The light portal frame is a single-layer steel structure with rigid connections between beams and columns. It has the characteristics of simple structure, lightweight, reasonable force, and convenient construction, and is convenient for standardized processing. The portal frame steel structure is mainly used for light industrial buildings. They are not suitable for use in environments with strong corrosive media due to the thin thickness of the portal frame parts.
According to the type of structure, the portal frame steel structure building can be divided into single-span (Pic 1-1a), double-span (Pic 1-1b), multi-span (Pic 1-1c), single-span with a canopy (Pic 1-1d) and double-span with adjoining house (Pic 1-1e). The connection between the middle column and the inclined beam of the multi-span steel frame is generally a hinged connection. The multi-span steel frame should adopt a double-slope or single-slope roof (Pic 1-1f). If necessary, it can also adopt a multi-span rigid frame composed of multiple double slope roofs (Pic 1-1g). The beam-column section can be equal section or variable section, and the column base is generally hinged or rigid.
A. The choice of building length and width
Generally speaking, the principle of length greater than width should be followed when arranging column nets, which can reduce the amount of steel used in the rigid frame and reduce the wind load of the column support at the same time, thereby reducing the amount of steel used in support system.
B. The choice of column space
The most economical column distance under the standard load is 8-9m. When it exceeds 9m, the steel consumption of the roof purlin and wall frame system increases too much, and the comprehensive cost is not economical. The standard load here refers to that the roof live load is 0.3KN/m2, the basic wind pressure is 0.5KN/m2, when the load is greater, the column distance should be reduced accordingly. For those steel workshops with cranes over 10 tons, the economic column distance should be 6-7m. If unequal column spacing is required when arranging the column distance, then the end span column spacing should be arranged as small as possible than the middle span because the wind load of the end span is larger than the middle span.
C. Determination of reasonable span
Different production processes and functions determine the span of the plant to a large extent. Some owners even require manufacturers to determine a more economical span based on the functions of their workshop. In order to meet the production process and functions as much as possible, a reasonable span should be determined according to the height of the house. When designing the portal steel frame, a more economical span should be selected according to the specific requirements, and it is not suitable to blindly pursue a large span.
D. The choice of roof slope
The roof slope needs to be determined according to the comprehensive factors such as the structure of the roof panel, the length of the drainage slope and the height of the column structure, and it is generally 1/10~1/30. Studies have shown that different roof slopes have a greater impact on the amount of steel used in rigid frames. For a single-span rigid frame, a better way to reduce the weight is to increase the slope of the roof. The greater the slope, the more saving the amount of steel. However, the situation is different for multi-span frames. A large slope will increase the amount of steel used in the frame. This is because a large slope will increase the length of the inner column. When the span of the building is large, the increase in slope can reduce the deflection of the roof beam.
E. The choice of eave’s height
The height of the eave has a great impact on the cost, which is mainly manifested in the following aspects:
a. The increase in the height of the eave will result in an increase in the area of the wall panel, wall purlins, and the amount of steel used for the columns.
b. If the steel column has no lateral support, the height of the eave will have a more prominent influence on the weight of the frame.
c. The increase in the eave’s height will result in an increase in the wind load on the frame. If the eaves height/building width>0.8, then in order to control the lateral displacement, sometimes it is even necessary to change the column feet from hinged to rigid.
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