Thursday, 18 April 2019

The ultimate guide to Thin-Walled Steel Profiles

In ConSteel there are two types of cross-section modeling:

  • the General Solid Section (GSS) is an accurate finite element based surface model for any kind of cross-section including inhomogeneous materials (reinforced concrete, composite sections)
  • the Thin-Walled Section (TWS) is a simplified way of cross-section calculation considering that the section is composed of relatively thin plates with uniform thickness which are modeled by their centerline.

The GSS model is used to determine the section properties for the structural analysis and the TWS model is used for the standard resistance evaluation of the steel hot-rolled, welded or cold-formed profiles. The TWS model is very suitable for the accurate and fast calculation of the actual effective cross-section with the effective widths and effective thickness of the different section plates. Based on the TWS model ConSteel can perform Eurocode 3 design verifications to steel members having thin-walled profiles. Thin-walled profiles can be classified into 2 main groups:
  • A. - general thin-walled profiles
  • B. - cold formed thin-walled profiles

Into category A belong all the common sections produced either by hot rolled fabrication procedure or by welding of plates to form the required shape. Eurocode 3 Part 1-1 provides for such sections design rules, assuming that they have a minimum wall thickness of 3 mm.

Into the category B belong members and sheetings produced by cold forming. Eurocode 3 Part 1-3 gives supplementary rules for the design of such profiles and accepts a minimum wall thickness of 0.45 mm.

ConSteel 13 provides a new function to create user-defined profiles of both categories. Due to the very different fabrication process involved, the steps of profile definition and available features are different when the user defined a general or a cold formed thin-walled profile.

General thin-walled profiles are produced either by hot-rolling or welding. Straight and curved parts with different but uniform thickness can be used to form the required shape. The final shape must be open, cannot contain closed parts. Apart from this, there are no more geometrical limitations, any number of branches and gaps are allowed. Important to note, that ConSteel will assume that the final cross section will move in its plane as a rigid body without any section distortion. Warping deformations of the flanges can be automatically considered by the special 7DOF beam elements.

Cold-formed sections are made of one single thin gauge strip. The final shape is obtained by adding bendings between flat parts and by rolling additional stiffening ribs into the flat parts. Due to this setup, the nominal thickness remains constant along the sections and no branching or interruption is allowed, the section is made of a single polyline. Only open sections are allowed, without closed part. Important to note, that ConSteel will be able to incorporate limited in-plane section distortion of the stiffener zones for the design verifications through the calculated effective cross section properties. Warping deformations of the flanges can be automatically considered by the special 7DOF beam elements.