Thin-walled members

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IDEA Connection for design of joints of thin-walled members should be left only to experienced engineers. Buckling analysis is a must and each mode shape must be carefully analyzed.

Software IDEA StatiCa Connection is dedicated to assessment of connections of hot-rolled members which are not significantly affected by buckling. Geometrically linear and materially non-linear analysis is performed because of its fast and stable calculation. However, this analysis is not sufficient for stability loss. If buckling may be a problem, performing a linear buckling analysis helps to detect dangerous areas and provide a factor for Euler’s bifurcation point but this is still not enough for thin-walled members. For thin-walled members, only geometrically nonlinear analysis with imperfections is suitable.

If the user still decides to use IDEA StatiCa Connection software to check connections of thin-walled members, he should:

  • Perform linear buckling analysis and carefully evaluate each buckling shape, the first 5 presented buckling shapes might not be enough
  • Do not rely on plasticity of steel plates and rather limit the von Mises stress to yield strength or even lower
  • Be aware that local buckling which is not taken into account can redistribute internal forces in components differently
  • Be aware that stiffness of components may be different due to different failure modes or their combination.
  • Be aware that presented checks and detailing of components (e.g. bolts, welds) are following guides for standard members. The checks for thin-walled members may vary and then the provided checks are not correct.

The design of connections of thin-walled members is very case-specific and no general guide can be provided. IDEA StatiCa Connection was not validated for this use.

Component checks – EN

In EN 1993-1-1 thin-walled members are defined as: “Class 4 cross-sections are those in which local buckling will occur before the attainment of yield stress in one or more parts of the cross-section.” The main part of Eurocode for steel is limited to members with material thickness t ≥ 3 mm. The chapter 4 – Welded connections applies only to material thickness of t ≥ 4 mm. Therefore, the checks of components provided by software do not apply to cold-formed members with smaller thickness. User should be aware of this and replace the checks with appropriate formulas from EN 1993-1-3 manually.

Analysis of hollow section joints should be also carefully performed for members which are out of the range of validity for welded joints – EN 1993-1-8 – Table 7.1. There are no guidelines for such joints and results of the software have not been validated.

Component checks – AISC

In Chapter A of AISC 360-16 there is a user note stating: “For the design of cold-formed steel structural members, the provisions in the AISI North American Specification for the Design of Cold-Formed Steel Structural Members (AISI S100) are recommended, except for cold-formed hollow structural sections (HSS), which are designed in accordance with this Specification.” AISI S100 and AS/NZS 4600 provide formulas to determine the shear and tension resistance of most common fastener types together with their range of application

Component checks – CISC

CSA S16-14 states in Chapter 1: “Requirements for steel structures such as bridges, antenna towers, offshore structures, and cold-formed steel structural members are given in other CSA Group Standards.”

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