Wind loads on porous structures

The wind loads on porous structures depend strongly on the resistance to through flow, which may be characterised by the loss coefficient. It is shown that for round win mesh screens the loss coefficient is related to the porosity (beta). For other structures the loss coefficient is a function of the porosity and the construction. It is therefore suggested that it is useful to use an effective porosity (beta(e)), which is the porosity of a round wire mesh screen with the same loss coefficient. It is shown that loads on porous structures are less than those on solid structures by a factor (1 - beta(e)). When porous structures are at an angle to the wind, the effective loss coefficient is reduced by a cos(2)(theta) factor, where theta is the angle between the wind and a normal to the surface. As a consequence the corresponding effective porosity increases and the loads decrease. These concepts are shown to match results from a number of sources. (C) 1999 Elsevier Science Ltd. All rights reserved.