Abstract :
This report summarizes the results of wind?tunnel tests carried out on scale models of latticed towers. These tests were reported in full in reports Refs. F/T24, ? F/T43, and F/T63, already issued to members of the Electrical Research Association. The present report is in a form suitable for publication and will be found more convenient for general use. Data are given whereby the wind load on a tower may be estimated with sufficient accuracy for practical purposes, by applying suitable coefficients for wind pressure and ?sheiding? to the ?shadow? area of the tower. Wind-tunnel tests carried out at the National Physical Laboratory to determine the effect of wind pressure on latticed towers are described. The tests were carried out on scale models of types of tower commonly employed to support overhead transmission lines. It is shown that the interference between the various members comprising the structure is such that an accurate prediction of the total wind load on a tower can only be made from wind?tunnel tests. Nevertheless, an estimate sufficiently accurate for most practical purposes can be formed by applying a figure of 10.5 lb. per sq. ft. to the shadow area of one face of the tower, and assuming that the shielding of the leeward face by the windward is allowed for by taking the total load on the tower as 1.5 to 1.7 times that on the windward face. The wind is assumed to be directed normally to one face of the tower and to have a speed of 50 m.p.h. The actual wind load is shown to depend on the design of the tower, on the aspect ratio of the members (i.e. length/breadth ratio), and on area ratio, which may be considered as a measure of the ?openness? or otherwise of the latticework. When the wind is directed normally to one face of the tower, the effect of the wind drag oil the side faces of the tower can be neglected in design.The greater part of the transverse load for which a tower is designed is due to the wind load on the conductors, and some considerati- on is given in this report to the effect on the total transverse load of differences in the methods of estimating the wind load on the tower itself. The Director of the E.R.A. will welcome comments and suggestions from those who may have occasion to make use of this report.
