Experimental Investigation Of Blockage Effects On Wind Forces And Wind-induced Responses Of Rectangular High-rise Buildings

Wind tunnel test is a common and useful method to study wind loads on building structures.Blockage effect is a common problem in wind tunnel tests.When the blockage ratio of testing models is large,the blockage effect will interfere with the flow near the testing models,resulting in the distortion of the experimental results.The present research situation at home and abroad shows that there is little research on the blockage effect on building structures,and the mechanism of blockage effect is not clear,and the blockage correction formula which is effective and widely applicable is less.In order to explore the action rule of the blockage effect and establish a modified model of the blockage effect in wind tunnel test of rectangular high-rise buildings,adopting a set of standard high-rise building models,which have blockage ratio of 1.7%,3.1%,4.5%,6.3%,8.6% and 10.9%,respectively,multipoint synchronous pressure measurement was carried out in smooth flow and in grid turbulent flow respectively.The influence of the blockage effect on wind loads and wind-induced responses of rectangular high-rise buildings under different wind fields was studied.The results show that in uniform turbulent flow,when blockage ratio is less than 4.5%,the blockage effect has little influence on the wind loads and wind-induced responses of rectangular high-rise buildings,so it can be ignored.When blockage ratio is greater than 4.5%,the blockage effect has different effects on the wind loads and wind-induced responses of rectangular high-rise buildings,so the test results should be modified by the blockage correction.In smooth flow,when the model block ratio greater than 4.5%,with the increase of the blockage ratio,the mean wind force coefficients,the fluctuating wind coefficients and the fluctuating base moment coefficients increase significantly;the special peaks appear in power spectra of fluctuating drag coefficients at frequency which is about twice of the Strouhal number,which may lead to the unexpected vibration in along-wind;the peak values of power spectra for fluctuating lift and torque coefficients increase first and then decrease slightly,meanwhile the Strouhal number increases gradually.The blockage effect on frequency domain characteristics of the fluctuating base moment coefficients are similar to that of the corresponding fluctuating local wind force.Under half height of the building,the vertical correlation and coherence of fluctuating drag coefficients of each layer increase but decrease above half height of the building and between building top and bottom;The vertical correlation and coherence of fluctuating lift and torque coefficients of each layer increase;The top displacement,acceleration,mean wind loads and inertial wind loads of the high-rise building increase.In the grid turbulence flow,compared with the results in smooth flow,due to the increase of the turbulence intensity,the influence of the blockage effect on wind loads and windinduced responses of the high-rise building was weakened in different degrees.Based on the test results,correction formulas for the blockage effect on wind loads and wind-induced responses of the rectangular high-rise building have been proposed,which have a effective correction and can also be applied to the blockage correction of equivalent static wind loads.