WIND INTERFERENCE EFFECTS IN TALL CHIMNEYS OF DIFFERENT HEIGHTS

Abstract

In the present work wind tunnel studies have been conducted to find out the interference effects on a tall chimney due to a similar and a dissimilar interfering chimney of same and different heights. For this, two prototype chimneys-one 102.3m tall and other 101.7m tall were selected. Investigations were carried out on an FRP model of the first chimney with rigid interfering models of both the chimneys. The study was carried out for terrain category 3. The results are presented in terms of buffeting factors defined as, jmt-ii-elrc,Ace Response of the chimney in stand-a14944€ condition Buffeting factor = Response in iaed-Gr-etiee position In the study of stand-alone case, it was found that the mean component of the along-wind base moment was similar in both analytical and experimental procedures. The fluctuating component of the along-wind response at base obtained analytically was 4.32% higher than the experimental value. The across-wind response obtained analytically at base was 19% smaller than the experimental one. It was found that the along-wind base moment was much greater than the across-wind base moment. The study of interference effects shows that the critical wind direction, which resulted in maximum bending moments was at 20° to the alignment of the two chimneys. The mean component of along-wind bending moment is reduced due to shielding effect. The shielding effect reduced with reduction in the height of the interfering chimney. The fluctuating component of along-wind response increased upto a maximum of 2.12 times in case of interference with a similar chimney of the same height and 1.97 times in case of dissimilar chimney of almost same height. The fluctuating part of the along-wind response reduced significantly when the height of • ' the interfering chimney was reduced. The across-wind response increased upto a . . . maximum of 2.29 times in case of interference with a similar chimney of the same height and 2.17 times in case of dissimilar chimney of almost same height. Across-wind response reduced very rapidly as the height of...the interfering chimney was reduced. Finally, a mathematical expression has been developed to fit into the experimental values, which gives very close and slightly conservative results..