Economical, transparent and fast steel design in version 17
SCIA Engineer 17.0 delivers an updated version of our new Steel Code Check. The user can use new features and improvements that could previously not be released due to technological incompatibility. New developments focus on the following:
- providing versatile tools for cross-section classification and the calculation of effective cross-section properties for the vast majority of cross-sections that the user may want to work with;
- extended support for EuroCode 3-related publications (e.g., SEMI-COMP+, ECCS Designers' Guide to EC3);
- efficiency of the Steel Check routine (better performance in terms of speed and stability, parallel processing) on one hand, and of working with the Check results on screen, on the other;
- improved report and clear indication of the decisions made by the automated check.
Why section classification?
The cross-section class directly determines which formulas should be used to derive the load-bearing capacity. Higher section classes are linked to:
- stricter and more thorough design verifications,
- increased material use, in terms of limited utilisation of the plastic cross-section capacity.
The section class does not depend solely on the geometry and material grade. The actual internal forces acting on a section determine which parts of it will be subject to tension and could therefore be susceptible to local buckling. But the actual internal forces vary not only along the member, but also between each load combination we consider during the design. This means that a different section class may be relevant per load combination.
Why effective section properties?
Due to the danger of local and distortional buckling failures, slender cross-sections require that reduced (effective) section properties be used in design verifications. But deriving the effective section for a random steel shape requires some intelligence to be automated: the shape should be split to walls and stiffeners, the wall location relative to other walls should be recognised, stresses in each wall should be derived.
|Intelligent section classification and effective section properties derivation for the vast majority of steel shapes the user may want to work with.|
|More economic design for semi-compact steel sections of class 3, based on the SEMI-COMP+ research reports.|
|Improved user experience in the Steel Code Check in terms of speed, stability, efficiency, and output.|
|Sneak preview of a new tubular connection design module.|
Calculating a different section class per combination is a lot of work... if you are calculating by hand. But in an automated computation, such attention to detail can deliver a notably more cost-efficient final result.
This is why we extended the steel design functionalities of SCIA Engineer with an intelligent tool for section classification. Any cross-section that can be reasonably approximated by a centre-line and thickness can now be classified into the 4 categories described in EN 1993-1-1 (and EN 1993-1-2 in the case of fire design).
The tool can be used in standalone mode, but is also integrated in the Steel Code Check. The standalone mode is intended mainly for testing, comparison to hand calculations, or even to support manual design. The real value of the tool is in its integration in the Steel Code Check routine. The Steel Code check "calls" the Classification Tool in each section and per each (sub-)combination and "feeds" it with relevant internal forces; in return, it gets a class that only depends on the section parts that are actually subject to compression.
For haunched and arbitrary members, the variation of section geometry along the member length is also taken into account during classification.
Plastic neutral axis
In order to apply the section classification formulas of the code, the neutral line location needs to be determined. In the case of N + My + Mz plastic interaction, finding the neutral line is not a straightforward task.
The Classification Tool offers the user three numerical methods for finding the neutral line. Each method offers different level of accuracy, and the more accurate the method, the more time-demanding it can be. The user can tweak the balance between accuracy and speed depending on the nature of the task he is currently occupied with.
The three methods explained:
- Elastic stresses: The elastic stress distribution is used to calculate the plastic stress distribution using closed-form formulas.
- Yield Surface Intersection: A discrete plastic (yield) surface, or a "cloud" of points is derived per cross-section. The actual internal forces are then scaled until they intersect that yield surface. The point from the discrete yield surface that lies closest to the intersection point is then used for further determination of the plastic stress distribution.
- Iterative approach: The actual forces are increased iteratively and each time the plane of deformation is calculated. If no plane can be determined then the yield surface has been surpassed. The algorithm then goes back one step and iterates with smaller increments. The plane of deformation of the last calculated step is used as a yield surface.
The Yield Surface Intersection method offers a very good balance between high accuracy and speed.
Not only thin-walled cold-formed steel members require the use of effective section properties. Other slender beams, especially the sheet-welded ones, often fall inside the Class 4 category. Such beams offer elegant engineering solutions and efficient material use if designed smartly.
We now provide an automatic derivation of the effective section for any steel shape -- hot-rolled or cold-formed, closed or open, library-defined or general thin-walled: any section that can be represented by a centreline and thickness. The user can benefit from SCIA Engineer's flexibility in the design of slender steel members. Various hot-rolled and cold-formed shapes (boxes, U-/L-profiles, etc.) can be analysed: these are split into flat walls and stiffeners, whose geometry is then reduced based on their slenderness and the stresses found in them.
The valorisation project SEMI-COMP+ n° RFS2-CT-2010-00023 provided a few publications on how to achieve a more economical design for cross-sections that fall under the class 3. The EuroCode 3 specifies that these 'semi-plastic' sections should be assumed to fail in purely elastic failure. This is rather conservative, and instead, some of the plastic reserve can be utilised depending on how slender the section actually is.
Plastic reserve based on the actual section slenderness is now implemented in SCIA Engineer for doubly-symmetric I-sections and RHS. Instead of a discontinuity at the transition between classes 2 and 3 (a jump from the plastic section resistance to the elastic section resistance), a gradual reduction of the plastic reserve is applied until the class 4 limit. Note that Eurocode 9, AISC 360, and AISI S100 already prescribe this gradual transition.
The modified classification limits published in the SEMI-COMP+ research report have also been implemented in SCIA Engineer. It is important that these limits be used in the case of semi-plastic design of class 3 sections, because these limits correspond to the safety level of EC3.
Other improvements in steel member design
- The Steel Code Check, the Classification Tool, and the Effective Section Tool support parallel and multi-core processing;
- The check is considerably faster, supporting the user in efficiently tackling daily engineering challenges;
- Various extensions allow the user to consult detailed results on screen;
- Subscripts, superscripts and Greek symbols are now visualised in the check reports;
- All Table Result features are now seamlessly supported in the Steel Code Check. Moreover, tables with selected check components are easily created;
- Errors, warnings and notes are now reported also directly in the 3D scene and the Brief output (read more);
- More intermediate values are provided in the detailed report and references to the chapters of the code and other publications are more detailed and explanatory (such improvements were gradually added in the last few releases of SCIA Engineer);
- A new method is provided for checking the stability of members with variable height, based on the ECCS Designer's Guide to Eurocode 3;
- Warping checks are now supported for any section with a centreline. The torsional moment is split to primary and secondary torsion; in this way, warping stresses are accounted for.
- A direct link to IDEA StatiCa Connection has been developed. It means that the user can select a joint inside SCIA Engineer, export all data to the third-party application (geometry, material, loads and internal forces), perform the necessary analysis, and store the connection project inside the SCIA Engineer project file (and thus return to it at any time in future).
- A sneak preview of our new Tubular Connection module is included in version 17.0. The feature performs all necessary design checks on a connection according to EN 1993-1-8, but is limited to CHS-to-CHS joints only.