With the rise and development of greenhouses, the demand for large-span, large-size, high-efficiency, and standard types of greenhouse structures increases, and a stronger anti-disaster ability of facility greenhouse becomes a key factor.
As a common form of greenhouse, plastic greenhouses are affected by wind load more frequently, and the disaster degree is heavier, which may lead to greater economic losses.
Wind force characteristics of plastic greenhouse
The force of plastic greenhouses on wind is mainly suction and pressure. The first force of the greenhouse is the surface maintenance structure. When the maintenance structure reaches its wind limit, the second important factor is its internal skeleton structure and materials.
The main skeleton of the plastic greenhouse is mostly fabricated galvanized steel pipe spaced about 4.00 ~ 5.00 m apart and spanning about 6 ~ 12.8 m. Steel pipe, film, and film line together form the main body of the plastic greenhouse and envelope structure.
Plastic greenhouses affected by a large wind load see their film floating up and down. The force is transmitted to the card slot, the film belt, different thicknesses of the film, and different sections of the film line can withstand different wind loads.
Greenhouse film is a flexible material but does not have external stiffness, so it can only withstand tension. Therefore, film damage is generally bad.
Film flexibility is good, high in strength, and no sharp or hard objects tend to destroy it. So a calculation of the plastic greenhouse structure is mainly a calculation of the structure's skeleton.
As shown in the figures, wind loads of 20m/s under finite element analysis are indicated by wind pressure stress blowing through the side and front respectively.
- On the left side of the vertical ribbon, the color from blue to red under normal conditions represents the stress value from small to large, the two ends of the maximum and the lowest peak.
- The color displayed on the right part is consistent with the color band on the left. The redder it is, the higher the stress value will be.
For facility plastic greenhouses, wind load is a complicated dynamic load in the total load. Wind load may cause a large area of film to shed, and the overall structure might become unstable. The consequences are serious.
In order to avoid loss and better protect the internal load-bearing skeleton, it is necessary to do a good job of windproofing in plastic greenhouse. Windproof points include:
1. Build greenhouses with strong wind resistance.
The wind resistance of greenhouses is positively related to the stability of greenhouses, which is closely related to the construction quality, skeleton material, canopy surface radian, and span of greenhouses.
2. In the greenhouse site selection, try to avoid tuyere.
To meet appropriate lighting conditions, try to build greenhouses near buildings with wind barriers.
3. Raise the awareness of windproofing and estimate the windproof ability of greenhouses.
Make frequent assessments so that appropriate windproof measures can be taken. Make timely repairs on damaged shed film, vent, and shed door, and check the condition of the greenhouse.
4. The key parts should be taken care of.
The lower vent of the greenhouse is often rolled up and down, which weakens the film pressing line. The part on the tuyere is key when it comes to protection and needs to be taken care of.
5. Slow down the wind speeds hitting the greenhouse.
Attention must be paid to the wind barriers to prevent strong winds from blowing down the greenhouse. The wind barrier built on the lee side of the greenhouses can significantly reduce the negative pressure film lifting effect of the wind on the windward side of the greenhouses.
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