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CONTENTS
Volume 5, Number 5, September 2002
 

Abstract
Aerodynamic pressures and forces were measured on a model of a solar panel containing six slender, parallel modules. Of particular importance to system design is the aerodynamically induced torque. The peak system torque was generally observed to occur at approach wind angles near the diagonals of the panel (45o, 135o, 225o and 315o ) although large loads also occurred at 270o, where windrnis in the plane of the panel, perpendicular to the individual modules. In this case, there was strong vortex shedding from the in-line modules, due to the observation that the module spacing was near the critical value for wake buffeting. The largest loads, however, occurred at a wind angle where there was limited vortex shedding (330o). In this case, the bulk of the fluctuating torque came from turbulent velocityrnfluctuations, which acted in a quasi-steady sense, in the oncoming flow. A simple, quasi-steady, model for determining the peak system torque coefficient was developed.

Key Words
wind loads; solar array; vortex shedding; wake buffeting.

Address
Boundary Layer Wind Tunnel Laboratory, Faculty of Engineering Science,rnUniversity of Western Ontario, London, ON, N6A 5B9, CanadarnPhotovoltaics International LLC, Sunnyvale, CA, 94086, USA

Abstract
Passive control of the flutter condition of suspension bridges using a combined vertical and torsional tuned mass damper (TMD) system is presented. The proposed TMD system has two degrees of freedom, which are tuned close to the frequencies corresponding to vertical and torsional symmetric modes of the bridge which get coupled during flutter. The bridge-TMD system is analyzed for findingrncritical wind speed for flutter using a finite element approach. Thomas Suspension Bridge is analyzed as an illustrative example. The effectiveness of the TMD system in increasing the critical flutter speed of the bridge is investigated through a parametric study. The results of the parametric study led to the optimizationrnof some important parameters such as mass ratio, TMD damping ratio, tuning frequency, and number of TMD systems which provide maximum critical flutter wind speed of the suspension bridge.

Key Words
tuned mass damper; bridge flutter; suspension bridges; passive control.

Address
Department of Civil Engineering, Engineering Faculty, Guilan University, Rasht, IranrnDepartment of Civil Engineering, Indian Institute of Technology, Hauz Khas, New Delhi 110 016, India

Abstract
The effects of the nonlinear (quadratic) term in wind pressure have been analyzed in many papers with reference to linear structural models. The present paper addresses the problem of the response of nonlinear structures to stochastic nonlinear wind pressure. Adopting a single-degree-of-freedom structuralrnmodel with polynomial nonlinearity, the solution is obtained by means of the moment equation approach in the context of Itô's stochastic differential calculus. To do so, wind turbulence is idealized as the output of a linear filter excited by a Gaussian white noise. Response statistical moments are computed for both the equivalent linear system and the actual nonlinear one. In the second case, since the moment equations form an infinite hierarchy, a suitable iterative procedure is used to close it. The numerical analyses regard a Duffing oscillator, and the results compare well with Monte Carlo simulation.

Key Words
quadratic wind pressure; nonlinear structures; wind response; Itô's calculus; moment equation approach; iterative closure method.

Address
Department of Structural Engineering, Politecnico di Milano,rnPiazza Leonardo da Vinci 32, I-20133 Milano, ItalyrnStructural Engineer, Via Bianzana 6, 24100 Bergamo, Italy

Abstract
This paper presents a practical numerical method to determine both the spatial and temporal distribution of driving rain on buildings. It is based on an existing numerical simulation technique and uses the building geometry and climatic data at the building site as input. The method is applied to determine the 3D spatial and temporal distribution of wind-driven rain on the facade a low-rise building ofrncomplex geometry. Distinct wetting patterns are found. The important causes giving rise to these particular patterns are identified : (1) sweeping of raindrops towards vertical building edges, (2) sweeping of raindrops towards top edges, (3) shelter effect by various roof overhang configurations. The comparison of thernnumerical results with full-scale measurements in both space and time for a number of on site recorded rain events shows the numerical method to yield accurate results.

Key Words
driving rain; wind-driven rain; building; CFD; numerical simulation; experimental verification.

Address
Department of Civil Engineering, Laboratory of Building Physics, Katholieke Universiteit Leuven, Kasteelpark Arenberg 51, 3001 Leuven, Belgium

Abstract
Lighting and traffic signal columns are mainly stressed by excitation due to natural, gusty wind. Such columns typically have a door opening about 60 cm above ground level for the connection of the buried cable with the column's electric system. When the columns around this notch are inadequately designed, vibrations due to gusty winds will produce considerable stress amplitudes in this area, which lead to fatigue cracks. To give a realistic basis for a reliable and economic design of lighting and traffic signal columns, a number of experimental and theoretical investigations have been made. The proposed design concept allows the life of such columns to be assessed with a satisfactory degree of accuracy.

Key Words
lighting column; traffic signal column; notch; steel; wind; gust; fatigue; dynamic; damping.

Address
Institute for Steel Structures, Technical University of Braunschweig,rnBeethovenstra


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