Field Measurement Analysis Of Tall Buildings And Wind-induced Responses Of Long Span Roofs

This thesis mainly presented the field measurement analysis of tall buildings during passages of several typhoons; the numerical evaluation of tall buildings was conducted. The wind tunnel test on a rigid model of long span cantilever roof and the computational methods for wind-induced response of long span cantilever roofs were also studied. Finally, a simplified approach for estimating the Equivalent Static Wind Load of long-span cantilever roof was proposed in this study for engineering application purpose. The thesis was focused on the following aspects:( 1 ) This study presented selected field measurement results of wind characteristics and structural responses of super tall buildings, during passages of several typhoons. The field data such as wind speeds, wind directions and acceleration responses were simultaneously and continuously measured from the super tall buildings during typhoons. Detailed analysis of the field data was conducted to investigate the characteristics of typhoon-generated wind and wind-induced vibrations of these super tall buildings under typhoon conditions. The dynamic characteristics of the buildings were determined on the basis of the field measurements and comparisons with those calculated from the computational models of the buildings were made. Furthermore, the full scale measurements were compared with wind tunnel results to evaluate the accuracy of the model test results and adequacy of the techniques used in wind tunnel tests. The full scale measurements of wind effects on the instrumented tall buildings can provide a fundamental improvement of knowledge in structural dynamic characteristics, wind-structure interaction, wind climate, wind field modelling and design wind loads.(2) A comprehensive numerical study of wind effects on the Commonwealth Advisory Aeronautical Council (CAARC) standard tall building was presented. The techniques of Computational Fluid Dynamics (CFD), such as Large Eddy Simulation (LES), Reynolds Averaged Navier-Stokes Equations (RANS) Model etc., were adopted in this study to predict wind loads on and wind flows around the building. The main objective of this study is to explore an effective and reliable approach for evaluation of wind effects on tall buildings by CFD techniques. The computed results were compared with extensive experimental data which were obtained at wind tunnels. The reasons to cause the discrepancies of the numerical predictions and experimental results were identified and discussed. It was found through the comparison that the LES with a dynamic sub grid-scale (SGS) model can give satisfactory predictions for mean and dynamic wind loads on the tall building, while the RANS model with modifications can yield encouraging results in most cases and has advantage of providing rapid solutions. Furthermore, it was observed that typical features of the flow fields around such a surface-mounted bluff body standing in atmospheric boundary layers can be captured numerically. It was found that the velocity profile of approaching wind flow mainly influences the mean pressure coefficients on the building and the incident turbulence intensity profile has a significant effect on the fluctuating wind forces. Therefore, it is necessary to correctly simulate both the incident wind velocity profile and turbulence intensity profile in CFD computations to accurately predict wind effects on tall buildings. The recommended CFD techniques and associated numerical treatments provide an effective way for designers to assess wind effects on a tall building and the need for a detailed wind tunnel test.(3)The wind tunnel test on a rigid model of long span cantilever roof was conducted in this study. Experimental results demonstrated that the mean pressure for the surface taps at the front part of roof were uplift forces. The coefficients of mean wind pressure for these taps increased when the wind azimuth increased from 0 to 60 degree. Then it decreased when the wind azimuth increased from 60 to 90 degree. However, the coefficients of mean wind pressure at these taps remained almost zero when the wind azimuth increased from 90 to 180 degree. For the taps at the middle part of cantilever roof, the uplift forces were also presented. The coefficients of mean wind pressure also increased when the wind azimuth increased from 0 to 90 degree, and relatively smaller values were observed for the pressures at these taps compared to those for the taps at the front part of the roof. The similarity facts also exist for the pressure taps at the rear part of the roof. However, the relatively smaller values in the coefficient of mean wind pressure were found for the taps at the rear part when the wind azimuth changed from 90 to 180 degree. For the front taps of the cantilever roof, the coefficients of fluctuating wind pressure decreased with the increase of the wind azimuth. This mainly due to the less interference effect from the windward roof when the wind azimuth increased. However, the coefficients of fluctuating wind pressure for the middle taps didn't vary with the wind azimuth. Meanwhile, the coefficients of fluctuating wind pressure for the rear taps normally increased with the increase of wind azimuth. The main reason would possibly be due to the fact that the rear taps were located in the area when the wind azimuth increased. Therefore, the intensity of turbulence would be magnified and the coefficient of fluctuating wind pressure would increase. Experimental results also showed that the coefficient of fluctuating wind pressure remained at the same value when the inclination of cantilever roof varied.(4) The computational methods for wind-induced response of long span cantilever roof were also studied in this study. The wind-induced responses include the mean wind-induced response and fluctuating response, while the latter response could be further divided into background and resonant component. As it is known, two types of structural systems are categorized for long-span cantilever roofs: main and sub-beam system and space truss system. The Load-Response-Correlation (LRC) method is adopted in this study to obtain the wind-induced response of long-span roofs. While the mean wind-induced response estimated by the common structural analysis method, the fluctuating wind-induced responses are obtained by the LRC method. By taking a long-span cantilever roof as an example, detailed study about its wind-induced response was conducted in this research work.( 5) Equivalent Static Wind Load (ESWL) for long-span roof was also investigated in this study. Several approaches to estimate the ESWL for long-span roofs, including gust wind load factor method, inertial wind load method, the method with the combination of background and resonant wind-induced component, the specific method proposed by Australia Wind Code, the time-history dynamic analysis method and LRC method, are studied comprehensively and compared with each other in this study. Finally, a simplified approach for estimating the ESWL of long-span cantilever roof was proposed in this study for engineering application purpose. The computational results obtained from this simplified method were compared with the results obtained from other mentioned approaches. It was found that that the proposed approach can be severed as a useful and effective tool for engineering application.