MODEL STUDY OF TALL RCC CHIMNEYS IN WIND TUNNEL INCLUDING INTERFERENCE EFFECTS

Abstract

The chimney is an essential part of any power plant. Chimney is a relative slender and tall structure, hence the dynamic forces, such as due to wind, are more critical in their design. It has, thus, become necessary to develop tools enabling the designer to estimate the effect of wind on chimneys with high degree of accuracy. Wind exerts forces on a chimney not only along the direction of wind but also in the transverse direction. Analytical methods are available to estimate the structural response in alongwind as well as acrosswind direction. When more than one chimneys are built in a row, the interference comes into picture. Due to interference effect of the wind, the response of the downstream chimney is quite different than in isolated the case. Till now no analytical method has been developed for estimating the interference effect. The only tool is the model study of chimney in a boundary layer wind tunnel. In the present work, wind tunnel studies have been conducted to find the interference effect on chimneys due to similar and dissimilar interfering chimney. For this, two chimneys one 224.4 m tall and another 235.5 m tall were selected. Investigation the first chimney were carried out for interference with both similar and dissimilar while the second chimney was studied for interference chimney with a similar chimney only. The study was carried out for terrain category 2. The results are calculated in terms of buffeting factor, which is defined as Buffeting factor = Response in interference configuration Response in standalone case In the study of standalone case, it is seen that the alongwind base moment is much greater than the acrosswind base moment. The study of interference effect shows the critical direction, which gives the maximum bending moment at 15 degree orientation from direction of wind flow. The mean component of alongwind bending moment is reduced by interference due to shielding effect. The fluctuating component of the alongwind response is increased due to interference upto a maximum of 3.5 times for the isolated chimney in the dissimilar interfering chimney case and up to maximum of 3.0 times in the similar interfering chimney case. The acrosswind response of the isolated chimney increased by 60% in similar interfering chimney case and 80 % in dissimilar interfering chimney case.