Experimental study of the wind forces on rectangular latticed communication towers with antennas

Abstract

With today's expanding communication systems, a large number of lattice towers to support cellular antennas are being constructed in Brazil. Due to the lightweight of these structures, wind forces are the primary concern in the design. An experimental investigation on the subject was carried out at the Boundary Layer Wind Tunnel Laboratory, University of Western Ontario (UWO), Canada. Three section models were designed and constructed based on existing latticed towers built in Brazil. The wind incidence angle; the tower solidity; the shielding effect; the influence of the wind turbulence on the drag coefficient were analyzed. Measurements were made of the mean and RMS drag and crosswind forces. The results were compared with some existing codes and standards including the Canadian (NBCC, 1995), American (ASCE 7-95, 1995), Australian/New Zealand (AS/NZS 1170.2-2002), Australian (AS 3995-1994), British (BS8100, 1986), Eurocode 1 (European Committee for Standardization, 1995) and Brazilian (NBR 6123, 1988). It is a common approach to consider the wind forces on antennas independent of the lattice tower, without considering the effects of their presence on the computation of the wind forces. The question arises whether this is a good approach or not. These effects can be described by introducing an interference factor. This factor depends, among other things, on the tower solidity. Two models with different solidity were tested for wind incidence angle of 0 degrees and antenna dishes simulated with disks made of Styrofoam attached to the windward face. The results were compared with ESDU.