Study On Snow Load Interference Effects On Flat Roof Buildings

In recent years,snow-induced building structure collapses occurred frequently,leading to great economic losses.The design of snow loads on building structures has attracted much attention.The interference effects of buildings on snow load will cause significant changes in the snow distribution of the building area compared with that of the isolated condition.In the current snow load code of building structures in China,the roof snow load is specified only by the product of snow distribution coefficient and basic snow pressure.The influence of the interference effects of buildings on snow load is ignored,resulting in unreasonable value of snow load in the design of building structures.The previous research focused on building snow load on a single building,and few researchers studied the interference effects of buildings on snow load.To reasonably consider the snow distribution on the roof under interference effects of buildings,systematic research on the interference effects of buildings on snow load is imperative.This paper focuses on the snow load interference effects of flat roof buildings.The main research contents are as follows:(1)Establishment of numerical model of wind and snow movementEstablishing the numerical model of wind and snow movement is the premise of systematically studying the interference effects of flat roof buildings on snow load.The present transport of drifting snow density method and multiphase flow method can not ful y consider the movement processes of snow particles.To build a numerical model of wind and snow movement suitable for the study of the interference effects of buildings on snow load,based on the Eulerian model and by modifying the governing equation of snow phases,a set of bi-directional coupled wind snow motion numerical model suitable for the whole range of wind field conditions and considering the diffusion of snow particles is established,which considers the complex motion process of snow particles more comprehensively.The experimental and measured results show that the numerical model of wind and snow movement established in this paper can be used to study the interference effects of buildings on snow load.(2)Study on snow load on an isolated flat roof buildingThe research on snow load on an isolated flat roof building is the basic work of the research on the interference effects of flat roof buildings on snow load.Firstly,the sensitivity analysis of the key parameters of the numerical model is carried out,and the effects of parameters such as snow particle density,particle size,and snow particle settlement velocity on wind and snow movement are studied,to reasonably define the key parameters in the numerical simulation of snow load on building roofs.Secondly,the influence of different inflow conditions on snow distribution on an isolated flat roof building is evaluated,and the setting method of inflow boundary is clarified.Finally,on this basis,the snow distribution on an isolated flat roof building is studied,focusing on the influence of key factors such as wind velocity and parapet height.(3)Study on snow load interference effects of two flat roof buildingsBased on the combined wind and snow test system,the snowfall tests of two flat roof buildings are carried out,and the influence of the interfering building location is preliminarily discussed.Then,a series of numerical simulations are carried out to further discuss the influence of the interfering building location.Through the analysis of the interference coefficients,four typical interference modes of the interfering building on the snow load on the target building roof are obtained.Finally,the influence of the interfering building height on the snow distribution on the target building roof under the four typical modes is studied,and the influence law of interfering building height on snow load on the target building roof is clarified.(4)Study on interference effects of flat roof building groups on snow loadBased on the study of the snow load interference effect of two flat roof buildings,the snow load interference effect of flat roof building groups is discussed.Through the numerical simulations of the snow load on the building group under the conditions of different building arrangements and different building heights,the influence of the key factors such as building arrangement and building height on the snow distribution on each building in the building groups is clarified.It is pointed out that when the building spacing is less than the critical building spacing,the interference effects of the building groups on snow load can not be ignored.In this case,the interference of building groups to the wind field will lead to a significant increase in the total amount of snow on some buildings in the building groups.(5)Snow load design method considering building interference effectsThe purpose of studying the interference effects of buildings on snow load is to put forward the snow load design method considering the interference effects of buildings.Firstly,this paper compares the relevant provisions of snow load interference effects in national codes.Then,according to the research results of the interference effects of buildings on the snow load in this paper,the snow load design method considering the interference effects of buildings is put forward;Finally,several cases are used to verify the effectiveness of the design method.