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CONTENTS
Volume 3, Number 2, June 2000
 

Abstract
Snowdrifts around buildings can cause serious problems when formed on undesirable places.rnThe formation of snowdrifts is highly connected to the wind pattern around the building, and the windrnpattern is again dependent on the building design. The shear stress on the surface and snowdrifting aroundrndifferent buildings are investigated through CFD analysis and compared to measurements. The computationsrnof shear stress shows local minima in the same areas as snowdrifts are formed. The snowdrifting computationsrnutilises a drift-flux model where a fluid with snow properties is allowed to drift through a fluid with airrnproperties. An apparent dynamic viscosity of the snow/air mixture is defined and used as a thresholdrncriterion for snowdrifting. The results from the snowdrifting computations show increased snow density wherernsnowdrifts are expected, and are in agreement with previous large-scale snowdrift measurements. The resultsrnshow that computational fluid dynamics can be a tool for planning building design in snowdrifting areas.

Key Words
snowdrift; building; numerical simulation; CFD; wind.

Address
Thomas K. Thiis, Narvik Institute of Technology, p.b. 385, N-8501 Narvik, Norway

Abstract
Due to their high corrosion and chemical resistance, fiber reinforced plastics (FRP) arernbecoming widely used as the main structural material for industrial chimneys. However, no national coderncurrently exists for the design of such type of chimneys. The purpose of this study is to investigaternanalytically the response of FRP chimneys to wind loads. The classical lamination theory is used tornsubstitute the angle-ply laminate of a FRP chimney with an equivalent orthotropic material that providesrnthe same stiffness. Dynamic wind loads are applied to the equivalent chimney to evaluate its response tornboth along and across wind loads. A parametric study is then conducted to identify the material andrngeometric parameters affecting the response of FRP chimneys to wind loads. Unlike the across-windrnresponse, the along-wind tip deflection is found to be highly dependent on the angle of orientation of thernfibers. In general, the analysis shows that FRP chimneys are very vulnerable to across-wind oscillationsrnresulting from the vortex shedding phenomenon.

Key Words
fiber reinforced plastics; chimneys; laminated; wind loads; vortex shedding; dynamic.

Address
A.S. Awad, Mccavour Eng. Ltd. Mississauga, Ontario, CanadarnA.A. El Damatty and B.J. Vickery, Department of Civil and Environmental Engineering, The University of Western Ontario, London, Ontario, N6A 5B9 Canada

Abstract
The technique of proper orthogonal decomposition is potentially useful in specifying thernfluctuating surface pressure field around structures. However there has been a degree of controversy overrnwhether or not the calculated modes have physical meanings. This paper addresses this issue throughrnconsideration of the results of full scale experiments, and through an analytical investigation. It is concludedrnthat the lower, most energetic modes are likely to reflect different fluctuating flow mechanisms, althoughrnno mode is likely to be associated with just one flow mechanism or vice versa. The higher, less energeticrnmodes are likely to represent interactions between different flow mechanisms, and to be significantlyrnaffected by the number of measurement points and measurement errors. The paper concludes with a briefrndescription of the application of POD to the problem of building ventilation, and the calculation of claddingrnpressures.

Key Words
proper orthogonal decomposition; low rise structures; full scale experiments; ventilation.

Address
C.J. Baker, School of Civil Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.

Abstract
Under special conditions of turbulent wind, suspension and cable-stayed bridges could reachrninstability conditions. In various instances the bridge deck, as like a bluff body, could exhibit single-degreerntorsional instability. In the present study the turbulent component of flow has been considered as arnsolution of a differential stochastic linear equation. The input process is represented by a Gaussian zero-meanrnwhite noise. In this paper the analytical solution of the dynamic response of the bridge has beenrndetermined. The solution has been obtained with a technique of closing on the order of the moments.

Key Words
turbulent wind; stochastic analysis; Gaussian processes; bridges.

Address
Dora Foti and Pietro Monaco, Department of Structural Engineering, Technical University of Bari, Via Orabona 4, 70125 Bari, Italy

Abstract
Engineered structures such as buildings and bridges in certain regions of the world need tornbe designed to withstand tropical cyclone winds, otherwise known as typhoons or hurricanes. In order torncarry out this design, it is necessary to be able to estimate the maximum wind speeds likely to bernencountered by the structure over its expected lifetime, say 100 years. Estimation of the maximum windrninvolves not only the overall strength of the tropical cyclone, but the variation of wind speed with radiusrnfrom the centre, circumferential position, and with height above the ground surface. In addition, not onlyrnthe mean wind speed, but also the gust factor must usually be estimated as well. This paper investigates arnnumber of recent mathematical models of tropical cyclone structure and comments on their suitability forrnthese purposes in a variety of scenarios.

Key Words
tropical cyclone; wind structure; mathematical model.

Address
J.A.B. Wills and B.E. Lee, Department of Civil Engineering, University of Portsmouth, Portsmouth PO1 3QL, U.K.rnT. A. Wy att, Department of Civil Engineering, Imperial College of Science and Technology, U.K.


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