Layout Of Spacing And Span Of Purlin
Purlin refers to the role of support in the construction process, representative of C-shaped steel and so on
The effect of purlin on reducing span and small secondary beam
Layout and Construction
The purlin members of the lightweight portal frame can adopt cold-formed thin-walled steel with C-type cold bending edge and Z-type with inclined or straight edge. The height of the member is generally 140-250mm, thickness 1. $number. 5mm. Cold-formed thin-walled steel members generally adopt Q235 or Q345, Purlin most of the purlin surface coating using anti-rust primer, but also the use of aluminum or galvanized anti-corrosion measures.
1. Spacing and span arrangement of purlin
Purlin design should first consider the skylight, ventilation roof, lighting belt, roofing materials, and purlin supply specifications of the impact to determine the spacing between purlin, and according to the main frame spacing to determine the span of purlin. Purlin It is a complex problem to determine the optimal purlin span and spacing. With the increase of span, the dosage of main frame and purlin will be increased. However, the reduction of the number of main frames can reduce the amount of steel, purlin spacing can also be increased to reduce the amount of purlin. The greater the thickness of purlin can also reduce the amount of steel in the unit price. But the increase of purlin span, support dosage also increases correspondingly. All these factors need to be considered comprehensively. Purlin The research on this aspect of our country is relatively few, the United Kingdom has done systematic research to 90 meters long construction, the result shows, for the span exceeding 20 meters frame, the frame spacing of 7.5 meters is optimal; for frames with a span less than 20 m, the 4.5 m frame is optimal. This result can only be used for reference in our country.
2, the structure of the simply supported Purlin and the continuous purlin
Purlin members can be designed as simply supported components or as continuous components. The simply supported Purlin and the continuous purlin are generally achieved by the different bridging methods. Simply supported Purlin do not need lap length, fig. 1 is the simple support method of Z-purlin, Purlin the lap length is very small, and the C-Purlin can be connected to the Purlin bracket respectively. The use of continuous components can withstand greater load and deformation, so it is more economical. The continuous structure of purlin is also relatively simple, which can be achieved by lap and tightening. The z-type purlin with oblique winding edge can be lapped, and the edge Groove type Purlin can be lapped by different types of cold bending steel sets, and fig. 2 shows the lap of the continuous purlin. Note that the overlap between the bridging and the intermediate spans is slightly different, Purlin mainly because the end-span frame is connected to the gable wall. The design of the purlin lap length of the continuous component has certain requirements, the working performance of the continuous purlin is obtained by the lap length of the component, so the continuous purlin is more than 6 m, otherwise it will not be able to achieve the economic goal.
The important constructional measure to improve the stability of purlin is to connect each purlin with a pull bar or a rod from one end of the cornice to the other end. Purlin side support should not be too little, according to the difference between purlin span, you can set up in the center of Purlin or at the center of Purlin and four equal points at each set together a total of three strips. In general, Purlin the upper flange of the purlin is under pressure, so the pull bar is arranged within the range of the 1/3 high flange of the flange.
Because of the need to consider the flange under the action of wind suction pressure, you need to set the pull bar near the next flange. Considering the skin effect, it is possible to consider the lateral stability of the upper flange provided by the housing panel connected by the self tapping screw, and only to set the pull bar near the lower flange, but for the housing panel connected to the non tapping screws, a double pull bar is needed near the purlin upper and lower flange edge. For a C-section purlin with a curling edge, the free flange will deform to the roof because of the wind suction, so it is advisable to use the angle section or the square tube section as a pole. The results show that the main reason for the damage of purlin and wall beams is that the wind suction leads to the instability of the lateral flange and the inner flange of the wall beam. Therefore, it is very important to set up a reasonable support arrangement.
The drawing bar shall be provided with a diagonal bar at the cornice and firmly connected with the node of the cornice at the rigid frame.
(a) A method for setting the general structural pull bar is given. The support of the ridge is used to link the support of the two sides to prevent all purlin from buckling in one direction, so the roof joints are more tightly connected.
(b) A roof connection with a grooved steel support is given.