Study Of Wind-induced Responses Of A Super-tall Building Based On Structural Health Monitoring

Super-tall buildings are generally featured with low weight,high flexibility,low nature frequency and low damping ratio as structural height increases.It is worth noting that the natural frequency of super-tall building approximates to the main frequency of fluctuating winds in typhoon events,which may lead to significant wind-induced structural responses under the attack of typhoons.Therefore,it is of great importance to conduct relevant studies with particular interests on monitoring of the dynamic responses of super-tall buildings during the passage of typhoons and investigating the wind-induced responses and dynamic characteristics of super-tall buildings.The studies addressed in this dissertation were carried out based on Shenzhen Ping An Finance Center(PAFC),which is currently the second tallest building in China and the fourth tallest building across the world.An integrated structural health monitoring(SHM)system was established in PAFC,and full-scale measurements of PAFC during the passage of typhoon Nida and typhoon Haima were carried out.Emphases were placed on the analysis of wind field characteristics,wind pressures on cladding,as well as the acceleration responses and strain responses of PAFC.Details of these studies are summarized as follows:(1)The wind field structure of typhoon Nida and its associated characteristics were examined using the wind measurement data obtained from Doppler radar wind profiler and surface meteorological stations.The existence of pronounced low-level jet feature was observed in the vertical profile of horizontal wind speed as the eye-wall approached.The height where low-level jet occurs was a function of topographic effect.whereas the wind speed at the gradient height was hardly affected by the topography.The heavy rainfall associated with the passage of rain-band in typhoon event will cause a sharp decrease in air temperature,which consequently leads to the temperature difference between the inside and outside of the structure.This is responsible to the development of moment and shear force in the connect components.(2)The wind pressures on structural cladding during the passage of two typhoons were analyzed,in which the magnitude and position of peak pressures on the front and corner were identified.During the period of typhoon Nida,both the peak negative and positive wind pressures occurred during the approach of the second eye-wall.During the period of typhoon Haima,it was found that the value of peak negative pressure obtained at the corner was somewhat lower than that at the front,which indicates that wind-induced damage is more likely to occur in the corner other than the front.Meanwhile,the non-Gaussian properties of cladding pressures were examined.The results reveal that the non-Gaussianity of negative pressure tends to strengthen with increasing negative wind pressure amplitude.Nevertheless,such a phenomenon is rarely observed associated with positive wind pressures.In addition,the frequency of vortex shedding and the Strouhal Number were determined based on field measurement data and the results were further compared with those derived from wind tunnel tests,which demonstrated good agreements.(3)The acceleration responses of the structure measured during the two typhoon events were applied to identify the modal parameters including the natural frequency,damping ratio and mode of the structure.The results of natural frequency were consistent with those obtain from finite element method.The first three swaying mode shapes and the first two torsional mode shapes were derived from full-scale measurements and compared with the results from finite element method.It was shown that the first two swaying mode shapes and the first torsional mode shape from these two methods matched well,whereas other concerned mode shapes characterized minor deviations.(4)The dependence of natural frequency and damping ratio on response amplitude were investigated.The relationship between natural frequency/damping ratio and normalized amplitude was identified.It was revealed that the variation of damping ratio with increasing amplitude has a trend of constant-increase-decrease-increase,while the natural frequency of the first swaying mode in north-south direction was found to decrease as the amplitude increases.The variation in east-west direction,on the other hand,was less distinct.The mutual verification associated with the correlation of the modal parameters with response amplitude and the structural mode shapes could further indicates their accuracy.(5)The strain responses of PAFC during typhoon Nida were estimated,which showed that the sharp decrease in air temperature accompanied with the passage of typhoon can cause the change of structural strain.Likewise,the serviceability was evaluated as well.The acceleration response of the structure during typhoon was smaller than the threshold acceleration,which therefore satisfies the specification requirement.To sum up,this dissertation mainly deals with the structural health monitoring and wind-induced responses of the super-tall building,PAFC.The outcomes are expected to provide valuable insight and information for engineers and researchers in the relevant areas.