In the Members | Base tab of the 'Ultimate configuration' or 'Strength configuration' dialog, you make basic settings for the design of members and member sets.
The 'Design parameters' are divided into several categories, which differ depending on the design standard.
General
The 'Perform stability analysis' check box controls whether, in addition to the cross-section checks, stability analyses such as flexural buckling or lateral-torsional buckling are performed. You should disable this check box if you do not want to perform a stability analysis or if the stability effects have already been taken into account in the determination of internal forces (for example, by a second-order analysis with imperfections and/or stiffness reduction).
If the stability analysis is activated, effective lengths or boundary conditions must be defined and assigned to the respective members or member sets. Otherwise, no stability analysis is possible. In the results table Errors & Warnings, a corresponding message is displayed after the calculation. Cable members and tension members are excluded from this, as they can only absorb tensile forces and do not require stability analyses.
The 'Perform advanced plastic design' check box offers the possibility to design the members or member sets according to the so-called "partial internal forces method" (PFM). You can set the parameters in the Members | Plasticity tab, which is available after activating the option.
Design ratio limits for ignoring internal forces and stresses
Design standards, which are mostly designed for manual calculations, contain design check formulas or interaction conditions that are often only designed for specific combinations of internal forces. In the structural analysis of the 3D model, however, very small values for internal forces are usually obtained. Although they are insignificant from an engineering point of view for the load-bearing capacity, they prevent certain design checks if the design standard is strictly observed, or they force the use of less favorable interaction formulas. The design ratio limits therefore offer a simple and transparent way of neglecting certain internal forces in the design check and avoiding the problems mentioned above.
The limit value η describes the ratio of the acting internal force to the plastic cross-section resistance, which is determined in a simplified way using the cross-section properties. These are not normatively regulated design resistances: standard-specific regulations (for example, on cross-section classification) are therefore not taken into account; this does not correspond to the purpose of the limit value setting. Therefore, you should only use high limit values for testing purposes.
If an internal force is below the limit value condition, the design is performed without a warning that the internal force is neglected. However, in the design check details, you can use the note 'Negligible' for the design internal forces to check which internal forces have been neglected due to the limit values and were not taken into account in the design check. If all internal forces at a location are negligible, only the check of the negligible internal forces is given as the design check.
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If the add-on Torsional Warping (7 DOF) is activated, a limit value for the bimoment and the shear stresses due to secondary torsion is also available for some design standards.
Analysis of thin-walled structures (for EN)
The determination of the effective section requires an iterative approach. In the 'Maximum number of iterations' input field, you can define the maximum number of calculation passes. As soon as the 'Maximum difference between iterations' between the results of two iterations is fallen below, the calculation ends.
For non-doubly-symmetric, compression-loaded cross-sections susceptible to local buckling, the centroid position of the effective section shifts compared to the gross cross-section. The external compressive force acting centrically on the gross cross-section now acts eccentrically on the effective section, resulting in an additional bending moment. By default, this bending moment is taken into account in the calculation. If this is not desired, activate the 'Neglect bending moments due to shifted centroid' check box.
With the 'Consider effective widths according to EN 1993-1-5 [5], Annex E' check box, you can control whether the alternative method for determining the effective section described in Annex E should be used for stresses below the yield strength.
Options (for EN, CSA, GB, SIA, etc.)
Depending on the design standard, further options are available in the ultimate configuration. They are presented for selected standards.
EN 1993
Cross-sections of classes 1 and 2 may be designed plastically. Activate the 'Elastic design (also for cross-sections of class 1 and 2)' check box if these cross-sections are to be designed without using the plastic reserves. In this case, you can use the 'Use design check according to [1] Equation 6.1 for elastic design' check box to control whether the general design check according to elasticity theory should be performed. This can be conservative, since no partial plastic stress redistributions are taken into account, which are normally allowed in elastic design.
For plastic design, the 'Use linear interaction according to 6.2.1(7) for cross-section check for M+N' check box offers the possibility to add the design ratios of the internal forces linearly. This approach is conservative and not permissible for cross-sections of class 4.
CSA S16
Cross-sections of classes 1 and 2 may be designed plastically. Activate the 'Elastic design also for cross-section class 1 or 2' check box if these cross-sections are to be designed without using the plastic reserves.
With the further options, you can control the 'Parameters for cross-section resistance in compression according to 13.3.1' and the 'Coefficient for the effect of uniform bending (ω1) according to 13.8.6'.
GB 50017
The description is in progress.
SIA 263
The shear force design is usually performed with the effective shear area Av. For doubly-symmetric I-sections and U-sections of cross-section class 3, the web area Aw can alternatively be used. To do this, activate the 'Consider shear area according to 5.2.4' check box.
The 'Consider shear buckling design' option is activated by default. This performs the shear buckling design according to Clause 4.5.4, 5.3.4, or Annex F.1. If you disable the check box, shear buckling is not investigated.
Cross-sections of cross-section class 3 may be designed for bending about both axes with axial force according to Clause 5.2.6. If you activate the 'Use alternative calculation of bending exponents α and β according to 5.1.6.4' check box, the design checks for these cross-sections are performed according to Clause 5.1.6.4.
Local buckling (for AISC)
In [2] Table B4.1b, the width-to-thickness ratios for compression-loaded elements (cross-section parts) of members with bending stresses are given. If you design cross-sections that are not regulated in this table, activate the check box. You can then define the limit values λr for both unstiffened and stiffened elements.
Single-angle compression members (for AISC)
The compressive strength of simple angle sections must be determined for flexural buckling according to Section E3 or E7, and for lateral-torsional buckling according to Section E4. The 'Use effective slenderness according to E5' check box offers the possibility to use the simplified design check method according to Section E5, in which angles are treated as axially loaded members by adjusting the slenderness. It can be applied when the longitudinal compressive force is introduced into one leg. The other leg must be fastened to the adjacent component by welding or by a bolted joint with at least two bolts. The calculation of the effective slenderness can be performed either for a 'Planar truss according to E5(a)' or for a 'space truss according to E5(b)'.
The method described in Section E5 allows the use of unequal leg lengths connected by the shorter leg – provided that the equivalent slenderness is increased by an amount that takes into account the ratio of the longer to the shorter leg length. Specify whether the 'connection through' the longer or the shorter leg is used.
Design of cold-formed sections (for EN, AISC, CSA)
For some design standards, the design checks of cold-formed sections are possible. They are presented for selected standards.
EN 1993
The 'Perform design of cold-formed sections' check box is activated by default. Members with such cross-sections are thus designed according to EN 1993-1-3 [4]. If you remove the check mark, the design of the cold-formed sections is performed according to EN 1993-1-1.
The 'Profiling factor k according to 3.2.2(3)' affects the calculation of the increased yield strength fya. You can select the method by which the section was manufactured. The list offers two options:
- Roll forming (k = 7)
- Other methods of forming (k = 5)
If you activate the 'Use elastic design according to 6.1.6' check box, the stress analyses are performed as regulated for the loading with torsion in [4] Section 6.1.6. Thus, the elastic stress formulas (6.11a), (6.11b), or (6.11c) are used for all combinations of internal forces. More economical plastic design methods, which may be applied for certain combinations of internal forces, are excluded in this case.
If the 'Consider web as stiffened according to Table 6.1' check box is activated, the resistance of the web under local load introduction is not determined. Local buckling cannot occur.
The 'Determine resistance of web under local load introduction according to 6.1.7' check box controls whether the design checks against local crushing, web crippling, or local buckling in the web are performed. The prerequisite for this is that a corresponding design support is defined.
The lateral-torsional buckling check for members subjected to bending is not applicable according to [4] Section 6.2.4(2) if the cross-section has a pronounced angular difference between the principal axes of the effective section and the principal axes of the gross cross-section. With the input field for the 'limit inclination of the principal axes according to 6.2.4(2)', you can define the angle αlim up to which the design check is still performed.
AISC 360
Specify whether the 'design of cold-formed hollow sections according to the standard' AISC 360 or AISI 100 should be performed.
For 'members outside the applicability limits' of the AISI Table B4.1-1, you can use the check box to specify whether the safety coefficient Ω or the drag coefficient Φ should be applied according to AISI S100, Section A1.2(c). This specification also applies to general cross-sections whose applicability limits are not regulated in the standard.
With the check boxes of the 'Members in bending' category, you can make detailed specifications for the stability analyses. For example, it is possible to use the inelastic reserve capacity according to the AISI Sections F2.4.2, F3.2.3, and F4.3. For doubly-symmetric I-sections, the elastic buckling stress Fcre can alternatively be determined according to Eq. (F2.1.1-6). If point-symmetric Z-sections are analyzed, the determination of Fcre according to Eq. (F2.1.3-2) is also possible.
The strength Pn against 'web crippling' is determined according to Eq. (G5-1). Alternatively, the value can be determined according to Eq. (G5-2). To do this, activate the corresponding check box.
CSA S16
Specify whether the 'design of cold-formed hollow sections according to the standard' CSA S16 or CSA S136 should be performed.
For 'members outside the applicability limits' according to [3] Table B4.1-1, you can use the check box to specify whether the safety coefficient Ω or the drag coefficient Φ should be applied according to [3] Section A1.2(c). This specification also applies to general cross-sections whose applicability limits are not regulated in the standard.
With the check boxes of the 'Members in bending' category, you can make detailed specifications for the stability analyses. For example, it is possible to use the inelastic reserve capacity according to [3] Sections F2.4.2, F3.2.3, and F4.3. For doubly-symmetric I-sections, the elastic buckling stress Fcre can alternatively be determined according to Eq. (F2.1.1-6). If point-symmetric Z-sections are analyzed, the determination of Fcre according to Eq. (F2.1.3-2) is also possible.
The strength Pn against 'web crippling' is determined according to Eq. (G5-1). Alternatively, the value can be determined according to Eq. (G5-2). To do this, activate the corresponding check box.
Shear buckling design (for EN)
The 'Perform shear buckling design' check box is activated by default. This checks whether the slenderness λ of the web requires a shear buckling design according to EN 1993-1-5 [5] Clauses 5.1, 5.2, 5.3, and 5.5. If the limit value λlim is met, the design check is considered fulfilled. However, if the slenderness is above the limit value, transverse stiffeners must be provided at the supports according to Section 5.1(2) so that the shear buckling design can be performed.
Design of longitudinal fillet welds (for EN, AISC, CSA)
For some design standards, the design check of longitudinal fillet welds is possible. The options are presented for selected standards.
EN 1993
If you want to check the resistance of the longitudinal welds of welded cross-sections, activate the 'Perform design' check box. The factor βw is stored as a material property for most steels in the library according to EN 1993-1-8, Table 4.1. If the cross-section parts consist of different steel grades, you can also define the correlation factor βw for the design of the fillet welds user-defined.
AISC 360
For components with welded cross-sections, the longitudinal fillet welds between web and flange can be designed according to [2] Section J2.4. The design strength of the welds can be determined using two methods.
- Minimum tensile strength of the base metal: Only the base metal of the plate is checked.
- User-defined minimum tensile strength of the filler material: Both the base metal of the plate and the weld filler material are checked.
CSA S16
For components with welded cross-sections, the longitudinal fillet welds between web and flange can be designed according to [3] Section 13.13.2.2. The design strength of the welds can be determined using two methods.
- Matching electrode classification Xu = Fu: When using a matching electrode according to CSA W59-18, Table 11.1 or Table 12.1, it is assumed that the tensile strength of the electrode Xu is higher than the tensile strength of the base metal Fu. As a simplification, Xu = Fu is therefore applied.
- User-defined ultimate tensile strength of the electrode: If a matching electrode according to CSA W59-18, Table 11.1 or Table 12.1 or a non-matching electrode is used, the ultimate tensile strength can be defined manually. However, when using an oversized electrode, the value of Xu according to [3] Section 13.13.2.2 must not exceed the value of Xu of the matching electrode.
For the design, the hydrogen content in the electrode also plays a role. Specify whether the hydrogen content meets requirement H8 or below. If this is the case, the material thickness t for determining Smin corresponds to the thickness of the thinner connected cross-section part. For electrodes that are certified without a designation for diffusible hydrogen, or those whose hydrogen content exceeds the requirements for H8, the material thickness t corresponds to the thickness of the thicker part.
Stability analyses with internal forces according to second-order analysis (for EN)
There is the possibility to perform the stability analyses not with the equivalent member method according to [1] Section 6.3, but with the internal forces according to second-order analysis taking into account torsional warping and imperfections. In this case, the 'use γM1 for determining the cross-section resistance' check box can be used to control whether the coefficient γM1 (instead of γM0) is used for the cross-section checks.
