降雪条件下屋面风吹雪模拟及屋面风致雪荷载重分布的概率模型研究

Study on unbalanced snow loads on roofs and corresponding load effects is an important issue in wind&snow engineering. However, the refined simulation on snow loads on roofs is still in the development phase. Thus, the project intends to effectively simulate snow drifting on roof surfaces and focuses on the simulation method during snowfall, using numerical method, wind tunnel test and field observation. The numerical method developed herein simulates the saltation of snow particles close to surface of roofs and suspension of snow particles in sky in snowfall conditions. The two-phase wind tunnel test on snow drifting on roof surfaces, in which some appropriate modeling particles are used as alternative particles, is also performed in snowfall conditions. The key similarity parameters related with snowfall, such as wind duration and snowfall intensity etc., are investigated at the same time. The field observation, which can validate the results of numerical method and wind tunnel test, is carried out in our built outdoor base. The outdoor base is located in frequency snowfall northeastern region, Harbin and natural falling snow particle is adopted to explore the redistributions of snow on large-scale roof models. The influences of roof profile, climate etc. on snow drifting, are analyzed through the simulation method proposed herein. And probability analysis on meteorological data of typical regions is performed. Then, probabilistic models of snow load redistribution on roofs, which are associated with key structural responses, are established. Finally, a practical method, which can calculate the unbalanced snow loads, is summarized for the convenient application of structural engineers.

建筑屋盖表面不均匀雪荷载分布及其效应研究是风雪工程领域的重要方向，但目前屋面雪荷载精细化模拟还处于发展阶段。为了细致地模拟屋面风致雪荷载重分布，本项目通过数值模拟、风洞试验并结合现场实测，重点研究降雪条件下建筑屋面风吹雪的模拟方法。在数值模拟中实现降雪条件，模拟屋盖表面颗粒的跃移运动和屋盖上方雪颗粒的悬移运动。采用替代颗粒开展降雪条件下屋面风吹雪的风洞试验，研究与降雪相关的风吹雪持续时间和降雪强度等关键性相似参数。在已建好的东北哈尔滨实测基地，利用自然降雪探讨大比例尺建筑屋盖模型表面雪荷载的分布规律，并验证数值模拟和风洞试验结果。利用本项目研究的模拟方法，分析典型建筑屋盖的外形、天气条件等多种因素对屋面风吹雪的影响规律，并对我国代表性地区气象资料进行概率统计分析，进而建立与结构控制性响应相关联的屋面风致雪荷载重分布概率模型。最后将提出计算屋面风致不均匀雪荷载的工程实用方法。

如何预测建筑屋盖表面不均匀雪荷载分布对于多雪地区屋盖结构的设计是非常重要的。为了细致地模拟屋面风致雪荷载重分布，本项目通过数值模拟、风洞试验并结合现场实测，研究了降雪条件下建筑屋面风吹雪的模拟方法；由于迁移雪将对屋面不平衡雪荷载的形成产生影响，项目同时对屋面迁移雪进行了模拟。主要工作包括：（1）数值模拟方法。对不同坡度的双坡屋盖屋面雪飘移进行了数值模拟，使用了取值常数的雪相湍流扩散系数，依据风洞试验获得的背风面捕捉率结果，对雪相湍流扩散系数进行了标定。为揭示风对双坡屋盖屋面迁移雪荷载的影响，对不同坡度下屋盖绕流风场、壁面摩擦速度、雪浓度和屋面积雪分布进行了详细分析。提出融雪模型和风吹雪模型的耦合模型。在耦合模型中，既可以模拟热力学过程引起的积雪物理性质变化，又可以考虑风吹雪过程对积雪分布的影响。（2）风洞试验。通过低温风洞试验对降雪条件下屋面风吹雪的质量输运规律进行了研究。在试验中利用人造雪模拟降雪，测量了风吹雪质量传输率沿屋面跨度的分布。基于试验结果，指出了降雪强度对风吹雪的影响，提出了更合理的质量传输率发展规律描述方程、饱和质量传输率计算公式以及饱和雪源长度预测方法。同时指出了考虑饱和雪源长度与屋盖几何长度同比例缩尺的重要性。（3）现场实测。在哈尔滨地区搭建大比例尺的双坡屋盖模型并采用自然降雪研究雪荷载的分布规律。（4）雪荷载的参数化模拟方法及雪荷载的概率模型。基于风洞试验得到的预测屋面风吹雪质量传输率的公式，建立了考虑降雪条件的屋面雪荷载参数化模拟方法。基于雪荷载概率模型的研究，对我国各地区屋盖结构的抗雪可靠度进行了评估，并对雪荷载设计值的概率估计方法进行了讨论。分析了多种因素对屋盖结构抗雪可靠度的影响。