EC steel and timber design in SCIA Engineer 15
Version 15 of SCIA Engineer features new EN 1993 stability checks for heavy gauge and cold-formed steel elements. The previously supported checks for heavy gauge steel members were fully rewritten according to the latest technology and programming practices, in order to increase speed and create more transparency in the calculations.
The mentioned improvements are part of a thorough rewriting of steel design modules and in-depth re-factoring of the overall check architecture. Previously, EN 1993 sections checks and flexural buckling checks were rewritten in versions 13.1 and 14. This version 15 focuses on torsional-flexural buckling, lateral-torsional buckling, shear buckling (with or without stiffeners), and stability under a combination of load effects.
Calculation reports have been improved significantly, following suggestions from users and other professionals. Tabulated overviews have been extended with additional clarifications, intermediate calculation steps (where needed), warnings and notes, and clear references to used clauses from the design code (or other technical publications). This updated output may be sent to Engineering Report or reviewed via the Report Preview window in the 3D GUI of SCIA Engineer.
The changes pertain to both checks at ambient temperatures and under fire conditions.
Flexural buckling in version 15
- A more accurate determination of buckling curves is featured in this latest version, especially for closed shapes and less commonly used sections like built-in beams, sections with haunches, paired sections, and various asymmetric sheet-welded sections.
- On user request, buckling curves that have been edited via the Cross-Section Properties are always used. In addition, a note is shown to the user to indicate that buckling curves have been adapted by the user.
Torsional and torsional-flexural buckling in version 15
- The critical axial load for torsional-flexural buckling is now derived as a root of the cubic equation for stability of a column, i.e. no simplifications are used. The universality of this approach means it is applicable to any cross-section shape.
- In the case of rectangular and circular hollow sections, the torsional-buckling / torsional-flexural buckling check are not executed and a message is shown instead that the failure mode is not critical.
- In the case of an I-section, if the check is not critical, it is not printed and a message is shown instead.
- Torsional stability checks are now also performed under fire conditions.
Diaphragms in version 15
In SCIA Engineer, the presence of diaphragms influences the check for lateral-torsional buckling.
- In this version, the stiffness of a diaphragm is first checked in the plane of the diaphragm. If sufficient, and if the diaphragm is located along the compression flange of the beam, the lateral-torsional buckling check is skipped and a note is added to the output to indicate that lateral-torsional buckling will not govern. If insufficient, a fictitious contribution of the diaphragm to the It torsional moment of inertia is calculated and the lateral-torsional buckling check is performed (as done in previous versions).
- The influence of diaphragms is, since this version, also taken into account in the check for torsional buckling.
Lateral-torsional buckling in version 15
- The general formula for Mcr (which includes the C1, C2, and C3 coefficients) is now used for any cross-section.
- The correct calculation of the zg and zj distances contributes to a more accurate and user-friendly lateral-torsional buckling check. For example, in this version, the user does not need to specify the point of load application as 'stabilising' or 'destabilising.' Instead, he only needs to specify whether the load is applied on the top flange, bottom flange, or in the shear centre of the section. The programme will then determine per section and per load combination whether the load is stabilising or destabilising.
- An inconsistency within the EN 1993-1-1 code, namely, the use of a limit slenderness equal to 0.4 for the general case in clause 220.127.116.11 is corrected in this version. A limit slenderness of 0.2 is used when determining whether the lateral-torsional buckling check should be performed or not.
- The alternative case for "Rolled and Equivalent welded" sections, given in clause 18.104.22.168 of EN 1993-1-1, is now only used for symmetric and asymmetric I-sections. The method is enabled by default as it leads to more economical design. A more accurate calculation of the kc coefficient is enabled, based on technical literature.
Stability under combined load effects
- Corrections have been introduced to the implementation of interaction method 1 from Annex A of the EN 1993-1-1 standard. The corrections are based on the ECCS Publication No 119 and the ECCS Design manual for EN 1993-1-1; for details, see the Theoretical Background.
- The mathematics behind Interaction method 1 requires that the applied force NEd not exceed any of the critical forces Ncr,y, Ncr,z, and Ncr,T. In fact, if NEd exceeds any of these, the member will fail in buckling under compressive force and there is no need to verify the combined check. Therefore, the combined checks are not executed for such cases and a note is printed in the output.
- In Interaction method 2, negative terms are prevented in the calculation of kyy and kzz (see the Theoretical Background).
- A combined check for stability under bending and axial tension has been added based on paragraph C5 of the AISI NAS S100-07. The check verifies stress at the fibre in the section under highest compression. To be performed, it is required that all three components of the tensile force and bi-axial bending are present in the section. In case only two of the three components are present, other, previously available checks will be performed.
- Interaction equations under fire conditions have also been reworked.
- The output of stability checks has been extended with additional tables, descriptions, and notes; intermediate calculation steps and motivation for design decisions are now shown.
- It is now possible to define a rigid end-post condition.
- In the case of interaction with bending moment for class 3 and 4 sections, an additional condition checks whether the applied moment is less than the effective moment resistance of the cross-section. The condition is derived from the publication "Commentary and Worked Examples to EN 1993-1-5 - Plated Structural Members," ECCS, 2007.
- Checks for shear buckling under fire conditions are now supported.
- Under fire conditions, in particular, the ε coefficient is calculated according to EN 1993-1-2, equation 4.2;
- The plate slenderness under fire conditions has been modified, see the Theoretical Background.
Version 15 improvements in steel connections
The scope of this new version of SCIA Engineer covers a few additional connection typologies. The design of these connections is based on technical publications that complement the EN 1993-1-8 standard and adopt the same principles and calculation methods.
Extended end-plate with multiple bolt-rows outside of beam
- The Eurocode exclusively addresses moment-rigid connections with a single bolt-row outside the tension flange of a connected beam. This does not cover all connections that we see in practice. The SCI publication "Moment-resisting joints to Eurocode 3" gives additional rules -- for the determination of yield-line patterns and the calculation of effective lengths -- for the case of multiple bolt-rows outside the beam.
- These rules have now been implemented in SCIA Engineer's steel connection design modules. The design method is based on the plastic yield-line theory and is, therefore, consistent with the previously available methodology for connection design.
- The method only applies to connections with a stiffened end-plate extension, where the stiffener (i.e., plate haunch) covers the whole height of the extension.
- The new development entails adaptations to the bolt-row classification, to the generation of bolt-row groups, to the verification for both the end-plate side and the column-flange side of the connection.
- A condition based on the geometry of the connection is added for the appropriate determination of yield-line patterns (taken from HERON vol. 20 publication by P. Zoetemeijer, see Theoretical Background for steel connection design).
- The design method in the case of an unstiffened end-plate extension remains unchanged -- i.e. only a single bolt-row outside the tension flange is allowed.
Haunch on top
- This version brings the possibility to define a haunch (flanged or from a single plate) at the top of the beam. Henceforth, the user may define a haunch at the top of the steel connection, at the bottom of the connection, or both at the top and bottom of the connection.
- The top haunches are taken into account in the bolt-row classification, in the determination of yield-line patterns, in the determination of centre of compression, in the determination of Mj,Rd, in the verification of connection components: bolts, welds, plates and stiffening elements.
Improved base plate design
- In previous versions, an interaction check for the simultaneous action of bending moment and axial force was performed during the design of base connections. After a careful review of the design code EN 1993-1-8, however, it was established that the effect of normal force on the connection is already taken into account in the calculation of the moment resistance.
- Therefore, the interaction check was removed from the base-plate design - both from the determination of critical combination, and from the verification of the base plate connection.
- In order to improve both the user experience and design workflow, it was necessary to stick as much as possible to the output style users are familiar with. Users will certainly benefit from an improved PC resource allocation and speed, however, they will also find that the logic behind the reporting of results has not changed.
- Additional notes and warnings are shown to the user to justify the use of a specific method or clause from the design code. Tables with intermediate values make the calculations easier to follow and preclude misinterpretations. Details are added to clarify the derivation of critical sections and load cases.
- All changes have been documented in the Theoretical Background, which has also been extended with more details on the formulas and code articles behind the steel check.
- A new formcode has been created for paired sections of two CFS channels connected back-to-back. The Steel Code Check-related settings for this formcode are similar to the ones for e.g. back-to-back Sigma sections/IS+ sections.
- A setting in the fire resistance parameters allows the user to exclude individual members when performing a fire resistance check according to EN 1993-1-2.
- The updated Swiss code SIA 263:2013 is now fully supported.
- The following updates to the Dutch national annexes for EuroCode 3 are now supported:
- NEN-EN 1993-1-1+C2:2011/NB:2011;
- NEN-EN 1993-1-2+C2:2011/Ontw. NB:2014
- NEN-EN 1993-1-3:2006/NB:2011
- NEN-EN 1993-1-5:2006/NB:2011
- NEN-EN 1993-1-8+C2:2011/NB:2011
- NEN-EN 1993-1-1+C2:2011/NB:2011;
- The Malaysian national annexes for EC0 (MS EN 1990: 2010), EC3 (MS EN 1993-1-1: 2010), and EC7 (MS EN 1997-1: 2012) have been implemented.
The Singaporean national annexes for EC0 (NA to SS EN 1990: 2008+A1:2010) and EC3 (NA to SS EN 1993-1-1:2010, NA to SS EN 1993-1-2:2009, NA to SS EN 1993-1-3:2010, NA to SS EN 1993-1-5:2009, and NA to SS EN 1993-1-8:2010) have been implemented.
Timber improvements in version 15
- It is now possible to disable the check for compression perpendicular to the grain when executing a Timber check. A check box is made available in the Timber Setup, where the setting may be enabled for all members; a check box in the member data settings allows for the setting to be enabled/disabled for individual members. The latter check box has higher priority. If the setting is enabled (regardless whether in the Timber Setup or in the member data settings), a note is printed in the output to notify the user.
- The environmental class may now also be defined via the member data settings (i.e., per member).