北墙不同外倾角对日光温室表面风压与体型系数的影响

为探明日光温室北墙外倾角的改变对其屋面风压系数和风荷载体型系数的影响，该研究基于计算流体力学原理，采用数值模拟方法，考虑北风和西北风2种风向，研究了不同北墙外倾角下日光温室表面风压分布规律，并给出不同北墙外倾角情况下的细化分区风荷载体型系数。结果显示：1）风压分布规律为：北风和西北风时日光温室前屋面和后屋面上半部风压系数为负，屋脊处和东、西边缘风吸力集中；随北墙外倾角减小，前屋面上部和后屋面风压系数绝对值明显减小，前屋面下部风压系数无显著变化。2）风荷载体型系数规律：北风时，以北墙外倾角90°（即竖直）为参照，外倾角减至30°可使前屋面上部体型系数的绝对值减小16%～26%，可使前屋面下部体型系数的绝对值增大6%～57%，可使后屋面体型系数绝对值减至0左右；西北风时，前屋面上部和后屋面体型系数绝对值均为西端大、东端小，前屋面下部体型系数绝对值为中间大两端小，屋面风荷载体型系数随北墙外倾角的变化不显著。因此，北墙外倾角的变化导致日光温室屋面风荷载分布发生变化较大，对日光温室结构的抗风性能影响较大，建议日光温室屋面风荷载计算应考虑北墙外倾角的影响，抗风设计时可合理选择北墙外倾角以减小屋面风荷载，边榀骨架结构和围护结构的边缘处需加强。

Influences of inclination angles of north wall on surface wind pressure and shape coefficient of solar greenhouses

The north wall of solar greenhouses is often designed to be very thick with a slope on the outside. Heat preservation and storage can be achieved in the solar greenhouses in most areas of northern China during autumn and winter, where the dominant wind direction is the north or northwest. This study aims to clarify the influence on the roof wind pressure coefficient and wind load shape coefficient, due to the dip angle change of the outer north wall of the solar greenhouse. The numerical simulation was carried out to determine the distribution pattern of surface wind pressure on the solar greenhouse under different north wall outer inclination angles. Both the north and northwest winds were considered under computational fluid dynamics. The results show that: 1) The negative wind pressure coefficients were observed on the front and the upper half of the rear roof under the north and northwest wind. The wind suction was concentrated at the ridge and two edges (east and west) of the roof. The absolute value of the wind pressure coefficient of the upper front and the rear roof decreased significantly with the decrease of the camber of the north wall. By contrast, there was little change in the wind pressure coefficient of the lower front roof. 2) The wind load partitions of the north wall and roof of the greenhouse were refined to determine the partition wind load shape coefficients under different wind directions and different north wall dip angles. Once the north wind appeared, the absolute value of the upper shape coefficient of the front roof decreased by 16%-26% with the decrease of the north wall angle. Meanwhile, the absolute value of the lower shape coefficient of the front roof increased by 6%-57% with the decrease of the north wall camber. The absolute value of the rear roof shape coefficient decreased significantly with the decrease of the north wall camber, or even changed from negative to positive. 3) Once northwest wind appeared, the absolute value of the shape coefficient of the upper part of the front and the rear roof was larger at the west end than the east end, while the absolute value of the shape coefficient of the lower part of the front roof was larger at the middle than at the both ends. The shape coefficient of the roof wind load was rarely changed at the camber of the north wall in case of northwest wind. Therefore, the camber of the north wall should be considered to calculate the wind load on the roof of the solar greenhouse. The dip angle of the north wall can be expected to reduce the wind load on the roof and edges of the side frame structure. The cover of the roof should be strengthened in the wind resistance design.