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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]

An appropriate probabilistic description of snow loads is important in reliability analysis. Probability distributions for annual maximum ground snow loads are studied in detail in this paper based on the samples of snow loads on the ground, which are simulated by a snowmelt model. Then, selection of probability distribution function and parameter estimation method for ground snow loads is found to have a great influence on reliability assessment results. The reliability of members of steel roof structures subjected to snow load at four representative sites in China is investigated. The reliability indices of studied roofs are found not to be enough to reach the target value 3.2. The possible reason is that characteristic value of snow loads on the ground specified in Chinese load code is not conservative and the partial factor 1.4 for snow loads on roofs is not enough. To ensure designed roofs subjected to extreme snow loads a target reliability index 3.2, large partial factors for snow load that varies with COV of ground snow loads are expected to be used. [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]

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]

Predicting structural responses under joint action of wind and snow loads is important in ensuring the safety of lightweight roof structures in snowy regions. In this paper, a series of similarity parameters that should be satisfied in the wind tunnel test to simulate structural responses under joint action of wind and snow loads are proposed from the perspective of similarity of wind field, particle movement, flow around the building, and structural dynamics. Then, with a double-pitched roof structure as research object, an aeroelastic model test with substituted snow particles is designed and structural responses are obtained through the wind tunnel test. The other two types of tests, namely, aeroelastic model test with additional weights and pressure measurement test, are also conducted; their results are compared with those of the aeroelastic model test with substituted snow particles. The mean and RMS response of the other two types of tests are both significantly lower than those of the aeroelastic model test with substituted snow particles. The preliminary conclusion is that wind-induced structural vibration is influenced by snowdrift and possible asynchronous vibration of the particle layer and roof structure, which could lead to a considerable increase in structural dynamic responses. [ABSTRACT FROM AUTHOR]

In regions prone to heavy snowfall, an accurate estimation of snow redistribution on roofs under the action of wind is vital for structural engineers. The content of unbalanced snow loads of flat roofs caused by snow transport is indispensable in current load codes/standards. Hence, the wind tunnel tests were performed to investigate the redistribution of snow on flat roofs, in which high-density silica sand was used. The characteristics of snow redistribution on flat roofs are discussed, and common features are pointed out. The largest snow depth usually occurs near the windward region, and for a large-span flat roof the peak point could also occur in the rear region of the roof. In addition the locations of peak points after snow redistribution and the influence of wind velocity, wind duration and roof span on transport rates and mass fluxes are analyzed in detail. The transport rate increases as wind velocity or roof span increases but it is not a simple proportional relationship with roof span. Moreover, the transport efficiency of particles declines as wind duration becomes longer. Mass flux of the entire roof, which is the transport rate per unit length, asymptotically decreases with the increasing of roof span. [ABSTRACT FROM AUTHOR]

Owing to the controllability and reliability, wind tunnel experiment is considered as a powerful and effective approach for the investigation of snow drifting. Most of the previous experimental studies were mainly concerned with snow drifting on roofs without snowfall, in which a layer of particles was uniformly paved on the roof surface to model the initial snow cover. Hence, a cryogenic wind tunnel experiment using artificial snow particles was conducted to investigate snow drifting on flat roofs during snowfall. The similarity requirement related to snowfall intensity is derived according to the similarities of snow distribution pattern and the development of snow transport. Based on the results of snow distributions and transport rates for different roof spans and snowfall intensities, the features of snow drifting under snowfall conditions are analyzed in detail. The concurrence of snowfall is further revealed to greatly affect the development of snow drifting on flat roofs and thereby result in a reduction in the required fetch for reaching the saturated state. And the typical distribution patterns for snow drifting on flat roofs with and without snowfall are also summarized. Besides, the snow transport rate is found to increase along the roof surface before the achievement of the saturated state, whereas a slight decrease in the degree of snow erosion with roof span is observed. But the location of the crest formed near the windward edge is nearly unaffected by roof span as well as snowfall intensity. The results also indicate obvious linear characteristics in the relationship between the degree of erosion on the roof surface and snowfall intensity. And the normalized development process of snow transport before reaching the saturated state is nearly independent of snowfall intensity, although both the saturated transport rate and the required fetch for saturated drifting are strongly affected in the meantime. • A cryogenic experiment of snow drifting on flat roofs under different roof spans and snowfall intensities is presented. • The location of the crest formed near the windward edge is nearly unaffected by roof span and snowfall intensity. • Transport rate increases along the roof before reaching the saturated state whileerosion slightly decreases with roof span. • The relationship between the degree of erosion and snowfall intensity presents obvious linear characteristics. • Normalized development process of snow transport before the saturated state is nearly independent of snowfall intensity. [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]