WIND EFFECTS ON TALL BUILDINGS

Abstract

With the increase in population and land cost in large cities, the construction of tall buildings is becoming increasingly a necessity. Use of higher strength materials, improved capabilities in analysis and design and also in construction technology have lead to the construction of tall slender buildings of lighter density. The continuing construction of taller and more flexible structures has necessiated a better understanding of wind effects on structures for improving the design methodology for wind-resistant buildings. High-rise buildings may oscillate excessively during wind storms because of dynamic effects of wind. Excessive drift may cause discomfort to the occupants and the building may even become unserviceable. Under the influence of dynamic wind loads, typical high- rise buildings vibrate in the along-wind and across-wind directions. The along-wind motion primarily results from pressure fluctuations on the windward and leeward faces, which generally follow the fluctuations in the approach flow, atleast in the• low frequency range. The across-wind motion is introduced mainly on account of alternate shedding of eddies from the two side faces and by the pressure fluctuations on these faces which are induced by the fluctuations in the separated shear layers and wake flow fields. The dynamic effects of wind are customarily represented by 'Gust Factors'. The velocity spectra of longitudinal fluctuations is required for gust factor computation. Various authors have come up with different spectras. Some of these are dependent and others independent of height of building. In this dissertation spectras of Davenport and Simiu are being considered for gust factor and response computation. Apart from velocity spectra, there are other parameters (i.e. height and cross-section of buildings, terrain turbulence, etc.) which must also be considered. Important of these is the along-wind cross-correlation function, which correlates pressure fluctuations of windward and leeward sides. Davenport has assumed the pressures on both faces perfectly correlated, which is far from truth. Simiu, on the other hand, has considered this aspect. In this dissertation various methods have been used for the computation of gust factors and the responses obtained have been compared with the values determining using the I.S. code.