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The Arrangement And Construction Of Purlins


The purlins are a building noun, along the length of the roof distribution of the horizontal components, located on the main rafters, supporting the secondary rafters. Purlins roughly divided into the main purlin and sub-purlin, mainly used in some housing decoration and other fields.

First, layout and construction

Light-type portal frame purlin components can be used C-type cold-rolled curling channel and Z-type with oblique curling or straight curling of the cold-formed thin-walled steel. Purlin The height of the component is generally 140-250 mm and the thickness is 1.4-2.5 mm. Cold-formed thin-walled steel components generally use Q235 or Q345, most purlin surface coating with anti-rust primer, Purlin but also the use of aluminum or galvanized anti-corrosion measures.

1, purlin spacing and span of the layout

The design of the purlins should first take into account the influence of the skylights, ventilation roofs, lighting belts, roofing materials, and purlin supply specifications to determine the purlin spacing and to determine the span of the purlins according to the spacing of the main frame. Determining the optimal purlin span and spacing is a complex issue. With the increase in the span, the amount of main frame and purlins is bound to increase. Purlin But the reduction of the number of main frame frame can reduce the amount of steel, purlin spacing can also increase the amount of purlins. Thicker purlins can also reduce the amount of steel units per unit. But the purlin span increases, the amount of support is also a corresponding increase. All these factors need to be considered. China's research on this content is relatively small, the British 90-meter-long building made a systematic study, Purlin the results show that the span of more than 20 meters of the framework, 7.5 m frame spacing is the best; for less than 20 meters span Frame, 4.5 m frame is optimal. This result can only be used in our country.

2, simple purlin and continuous purlins structure

The purlin member may be designed as a simple support member or may be designed as a continuous member. Simple purlin and continuous purlins are generally achieved by means of lap. Purlin Figure 1 is the Z-type purlins simple branch lap way, the lap length is very small, for the C-type purlins can be connected to the purlin. The use of continuous components can withstand greater load and deformation, Purlin and therefore more economical. The continuous construction of the purlins is also relatively simple and can be achieved by lap and tightening. Z-type purlin with oblique crimping can be used to overlap lap, crimp-type purlins can be used in different types of curled groove-type cold-formed steel sets to lap, continuous purlins lap method. Purlin Note that the overlap between the end of the purlin and the lap is slightly different, mainly because the end of the frame to connect with the gable wall. The length of the purlin lap is designed to be continuous, and the working performance of the continuous purlins is obtained by the length of the overlapped components. Therefore, the continuous purlin is more than 6 meters in length, Purlin otherwise it will not be able to achieve the economic purpose.

3, lateral support settings

Under the external load, the purlins produce the same effect of bending and twisting. The thickness of the cold-formed thin-walled steel plate is large and the torsional rigidity is insufficient. Purlin The load is usually located at the center of the upper flange. The load centerline is larger than the center of the shear force. Because of the influence of the slope roof, the purlin web is tilted and twisted Will be more prominent. Purlin All these instructions, lateral support is to ensure that the stability of cold-formed thin-walled steel purlin important guarantee.

(1) roof support role

First, the roof can be regarded as a large component, bear the parallel to the roof direction of the load (such as wind, earthquake, etc.), known as the roof of the skin effect. Considering the skin effect of the roof must have a suitable plate type, thickness and connection performance, Purlin mainly with some tapping screws connected to the roof, can be used as purlin side support, so that the stability of the purlin greatly improved. Closed or bite-type roof panels can not provide a good lateral support for the purlins.

(2) pull and support

An important structural measure to improve the stability of the purlins is to use a strip or strut to connect one end of the cornice to the other end, connecting each purlins. Purlin side of the lateral support should not be too small, depending on the purlin span, you can set up a purlin in the central or in the purlin at the central and four points each set a total of three pull. Under normal circumstances purlin on the flange pressure, so the bar is set in the purlin on the flange 1/3 high web range.

As the need to consider the purlin in the wind suction under the flange pressure, the need to pull the bar in the vicinity of the lower flange. Taking into account the skin effect, you can consider the lateral stability of the upper flange provided by the tapping screws connected to the roof, Purlin and only in the vicinity of the lower flange to set the pull; but for non-self-tapping screws connected to the roof, you need to Purlin up and down the flange near the set double pull. For the C-shaped cross-section purlins, due to the action of the wind under the free flange will be deformed to the roof, it is appropriate to use angle cross-section or square tube section for the pole. Purlin The results show that the wind suction caused the lateral unsupported purlins and the instability of the inner flange of the wall, which is the main reason for the destruction of purlins and wall beams. Therefore, it is very important to set a reasonable support arrangement.

The use of a pull bar shall be provided with a beveled bar at the cornice and firmly connected to the node at the frame at the purse purse. Gives the general structure of the pull bar set method. The support at the ridge serves to link the support on both sides to prevent all purlin from settling in one direction, so the roof joints are more securely connected. Given the use of channel support roof connection.

(3) purlin

At the end of the simple purlins or the lap of the continuous purlins, consider the provision of the purlin is a more appropriate way to prevent the purlin from overturning or twisting at the support. The purlin is often angled and has a height of 3/4 of the purlin height and is bolted to the purlins.

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