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Wind and Structures
  Volume 22, Number 1, January 2016 , pages 65-87
DOI: https://doi.org/10.12989/was.2016.22.1.065
 


Capacity of a transmission tower under downburst wind loading
T.G. Mara, H.P. Hong, C.S. Lee and T.C.E. Ho

 
Abstract
    The wind velocity profile over the height of a structure in high intensity wind (HIW) events, such as downbursts, differs from that associated with atmospheric boundary layer (ABL) winds. Current design codes for lattice transmission structures contain only limited advice on the treatment of HIW effects, and structural design is carried out using wind load profiles and response factors derived for ABL winds. The present study assesses the load-deformation curve (capacity curve) of a transmission tower under modeled downburst wind loading, and compares it with that obtained for an ABL wind loading profile. The analysis considers nonlinear inelastic response under simulated downburst wind fields. The capacity curve is represented using the relationship between the base shear and the maximum tip displacement. The results indicate that the capacity curve remains relatively consistent between different downburst scenarios and an ABL loading profile. The use of the capacity curve avoids the difficulty associated with defining a reference wind speed and corresponding wind profile that are adequate and applicable for downburst and ABL winds, thereby allowing a direct comparison of response under synoptic and downburst events. Uncertainty propagation analysis is carried out to evaluate the tower capacity by considering the uncertainty in material properties and geometric variables. The results indicated the coefficient of variation of the tower capacity is small compared to those associated with extreme wind speeds.
 
Key Words
    transmission towers; downbursts; extreme winds; nonlinear analysis; Monte Carlo technique
 
Address
T.G. Mara and T.C.E. Ho: The Boundary Layer Wind Tunnel Laboratory, University of Western Ontario, London,
ON, Canada, N6A 5B9
H.P. Hong: Department of Civil and Environmental Engineering, University of Western Ontario, London, ON, Canada, N6A 5B9
C.S. Lee: Department of Civil and Environmental Engineering, University of Western Ontario, London, ON, Canada, N6A 5B9;
Rowan Williams Davies & Irwin Inc., 650 Woodlawn Road West, Guelph, ON, Canada, N1K 1B8
 

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