Study On Numerical Simulation Approach Of Snowdrifts And Snow Load Characteristics On Long-span Roofs

China is a vast country with complex landforms.The snow area covers a large area of land.The dense occurrence of long-term snowfall weather would inevitably lead to snow-induced structural collapses,which directly endanger people's life and property safety.According to the accident investigation,the sudden increase of snowfall and the formation of local snow piled up under the action of airflow are the main reasons of such collapses.Due to the features of light weight,large area,complex shape and large proportion of snow load in the total loads,the long-span space structure is more sensitive to the snow load and should be paid more attention to.Unfortunately,the Chinese load code for building structure mainly provides the snow load patterns for the simple shaped roofs,and there are few provisions for the long-span space structures.To improve the load code of our country,this paper systematically analyzes the snowdrift characteristics on the long-span space structure roofs based on the numerical simulation method.The main contents are as follows:1.Snowdrift theory and the improvement of the numerical method.Two numerical methods(drifting snow method and multiphase flow method)have been put forward in the development of numerical simulation of snowdrifts.However,both methods could hardly reproduce the two-way coupling between snow and airflow as well as the nonequilibrium snow drifting process.Therefore,a non-equilibrium mixture model with drift and without drift is proposed based on a two-way coupling mixture model.In the case of drift,the variation of snow concentration in the saltation layer is considered by introducing a source term into the continuity equation of snow phase.It is proved that the revised model can effectively restore the development process of snow drifting under the non-equilibrium state.In the case of no drift,the continuity equation of snow phase and the deposition/erosion model are modified.Through comparison with the field measurements,it shows that the revised model can effectively reproduce the trajectory of the free-falling snow particles and the uneven distribution of snow on the building roof.2.Analysis of key parameters of snow drifting.Based on the non-equilibrium mixture models,the values of key parameters and their influence on snowdrifts are analyzed.In terms of snow particle density,ice density overstates the gravity effect of snow particles and overestimates the snow concentration near the ground.The snow particle density calculated based on the theory of random sphere pack can better predict the snow concentration value and snow distribution around the building.In terms of the viscosity of snow phase,it is proved by comparative analysis that the fluidized snow can be simplified to Newtonian fluid for simulation.The influence of the viscosity of snow phase on the flow and snow fields is limited by the snow concentration.In terms of wind speed,it is further proved that the improved model can effectively reproduce the "selfbalancing mechanism" of snow drifting through comparative analysis,and it is also pointed out that wind speed plays a decisive role in the snowdrift pattern.3.Snow loads on long-span spherical roofs.Firstly,the reliability of nonequilibrium mixture models in predicting the snow distribution on spherical roofs is verified by comparing with the experimental results.Then,through the simulation of snowdrifts under different wind speed conditions,uniform full-span snow load,uneven full-span snow load,and uneven half-span snow load on the leeward surface are obtained.Finally,the effects of the shape and the size of the roof on snowdrifts are determined by simulating the snow distribution with different rise/span ratios and spans.With the increase of the rise/span ratio,the uneven distribution of snow on the roof would be intensified.However,the mean and peak snow loads would be smaller.With the increase of the span,the uneven distribution of snow on the roof would be weakened.However,the mean and peak snow loads would be larger.4.Snow loads on multi-span arch roofs.Firstly,the prediction accuracy of the numerical simulation method for snow distributions on multi-span arch roofs is confirmed by comparing with the experimental results.Then,through the simulation of snowdrifts under different rise/span ratio and span number conditions,the formation mechanism of snow distributions on multi-span arch roofs is analyzed.Finally,through the investigation of snow distributions on different multi-span arch roofs,the snow load pattern on the arch roof with or without obstructions is obtained.The snow load formed at the trough and the snow load characteristics on multi-span arch roofs are clarified.