Wind-Induced Responses And Equivalent Static Wind Loads Of Large Hyperbolic Cooling Towers

Large hyperbolic cooling towers which can produce recirculated water are widely used in electric power, petroleum and nuclear industries. With the development of these industries in recent years, many large cooling towers have been built. As the height of cooling towers becomes higher and the volume becomes larger, many towers have exceeded the maximum size limitation specified by the design code. As wind load is always the dominated load in the design, it is meaningful to conduct systematic research on wind-induced responses and equivalent static wind loads(ESWLs) of cooling towers.Firstly, the wind load distribution characteristics has been obtained employing wind tunnel test of a cooling tower. Then the collapse of Ferrybridge cooling towers is reviewed and the contribution of tower shape to the accident is discussed through the comparison on responses between the Ferrybridge tower and a hyperbolic tower. For the hyperbolic cooling towers, the characteristics of vibration is studied through analysis of different finite element(FEM) models. The good match between the results from the fitting equation and the results from FEM and full-scale tests indicate that the fitting equation has a high credibility in predicting the first vibrating frequency of cooling towers.Based on wind tunnel test redults, the wind-induced responses are calculated through time domain method and frequency domain method. The ESWLs are then calculated using three methods which are GLF method, three-component method and modal decomposition method. Finally, the difference of responses when considering the soil-structure interaction(SSI) effect is investigated.The main conclusions of this paper are shown as follows. Firstly, the analysis of wind-induced responses of Ferrybridge cooling towers shows that the radial displacements and meridian membrane forces of Ferrybridge tower under wind load are much larger than those of the hyperbolic tower under the same wind loadings. The significant difference between the two towers implies that the tower shape is a contributing factor for the collapse of Ferrybridge cooling towers, which is a new explanation to the collapse of the Ferrybridge cooling towers. Secondly, the analysis of the vibration characteristics shows that, the fundamental frequency and overturning frequency are proportional to the concrete material property (?) and the thickness of tower wall, and are inversely proportional to the height of tower. These two frequencies also have a quadratic relationship with the total cross-sectional area of supporting columns and the median regressive parameter. Thirdly, the results of wind-induced responses show that the radial displacements and meridian membrane forces of 0°and 70°meridian reach their maximum values under mean wind loadings. The discrepancy between the results of time domain and frequency domain is found, which can mainly be contributed to the factor that the time domain method uses continuous model whereas the frequency domain method uses discrete model. Fourthly, the redults from the study of ESWLs show that the GLF method gives conservative results. The three-component method and modal decomposition method will get different results to different specified response. Finally, when SSI effect is considered, the frequency of the cooling tower decreases significantly and the displacement responses are significantly increased, whereas the meridional membrane forces are slightly reduced.