Influence Of Architectural Facades On Wind Loads Of Tall Buildings

With the demand for architectural aesthetics and functions,architectural facades including balconies,mullions,shading board and other ribs are widely used outside of the tall building.Obviously,these facades of tall building will greatly affect the wind pressure distribution on the building surface,resulting in a different local wind pressure from that on the building without facades.In addition,the facades may also change the aerodynamic forces of tall building,such as story forces,base moments and base shear forces.Building codes provide provisions for building cladding design,which are mainly derived from wind tunnel experiments for buildings without facades.Therefore,in fact,the wind pressures and aerodynamic forces of tall building with facades cannot be directly obtained by building codes.However,the facades of the building are usually ignored during the experiments because of the difficulties of being simulated,and the wind loads on the facade itself is also of concern.As a result,it is very necessary to systematically study the wind loads of tall building with architectural facades.Based on the wind tunnel experiments,the effects of different building facades on the local wind pressure and aerodynamic forces of tall building are systematically studied,and the wind loads on the facade itself are also analyzed.The effects of horizontal and vertical facade on local and total wind loads of tall buildings are obtained,and the wind loads characteristics of the facade itself are verified.Then the LES numerical computations are carried out to simulate the wind loads of the tall building with facades,and the action mechanism of different building facades is analyzed in detail,and the local shape coefficient of architectural facades is quantified.The difference of the development process of two kinds of conical vortices on tall buildings with different facades is proved,and the influence mechanism of different facades on the wind loads of tall buildings is summarized,and the variation rule of local shape coefficient of facade is obtained.Finally,the genetic algorithm is used to optimize the vertical facades and the optimal vertical facade parameters are obtained.The main work of this study is arranged as follows:Firstly,in order to study the effect of architectural facade on the local wind pressure of tall building,a series of multiple point synchronous pressure measurement wind tunnel experiments were carried out to systematically analyze the effect.Existing studies have not considered the situation of architectural facade on four surfaces of typical tall buildings,or have not studied the distribution law of local wind pressure and the influence rule of different types of architectural facade on local wind pressure,and have not analyzed and compared the wind loads of architectural facade itself.Therefore,the effects of different types of architectural facade with different sizes on the mean wind pressure,RMS values of wind pressure,and peak wind pressures of the tall buildings were systematically,qualitatively and quantitatively analyzed.The horizontal facade has little influence on the distribution of mean and RMS values of wind pressures on the surface of tall building except that it leads to the more uniform distribution of the wind pressure.And the vertical facade results in the noticeably larger wind pressure gradient and has significant influence on these wind pressures.The largest suction(minimum wind pressure)decreases with the increase extensional depth of horizontal facades,and the suction increases with the larger extensional depth of vertical facades and the relative difference is up to 25.8%.Furthermore,the peak wind pressures on the facade itself were analyzed and compared with that on the surface of tall buildings,which revealed that the existence of facade can reduce the local wind pressure on the building surface to varying degrees,but the greater local wind pressure can be found on the facade itself.Secondly,in order to study the effect of architectural facades on the aerodynamic forces of tall buildings,a series of high-frequency force balance(HFFB)experiments for tall buildings were carried out.Existing study have only analyzed the aerodynamics of an actual tall building with vertical facades,and the conclusions obtained are not typical,and the effects of different types of facade have not been considered.Combined with the pressure data,the difference of the mean base shear force obtained by the two wind tunnel experiments is analyzed.The mean base shear force obtained by the HFFB or CFD is smaller than that obtained by the pressure measurement for the model with vertical facades and the largest relative difference reaches about 7.1%.This means that the mean base shear force obtained by the pressure measurement is conservative for the models with vertical facades.Furthermore,the effect of different types of architectural facade with different sizes on the overall force and story force of tall buildings,and the wind force of the vertical facade itself are studied.Compared with the model with smooth surfaces,the mean base shear force and base moment for the model with horizontal facades decrease slightly.These forces for the model with vertical facades are noticeably smaller than those of the model with smooth surfaces.In addition,the existence of architectural facades leads to the increase of RMS value of aerodynamic forces.The wind tunnel experiments can reveal the influence rule of facade on the wind load of tall buildings,but no scholars have studied the influence mechanism,so an in-depth exploration of the influence mechanism is conducted by means of CFD.In order to establish a more reasonable numerical wind tunnel,a reasonable inlet turbulence generation technology of LES called CDRFG method is introduced.Based on LES-CDRFG,the reasonable computational domain size of numerical wind tunnel is explored.And this numerical wind tunnel is used to compute the wind loads of tall building with architectural facades and analyzes the wind pressure,the iso-surface of wind pressure,aerodynamic forces and the flow field around the model.The mechanism analysis of the wind loads on the tall building with architectural facades is carried out to deeply explore the effect of architectural facades on wind loads on tall buildings.The difference of the development process of two kinds of conical vortices on tall buildings with different facades is proved,and the influence mechanism of different facades on the wind loads of tall buildings is summarized.In addition,the local shape coefficients of facades are quantified by three-dimensional LES data to provide a reference for engineering design compared with the building codes.Finally,based on the genetic optimization algorithm,the CFD simulation data and BP neural network are used to optimize the aerodynamic drag and lift of tall building with vertical facades.Because the calculation of the LES numerical simulations under the three-dimensional atmospheric boundary layer is too large,the drag and lift are calculated by using the 3D LES of two-dimensional flow.And the comparison shows that the 3D LES of two-dimensional flow can represent the simulated values of the LES numerical simulations under the three-dimensional atmospheric boundary layer.Then these drags and lifts are used to train the BP neural network.Finally,the trained BP neural network is used as the objective function for the genetic algorithm optimization process and the optimization results are verified by the LES numerical simulations under the three-dimensional atmospheric boundary layer.The results show that the optimization for vertical facades is very effective,and the optimal vertical facade parameters are obtained.