Purlin Internal Force Calculation


★ Purlin cross-section checking - strength, the overall stability, deformation

Strength calculation - calculated by bidirectional bending members

When the roof can prevent the purlins from breaking and twisting, the following strength formula can be used to check the cross section:




Section points of normal stress calculation formula is as follows:


overall stability calculation

When the roof can not prevent the purlin lateral instability and reverse (such as the use of snap-in roof panel), should be calculated according to the stability formula cross section:


Deformation calculation

The real purlins shall be checked for deflection in the direction perpendicular to the roof.

On both sides of the curled groove-shaped section of the simple purlin:


On both ends of the Z-shaped section simply purlin:


Allow the deflection [v] by the table to take the value


Purlin structure requirements

●When the purlins span more than 4m, should be in the purlin between the middle of the set bar. When the purlins span 6m, should be in the purlin span three points to set a bar.

The effect of the pull is to prevent the purlin from being laterally deformed and twisted and providing an intermediate fulcrum in the x-axis direction. The force of the intermediate fulcrum needs to be transmitted to a larger member. For this purpose, a stay and a stiff stay are required at the roof or cornice.



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