Why is the greenhouse so "fragile"?
A heavy snowfall on November 11~12 brought huge losses to the vegetable production in our province. After the snowfall, the author visited several vegetable production concentration areas in our province—the northern suburbs of Zhengzhou City, Fugou County, Leiyang City, Boai County and other places, and witnessed the collapse of the sheds, the frozen vegetables, and the tears of vegetable farmers. Stand in front of the destroyed shed. Sudden natural disasters are indeed unexpected, but on the other hand, the same snowstorm has caused many greenhouses that have not collapsed. Perhaps we should also think more when we are actively carrying out disaster relief work. There are dangers in the sky, and no one can guarantee that the same disaster will not come again. Reflection is a rational and correct approach though it is a dead-end supplement.
The existence of the paralysis of the enemy
For many years, there have been few rain and snow in winter, and the temperature is high. This fact has caused people to paralyze the idea of ​​subversion. However, changes in the weather are difficult to predict. It is not surprising that there are special circumstances under normal circumstances. In spite of a special situation, even if it happens in ten years, we must focus our attention on responding to special circumstances. However, a large number of decision-makers or the masses have neglected this important point and thought that as long as the film can be supported, the performance of wind resistance and snow pressure resistance of the shed body can be ignored. This is a major loss. The main reason. Snow disaster is not a scourge, people do not have time to dodge, if the snow before the height of prevention, snow monitoring at any time, snow cleared at any time, the loss is not it can be reduced to a minimum?
Lack of enough understanding of "snow pressure"
The fluttering snow falls on the body. People do not seem to feel it. However, the pressure caused by the accumulation of countless snowflakes cannot be ignored. Take the 32-cm snow cover thickness in Zhengzhou as an example to calculate the pressure on the shed body. In general, the amount of snowfall in meteorology refers to the amount of water melted by snowfall. It is a different concept from the thickness of snow. In general, the ratio of snowfall to snow thickness is approximately 1:15, ie, 15 mm thick snow received under the same vessel can melt approximately 1 mm of water. Therefore, the proportion of snow is about 0.15. The area of ​​one mu of land is 667 square meters, and 1 millimeter of rain falls in the sky, equivalent to 0.667 cubic meters of water per acre. One cubic meter of water weighs 1,000 kilograms, so every 1 millimeter of rain equates to about 667 kilograms of water per acre. The snowfall in Zhengzhou is 48 millimeters, which is classified as heavy rain. According to this, the snow pressure (weight pressure) on the sheds and arches per acre is estimated to be about 32,000 kilograms. If you take a greenhouse with a span of 10 meters and a length of about 67 meters, you will have about 40 kilograms of grasshoppers, about 80 grasshoppers, and a total weight of 3,200 kilograms. This snowfall pressure on the film and arches is similar to that of covering 10 layers of haystacks. Such a heavy pressure is generally unacceptable.
Due to the different arches of different arches, the size of the land covered by the lower part of the arc is also different. That is to say, with the increase of radian, the area of ​​the land covered by it is also smaller. However, the greater the arc, the more conducive to the decline in snow.
Considering the load of the greenhouse
In recent years, the greenhouses have become larger, with more than two acres of individual greenhouses and more than five acres of multi-story giant greenhouses. "Large" can improve the land utilization rate, and the large volume change of temperature is stable and conducive to the production of vegetables in low temperature season. Therefore, "big" is not an exaggeration. The problem is that people only see the positive side, but they neglect to reinforce the anti-risk side. In order to reduce investment and facilitate farming, they use as few pillars as possible; some increase the span to 10 meters and lack proper support; others misuse inferior materials... These are the reasons why greenhouses cannot withstand this heavy snow and collapse. .
Design lacks rationality
This year's snow pressure is the largest number of large-scale sheds. In spite of the large number of pillars in the huge, multi-story sheds, there is no space for snow to slide between the ridges, and manual snow removal is impossible, making it difficult to support and collapse. In addition, some arch spans are more than 1m wide, and the horizontal drawbars are small and small, and the bearing capacity is not strong enough to collapse.
From the results of the survey, the prefabricated arches of cement and the double arches welded to the steel pipe (with a reasonable distance between the arches, generally within 1 meter) have strong endurance and collapse. In addition, the string-type greenhouses are mostly bamboo-wood structures, with multiple rows of column supports in the room. The arches are connected with bamboo rafts, steel wires and main arches (also known as reinforced frames, mostly double-arched steel frame or rough bamboo) every 30-40 cm. As one, the film clings to the arches and is strong and strong. People can stand on the shed film to remove snow, and there is less collapse.
If the arches in the shed are thin, the temporary pillars of l~2 rows will be set in the winter and will be removed after the snow is over, which is also a way to prevent disasters.
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