Drag Coefficients of Latticed Towers

Abstract

Recent building codes require that wind loads be determined by multiplying a calculated velocity pressure by the drag coefficient of the structure. It is suggested that the drag coefficients given in the codes for latticed towers are conservative. To determine appropriate drag coefficients for square self‐supported latticed towers two models were constructed and tested in a wind tunnel. Drag forces of the two models with and without heel angles as well as half of one model and tilting to different angles of the other model were determined. Results are analyzed and drag coefficients are calculated and compared to other published test results and to the ANSI A58.1 Code. Recommended equations are given for determining the drag coefficient of latticed towers with solidity ratios in a given range. For the wind direction on the diagonal axis of the tower the drag was found to be independent of the solidity ratio and, therefore, a multiplier is recommended. A multiplier is also recommended for towers with legs that have a heel angle.