Research On Combined Wind And Snow Test System And Snow Distribution On Roofs

Snow disaster is one of the main disasters in nature,which would severely affect transportation,energy,animal husbandry,construction and many other industries and bring serious impact on the production and life of human society.In recent years,with the global climate change intensifying,snow disaster with extreme low temperature has frequently occurred.The collapses of buildings and structures caused by snow accumulation have also increased,which have caused significant loss of life and property to people.Through a lot of post-disaster investigations all around the world,it was found that the unbalanced snow distribution on roofs caused by the motion of snow particles is one of the main reasons for collapses of buildings.The combined wind and snow test is one of the main research methods of snow distribution.It is currently the most reliable and feasible research method to study snow distribution and has the advantages of high reproduction,controllable parameters,strong repeatability,and the ability to study the mechanism of snow distribution.However,at present,the combined wind and snow test is still in its infancy,the test methods need to be studied and improved.There are few related studies on the snow distribution on different types of building roofs and the study on snow distribution on building roofs is of great significant for the design of buildings and revision of snow load codes in China.Based on the above background,this paper took the combined wind and snow test method as the main research point and conducted a series of research on the similarity criterion and snow distribution on the typical building roofs,the main research contents and results were as follows:(1)Design of the outdoor large-scale combined wind and snow test system based on snowing modeA combined wind and snow test method using snowing mode was proposed,and the climatic characteristics of snowy winter and long-term low-temperature environment in Harbin were fully used to develop and firstly design an outdoor large-scale combined wind and snow test system based on vibration-sowing snowing mode which can use stored natural snow and artificial snow particles.The key parameters such as the wind field and snow field at the test section were calibrated,and then representative standard cube model,high-span roof and arched roof were selected to conduct a series of snow distribution tests.The repeated experiments on snow distribution around the standard cube model and on stepped roof and arched roof validated the repeatability of the test system And according to the results of the whole process reproduction test of the field observation of snow distribution around the cube,it was proved that the test system developed in this paper meets the accuracy and reliability requirements of the experimental research.(2)Research on similarity criteria for combined wind and snow test based on snowing modeThe differences between the physical processes of natural snow ing and blowing snow from the ground were analyzed,and the calculation method of snow mass flux in snowing mode was proposed and the concept of snowfall rate was introduced.The classical similarity theories of combined wind and snow tests are summarized,and based on the similarity of saltation trajectory of particles,similarity of state of snow accumulation per unit time and similarity of shape of snowpack,the basic similarity criterion of the combined wind and snow test based on the snowing mode was derived and verified.The accuracy was verified by the multi-dimensional scale test of the standard cube model,and then a revised Froude Number similarity parameter based on the lower limit value of the friction speed ratio was proposed.Through the multi-dimensional scale test,the accuracy of the revised similar parameters was proved.In addition,through comparison of scale reproduction tests of the prototypes of cube and stepped roof models and the pre-paving tests conducted by other scholars,the advancement and accuracy of the test method and similar parameters proposed in this paper were proved.Finally,the minimum feature dimensions of plane-type and curved-type roof models were confirmed through multi-scale model tests.(3)Research on the snow distribution around the building and on the typical plane-type roofsBased on the combined wind and snow test method using snowing mode,the snow distribution around buildings was studied using a standard cube model with a side length of 0.5m.The effects of wind speeds and wind angles on the surrounding snow distribution around model were analyzed.The mechanism of snow distribution around the cube was obtained,and the characteristic of snow distribution around the cube were obtained.And through the characteristics of snow distribution around two adjacent cubes were studied,it was found that the snow distribution around two adjacent cubes can be regarded as the spatial superposition of the snow distribution around two single cubes.The snow distributions on gable roofs,stepped roofs,continuous multi-span gable roofs and continuous multi-span single slope roofs were studied.The effects of wind speed,wind angles and shape parameters of roofs on the snow distribution on different kinds of roofs were analyzed.The mechanism and characteristic patterns of snow distribution on the four different kinds of roofs were obtained,combined with the analysis of results of field observation and numerical simulation,and suggestions for the snow resistance design of building roofs and the revision of China’s current load codes were provided.(4)Research on the snow distribution on the curved-type roofsThe snow distributions on arched roofs,single concave roofs,continuous multi-span arched roofs and spherical roofs were studied based on the wind and snow combined test method using snowing mode.The effects of wind speed and shape parameters of roofs on the snow distribution on different kinds of roofs were analyzed.The mechanism and characteristic patterns of snow distribution on the four different kinds of roofs were obtained,combined with the analysis of results of field observation and numerical simulation,basic data bases for snow resistance design of building roof and revision of China’s current load code were provided.Taking a long-span M-type coal storage warehouse in He Nan Province as an example,the experimental study of snow loads distribution on a large-span building roof was carried out.Experiments under twelve different wind directions were investigated.A calculation method for the cumulative snow load distribution coefficients on the roof based on the weighting of each dominant wind direction is proposed.The cumulative snow load distribution coefficients of different areas on the roof was obtained,which provided the basis for the snow resistance design of the construction project.