Bimodal Distribution Of Wind Pressure On Windward Side Of High-rise Building Induced By Interference Effects

With the development of economy and building technology,increasingly more high-rise buildings have been constructed than ever before,and curtain walls has also been widely utilized in such modern buildings.However,the curtain wall structures,especially the glazing walls,are vulnerable to strong wind,which challenges the maintenance of the curtain walls as well as the security of surrounding community.Therefore,it is of great significance to investigate the wind-resistant performance of curtain wall structures.Characteristics of wind pressure on the curtain walls are involved as prerequisite information for the wind-resistant design of these maintain structures.The thesis presents a detailed study on the wind-pressure characteristics for high-rise buildings,and has found a phenomenon of bimodal distribution of wind pressure acting on the windward side of a high-rise building interfered by an adjacent building.A systematic study via pressure-model wind tunnel test,particle-image-velocimetry(PIV)test and numerical simulation has been carried out to further analyze this phenomenon.A pressure-model test can be adopted to obtain the local wind pressure on buildings' surfaces,which directly serves for the wind-resistant design of curtain walls.Pressure signals are experimentally measured by a tube-transducer system which in practice can result in significant distortion-effects on the measurements.However,some issues remain unsolved in literature on the correction of pressure measurements.To this end,this thesis firstly proposes a novel method for accurate determination of the inner diameter(D)of pressure tubes and the inner volume(V)of pressure transducers involved in a tube-transducer system.The value of D is estimated first by measuring the weight of water filled in a tube.The value of V is then determined by fitting the measured frequency-response-function(FRF)with those predicted by the theoretical model.Results show that there can be a difference of as much as 6% between the nominal inner diameter and the real value of some pressure tubes.In addition,the inner volume of some transducers(e.g.,Honeywell)cannot be ignored.Based on such refined wind tunnel testing techniques,the wind pressure on the surface of a high-rise building is systematically studied,with a highlight on the bimodal probability distribution(BPD)of wind pressure acting on the windward side of the studied building.It is also found that the wind pressure involves both positive and negative components which alternate along time at a frequency that is consistent with the shedding frequency of upstream vortex.According to the above findings,a potential failure mechanism for the curtain walls and associated supporting structure under alternating load is proposed,and a mixed probability-density-function(PDF)model of wind pressure signal is established.These results provide a new way for evaluating the extreme values of non-Gaussian wind pressure signals,and also enrich greatly the mechanism for the wind-induced damage of curtain walls.Besides,the techniques of large eddy simulation(LES)and PIV test are used to further investigate the generation mechanism of BPD-featured wind pressure.Such techniques are able to provide detailed information of wind field in both time and space domains.The obtained results show that in conjunction with the background flow,vortexes shedding from the upstream building can distort the separation layers and the wind structure within the wake range.When wind flows with such complex structures act on the studied building,corresponding interference effects for the pressure on the building's windward facade become evident,which further results in the BPD phenomenon.In addition,results from PIV tests show that wind flow structures in the wake region downwind of the interference building are closely related to the building's orientation.Wake flow structures with the orientation of the interference building set as 45° are much more turbulent than those with an orientation of 0°.Detailed flow-field information through PIV tests at a high-sampling-frequency working mode facilitates to explore a complete process of the vortex structure,i.e.,from shedding to transporting/developing and then to dissipating.It is demonstrated that moderate development distance of shedding vortex can favors more severe influence of the vortexes on the facades of downstream building.Overall,the results illustrate that numerical simulation and PIV techniques have significant advantages in obtaining flow-field-information and in analyzing phenomena of complex flows.It is expected that the results presented in this thesis will promote current understanding of the wind pressure on buildings' facades and enrich the mechanism for wind-induced damage of curtain walls.The proposed wind tunnel testing techniques can also enhance the accuracy of wind tunnel testing results.