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CONTENTS
Volume 17, Number 3, September 2013
 

Abstract
The flow interaction between two identical neighboring twin square prisms in a staggered arrangement in an open terrain was investigated experimentally. The downwind prism was mounted on a rigid-aeroelastic setup in an open-terrain boundary layer flow to measure its acrosswind root-mean-square responses and aerodynamic damping ratios. By varying the relative location of the upwind prism and the Scruton number associated with the downwind prism, the acrosswind aeroelastic behavior of the downwind prism was analyzed and compared to that of an isolated one. Results showed that the acrosswind root-mean-square response of the downwind prism could be either suppressed or enhanced by the wake flow produced by the neighboring upwind prism. Besides the assessment of the wake effect of the downwind prism, finally, regressed relationships were presented to describe the variation of the aerodynamic damping ratio so as to predict its acrosswind fluctuating response numerically.

Key Words
high-rise building; aerodynamic damping; wind tunnel tests

Address
Fuh-Min Fang and Cheng-Yang Chung : Department of Civil Engineering, National Chung Hsing University, Taichung, Taiwan 40227
Yi-Chao Li and Wen-Chin Liu : Architecture and Building Research Institute, Tainan, Taiwan 71150
Perng-Kwei Lei: Department of Bio-Industrial Mechatronics Engineering, National Chung Hsing University,
Taichung, Taiwan 40227

Abstract
A numerical technique for fluid-structure interaction, which is based on the finite element method (FEM) and computational fluid dynamics (CFD), was developed for application to an industrial chimney equipped with a pendulum tuned mass damper (TMD). In order to solve the structural problem, a one-dimensional beam model (Navier-Bernoulli) was considered and, for the dynamical problem, the standard second-order Newmark method was used. Navier-Stokes equations for incompressible flow are solved in several horizontal planes to determine the pressure in the boundary of the corresponding cross-section of the chimney. Forces per unit length were obtained by integrating the pressure and are introduced in the structure using standard FEM interpolation techniques. For the fluid problem, a fractional step scheme based on a second order pressure splitting has been used. In each fluid plane, the displacements have been taken into account considering an Arbitrary Lagrangian Eulerian approach. The stabilization of convection and diffusion terms is achieved by means of quasi-static orthogonal subscales. For each period of time, the fluid problem was solved and the geometry of the mesh of each fluid plane is updated according to the structure displacements. Using this technique, along-wind and across-wind effects have been properly explained. The method was applied to an industrial chimney in three scenarios (with or without TMD and for different damping values) and for two wind speeds, showing different responses.

Key Words
finite element method; computational fluid dynamics; fluid-structure interaction; vortex shedding; damping

Address
A.L. Iban : ITAP, Escuela de Ingenierias Industriales, Universidad de Valladolid, Valladolid, 47011 Spain
J.M.W. Brownjohn: Vibration Engineering Section, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK
A.V. Belver and P.M. Lopez-Reyes : Centro Tecnologico CARTIF, Parque Tecnologico de Boecillo, Valladolid, 47151 Spain
K. Koo : School of Construction Engineering, Kyoungil University, 712-701, Korea

Abstract
This paper presents a number of approximated analytical formulations for the flutter analysis of long-span bridges using the so-called uncoupled flutter derivatives. The formulae have been developed from the simplified framework of a bimodal coupled flutter problem. As a result, the proposed method represents an extension of Selberg\' s empirical formula to generic bridge sections, which may be prone to one of the aeroelastic instability such as coupled-mode or single-mode (either dominated by torsion or heaving mode) flutter. Two approximated expressions for the flutter derivatives are required so that only the experimental flutter derivatives of (H*2A*1) are measured to calculate the onset flutter. Based on asymptotic expansions of the flutter derivatives, a further simplified formula was derived to predict the critical wind speed of the cross section, which is prone to the coupled-mode flutter at large reduced wind speeds. The numerical results produced by the proposed formulas have been compared with results obtained by complex eigenvalue analysis and available approximated methods show that they seem to give satisfactory results for a wide range of study cases. Thus, these formulas can be used in the assessment of bridge flutter performance at the preliminary design stage.

Key Words
bridges; eigenvalue; flutter; flutter derivatives; selberg formula; simplified formulations

Address
Tan-Van Vu : Faculty of Civil Engineering, Ho Chi Minh City University of Architecture, Vietnam
Ho-Yeop Lee and Hak-Eun Lee: School of Civil, Environmental and Architectural Engineering, Korea University, Seoul, Korea
Byung-Ho Choi : Department of Civil Engineering, Hanbat National University, Seoul, Korea

Abstract
Numerical research on four typical configurations of noise mitigation structures and their characteristics of wind loads are reported in this paper. The turbulence model as well the model parameters, the modeling of the equilibrium atmospheric boundary layer, the mesh discretization etc., were carefully considered in the numerical model to improve the numerical accuracy. Also a numerical validation of one configuration with the wind tunnel test data was made. Through detailed analyses of the wind load characteristics with the inclined part and the wind incidence angle, it was found that the addition of an inclined part to a noise mitigation structure at-grade would affect the mean nett pressure coefficients on the vertical part, and that the extent of this effect depends on the length of the inclined part itself. The magnitudes of the mean nett pressure coefficients for both the vertical part and the inclined part of noise mitigation structure at-grade tended to increase with length of inclined part. Finally, a comparison with the wind load code British/European Standard BS EN 1991-1-4:2005 was made and the envelope of the mean nett pressure coefficients of the noise mitigation structures was given for design purposes. The current research should be helpful to improve current wind codes by providing more reasonable wind pressure coefficients for different configurations of noise mitigation structures.

Key Words
wind loads; noise mitigation structure; SST k-e turbulence model; equilibrium atmospheric boundary layer

Address
K.T. TSE and Yi Yang : Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
Yi Yang and Zhuangning Xie : State Key Laboratory of Sub-tropical Building Science, South China University of Technology,Guangzhou 580641, China
K.M. Shum : The CLP Power Wind/Wave Tunnel Facility, The Hong Kong University of Science and Technology,Clear Water Bay, Kowloon, Hong Kong

Abstract
When evaluating flutter instability, it is often assumed that incident wind is normal to the longitudinal axis of a bridge and the flutter critical wind speed estimated from this direction is most unfavorable. However, the results obtained in this study via oblique sectional model tests of four typical types of bridge decks show that the lowest flutter critical wind speeds often occur in the yaw wind cases. The four types of bridge decks tested include a flat single-box deck, a flat T-shaped thin-wall deck, a flat twin side-girder deck, and a truss-stiffened deck with and without a narrow central gap. The yaw wind effect could reduce the critical wind speed by about 6%, 2%, 8%, 7%, respectively, for the above four types of decks within a wind inclination angle range between -3 and 3, and the yaw wind angles corresponding tothe minimal critical wind speeds are between 4 and 15. It was also found that the flutter critical wind speed varies in an undulate manner with the increase of yaw angle, and the variation pattern is largely dependent on both deck shape and wind inclination angle. Therefore, the cosine rule based on the mean wind decomposition is generally inapplicable to the estimation of flutter critical wind speed of long-span bridges under skew winds. The unfavorable effect of yaw wind on the flutter instability of long-span bridges should be taken into consideration seriously in the future practice, especially for supper-long span bridges in strong wind regions.

Key Words
long-span bridge; flutter; yaw wind effect; flat single-box deck; flat

Address
Le-Dong Zhu : State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China;
Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University,Hung Hom, Kowloon, Hong Kong, China;
Key Laboratory of Wind Resistance Technology of Bridges (Shanghai) of Ministry of Transport,Tongji University, Shanghai 200092, China;
Department of Bridge Engineering, Tongji University, Shanghai 200092, China
You-Lin Xu : Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University,Hung Hom, Kowloon, Hong Kong, China
Zhenshan Guo : Key Laboratory of Wind Resistance Technology of Bridges (Shanghai) of Ministry of Transport,
Tongji University, Shanghai 200092, China;
Department of Bridge Engineering, Tongji University, Shanghai 200092, China
Guang-Zhao Chang and Xiao Tan : Lin Tung-Yen and Li Guo-Hao Consultants LTD, Shanghai 200437, China

Abstract
Turkey has been hosted various civilizations throughout centuries and it has become one of the oldest settlements all over the world due to the geographical location. Therefore, it has accommodated innumerable historical structures remain from the past civilizations. Protection and conservation of these historical constructions should be the major points for continuity of history. Crooked minaret is one of between these historical invaluable structures. It is located at the city of Aksaray and it dates back approximately 800 years. The minaret has lost its vertical position in time and bends on the North-West direction. In this study, general information is given about minarets and some restoration recommendations are given for crooked minaret based on performed some finite element structural analyses. These analyses are considered into three cases; 1-Dead loading, 2- Wind loading, and 3-Earthquake loadings. Results from the analyses are discussed detailed and some useful recommendations are given in the end of the study.

Key Words
crooked minaret; Aksaray; finite element method; LUSAS; restoration; wind

Address
Ali Ural: Department of Civil Engineering, Aksaray University, 68100, Aksaray, Turkey
Adem Doğangun : Department of Civil Engineering, Uludağ University, 16100, Bursa, Turkey
Şakir Meraki: A-Project Eng. Archt. Ltd., 06580, Ankara, Turkey


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