Steel Cold-formed EN 1993 (esasd.15.01)

 

esasd.15.01

The steel design module Steel Cold-formed EN 1993 is an extension to the EC-EN module esasd.01.01 Steel code check. It enables the design of cold-formed steel elements according to the European standards EN 1993-1-3 and EN 1993-1-5.

  • Both section and stability checks are supported; the user executes these in the same way as for conventional steel members;
  • In addition, the reduced effective section properties due to local and distortional buckling are taken into account;
  • The specialised design procedures for local transverse forces and purlins attached to sheeting are applied as specified in the code.

Benefits

  • A wide variety of open cross-sections can be analysed for localized buckling effects;
  • The Profile Library of SCIA Engineer contains a long list of products from manufacturers of cold-formed steel; the geometry of these profiles can be edited before analysis;
  • Using the General Cross-section Editor (included in module esa.07), it is possible to define custom cross-sections in terms of centrelines and thickness; beside the integrated drawing tools, cross-sections can be imported from dxf and dwg files;
  • The intelligence behind the calculation of effective sections increases productivity and requires very limited user input;
  • The detailed analysis of the effective shape includes distortional buckling of edge and intermediate stiffeners and double edge folds;
  • The obtained effective sections can be displayed graphically;
  • The effective width derivation is fully integrated in SCIA Engineer's general design work flow for steel structures;
  • An automated optimisation procedure (AutoDesign) selects suitable profiles depending on (1) the internal forces in the structure and slenderness of members and (2) the set of preferred profiles indicated by the user.

How does it work?

This unique feature of SCIA Engineer analyses a cross-section's geometry to recognize internal elements, outstands, edge and intermediate stiffeners, and performs a comprehensive calculation according to the rules given in the specialized standard EN 1993-1-3:2006/AC:2009.

  • The user assigns cold-formed steel cross-sections to members in the 3D model;
  • These cold-formed steel profiles are analysed. Their walls are classified as internal, symmetrical/asymmetrical outstands (with or without intermediate reinforcement) and rigid parts; the automatically determined classification may be adapted by the user, if needed;
  • It is checked whether the modelled cross-section complies with the limitations of the code (in terms of width-to-thickness ratios, adequate size of stiffeners, etc.);
  • The effective-width analysis approach is applied for each of the profile elements; reductions due to localised buckling effects are taken into account;
  • Notional widths are used in the determination of effective section properties;
  • Local buckling is taken into account by reducing the widths of straight parts and distorsional buckling -- by reducing the effective thickness of the stiffeners. Iterations may be performed to establish a more accurate geometry of the stiffeners (stiffener iterations) and a more accurate stress distribution in the cross-section (full-section iterations);
  • A reduced section geometry is derived for the cases of pure bending and pure compression. Stress gradients for both weak- and strong-axis bending are correctly generated. Interaction of load effects is taken into account as per EN 1993-1-1 during section and stability checks;
  • For sections from the Profile Library, the user may select to directly use effective section properties provided by the manufacturer. In this case, effective section calculations will not be performed and catalogue values will be used;
  • With the established cross-section properties and shifts in neutral axes, section and stability checks are performed according to EN 1993-1-3;
  • To improve stability, additional elements may be included in the model - diaphragms, lateral-torsional buckling restraints, stiffeners;
  • Special considerations are followed in the design of purlins restrained by sheeting (according to Chapter 10 of EN 1993-1-3);
  • Serviceability limit state provisions are applied based the rules for conventional steel members.

Special considerations

Average yield strength

In cases that fulfil the requirements of the code (e.g., fully effective sections in case of axial compression) the average yield strength will be taken into account when deriving the resistance and stability of a member. Only the production method (roll forming vs. press braking) needs to be specified by the user; the correct value of the k coefficient will be taken into account accordingly.

Steel core thickness

SCIA Engineer automatically reduces the nominal thickness defined by the user (or specified in the manufacturer's catalogue when the profiles are taken from the Profile Library) to take into account the thickness of corrosion protection layers. By default, a reduction of 0.04 mm is taken into account, which corresponds to the standard galvanisation practice, i.e., 275 g/m2 of zinc coating on both sides of the profiles.

Corner roundings

In the cases where the analysed cross-section has a standard shape, SCIA Engineer correctly takes into account the presence of rounded corners in the profiles. Standard shapes are provided in the Profile Library:

  • common shapes, such as channels, U-, point-symmetric and asymmetric Z- (with or without edge stiffeners), Σ-, Ω-sections;
  • special shapes, such as point-symmetric and asymmetric Z-sections with inclined edge stiffeners, Channel and Σ-profiles with complex (2-fold) edge stiffeners, Sigma shapes with inclined flanges or arched segments;
  • paired sections, such as back-to-back C's, back-to-back Σ's.

For profiles that do not fit within these limitations, corner rounding should be ignored and the sections should be represented by flat elements.

Purlin design

The special checks for purlins restrained by sheeting are performed for profiles that meet the requirements of Chapter 10 of EN 1993-1-3. This results in increased load-bearing capacity, because not all standard design checks need to be performed for such members (e.g., for lateral torsional buckling, combined stability in axial compression and bending).

The module allows for the flexible support coming from diaphragms to be taken into account as rotational spring at the point of fastening.

  • The analysis correctly takes into account the position and stiffness of roof diaphragms. Depending on the load case, a diaphragm is attached to the compression side or to the tension side of a member and that leads to different stability behaviour.
  • The geometry of the free flange is determined, as well as the magnitude of fictitious lateral load.
  • From the calculated buckling resistance of the free flange, a suitable spacing between the anti-sag bars can be determined.

Supported cross-sections

  • Standard cross-sections from the Profile Library (see above);
  • Thin-walled geometric sections (introduced by means of a concept shape and wall dimensions);
  • Paired cold-formed steel profiles;
  • General thin-walled sections with thin walled representation;
  • All other sections which can be represented by a centreline and uniform thickness and do not have roundings.

Summary of performed checks

The following section checks are performed:

  • Axial tension;
  • Axial compression;
  • Bending moment;
  • Shear force;
  • Torsion (not performed in case of sufficient support from roof diaphragm);
  • Local transverse forces for stiffened or not stiffened webs;
  • Combined tension and bending (not performed in case of sufficient support from roof diaphragm);
  • Combined compression and bending (not performed in case of sufficient support from roof diaphragm);
  • Combined shear, axial force and bending moment;
  • Combined bending and local transverse force.

The following stability checks are performed:

  • Flexural buckling;
  • Torsional and torsional-flexural buckling;
  • Lateral-torsional buckling (according to EN 1993-1-1, the elastic buckling force is determined from the cubic equation of overall stability);
  • In the case of purlins, special checks for buckling of the free flange are performed according to Chapter 10;
  • Combined stability -- bending and axial compression (according to the interaction equations in EN 1993-1-1 or the simplified formula in EN 1993-1-3);
  • Combined stability -- bending and axial tension;

In the case of sufficient support from a roof diaphragm, only flexural buckling checks for the strong axis are performed.

22/07/2014