Steel cold formed AISI NAS 2007 (esasd.15.05)

 

esasd.15.05

Cold-formed steel members are made from structural quality sheet steel that are formed into shape either through press-braking blanks sheared from sheets or coils, or more commonly, by roll forming the steel through a series of dies. No heat is required to form the shapes (unlike hot-rolled steel), and thus the name cold-formed steel. Cold-formed steel members and other products are thinner, lighter, easier to produce, and typically cost less than their hot-rolled counterparts because of the weight reduction. A variety of steel thickness is available to meet a wide range of structural and non-structural applications.

Cold-formed steel possesses a significant market share because of its advantages over other construction materials and the industry-wide support provided by various organizations that promote cold-formed steel research and products.

Highlights
Fully integrated cold formed checks in the standard SCIA Engineer AISC 360 steel design environment, including mixed material structures
Detailed analysis of the effective shape, including distortional buckling for edge stiffen- ers, double edge folds and internal stiffeners
Advanced checks available as web crippling and shear in case of sections with stiffened webs
Special purlin design checks including free flange geometry, advanced loading determination...
Available for arbitrary cold formed sections, including the average yield strength and steel core thickness
Implementation of the AISI NAS S100-07

The steel design module according to AISI NAS 2007 for the design of cold-formed steel members is integrated within the existing design of steel members according to AISC (IBC2006) and is an extension to the standard steel code check (esasd.01.05).

This module covers the following:

  • Determination of the initial shape
  • ULS Design Checks including distortional buckling and web crippling
  • Special considerations for purlins restrained by sheeting

Supported cross-section types

The following cross-section types are supported for generation of the initial shape and effective cross-section:

  • Standard profile library cross-sections
  • Cold formed pair cross-sections
  • General thin walled sections
  • General sections with thin walled representation
  • Thin walled geometric sections
  • All other sections which support the centreline and do not have rounding

Using the general cross-sections editor, it is possible to draw user-defined cross-sections with the integrated drawing tools or to import cross-sections from dxf- or dwg-files.

Determination of the Initial Shape

When a cold formed section is selected from the standard library, or when it has been imported via the general cross-section utility using the thin-walled representation, the initial shape of the cross-section is automatically calculated and divided to several parts and visualized. Supported and automatically associated element types are:

  • I (internal element)
  • F (fixed element – no reduction is needed)
  • SO (outstand element (symmetrical))
  • UO (outstand element (unsymmetrical))
  • RUO (Reinforced Unsymmetrical Outstand Reinforcement types)

The generated initial shape can be viewed and modified by the user

This generated, or adapted initial shapes, can also be checked manually for compression and bending according to both local axes before being applied to the model.

Effective shape

Calculation of the effective widths always starts with the determination of the stress in the compression element. The obtained effective sections can be displayed graphically.

Section and stability checks

Section Checks

The following section checks are executed: axial tension, axial compression, bending moment, shear force, torsional moment, local transverse forces, combined tension and bending, combined compression and bending, combined shear, axial force and bending moment, combined bending and local transverse force.

Stability Checks

The following stability checks are executed: flexural buckling, torsional and torsional-flexural buck- ling, lateral-torsional buckling, bending and axial compression, bending and axial tension, combined bending and tension check. For determining the torsional-flexural buckling resistance, the general cubic equation is applied.

Additional steel member information

In general, the additional information on the steel member to define the boundary conditions of the selected members are available in accordance with the basic steel code checks: Member buckling data, (double) LTB restraints, Stiffeners, Diaphragms.

Also Second Order analysis according to Appendix 2 is supported.

Diaphragms and one flange sheeting fastening

Diaphragms are used the same way as currently implemented in SCIA Engineer. The available lateral strength is checked and the torsional stiffness of a member can be augmented. SCIA Engineer also supports flexural and compression members with one flange fastened to sheeting as specified in AISI NAS 2007 when the conditions are applicable.

Web crippling data

Web crippling concerns the local failure of the web due to a high local intensity of the loading. This typically occurs at locations of point loads on a purlin or at connections between the purlin and rafter (since the rafter is in fact a support for the purlin and this support-”reaction” can again be seen as a local point load on the purlin). The web crippling check is executed only for shear force Vy in the positions where there is a skip-change in the shear force diagram but it can be disabled by the user.

Lapped purlin design

C-sections and Z-sections can be so-called ‘lapped’ which implies that they are shoved one in the other, which means that separate purlins are combined into one long continuous purlin. This lapped length zone can be introduced by the user symmetrically or asymmetrically. When the check is executed in a section located in the lapped zone, the check is executed using the combined strength of both sections. The overlap can option- ally be fully braced at the bottom flange.

The lapped length can be optimized by the application based on a user defined dimension list.

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