; aero-elastic model; self-excited force; wind-induced vibration response

Address
Lin Zhao, Xu Chen and Yaojun Ge: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Siping Road 1239, Shanghai 200092, China
Shitang Ke: Department of Civil Engineering, Nanjing University of Aeronautics and Astronautics, Youdao Road 29,
Nanjing 210016, China


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