Design simple supported, continuous and over-lapped purlins systems

The Place purlin line function allows you to create and configure a purlin line object and place it precisely within your structural model.

You can also control the sheeting eccentricity in the Z direction, either by selecting predefined positions or by entering custom values. A graphical interface supports these settings to ensure intuitive and accurate placement.

An important feature of this function is the ability to simulate the supporting effect of roof sheeting on the purlins. This is done by applying spring stiffnesses that reflect how the sheeting contributes to the overall structural behavior. Two types of springs are considered:

• Translational (shear) spring, representing the shear stiffness of the roof covering.
• Rotational spring, accounting for both the connection stiffness and profile distortion.

Depending on the selected sheeting type (trapezoidal sheeting or sandwich panels) the stiffness values can be entered manually or calculated automatically. Automatic calculations follow the guidelines of EN 1993-1-3, providing reliable and standards-based results.

The Support zone function allows you to define the geometrical and mechanical parameters at the points where the purlins are supported. The geometry and bearing capacity can be set by specifying the support width and selecting how the load capacity is defined.

The Purlin overlap function helps define how individual purlins are connected in continuity. The standard (EN 1993-1-3) distinguishes between simple overlap joints and joints with coupling elements. Currently, only overlap joint is available in the program. You can define the length of the overlap either in millimeters or as a percentage of the member length. Additionally, the stiffness distribution between the two overlapping members can be adjusted.

Together, these functions ensure accurate modeling of purlin behavior, support conditions, and connection details, aligning with design standards and practical requirements.

To ensure that all purlin line related objects are properly considered in the analysis, make sure to activate the Cold formed purlin design mode in the analysis settings. When this mode is enabled, both the buckling analysis and the global design are performed on a submodel that includes only those members associated with purlin line objects. This mode is intended exclusively for the design of the roof purlin system.

If purlin related objects are present in the model but the cold formed purlin design mode is not active, the structural elements connected to these objects will be excluded from the second-order stiffness matrix. As a result, their influence will not be considered during linear buckling or second-order analysis.