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Wind and Structures
  Volume 13, Number 5, September 2010 , pages 413-431
DOI: https://doi.org/10.12989/was.2010.13.5.413
 


Assessment of vertical wind loads on lattice framework with application to thunderstorm winds
T.G. Mara, J.K. Galsworthy and E. Savory

 
Abstract
    The focus of this article is on the assessment of vertical wind vector components and their aerodynamic impact on lattice framework, specifically two distinct sections of a guyed transmission tower. Thunderstorm winds, notably very localized events such as convective downdrafts (including downbursts) and tornadoes, result in a different load on a tower structural system in terms of magnitude and spatial distribution when compared to horizontal synoptic winds. Findings of previous model-scale experiments are outlined and their results considered for the development of a testing rig that allows for rotation about multiple body axes through a series of wind tunnel tests. Experimental results for the wind loads on two unique experimental models are presented and the difference in behaviour discussed. For a model cross arm with a solidity ratio of approximately 30%, the drag load was increased by 14% when at a pitch angle of 20o. Although the effects of rotation about the vertical body axis, or the traditional angle of attack, are recognized by design codes as being significant, provisions for vertical winds are absent from each set of wind loading specifications examined. The inclusion of a factor to relate winds with a vertical component to the horizontal speed is evaluated as a vertical wind factor applicable to load calculations. Member complexity and asymmetric geometry often complicate the use of lattice wind loading provisions, which is a challenge that extends to future studies and codification. Nevertheless, the present work is intended to establish a basis for such studies.
 
Key Words
    lattice tower; wind tunnel testing; thunderstorm winds; non-horizontal wind; downburst simusimulation; transmission tower.
 
Address
T.G. Mara: The Boundary Layer Wind Tunnel Laboratory, The University of Western Ontario, London, ON, Canada N6A 5B9
J.K. Galsworthy: Rowan Williams Davies & Irwin Inc., 650 Woodlawn Road West, Guelph, ON, Canada, N1K 1B8
E. Savory: Department of Mechanical and Materials Engineering, The University of Western Ontario, London, ON, Canada N6A 5B9
 

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