Wind Loads And Wind-Induced Responses Of Tall Buildings

With the application of light and high-strength materials, modern tall buildingsare developing to be increasingly higher and more flexible, which has made thefundamental frequency of such structures reduce to be close to the predominantfrequency of wind. The decrease of damping ratios of tall buildings makes thestructure more and more sensitive to wind loads. Thus, wind loading has become oneof the main control loads of tall buildings. In addition, the glass curtain walls of manytall buildings are often damaged by strong winds, which is a great danger to publicsecurity. Therefore, it is necessary to make more in-depth studies on the wind effectsand wind-induced responses of tall buildings.Based on wind tunnel test results of a tall building, this study investigates thewind pressure distributions on the tall building. The results show that the downstreamsurrounding buildings made the along-wind loads on the principal building increasewhile such effect on the cross-wind or torsional-wind loads is negligible. While thesurrounding buildings are arranged side-by-side, due to the channeling effects, themean negative pressures of several locations can be risen to four-fold. But for theoverall structure, the inertial wind loading caused by fluctuating wind actions reduces.Through studies on the power spectra of along-wind loads, cross-wind loads andtorsional loads on each storey, it has been concluded that what mainly affect thevortex shedding are the wind speed, turbulence intensity and windward area. Thefrequency of vortex shedding becomes higher and the high-frequency energy becomesmore significant when the wind speed increases. The bandwidth of spectrum becomeswider and the energy decreases when turbulence intensity increases. And the biggerthe windward area is, the stronger the phenomenon of vortex shedding becomes.This study, through a calculation of the wind-induced responses of high modes ofthe tall building, shows that the1st-order mode dominates the responses ofdisplacement and the higher mode effects can be ignored. But in terms of theresponses of acceleration, higher modes must be taken into account. Anunderestimation of the peak acceleration up to24%is observed, when only the1st-oder mode is considered. As for tall buildings which are sensitive to winds, it isadvisable to take the2nd-order mode and even3rd-to-4th mode for calculating theresponses of acceleration. The calculating formula of dynamic amplify coefficient specified in the Load Code of China is discussed, and the comparison of the resultsbetween the old and new codes is made. In addition, the dynamic amplify coefficienthas also been calculated base on the wind tunnel test results. As the maximumshearing force under each wind direction in the wind tunnel test includes bothalong-wind loads and cross-wind loads, the coefficient is bigger than that in the codeswhich considers only the along-wind loads.Through calculating the design wind pressures acting on the glass curtain wallsof the tall building on the basis of the Load Code2001,2012of China and AIJ2004respectively, and then the results are compared with those from wind tunnel test. Itcan be found that the results calculated by the codes are not rational. Based on thecross-section shape and combined with the data obtained from the wind tunnel testand AIJ2004, this study makes a several section in the negative pressure sections ofthe building curtain walls and takes the minimum value of each section for the designvalue. Compared with studies based on taking a minimum value on every storey, themethod proposed in this study is more rational. The probability distribution of eachcritical point are analyzed and a fitting of the probability density function of eachpoint is also made. It is concluded that the probability of those maximum pressures ateach storey are close to Gaussian distribution, while the distribution of minimumpressures generally fellow weibull distribution. The probability method has beenadopted to modify peak factors so that the design wind pressures on glass curtainwalls are more accurate.This thesis studies the wind loads and wind-induced responses of a tall buildingmainly based on the wind tunnel test and also combining with theoretical analysis anddesign Codes, aiming to further our understanding of wind effects on tall buildingsand to apply that knowledge to design.