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• A soil-large pile group-supertall building model (SSI model) is proposed. • The wind-induced responses of SSI models are computed and parametrically analyzed. • Empirical equations of SSI factors are developed for wind-induced responses. A simplified three-dimensional soil-structural interaction (SSI) model is established for large pile groups-supertall buildings (>300 m height) to simulate the dynamic response of the building to wind loading. The displacement and acceleration responses to wind loading at the top of the supertall building are calculated using the established model. The effects of SSI on the wind-induced mean displacement, root-mean-square (RMS) displacement and RMS acceleration are analyzed considering different values of soil shear wave velocity and material damping, and different total mass, first natural frequency and damping ratio of the superstructure as well as different terrain conditions. The results from the comprehensive parametric study are used to derive empirical equations of the mean displacement, RMS displacement and RMS acceleration SSI factors. The findings demonstrate that the mean displacement of the top of supertall building increases considering SSI. As the soil shear wave velocity decreases, the mean displacement SSI factor increases. It was also found that the mean displacement SSI factor increases with the increase in total mass and first natural frequency of the superstructure. In addition, the RMS displacement and acceleration SSI factors decrease with the increase of the soil shear wave velocity and material damping. Finally, the RMS displacement and acceleration SSI factors increase as the superstructure first damping ratio increases. [ABSTRACT FROM AUTHOR]

Snow saltation is governed by the shear stress from wind on the snow surface, in form of the friction velocity. In most previous studies, the friction velocity was measured or estimated by wind velocity at a certain height using the log law, which is suitable for the fully developed wind field of an open area. However, the applicability of such method to roofs has not been tested. In this study, Large Eddy Simulation (LES) of wind flow around a flat roof was performed to study the flow field characteristics above a flat roof and the results were compared with those from the wind tunnel measurement. Owing to the flow separation and the reversed flow above the roof, the log law is observed to exist only on the leeward part of the roof; therefore, measurement based on the log law is not universally suitable to estimate the friction velocity on roofs. The comparison of the simulation results against experimental data shows that LES reasonably reproduces the flow field around the roof and can be an alternative approach to estimate the friction velocity on building roofs. The fluctuating friction velocity is found to be unneglectable compared with the mean friction velocity and should be considered in the estimation of the snow transport on roofs. [ABSTRACT FROM AUTHOR]

In this paper, wind tunnel tests and CFD (Computational Fluid Dynamics) simulations are conducted to measure and simulate the near-roof wind speed and friction velocity on gable roofs. By comparing the results of Irwin sensor wind tunnel tests with CFD simulations of different turbulence models, it is found that the Realizable k - ε turbulence model performs better. The CFD simulations and wind tunnel tests show that the mean near-roof wind speed and the mean friction velocity on the windward and leeward gable roofs have the same variation trend with the slope. Moreover, the mean near-roof wind speed and the mean friction velocity reach the maximum on the windward roof when the slope is 20°, the mean wind speed and the mean friction velocity on the leeward roof decrease with the increase of the slope. Finally, based on the snow transport rate on the windward roof with different slopes, it can be obtained that the snow transport rate on the windward gable roof with 20° is the largest among the four slopes selected in this paper. Meanwhile, when the roof slope is 20°, it is most likely to lead to the unbalanced snow load on the windward side and leeward side. • The wind speed and friction velocity on roof surface are obtained by wind tunnel test and CFD simulation. • The influence of slope on roof wind speed and friction velocity is analyzed. • The effect of slope on snow transport rate and unbalanced snow load on the roof is studied. [ABSTRACT FROM AUTHOR]

A numerical model based on Lagrangian description is developed in this study to predict wind-induced snow drifting on flat roofs, which fully considers the key physical processes of snow particle saltation. A scaled experiment of snow redistributions on the model roof was carried out in the wind tunnel for the verification and evaluation of different numerical methods selected from related literature. The optimal model is determined by comparing the predicted transport rate on the roof with estimations from empirical formulas and by comparing simulated snow distributions with experimental data. Characteristics of the saltation layer above the flat roof surface are then presented in detail based on the developed model. The rebound particles account for approximately 60% of the total transported particles above the roof, indicating the dominant role of rebound in the lift-off process for saltating snow particles. The developing snow transport along the roof span leads to the increase of surface erosion flux caused by the splash entrainment with downwind distance. The splash entrainment could thus contribute considerably to unsaturated snow transport on the flat roof, which is also found to be influenced by the approaching wind velocity and threshold friction velocity to varying degrees. • A numerical model is developed using the Lagrangian approach to investigate the mechanisms of snow drifting on flat roofs. • A scaled experiment of snow redistributions on flat roof is conducted in the wind tunnel to evaluate the simulated results. • Characteristics of the saltation layer above the flat roof are presented based on the developed model. • The role of splash entrainment and its contribution to unsaturated snow transport on flat roofs are preliminarily explored. [ABSTRACT FROM AUTHOR]

This paper introduces a novel snow transport model for the analytical simulation of wind-induced snow transport on flat roofs. In the novel model, the differences between precipitation and deposited snow particles on roofs, including the differences in threshold friction velocity and fetch distance for saturated drifting state, are considered. Thus, snow drifting on a roof is divided into drifting without and during snowfall. The effects of terrain category and roof height are also considered using the friction velocity on roofs to compute snow transport rate instead of directly using the wind speed data reported by weather stations. Parametric analysis and case study are conducted to explain the novel model in detail and compare the results with those obtained from the model developed by O'Rourke et al. (2005). The estimated fetch distance for saturated snow drifting by the proposed approach in this study ranges from zero to thousands of meters, which is consistent with field measurement results and more reasonable than the use of constant values. Results of the case study indicate that the proposed snow transport model might be more reasonable because the effects of more factors are considered. • A novel snow transport model considering the effects of wind exposure on snow load is introduced. • Snow drifting is divided into drifting without snowfall and drifting during snowfall. • Methods for estimating fetch distance for saturated drifting are developed. • Impacts of terrain and roof height are taken into consideration. [ABSTRACT FROM AUTHOR]

In cold and snowy regions, roof slopes can affect the snow distribution on the gable roof. The finite area element (FAE) method is modified by considering the effect of the snow transport rate, the developmental law of snow transport and the saturated transport distance on the calculation of drifting snow load in this paper. Saltation and suspension of snow transport are also considered respectively in the process of modification. Then, based on the modified FAE method and computational fluid dynamics (CFD), the influence of roof slopes (10°, 20°, 30° and 40°) on the gable roof snow distribution is studied. Meanwhile, for compare the simulation results of the modified FAE method with different combinations of the snow transport rate, the developmental law of snow transport and the saturated transport distance, the test of wind-blown snow redistribution is completed in the wind tunnel using the substitute particles (silica sand) on the scaled gable roofs. The results show that when the saturated transport distance of snow is 210 m, the modified FAE method can reproduce the snowdrift phenomenon on the gable roof more reasonably if adopting the snow transport rate proposed by Owen (1964) and the developmental law of snow transport suggested by O'Rourke et al. (2005) at the same time. Through CFD simulation, it's discovered that the distribution of flow field around the gable roof and friction velocity on snow surface change noticeably with roof slopes, resulting in the increase of the upwind erosion flux and the leeward deposition flux with the incoming wind speed and the roof slope. In addition, when the incoming wind speed remains unchanged, simulation results using the modified FAE method show that the larger slope of the gable roof, the more likely it is to cause the uneven distribution of snow load on the windward and leeward roofs. Moreover, fresh snow is more likely to cause the uneven distribution of snow load on gable roofs than aged snow through analysis sensitivity of the threshold friction velocity. • The FAE method is modified based on the development process of snow transport and CFD simulation. • The modified FAE method is validated through wind tunnel tests. • The snow distribution on gable roofs is simulated using the modified FAE method. • The influence of slope on the snowdrift load coefficient is analyzed though the characteristics of snow distribution. [ABSTRACT FROM AUTHOR]

Abstract A series of 2D steady RANS CFD simulations are conducted in this study to investigate the impact of roof slope on the snow redistribution on gable roofs. A small value of turbulent Schmidt number, which is calibrated by trapping efficiency from experiments, is adopted to enhance the snow particles' turbulent diffusion in the CFD simulations for snow phase. And a scaled model test is conducted in the wind tunnel to validate the accuracy of numerical simulation, in which the silica sand was used to model snow particles. To uncover the mechanism of wind effects on the snow redistribution on gable roofs, the simulation results of wind-flow patterns, wall friction velocity of the roof surface, snow concentration and snow distributions are analyzed in detail for various roof slopes (5°–60°). Based on the features of wind-flow patterns and distribution patterns of snow, the gable roofs are classified into two categories: low slope where flow separates strongly at the leading edge and high slope where flow separates strongly at the roof ridge. The critical roof slope is between 20° and 25°. Highlights • A series of 2D steady RANS CFD simulations are conducted for snow redistribution on gable roofs. • CFD simulation results of snow redistribution are validated by scaled model experiments. • The impact of roof slope on the snow redistributions for gable roofs is explored. • Simulation results of flow filed, friction velocity, snow concentration and snow redistributions are analyzed in detail. [ABSTRACT FROM AUTHOR]

Roof slopes would have a great impact on snow drifting on roofs. The existing Eulerian-Lagrangian model is not suitable for simulations of snow drifting on gable roofs. This study improves the Eulerian-Lagrangian snow drifting model by modifying the threshold friction velocity and the splash functions to fully consider the impact of the roof slope. To evaluate the rationality of the improved model, scaled tests of snow redistributions on gable roofs were conducted in a wind tunnel. The improved model is demonstrated to perform better on the prediction of snow redistributions on gable roofs. Characteristics of snow drifting on gable roofs with different slopes are investigated in terms of flow pattern, particle motion and snow transport. For roofs with different slopes, features of particle motion near the snow bed show significant differences, which are reflected in the spatial distribution, the saltation height and the impact velocity of snow particles. Snow erosion occurs on the windward roof at each slope, and it also occurs on the leeward side at the slope of 5° or 10°. However, on the entire leeward surface at the slope of 15° and near the ridge at the slope of 20°, snow deposition would occur. • An Eulerian-Lagrangian snow drifting model for gable roofs considering the effect of roof slope is established. • Scaled wind tunnel tests of snow redistributions on gable roofs were conducted to evaluate the rationality of the model. • Features of particle motion close to the roof surface are revealed through the analyses of the simulated results. • Characteristics of snow erosion/deposition flux and snow transport rate on gable roofs are discussed. [ABSTRACT FROM AUTHOR]

The insight into the influences of roof slope on the characteristics of snow drifting on monoslope roofs during snowfall is still inadequate so far. Scaled tests of snow drifting on monoslope roofs with varying slopes (0° to 25°) were thus carried out in a wind tunnel equipped with a snowfall simulator, employing silica sand particles to model the snow precipitation environment. Typical snowdrift patterns on monoslope roofs were summarized, and elaborations were provided on the variation for the characteristics of snow drifting with roof slope. Similar features in terms of particle distributions, transport rate, and degree of erosion are observed for lower-sloped roofs (0°, 5°, and 10°), which all differ from those on higher-sloped roofs (15°, 20°, and 25°). The difference caused by the variation of approaching wind velocity on particle erosion is found to be more pronounced compared with that of snowfall intensity, and the increase in the degree of erosion with snowfall intensity can be reasonably represented by the linear relationship. The flow pattern around the roof and surface friction velocity before (without snow) and after snowfall (with snow cover) were then explored via numerical simulation for different roof slopes. Based on the simulated flow characteristics, the mechanisms of snow drifting on the sloped roofs under snowfall were further discussed. • Scaled tests of snow drifting on monoslope roofs with the concurrence of snowfall are conducted in a wind tunnel. • Effects of the approaching wind velocity and snowfall intensity on the characteristics of snow drifting are discussed. • Flow pattern around the roof and surface friction velocity before and after snowfall are explored via numerical simulation. • Typical snow distribution patterns on monoslope roofs with different slopes are presented. [ABSTRACT FROM AUTHOR]

Snow redistribution caused by snowdrift may worsen the traffic condition of bridge decks in snowy regions, hence it needs to be considered in bridge designs. In this study, a quasi-steady numerical method is adopted to simulate snowdrift on a typical bridge deck with barriers. The whole process of snowdrift on bridge decks is divided into several phases to simulate the variation in profile of snowpack, and a two-dimensional (2D) steady Computational Fluid Dynamics (CFD) simulation method is employed in each phase. To investigate the effect of barriers on the snow redistribution on bridge decks, the simulation results of wind velocity field, wall friction velocity, snow concentration field and snow redistributions are analyzed in detail. Generally, as the barrier porosity decreases, the total amount of snow erosion decreases due to the blocking effect of the barrier, but the decrease is limited when the barrier porosity is below 37.5%. Heavy snow accumulation mainly occurs behind the windward barrier when the barrier porosity is below 62.5%. To avoid snow accumulation, barrier porosity above 75% is suggested as the optimal choice for improving the traffic condition of bridge decks. • Snowdrift on a typical bridge deck with porous barriers using CFD method is simulated. • The effects of barriers with different porosities on the snow redistribution on the bridge deck are analyzed. • The optimal suggestion for design of the barrier porosity is presented. [ABSTRACT FROM AUTHOR]