Light Gauge Steel Framing Villa Roof System

9.2.2 The simplified mechanical model in this article is completely consistent with the actual roof truss structure. In practical engineering, the chord is a continuous member, while the ventral rod is connected to the chord through a screw. The bearing capacity and overall stability of the chord are calculated in accordance with the relevant provisions of bending members in Article 6.1.5 of this code, and the calculation of the belly rod is in accordance with the relevant provisions of articles 6.1.2 and 6.1.3 of this code for axial bearing members.

9.2.3 The roof of cold-formed thin-wall steel structure (light-steel villa) differs from other types of roof in that the winding rod will lay structural panels such as oriented strand board (OSB), which has a strong constraint effect on the buckling of the upper flange of the winding rod. To calculate the length, take twice the spacing of the screws in consideration of the possibility of failure of a single screw in the process of screw playing. In order to ensure the reliability of the stability calculation of the chord, take twice the spacing of the screws.

9.2.4 The ventral bar is usually calculated according to axial compression or axial tension members, without considering the influence of eccentricity.For the problem of the correlation between the overall stability and the local stability of the thin-walled members in the light steel villas, the calculation and test show that when the belly rod and chord are connected back to back, the existence of the off-face eccentricity will reduce the bearing capacity of the belly rod by about 10%-15%, so the eccentricity should be considered in the calculation.

9.3 Roof truss node structure

9.3.1 When there is no concentrated load at the roof ridge, the ventral rod of the roof truss and the chord rod can be directly connected at the roof ridge (FIG. 9.3.1a); When there is concentrated load at the roof ridge, it should be connected by connecting plate (FIG. 9.3.1b and C). When connecting with the connecting plate, the connecting plate shall be flanged and strengthened (FIG.

9.3.1b) or reinforced (FIG. 9.3.1c) shall be set.The number of connecting screws between chord rod and ventral rod or nodal plate should not be less than 4. When using direct connection, the roof ridge must be provided with longitudinal rigid support.
 

9.3.2 When the belly rod and chord are connected in the middle of the main roof truss of light steel villas, they can be directly connected or connected through the connecting plate. When the roof truss ventral rod is directly connected to the chord rod, the end of the ventral rod can be cut Angle, the length of the extension of the cutting Angle should not be more than 30mm, the end of the ventral rod should be set within the line of the crimping side

Place not less than 2 screws (FIG. 9.3.2a); When connecting plates are used between roof truss and chord, there shall be at least one ventral rod directly connected to chord < FIG. 9.3.2b).When necessary, the joint of the chord can be strengthened with a split closed section, and the length of the stiffener should not be less than 200mm.
 

9.3.3 When the upper chord and the lower chord are connected in the same direction with an open connection, it is appropriate to set vertical or horizontal stiffeners on the lower chord web. The thickness of the stiffeners should not be less than the thickness of the chord member (Figure 9.3.3). The lower flange at the bearing joint of the lower chord of the truss should extend to meet the lower flange of the upper chord.When horizontal stiffeners are used, the length of the horizontal stiffeners shall not be less than 200mm. In the beam type structure, the inclined beam should be connected with the house back beam through the connector.
 

9.3.4 When the roof truss of the main body of the light steel villa is connected with the top guide beam of the external wall, three-way connectors or other types of tensile connectors should be used to ensure the reliable transmission of vertical and horizontal forces between the roof truss and the wall. The number of connecting screws should not be less than 3.

9.3.5 The abutments of the gable roof truss should correspond to the gable posts up and down, and bar connectors with spacing no more than 2m should be set along the outside (FIG. 9.3.5).
 

9.3.6 When there is a reliable basis, other structural methods can be adopted for the main roof truss structure of the light steel villa.

9.3.1 The test shows that when there is a concentrated load near the roof ridge, if the stiffness of roof ridge joints is weak, the failure of joints will precede the instability failure of members. Therefore, according to the load situation, to choose the corresponding roof ridge joint form. In FIG. 9.3.1, (a) is applicable to the roof without concentrated load, (c) is applicable to the roof with concentrated load, and (b) node stiffness is between the two.

9.3.2 The existence of horizontal stiffening can increase the torsion stiffness of the lower chord, and prevent the torsion buckling failure of the chord at the connecting part when the load transmitted from the abdominal bar to the chord is large. Considering that there is a possibility of instability of the outrigger plate when screws are set only within the range of the outrigger Angle, it is stipulated that no less than 2 screws should be set within the connecting line of the winding edge of the end of the abdominal rod.

9.3.5 The strip connector on the main body of the light steel villa can resist the upward wind suction and the upward pulling force generated by the stripping action, so as to enhance the integrity of the wall and roof system and prevent the separation of the roof and wall under the action of hurricane and strong earthquake.

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