STUDY OF FREE STANDING LATTICED STEEL TOWERS UNDER WIND LOADS

Abstract

The advancement in the design and construction techniques and development of modern improved materials have resulted in a new generation of structures which are more tall and slender, flexible, ` low in damping and light in weight. Such structures show an increased susceptibility to wind loads, which are random in their character. Collapse of some of well known structures gave rise to fresh thinking and to assign qualitative values to the wind loads. Accordingly; it has become necessary to develop tools enabling the designer to estimate the effects of these forces with higher degree of accuracy than was previously required. These improvements in the knowledge have to a large extent been made possible by the increased availability of Wind Tunnels in which tests on models of prototypes can be performed, besides studies of the nature and characteristics of atmospheric winds to which the structures are subjected. The Free Standing Latticed Steel Towers, with ease of fabrication, transportation and erection, can be constructed in diverse field conditions which pose different wind environment. Analytical methods exist to predict the alongwind response of the structure. However, no closed-form, solution exists to obtain the acrosswind response, being complex in nature. Thus wind tunnel studies are resorted to for predicting accurate response of a tower in both alongwind and acrosswind directions and at different angles of yaw. Angle of yaw is the angle in plan of the wind direction, measured from the normal to the face. In the present . work, wind tunnel studies have been conducted to predict the aerodynamic response of a free-standing latticed steel tower, 173.4m high, at different angles of yaw, i.e., 0°, 10°, 20°, 300 & 45° for varying wind speed. The study has been carried out on an aeroelastic model of the prototype tower in a boundary layer flow simulating terrain category 2 with a power law coefficient of 0.14 having turbulent intensity variation of 6% to 16% at top and base respectively. The results show that the mean alongwind response is in close agreement with the analytical results while the alongwind peak response (i,e., fluctuating component) is somewhat lower, than the analytical values for all angles of yaw. Also, the maximum response obtained lies between angle of yaw, 200 and 300 for all wind speeds. Further, the tower response in the acrosswind direction has been found to be always smaller than that in the direction of the wind, so that the .alongwind forces are only of consequence in the design of latticed towers.