Did you know that you can use Consteel to design simple supported, continuous and over-lapped purlins systems in Consteel, considering shear and rotational stiffness of attached roof sheeting?
To use the purlin design functions, you first need to place cold formed Z or C purlins in your model, these are the only profile types supported for purlin design. All functions related to purlin lines can be found in the Structural members tab.
With these three main functions you can define the purlin line object, specify the support zones, and set the overlap zones. A detailed explanation of each can be found in the Consteel Manual – Purlins Chapter.
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.
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Try Consteel for freeDid you know that you could use Consteel to perform local and distortional buckling checks for cold-formed members?
First, sections must be loaded into the model. To load cold-formed sections, you can choose from four options: From library, Macro section, Draw section, or My library.
After the first-order and buckling analyses are completed, you can proceed to the Ultimate limit state check settings and enable the steel design cross-section and buckling checks. At the bottom of the steel design section, there is an option to Consider the supplementary rules from EN 1993-1-3 for the design of cold-formed sections. This checkbox must be selected if you want to design cold-formed sections.
When the calculation is finished, by opening the Section module, we can review all the properties of the Effective section of the elastic plate segment model. By opening each plate element, we can verify the length, effective length, thickness, effective thickness, slenderness, and reduction factor separately. In addition, the properties of the stiffeners can also be verified: area, moment of inertia, lateral spring stiffness, critical stress, reduction factor, compressive stress, reduced effective area, and reduced thickness.
Similarly, the stresses can also be checked from the Properties tab. In the colored figure or diagram view, all the calculated stresses can be seen together with their resultants.
Consteel automatically takes into account the effect of distortional buckling when calculating the effective sections of cold-formed thin-walled sections.
Moving on to the Standard resistance tab in the Section module, all calculated results can be verified, not only the dominant one. By opening the Global stability resistance check, we can see that, since we enabled the option to consider the supplementary rules from EN 1993-1-3 for the design of cold-formed sections, results are available both according to EN 1993-1-1 and according to EN 1993-1-3.
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Try Consteel for freeDid you know that you could use Consteel to include in your model a wide range of cold-formed macro sections?
For line member modelling, the cross-section must first be loaded into the model. In Consteel, there are four options to do this, either starting from the Section Administrator or directly during beam or column modelling: From Library, Macro Section, Draw Section, or My Library.
Cold-formed sections can be created using any of these four methods. Standard cold-formed cross-sections can simply be selected from the library. However, if a special cold-formed section is needed, it can be created via Macro Sections, including: RHS, CHS, L profile, Z shape, C shape, Sigma section, Zeta section, Hat section with stiffeners, double C section, double Sigma section, and double user-defined sections.
Macro sections are easy to create because the essential geometric characteristics are predefined, and the parameters can be modified intuitively. It is also possible to add profile stiffeners. Flange and web stiffeners can be configured in various forms, including single and double options. These defined stiffeners are included in the structural evaluation of distortional buckling, according to EN 1993-1-3.
The thickness tolerance category must be specified. This determines the design wall thickness for the section. In practice, macros follow the commonly applied tolerance categories used for coated steel sheet products.
If you want to use a double section, make sure to load into the model first the section that you want to duplicate.
For very special or unique sections, the Draw Section function can be used. This allows users to create fully custom cross-sections when standard or macro shapes are insufficient, by manually sketching the geometry.
Sections can be defined as cold-formed or general thin-walled, which determines how they are analyzed: cold-formed sections have uniform thickness and account for distortional buckling, while general thin-walled sections allow varied thicknesses and closed shapes, typically for welded or fabricated profiles.
This approach is especially useful for modelling unique shapes, prototypes, or as-built sections, giving full control over every segment to accurately capture geometries that standard libraries or macros cannot reproduce.
Download the example model and try it!
Download modelIf you haven’t tried Consteel yet, request a trial for free!
Try Consteel for freeDid you know that you could use Consteel to design simple supported, continuous and over-lapped purlins systems, considering shear and rotational stiffness of attached roof sheeting?
Download the example model and try it!
Download modelIf you haven’t tried Consteel yet, request a trial for free!
Try Consteel for free